- Email: [email protected]
Tribocorrosion properties of polycrystalline diamond compact in saline environment
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
Contents lists available at ScienceDirect
International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Tribocorrosion properties of polycrystalline diamond compact in saline environment
T
⁎
Liang Penga, Bingsuo Pana,b, , Yuanji Yaoa, Songcheng Tana a b
Faculty of Engineering, China University of Geosciences, Wuhan 430074, China International Joint Research Center for Deep Earth Drilling and Resource Development, Wuhan 430074, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Polycrystalline diamond compact Abrasion-corrosion Wear Drilling Point cloud
Tribocorrosion properties of polycrystalline diamond compact (PDC) in solution containing sodium chloride were investigated using a modified pin-on-disc wear test rig. Tests were conducted at various salinities (0–20%) for a better understanding of the abrasion-corrosion interaction. The corrosion behavior was examined through a three-electrode electrochemical cell. The contributions of pure abrasion and pure corrosion as well as their synergy to the total volume loss were calculated. The influence of cathodic protection on the abrasion-corrosion performance of PDC was also evaluated. Experimental data in this paper shows that the PDC suffers more severe damage as the sodium chloride concentration increases gradually and the applied potential of −1.0 V vs. SCE can suppress the corrosion-related effects to a negligible level. Both electrochemical measurements and SEM micrographs of worn surfaces were used to detail the degradation mechanism. Despite the fact that it is the mechanical wear that dominates the abrasion-corrosion mechanism, results reveal that the interaction between the abrasion and corrosion plays a significant role. Moreover, an effective volume calculation method based on three dimensional point cloud was proposed to determine the wear volume of PDC. Validation studies demonstrate that the measurement method is feasible and accurate with an error of no more than 5%.
1. Introduction Polycrystalline diamond compact (PDC) has been extensively employed in the field of oil and gas drilling due to its excellent performance in terms of hardness, toughness and wear resistance [1–3]. As a significant engineering factor to evaluate the quality of PDC, tribological properties have been widely investigated to make it more effectively applicable under various environments [4–8]. Besides mechanical wear, PDC also has to withstand severe corrosion environments in some applications, such as offshore drilling [9] and evaporite bed drilling [10]. The common characteristic for those applications is that the liquid medium containing sodium chloride continuously erodes the exposed bit, leading to the accelerated bit deterioration due to the combined effect of mechanical abrasion and electrochemical corrosion [9]. Over the past decades, various techniques for improving the wear resistance of PDC bits in corrosive environments have been extensively investigated by many researchers, a typical example of which is the WC/CO-based coating used for protecting the steel body of bits in severe erosion-corrosion environment [10–12]. However, the tribocorrosion behaviors of the polycrystalline diamond (PCD) layer itself under corrosive condition have not attracted sufficient attention of
⁎
researchers. Specially, interpretation for the mechanism of coupling effect of mechanical wear and corrosion, sometimes referred to as abrasion-corrosion synergy, requires considerable efforts. Hence, investigating the tribological performances of PDC in corrosive environment is of both immensely scientific and technological interests. In addition, weighing method has been widely used to evaluate the wear resistance of PDC tools in previous studies [11,13–15]. Nonetheless, there are inherent limitations impeding its further applications. A typical example is that the measuring results extracted from the weighing method refer to the total weight loss of the integrated sample including the undesired part, which obscures the wear volume for the specific component. Take the PDC bits for example, the volume loss measured by weighing method can be segregated into two components, PDC weight loss and the steel material loss, when abrasion and corrosion attack the bit simultaneously. Besides, result extracted from the weighing method shows the weight change rather than the visualized volume loss. Though the volume change could be further determined through dividing the measuring result by the density of the material, the key point is that the requisite density is sometimes imprecise especially for composite materials, leading to an increasing workload for the research. On the other hand, three dimensional point clouds
Corresponding author at: Faculty of Engineering, China University of Geosciences, Wuhan 430074, China. E-mail address: [email protected] (B. Pan).
https://doi.org/10.1016/j.ijrmhm.2019.03.016 Received 4 February 2019; Received in revised form 12 March 2019; Accepted 17 March 2019 Available online 18 March 2019 0263-4368/ © 2019 Elsevier Ltd. All rights reserved.
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
technology have been widely employed to represent 3D spatial feature in recent years due to its simplicity, flexibility and powerful representation capability [16,17]. Therefore, it is considerable to introduce such an effective technology into the wear volume calculation of PDC bits. Motivated by the abrasion-corrosion effect on the PDC, this paper investigated the tribological properties of PDC in saline environment using a pin-on-disk tribometer. Special efforts had been devoted to understand the coupling effects of mechanical wear and corrosion on the degradation mechanisms of PDC. What's more, a method based on three dimensional point clouds that would be discussed later was proposed to calculate the wear volume loss based on previous studies [18–20]. Although the emphasis of this paper is on the tribocorrosion properties of PDC, the results have substantial relevance to numerous researches, especially for those whose volume loss is out of the detection by weighing method.
Fig. 2. Schematic of the tribocorrosion test (WE: Working Electrode, RE; Reference Electrode, CE: Counter Electrode).
2. Experimental
three-electrode electrochemical cell connected to an electrochemical workstation (Wuhan CorrTest, CS310H) was set up as shown in Fig. 2, in which the specimen served as working electrode and a graphite sheet and a saturated calomel electrode (SCE) were selected as counter electrode and reference electrode respectively. Two kinds of electrochemical tests were undertaken to isolate the contributions of pure corrosion(C) and pure abrasion (E) to the total volume loss (TVL) of PDC under tribocorrosion condition. Firstly, potentiostatic test was carried out at a constant potential of −1.0 V vs. SCE to apply cathodic protection (CP) to the cutter under test environment. Secondly, potentiodynamic polarization test was performed under static condition. With reference to SCE, the electrochemical polarization curve was obtained by scanning from 200 mV nobler than open circuit potential (OCP) to 100 mV more negative than the OCP at a rate of 2 mV/s. Specially, to evaluate the charge transfer resistance values across the electrode-electrolyte interface, a frequency in range of 105 Hz to 10−2 Hz with amplitude potential of 10 mV was used to conduct electrochemical impedance spectroscopy (EIS). Both before and after the wear test, the micro topography and elements distribution of the samples surface were analyzed by scanning electron microscopy (SEM, G2 PRO, Phenom) equipped with an energydispersive X-ray spectroscope (EDS, EM-30AX PLUS+, Coxem).
2.1. Materials Commercial sintered polycrystalline diamond compact (SF Diamond Co.Ltd.) was used in this study. The polycrystalline diamond (PCD) layer composed of diamond (particle size mostly in 20-30 μm) and Co binder (8%–10%) was sintered onto a circular face of WC-Co substrate with a diameter of 13 mm (Fig. 1). The total height of PDC sample is 8 mm with 1 mm of PCD layer. 2.2. Tribocorrosion test A pin-on-disc wear test rig was used to simulate drilling conditions. PDC cutter brazed on a sample holder was fixed on the stationary pin holder of the apparatus and the counter face material was 60 mesh SiC grinding wheel. To have a better understanding of the effects of salinity on the tribological performance of PDC, five different sodium chloride concentrations varying from 0% to 20% in steps of 5% were adopted for this research. Prior to the test, a long soak of 24 h in the corresponding sodium chloride solution was given to the SiC grinding wheels. During the test, the SiC grinding wheel exposed to the test solution was rotated with a cutting diameter of 8 cm at 200 r/min. The corresponding initial contact load was set to 5 N, followed by a constant load of 200 N being applied on the cutter. The duration of the experiment was set as the time when the cutter completed a four-centimeter penetration and the operation time was recorded simultaneously. In all of the mentioned tests, the samples including their holders were electrically insulated from the surrounding environment except for the studied areas. The testing conditions were schematically shown in Fig. 2. To accurately provide insights into the local interaction between mechanical abrasion and electrochemical corrosion during the test, a
2.3. Wear volume calculation After an ultrasonic bath and drying process, the assembled PDC and its holder was fixed on the operation platform of a confocal laser scanning microscope (VK-X100K, manufactured by KEYENCE). Using a magnification of 100 times, nine sets of point cloud data were measured to cover the whole worn region of PDC. Subsequently, the registered points cloud data were obtained through pre-positioned software on the computer of the facility. Once all processes mentioned above got finished, the data was imported to CloudCompare software where the extraction of the boundary and PDC surface was carried out, a preprocessing for the subsequent worn volume calculation. Based on the results of point clouds processing, 2D Delaunay triangulation was performed after the points were projected to the bottom, followed by the generation of the triangular infinitesimal volume elements. According to integral thought, the sum of all volumes of triangular infinitesimal elements could replace the volume of measured PDC approximately and the detailed calculation principle has been shown somewhere else [18]. Generally speaking, the measurement of the total volume loss of PDC comprises the volume measurement before and after the tribocorrosion test, represented by V1 and V2 respectively. However, there are something different about the method proposed in this paper. In particular, the initial volume of PDC could also be calculated based on the point cloud of worn PDC. As previously analyzed, the plane fitting
Fig. 1. The optical characteristics of PDC. 308
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 3. Scatter diagram illustrated the processed point cloud and the 3D reconstruction of the top surface, where the insert is the enlarged image of red marked region. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
volume loss for specific region of the specimen.
of the extracted top surface of worn PDC point cloud was carried out followed by the acquisition of the plane fitting equation. As the red reintegrated plane presented in Fig. 3D reconstruction of the top surface was implemented subsequently by combining the obtained equation with the 2D coordinate point on the projection plane. In principle, the value of TVL can be defined as the difference between V1 and V2. Considering the interference (denoted by V3) between extracted and restored top plane incorporating into the final result, the volume of the material measured at the end of the experiment corresponds to the following expression.
VTVL = V1 − V2 − V3
3.2. Electrochemical characteristic As a basic parameter to characterize the electrochemical behavior of the PDC under various saline solution, corrosion current density was determined as a measure of corrosion rate based on the potentiodynamic polarization curves as shown in Fig. 5, in which semi logarithmic current density versus potential has been plotted. It can be seen that the PDC exhibits similar polarization behavior in different salinity solutions. The corrosion current density (icorr) and the free corrosion potential (Ecorr) obtained by Tafel extrapolation method were present in Table 1. Despite the fact that only the anodic part of the potentiodynamic polarization curves was used to determine the corrosion current density, the accuracy had been proved by M. Stern [21]. When the test is performed without nitrogen or argon purging, the activation polarization and concentration in cathodic part would lead to marked deviations and uncertainties on the value of corrosion current density [21,22]. It seems that the presence of sodium chloride in the test solution shifted the Ecorr in the active direction. The influence of salinity could also be evaluated through the corrosion current density data in Table 1. When PDC was immersed in the 5% salinity solution, the obtained icorr was about 0.01805mA/cm2. As the salinity in the solution gradually increased to 20%, the corresponding icorr showed a much higher value of 0.04579mA/cm2, indicating a more active behavior. All those findings could be related to the higher concentration of chloride ions around the anode, which facilitated the ion-exchange between the binder and solution. The measurement of EIS shown in Fig. 6 presents a consistent result with the potentiodynamic polarization test. It shows that the size of the semicircle shrank with the increasing concentration of sodium chloride contained in the test solution. Since the semicircle represents the resistance of charge-transfer reaction at the interface between the
(1)
Referring to all those analyses exhibited above, a program based on Matlab had been designed for the volume calculation. 3. Results and discussion 3.1. Validation of proposed method for wear volume calculation To validate the accuracy and reliability of the volume calculation method proposed above, a 45# steel cylinder was employed to replace the PDC cutter in the wear test. There are accessible approaches to its density and initial volume. Both before and after the test, the steel cylinder was first cleaned in an ultrasonic ethanol bath and then dried in vacuum to obtain a more accurate record of weight change. The point cloud acquisition and processing was conducted after the abrasion test, and the result was shown in Fig. 4. The volume loss determined by weighting method was 0.6966mm3, while the point cloud method reported a 0.6637mm3 material removal. It was believed that this small discrepancy was derived from the mismatching between the reconstructed and the original top surface of PDC since the concerned surface was not a geometrical plane in real micro-level. However, this small difference of only 4.94% in application of the point cloud measurement system was far outweighed by the ability to capture the
Fig. 4. Photograph illustrating the wear of a 45# steel cylinder: (a) optical characteristics; (b) the point cloud corresponding to the wear part of (a). 309
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Table 2 Result of volume loss in tribocorrosion test (mm3).
Table 1 Corrosion data of PDC under different salinity. 5%
10%
15%
20%
Ecorr(V) icorr(mA/cm2)
−0.23073 0.01805
−0.2355 0.03222
−0.2556 0.03288
−0.2739 0.04579
Fig. 6. Nyquist diagrams measured on the PDC immersed in various saline solutions.
solution and PDC, those semicircles in Fig. 6 mean that the corrosion resistance of the PDC decreased when the sodium chloride concentration increased in the solution. Notably, the degree of the increase in icorr slowed down in higher salinity, which could be interpreted by the limited distribution of cobalt on the exposed surface. 3.3. Abrasion–corrosion material loss According to previous research results [23–25], the total volume loss (TVL) under abrasion-corrosion condition can be divided into three constituent parts, as is demonstrated by Eq. (2).
TVL = E + C + S
0%
5%
10%
15%
20%
TVL E(under CP) C S
0.5526 ━ ━ ━
0.5994 0.5415 0.0048 0.0531
0.6258 0.5549 0.0086 0.0623
0.6478 0.5216 0.0088 0.1174
0.7445 0.5371 0.0122 0.1952
respectively; however, we failed to accomplish it due to a lack of necessary equipment. Hence, distinction between EC and CE has not been made and S is defined to quantify the coupling effect between the corrosion and abrasion. Results on the effect of salinity on TVL were recorded in Table 2 and compared with the volume loss with applied CP. The values of TVL were derived from the samples being attacked under tribocorrosion condition and the pure mechanical abrasion E were calculated from the potentiostatic test in which the effect of corrosion-related activities were suppressed to a negligible level, both of which were calculated based on the point cloud. As for the accurate estimation of the pure corrosion contribution, the calculation results were determined through Faraday's law [26–28] since the corrosion density had been well defined in Table 1. Mathematically, the synergy contribution(S) to total material loss could be calculated through Eq. (2). During the analysis of the obtained results, it becomes apparent that the material loss due to mechanical abrasion dwarfs the material loss due to corrosion, which is to be expected of PDC for the strong corrosion resistant properties of its main component – diamond. It can be seen from Table 2 that the values of TVL trend to increase linearly with the concentration of sodium chloride in the aqueous solutions, from 0.5526μm3 at 0% salinity to 0.7445μm3 at 20% salinity. Besides, a significant reduction of material loss is observed from Table 2 in the presence of applied CP compared with one measured without applied CP. The TVL values with CP applied under varied salinity does not suffer drastic fluctuation since the standard deviation is no more than 0.02. Moreover, their average value has not even exceeded 5% of that under clean water. Fig. 7 presents the morphology of the worn surface formed on the PDC after cutting operation under different salinity. It can be found that massive gray attachments are deposited on the contact area of the cutter, which have been marked in Fig. 7(a). In addition, compared with the surface worn in the clean water, plenty of pits can be observed on the surface (Fig. 7(b) and Fig. 7(c)). Similar to the TVL, the number of pits has increased as the salinity increased, indicating an increase in corrosion activity due to the activation of the anodic reaction. To further reveal the chemical composition of worn surface, corresponding EDS measurements were carried out and the results were displayed in Fig. 8. Different from the initial surface of PDC, there are several noticeable changes after the cutting operation. As mentioned above, many gray areas appear on the worn surface and their main chemical composition is proved Si element arising from the aggregated debris of the SiC grinding wheel. Meanwhile, much attention should be paid on the bright region marked in Fig. 8(c) since the occurrence of oxygen in the cobalt-rich region represents the cobalt oxide film formed during the cutting process, which has not been found on the unworn surface. Corresponding to the contact surface of the worn PDC cutter, the cross sections of the PDC are present in Fig. 9, from which a reasonable support for the TVL change can be drawn. For the PDC tested in clean water, there are almost no visible crevices on the cross section, meaning no corrosion attack. In contrast, micro-cracks in Fig. 9(b), implying the appearance of mild corrosion, come into sight clearly when the test salinity utilized turned to 10%. Fig. 9(c) depicts the cross section of PDC tested at 20% salinity where an exacerbated deteriorating corrosion occurs since the crevices have aggregated and enlarged more evidently. In addition, investigation into the cross section of the PDC with applied
Fig. 5. Polarization curves of PDC in different salinity.
Salinity
Salinity
(2)
where E, C and S are wear material loss component associated with pure abrasion, pure corrosion and abrasion-corrosion synergy, respectively. Synergistic wear has been further defined as the aggregate of change in abrasion wear due to corrosion, EC, and change in corrosive wear due to abrasion, CE. It is desirable to determine EC and CE 310
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 7. SEM images of the worn surface of PDC as the salinity varied: (a) 0%; (b)10%; (c) 20%.
tribocorrosion test, the corrosion and corrosion-related mechanisms, i.e. (C + S) forms up to 28% of the overall degradation of the PDC. Such an enhancement to the existing degradation processes due to synergism is not surprising. Similar results have been reported for WC-Co hardmetal (a material comparable in microstructure to PDC) abraded in corrosive media containing silica sand, since the main rate controlling mechanism of the material removal has changed from the fracture or pluckout of WC grain under non-corrosive conditions to the binder dissolution in sulphuric acid solution (pH 1.1) [33,34]. However, the related research conclusions must be used with caution in the current study for two reasons: the different corrosive medium (various concentrations of chloride ion rather than hydrogen ion) and the inertia interface between the diamond grain and the binder. Fig. 10 shows a schematic interpreting the possible interaction between the PDC and the SiC grinding wheel during abrasion-corrosion. In addition to the two bodies in contact, the wear particles between the contact surfaces mainly originate from SiC grinding wheel. It clearly shows in the schematic that the abrasion–corrosion resistance of the PDC cutter primarily depends on the ability of the diamond to resist fragmentation. Besides, the intergranular corrosion toward the binder cobalt has occurred in form of pitting leaving the diamond being exposed. The presence of the binder depleted regions could be explained
CP had also been conducted and the morphologic details were given in Fig. 9(d). Obviously the micrograph is present with no sign of corrosion, due to the positive impact of cathodic protection.
3.4. Discussion Metallic-related materials functioning in corrosive environments and subject to abrasive wear often lose durability due to the combined effect of mechanical wear and electrochemical corrosion. However, material loss under those conditions is not necessarily just the summation of mechanical abrasion and corrosion measured separately [28–30]. In-depth understanding of the mechanism of abrasion–corrosion cannot be achieved without a clear insight into the role of synergy. Although abrasion–corrosion interaction sometimes result in a reduction in overall mass loss [31,32], this is not the case in this paper anyhow. As the data in Table 2 shows, the enhanced damage to PDC is evident due to the combined effect of abrasion and corrosion. Corrosion contribution to total volume loss considered alone gives the impression that it is not the main factor, but when taking the corrosion-related mechanisms into account it becomes clear that focusing attention only on mechanical abrasion is unreasonable. Even though the corrosion contributes little to the total volume loss under 20% salinity in the 311
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 8. SEM images and EDS of the surface of PDC test under 20% salinity: (a) SEM image of initial surface; (b) EDS surface chemical composition of (a); (c) SEM image of worn surface; (d) (e) (f)corresponding EDS measurement of (c).
existence of the localized microenvironment dramatically different to that of the bulk conditions, an effect of which has been thought to associate with crevice or pitting corrosion [40]. Those uneven corrosion activities during tribocorrosion processes will in turn contributes to enhanced material removal. Although the passive oxide films, represented in orange in Fig. 10, have formed during the abrasion-corrosion process, it shows no marked improvement in the tribocorrosion performance of PDC since the mechanically weak films can be easily removed. Besides, the formation of the passive protective film is also a time-consuming process. It has been typically observed that the presence of chloride ions in solution increases the dissolution rate of other passive metal systems by creation of locally active sites on the metal surface and increasing the rate of pit propagation [38,41–43], both of which will impair the positive effect of the passive film against corrosion. The wear morphology as observed in Fig. 7 indicates that it is the mechanical wear that dominates on the prevailing degradation mechanism. Moreover, a SEM investigation of worn specimens with high
through galvanic coupling as electrons can move between the conductive phases such as the binder and the substrate due to the heterogeneous property of PDC as depicted above. In addition, such microstructural inhomogeneities at the contact point may provide localized conditions which could promote the early stages of damage accumulation as found in the analogous hard materials (e.g. WC/Co hardmetal) [35]. Specially, the effect of chloride ions on the corrosion behavior could be interpreted as being a result of specific absorption of ions on the metal surface, and the extent of absorption depends on both metal and halide [36–38]. Undoubtedly, increased chloride concentration while abrasion would create active chemical environment for accelerated ions transfer [39], resulting in a greater degree of binder removal. At open circuit potential this preferential removal of the binderphase subsequently leads to the heavily undermining of the exposed diamond by the abrasion of debris, which will further cause much more material removal as can be inferred from the presence of cavities filled with SiC in Fig. 8. Moreover, the presence of such a mixture of fragments on the surface (shown in light green in Fig. 10) could enable the
312
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 9. SEM images of the corresponding cross section of worn PDC as the salinity varied: (a) 0%; (b)10%; (c) 20%; (d) 20% with applied CP.
would lead to the simultaneous stripping of the protective passive film formed on the binder of the worn PDC surface, followed by an increase in electrochemical activity as the active bare binder had been
magnification further revealed the wear mode (Fig. 11). The diamond shows a heavily deformed, multiple indented wear surface with clear evidence of abrasion wear. Inevitably, such kind of abrasion wear
E
e-
A B
e-
C
D
F
E
313
Fig. 10. Schematic illustration of the tribocorrosion process between the PDC and the SiC grinding wheel (A: micro galvanic coupling between the binder and the substrate; B: passive film; C: micro galvanic coupling between the binder and the binder/agglomeration; D: corrosion of the binder; E: cracking of diamond; F: release of diamond and filled with agglomeration).
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
[5]
[6]
[7]
[8] [9]
[10] [11]
[12]
[13] [14]
Fig. 11. SEM image of a diamond grain on the worn surface of PDC.
[15]
continuously exposed to the corrosive fluid again. Consequently, further material loss turns up due to the mechanical wear accelerated corrosion.
[16] [17]
4. Conclusions
[18]
The present study reveals the tribological properties of PDC under saline solution environment and the following main conclusions can be drawn from the results:
[19] [20] [21]
(1) A new method based on three-dimensional point cloud for calculating the wear volume of PDC has been proposed and experimental results show that the measurement method is feasible with an error of no more than 5%. Further study is still necessary to improve its measurement accuracy. (2) Under salinity conditions, the wear volume of PDC increases significantly compared with that of clean water and the increased salinity causes more severe damage to the PDC cutter. Moreover, the employment of −1.0 V as the protection potential can effectively reduce the corrosion to a negligible level. (3) Degradation mechanism of PDC in abrasion-corrosion environment is complex since it is a synergistic effect between mechanical processes and electrochemical processes. Overall, the abrasion-corrosion is prominently controlled by mechanical wear since the pure abrasion provide more than 70% of the total material loss. Despite the fact that pure corrosion contributes little to the total volume loss, the corrosion attack toward the binder will result in a significant increase in material loss.
[22]
[23] [24] [25] [26] [27] [28] [29]
[30]
[31]
Acknowledgements [32]
This work was supported by the National Natural Science Foundation of China [Grant number 41872187].
[33]
References
[34] [35]
[1] R.H. Wentorf, R.C. DeVries, F.P. Bundy, Sintered superhard materials, Science 208 (4446) (1980) 873–880. [2] A. Lammer, Mechanical properties of polycrystalline diamonds, Mater. Sci. Technol. 4 (11) (1988) 949–955. [3] X. Sha, W. Yue, W. Qin, et al., Enhanced tribological behaviors of sintered polycrystalline diamond by annealing treatment under humid condition, Int. J. Refract. Met. Hard Mater. 80 (2019) 85–96. [4] S.G. Moseley, K.P. Bohn, M. Goedickemeier, Core drilling in reinforced concrete
[36] [37] [38]
314
using polycrystalline diamond (PCD) cutters: wear and fracture mechanisms, Int. J. Refract. Met. Hard Mater. 27 (2) (2009) 394–402. M. Yahiaoui, J.Y. Paris, K. Delbé, et al., Quality and wear behavior of graded polycrystalline diamond compact cutters, Int. J. Refract. Met. Hard Mater. 56 (2016) 87–95. Y. Li, X. Sha, W. Yue, et al., Effects of tribochemical reaction on tribological behaviors of Si3N4/polycrystalline diamond in hydrochloric acid, Int. J. Refract. Met. Hard Mater. 79 (2019) 197–203. T. Yue, W. Yue, J. Li, et al., Effect of vacuum annealing temperature on tribological behaviors of sintered polycrystalline diamond compact, Int. J. Refract. Met. Hard Mater. 64 (2017) 66–74. P.L. Tso, Y.G. Liu, Study on PCD machining, Int J Mach Tool Manu 42 (3) (2002) 331–334. Z.M. Akhtari, S.A.A.D. Mohammed, Z.P. Akhtari, et al., Electrochemical corrosion behavior of carbon steel pipes coated with a protective ceramic layer using plasma and HVOF thermal spray techniques for oil and gas, Ceram. Int. 42 (2) (2016) 3397–3406. J. Gu, K. Huang, Role of cobalt of polycrystalline diamond compact (PDC) in drilling process, Diam. Relat. Mater. 66 (2016) 98–101. C. Liu, Z. Kou, D. He, et al., Effect of removing internal residual metallic phases on wear resistance of polycrystalline diamond compacts, Int. J. Refract. Met. Hard Mater. 31 (2012) 187–191. L. Wang, P. Qiu, Y. Liu, et al., Corrosion behavior of thermal sprayed WC cermet coatings containing metallic binders in saline environment, Trans. Nonferrous Metals Soc. China 23 (9) (2013) 2611–2617. Patrick S.M. Dougherty, et al., Elucidating PDC rock cutting behavior in dry and aqueous conditions using tribometry, J. Pet. Sci. Eng. 133 (2015) 529–542. D. Toma, W. Brandl, G. Marginean, Wear and corrosion behaviour of thermally sprayed cermet coatings, Surf. Coat. Technol. 138 (2) (2001) 149–158. J. Berget, T. Rogne, E. Bardal, Erosion-corrosion properties of different WC-co-Cr coatings deposited by the HVOF process-influence of metallic matrix composition and spray powder size distribution, Surf. Coat. Technol. 201 (18) (2007) 7619–7625. X.F. Han, J.S. Jin, M.J. Wang, et al., A review of algorithms for filtering the 3D point cloud, Signal Process. Image Commun. 57 (2017) 103–112. N. Chen, J. Kemeny, Q. Jiang, Z. Pan, Automatic extraction of blocks from 3D point clouds of fractured rock, Comput. Geosci. 109 (2017) 149–161. Q. Zhao, Y. Wu, X. Li, et al., A method of measuring stacked objects volume based on laser sensing, Meas. Sci. Technol. 28 (10) (2017) 105002. H. Li, Y. Qian, P. Cao, et al., Calculation method of surface shape feature of rice seed based on point cloud, Comput. Electron. Agric. 142 (2017) 416–423. T. Hou, J. Liu, Y. Liu, Algorithmic clustering of LiDAR point cloud data for textural damage identifications of structural elements, Measurement 108 (2017) 77–90. Milton Stern, L. Geary Al, Electrochemical polarization I. A theoretical analysis of the shape of polarization curves, J. Electrochem. Soc. 104 (1) (1957). V.A.D. Souza, A. Neville, Corrosion and synergy in a WC-Co-Cr HVOF thermal spray coating—understanding their role in erosion-corrosion degradation, Wear 259 (1–6) (2005) 171–180. M. Reyes, A. Neville, Degradation mechanisms of Co based alloy and WC metalmatrix composites for drilling tools offshore, Wear 255 (7–12) (2003) 1143–1156. V.A. De Souza, A. Neville, Corrosion and erosion damage mechanisms during erosion-corrosion of WC-Co-Cr cermet coatings, Wear 255 (1–6) (2003) 146–156. ASTM, ASTM G119-2003(1998) Standard Guide for Determining Synergism between Wear and Corrosion, (2003). C. Hodge, M.M. Stack, Tribo-corrosion mechanisms of stainless steel in soft drinks, Wear 270 (1) (2010) 104–114. K.R. Trethewey, J. Chamberlain, Corrosion for Students of Science and Engineering, Longman Sc & Tech, 1988. S. Mischler, A. Spiegel, M. Stemp, et al., Influence of passivity on the tribocorrosion of carbon steel in aqueous solutions, Wear 251 (1) (2001) 1295–1307. P.E. Sinnett-Jones, J.A. Wharton, R.J.K. Wood, Micro-abrasion-corrosion of a CoCrMo alloy in simulated artificial hip joint environments, Wear 259 (7) (2005) 898–909. M.R. Thakare, J.A. Wharton, R.J.K. Wood, C. Menger, Investigation of micro-scale abrasion–corrosion of WC-based sintered hardmetal and sprayed coating using in situ electrochemical current-noise measurements, Wear 267 (11) (2009) 1967–1977. J.O. Bello, R.J.K. Wood, J.A. Wharton, Synergistic effects of micro-abrasion-corrosion of UNS S30403, S31603 and S32760 stainless steels, Wear 263 (1) (2007) 149–159. F. Ferrer, H. Idrissi, H. Mazille, et al., A study of abrasion-corrosion of AISI 304L austenitic stainless steel in saline solution using acoustic emission technique, Ndt & E Int. 33 (6) (2000) 363–371. A.J. Gant, M.G. Gee, A.T. May, The evaluation of tribo-corrosion synergy for WC–co hardmetals in low stress abrasion, Wear 256 (5) (2004) 500–516. A.J. Gant, M.G. Gee, A.T. May, Microabrasion of WC–Co hardmetals in corrosive media, Wear 256 (9) (2004) 954–962. A.J. Gant, M.G. Gee, D.D. Gohil, et al., Use of FIB/SEM to assess the tribo-corrosion of WC/Co hardmetals in model single point abrasion experiments, Tribol. Int. 68 (6) (2013) 56–66. S.M. Sharland, A review of the theoretical modelling of crevice and pitting corrosion, Corros. Sci. 27 (3) (1987) 289–323. T.P. Hoar, The production and breakdown of the passivity of metals, Corros. Sci. 7 (6) (1967) 341–355. F. Al-Kharafi, W. Badawy, J. Al-Ajmi, Effect of chloride ions on the corrosion and passivation behaviours of cobalt in neutral solutions, Indian J. Chem. Technol. 6 (4)
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
[41] H. Jung, A. Alfantazi, Corrosion properties of electrodeposited cobalt in sulfate solutions containing chloride ions, Electrochim. Acta 55 (3) (2010) 865–869. [42] S.S. Abd El Rehim, A.A. El Basosi, M.M. Osman, The influence of halide ions on the corrosion and passivity of cobalt in an alkaline medium, J. Electroanal. Chem. 348 (1–2) (1993) 99–106. [43] O.J. Murphy, Bockris J.M. Pou, Chloride ion penetration of passive films on iron, J. Electrochem. Soc. 8 (130) (1983) 1792–1794.
(1999) 194–201. [39] K.M. Emran, A.K. Al-Harbi, Comparison of the corrosion resistance behaviour for two metal-metal glassy alloys in neutral solution with chloride impact, J. Alloys Compd. 767 (2018) 753–762. [40] Robert J.K. Wood, Stephen Herd, R. Mandar, A critical review of the tribocorrosion of cemented and thermal sprayed tungsten carbide, Tribol. Int. 119 (2018) 491–509.
315
Contents lists available at ScienceDirect
International Journal of Refractory Metals & Hard Materials journal homepage: www.elsevier.com/locate/IJRMHM
Tribocorrosion properties of polycrystalline diamond compact in saline environment
T
⁎
Liang Penga, Bingsuo Pana,b, , Yuanji Yaoa, Songcheng Tana a b
Faculty of Engineering, China University of Geosciences, Wuhan 430074, China International Joint Research Center for Deep Earth Drilling and Resource Development, Wuhan 430074, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Polycrystalline diamond compact Abrasion-corrosion Wear Drilling Point cloud
Tribocorrosion properties of polycrystalline diamond compact (PDC) in solution containing sodium chloride were investigated using a modified pin-on-disc wear test rig. Tests were conducted at various salinities (0–20%) for a better understanding of the abrasion-corrosion interaction. The corrosion behavior was examined through a three-electrode electrochemical cell. The contributions of pure abrasion and pure corrosion as well as their synergy to the total volume loss were calculated. The influence of cathodic protection on the abrasion-corrosion performance of PDC was also evaluated. Experimental data in this paper shows that the PDC suffers more severe damage as the sodium chloride concentration increases gradually and the applied potential of −1.0 V vs. SCE can suppress the corrosion-related effects to a negligible level. Both electrochemical measurements and SEM micrographs of worn surfaces were used to detail the degradation mechanism. Despite the fact that it is the mechanical wear that dominates the abrasion-corrosion mechanism, results reveal that the interaction between the abrasion and corrosion plays a significant role. Moreover, an effective volume calculation method based on three dimensional point cloud was proposed to determine the wear volume of PDC. Validation studies demonstrate that the measurement method is feasible and accurate with an error of no more than 5%.
1. Introduction Polycrystalline diamond compact (PDC) has been extensively employed in the field of oil and gas drilling due to its excellent performance in terms of hardness, toughness and wear resistance [1–3]. As a significant engineering factor to evaluate the quality of PDC, tribological properties have been widely investigated to make it more effectively applicable under various environments [4–8]. Besides mechanical wear, PDC also has to withstand severe corrosion environments in some applications, such as offshore drilling [9] and evaporite bed drilling [10]. The common characteristic for those applications is that the liquid medium containing sodium chloride continuously erodes the exposed bit, leading to the accelerated bit deterioration due to the combined effect of mechanical abrasion and electrochemical corrosion [9]. Over the past decades, various techniques for improving the wear resistance of PDC bits in corrosive environments have been extensively investigated by many researchers, a typical example of which is the WC/CO-based coating used for protecting the steel body of bits in severe erosion-corrosion environment [10–12]. However, the tribocorrosion behaviors of the polycrystalline diamond (PCD) layer itself under corrosive condition have not attracted sufficient attention of
⁎
researchers. Specially, interpretation for the mechanism of coupling effect of mechanical wear and corrosion, sometimes referred to as abrasion-corrosion synergy, requires considerable efforts. Hence, investigating the tribological performances of PDC in corrosive environment is of both immensely scientific and technological interests. In addition, weighing method has been widely used to evaluate the wear resistance of PDC tools in previous studies [11,13–15]. Nonetheless, there are inherent limitations impeding its further applications. A typical example is that the measuring results extracted from the weighing method refer to the total weight loss of the integrated sample including the undesired part, which obscures the wear volume for the specific component. Take the PDC bits for example, the volume loss measured by weighing method can be segregated into two components, PDC weight loss and the steel material loss, when abrasion and corrosion attack the bit simultaneously. Besides, result extracted from the weighing method shows the weight change rather than the visualized volume loss. Though the volume change could be further determined through dividing the measuring result by the density of the material, the key point is that the requisite density is sometimes imprecise especially for composite materials, leading to an increasing workload for the research. On the other hand, three dimensional point clouds
Corresponding author at: Faculty of Engineering, China University of Geosciences, Wuhan 430074, China. E-mail address: [email protected] (B. Pan).
https://doi.org/10.1016/j.ijrmhm.2019.03.016 Received 4 February 2019; Received in revised form 12 March 2019; Accepted 17 March 2019 Available online 18 March 2019 0263-4368/ © 2019 Elsevier Ltd. All rights reserved.
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
technology have been widely employed to represent 3D spatial feature in recent years due to its simplicity, flexibility and powerful representation capability [16,17]. Therefore, it is considerable to introduce such an effective technology into the wear volume calculation of PDC bits. Motivated by the abrasion-corrosion effect on the PDC, this paper investigated the tribological properties of PDC in saline environment using a pin-on-disk tribometer. Special efforts had been devoted to understand the coupling effects of mechanical wear and corrosion on the degradation mechanisms of PDC. What's more, a method based on three dimensional point clouds that would be discussed later was proposed to calculate the wear volume loss based on previous studies [18–20]. Although the emphasis of this paper is on the tribocorrosion properties of PDC, the results have substantial relevance to numerous researches, especially for those whose volume loss is out of the detection by weighing method.
Fig. 2. Schematic of the tribocorrosion test (WE: Working Electrode, RE; Reference Electrode, CE: Counter Electrode).
2. Experimental
three-electrode electrochemical cell connected to an electrochemical workstation (Wuhan CorrTest, CS310H) was set up as shown in Fig. 2, in which the specimen served as working electrode and a graphite sheet and a saturated calomel electrode (SCE) were selected as counter electrode and reference electrode respectively. Two kinds of electrochemical tests were undertaken to isolate the contributions of pure corrosion(C) and pure abrasion (E) to the total volume loss (TVL) of PDC under tribocorrosion condition. Firstly, potentiostatic test was carried out at a constant potential of −1.0 V vs. SCE to apply cathodic protection (CP) to the cutter under test environment. Secondly, potentiodynamic polarization test was performed under static condition. With reference to SCE, the electrochemical polarization curve was obtained by scanning from 200 mV nobler than open circuit potential (OCP) to 100 mV more negative than the OCP at a rate of 2 mV/s. Specially, to evaluate the charge transfer resistance values across the electrode-electrolyte interface, a frequency in range of 105 Hz to 10−2 Hz with amplitude potential of 10 mV was used to conduct electrochemical impedance spectroscopy (EIS). Both before and after the wear test, the micro topography and elements distribution of the samples surface were analyzed by scanning electron microscopy (SEM, G2 PRO, Phenom) equipped with an energydispersive X-ray spectroscope (EDS, EM-30AX PLUS+, Coxem).
2.1. Materials Commercial sintered polycrystalline diamond compact (SF Diamond Co.Ltd.) was used in this study. The polycrystalline diamond (PCD) layer composed of diamond (particle size mostly in 20-30 μm) and Co binder (8%–10%) was sintered onto a circular face of WC-Co substrate with a diameter of 13 mm (Fig. 1). The total height of PDC sample is 8 mm with 1 mm of PCD layer. 2.2. Tribocorrosion test A pin-on-disc wear test rig was used to simulate drilling conditions. PDC cutter brazed on a sample holder was fixed on the stationary pin holder of the apparatus and the counter face material was 60 mesh SiC grinding wheel. To have a better understanding of the effects of salinity on the tribological performance of PDC, five different sodium chloride concentrations varying from 0% to 20% in steps of 5% were adopted for this research. Prior to the test, a long soak of 24 h in the corresponding sodium chloride solution was given to the SiC grinding wheels. During the test, the SiC grinding wheel exposed to the test solution was rotated with a cutting diameter of 8 cm at 200 r/min. The corresponding initial contact load was set to 5 N, followed by a constant load of 200 N being applied on the cutter. The duration of the experiment was set as the time when the cutter completed a four-centimeter penetration and the operation time was recorded simultaneously. In all of the mentioned tests, the samples including their holders were electrically insulated from the surrounding environment except for the studied areas. The testing conditions were schematically shown in Fig. 2. To accurately provide insights into the local interaction between mechanical abrasion and electrochemical corrosion during the test, a
2.3. Wear volume calculation After an ultrasonic bath and drying process, the assembled PDC and its holder was fixed on the operation platform of a confocal laser scanning microscope (VK-X100K, manufactured by KEYENCE). Using a magnification of 100 times, nine sets of point cloud data were measured to cover the whole worn region of PDC. Subsequently, the registered points cloud data were obtained through pre-positioned software on the computer of the facility. Once all processes mentioned above got finished, the data was imported to CloudCompare software where the extraction of the boundary and PDC surface was carried out, a preprocessing for the subsequent worn volume calculation. Based on the results of point clouds processing, 2D Delaunay triangulation was performed after the points were projected to the bottom, followed by the generation of the triangular infinitesimal volume elements. According to integral thought, the sum of all volumes of triangular infinitesimal elements could replace the volume of measured PDC approximately and the detailed calculation principle has been shown somewhere else [18]. Generally speaking, the measurement of the total volume loss of PDC comprises the volume measurement before and after the tribocorrosion test, represented by V1 and V2 respectively. However, there are something different about the method proposed in this paper. In particular, the initial volume of PDC could also be calculated based on the point cloud of worn PDC. As previously analyzed, the plane fitting
Fig. 1. The optical characteristics of PDC. 308
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 3. Scatter diagram illustrated the processed point cloud and the 3D reconstruction of the top surface, where the insert is the enlarged image of red marked region. (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)
volume loss for specific region of the specimen.
of the extracted top surface of worn PDC point cloud was carried out followed by the acquisition of the plane fitting equation. As the red reintegrated plane presented in Fig. 3D reconstruction of the top surface was implemented subsequently by combining the obtained equation with the 2D coordinate point on the projection plane. In principle, the value of TVL can be defined as the difference between V1 and V2. Considering the interference (denoted by V3) between extracted and restored top plane incorporating into the final result, the volume of the material measured at the end of the experiment corresponds to the following expression.
VTVL = V1 − V2 − V3
3.2. Electrochemical characteristic As a basic parameter to characterize the electrochemical behavior of the PDC under various saline solution, corrosion current density was determined as a measure of corrosion rate based on the potentiodynamic polarization curves as shown in Fig. 5, in which semi logarithmic current density versus potential has been plotted. It can be seen that the PDC exhibits similar polarization behavior in different salinity solutions. The corrosion current density (icorr) and the free corrosion potential (Ecorr) obtained by Tafel extrapolation method were present in Table 1. Despite the fact that only the anodic part of the potentiodynamic polarization curves was used to determine the corrosion current density, the accuracy had been proved by M. Stern [21]. When the test is performed without nitrogen or argon purging, the activation polarization and concentration in cathodic part would lead to marked deviations and uncertainties on the value of corrosion current density [21,22]. It seems that the presence of sodium chloride in the test solution shifted the Ecorr in the active direction. The influence of salinity could also be evaluated through the corrosion current density data in Table 1. When PDC was immersed in the 5% salinity solution, the obtained icorr was about 0.01805mA/cm2. As the salinity in the solution gradually increased to 20%, the corresponding icorr showed a much higher value of 0.04579mA/cm2, indicating a more active behavior. All those findings could be related to the higher concentration of chloride ions around the anode, which facilitated the ion-exchange between the binder and solution. The measurement of EIS shown in Fig. 6 presents a consistent result with the potentiodynamic polarization test. It shows that the size of the semicircle shrank with the increasing concentration of sodium chloride contained in the test solution. Since the semicircle represents the resistance of charge-transfer reaction at the interface between the
(1)
Referring to all those analyses exhibited above, a program based on Matlab had been designed for the volume calculation. 3. Results and discussion 3.1. Validation of proposed method for wear volume calculation To validate the accuracy and reliability of the volume calculation method proposed above, a 45# steel cylinder was employed to replace the PDC cutter in the wear test. There are accessible approaches to its density and initial volume. Both before and after the test, the steel cylinder was first cleaned in an ultrasonic ethanol bath and then dried in vacuum to obtain a more accurate record of weight change. The point cloud acquisition and processing was conducted after the abrasion test, and the result was shown in Fig. 4. The volume loss determined by weighting method was 0.6966mm3, while the point cloud method reported a 0.6637mm3 material removal. It was believed that this small discrepancy was derived from the mismatching between the reconstructed and the original top surface of PDC since the concerned surface was not a geometrical plane in real micro-level. However, this small difference of only 4.94% in application of the point cloud measurement system was far outweighed by the ability to capture the
Fig. 4. Photograph illustrating the wear of a 45# steel cylinder: (a) optical characteristics; (b) the point cloud corresponding to the wear part of (a). 309
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Table 2 Result of volume loss in tribocorrosion test (mm3).
Table 1 Corrosion data of PDC under different salinity. 5%
10%
15%
20%
Ecorr(V) icorr(mA/cm2)
−0.23073 0.01805
−0.2355 0.03222
−0.2556 0.03288
−0.2739 0.04579
Fig. 6. Nyquist diagrams measured on the PDC immersed in various saline solutions.
solution and PDC, those semicircles in Fig. 6 mean that the corrosion resistance of the PDC decreased when the sodium chloride concentration increased in the solution. Notably, the degree of the increase in icorr slowed down in higher salinity, which could be interpreted by the limited distribution of cobalt on the exposed surface. 3.3. Abrasion–corrosion material loss According to previous research results [23–25], the total volume loss (TVL) under abrasion-corrosion condition can be divided into three constituent parts, as is demonstrated by Eq. (2).
TVL = E + C + S
0%
5%
10%
15%
20%
TVL E(under CP) C S
0.5526 ━ ━ ━
0.5994 0.5415 0.0048 0.0531
0.6258 0.5549 0.0086 0.0623
0.6478 0.5216 0.0088 0.1174
0.7445 0.5371 0.0122 0.1952
respectively; however, we failed to accomplish it due to a lack of necessary equipment. Hence, distinction between EC and CE has not been made and S is defined to quantify the coupling effect between the corrosion and abrasion. Results on the effect of salinity on TVL were recorded in Table 2 and compared with the volume loss with applied CP. The values of TVL were derived from the samples being attacked under tribocorrosion condition and the pure mechanical abrasion E were calculated from the potentiostatic test in which the effect of corrosion-related activities were suppressed to a negligible level, both of which were calculated based on the point cloud. As for the accurate estimation of the pure corrosion contribution, the calculation results were determined through Faraday's law [26–28] since the corrosion density had been well defined in Table 1. Mathematically, the synergy contribution(S) to total material loss could be calculated through Eq. (2). During the analysis of the obtained results, it becomes apparent that the material loss due to mechanical abrasion dwarfs the material loss due to corrosion, which is to be expected of PDC for the strong corrosion resistant properties of its main component – diamond. It can be seen from Table 2 that the values of TVL trend to increase linearly with the concentration of sodium chloride in the aqueous solutions, from 0.5526μm3 at 0% salinity to 0.7445μm3 at 20% salinity. Besides, a significant reduction of material loss is observed from Table 2 in the presence of applied CP compared with one measured without applied CP. The TVL values with CP applied under varied salinity does not suffer drastic fluctuation since the standard deviation is no more than 0.02. Moreover, their average value has not even exceeded 5% of that under clean water. Fig. 7 presents the morphology of the worn surface formed on the PDC after cutting operation under different salinity. It can be found that massive gray attachments are deposited on the contact area of the cutter, which have been marked in Fig. 7(a). In addition, compared with the surface worn in the clean water, plenty of pits can be observed on the surface (Fig. 7(b) and Fig. 7(c)). Similar to the TVL, the number of pits has increased as the salinity increased, indicating an increase in corrosion activity due to the activation of the anodic reaction. To further reveal the chemical composition of worn surface, corresponding EDS measurements were carried out and the results were displayed in Fig. 8. Different from the initial surface of PDC, there are several noticeable changes after the cutting operation. As mentioned above, many gray areas appear on the worn surface and their main chemical composition is proved Si element arising from the aggregated debris of the SiC grinding wheel. Meanwhile, much attention should be paid on the bright region marked in Fig. 8(c) since the occurrence of oxygen in the cobalt-rich region represents the cobalt oxide film formed during the cutting process, which has not been found on the unworn surface. Corresponding to the contact surface of the worn PDC cutter, the cross sections of the PDC are present in Fig. 9, from which a reasonable support for the TVL change can be drawn. For the PDC tested in clean water, there are almost no visible crevices on the cross section, meaning no corrosion attack. In contrast, micro-cracks in Fig. 9(b), implying the appearance of mild corrosion, come into sight clearly when the test salinity utilized turned to 10%. Fig. 9(c) depicts the cross section of PDC tested at 20% salinity where an exacerbated deteriorating corrosion occurs since the crevices have aggregated and enlarged more evidently. In addition, investigation into the cross section of the PDC with applied
Fig. 5. Polarization curves of PDC in different salinity.
Salinity
Salinity
(2)
where E, C and S are wear material loss component associated with pure abrasion, pure corrosion and abrasion-corrosion synergy, respectively. Synergistic wear has been further defined as the aggregate of change in abrasion wear due to corrosion, EC, and change in corrosive wear due to abrasion, CE. It is desirable to determine EC and CE 310
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 7. SEM images of the worn surface of PDC as the salinity varied: (a) 0%; (b)10%; (c) 20%.
tribocorrosion test, the corrosion and corrosion-related mechanisms, i.e. (C + S) forms up to 28% of the overall degradation of the PDC. Such an enhancement to the existing degradation processes due to synergism is not surprising. Similar results have been reported for WC-Co hardmetal (a material comparable in microstructure to PDC) abraded in corrosive media containing silica sand, since the main rate controlling mechanism of the material removal has changed from the fracture or pluckout of WC grain under non-corrosive conditions to the binder dissolution in sulphuric acid solution (pH 1.1) [33,34]. However, the related research conclusions must be used with caution in the current study for two reasons: the different corrosive medium (various concentrations of chloride ion rather than hydrogen ion) and the inertia interface between the diamond grain and the binder. Fig. 10 shows a schematic interpreting the possible interaction between the PDC and the SiC grinding wheel during abrasion-corrosion. In addition to the two bodies in contact, the wear particles between the contact surfaces mainly originate from SiC grinding wheel. It clearly shows in the schematic that the abrasion–corrosion resistance of the PDC cutter primarily depends on the ability of the diamond to resist fragmentation. Besides, the intergranular corrosion toward the binder cobalt has occurred in form of pitting leaving the diamond being exposed. The presence of the binder depleted regions could be explained
CP had also been conducted and the morphologic details were given in Fig. 9(d). Obviously the micrograph is present with no sign of corrosion, due to the positive impact of cathodic protection.
3.4. Discussion Metallic-related materials functioning in corrosive environments and subject to abrasive wear often lose durability due to the combined effect of mechanical wear and electrochemical corrosion. However, material loss under those conditions is not necessarily just the summation of mechanical abrasion and corrosion measured separately [28–30]. In-depth understanding of the mechanism of abrasion–corrosion cannot be achieved without a clear insight into the role of synergy. Although abrasion–corrosion interaction sometimes result in a reduction in overall mass loss [31,32], this is not the case in this paper anyhow. As the data in Table 2 shows, the enhanced damage to PDC is evident due to the combined effect of abrasion and corrosion. Corrosion contribution to total volume loss considered alone gives the impression that it is not the main factor, but when taking the corrosion-related mechanisms into account it becomes clear that focusing attention only on mechanical abrasion is unreasonable. Even though the corrosion contributes little to the total volume loss under 20% salinity in the 311
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 8. SEM images and EDS of the surface of PDC test under 20% salinity: (a) SEM image of initial surface; (b) EDS surface chemical composition of (a); (c) SEM image of worn surface; (d) (e) (f)corresponding EDS measurement of (c).
existence of the localized microenvironment dramatically different to that of the bulk conditions, an effect of which has been thought to associate with crevice or pitting corrosion [40]. Those uneven corrosion activities during tribocorrosion processes will in turn contributes to enhanced material removal. Although the passive oxide films, represented in orange in Fig. 10, have formed during the abrasion-corrosion process, it shows no marked improvement in the tribocorrosion performance of PDC since the mechanically weak films can be easily removed. Besides, the formation of the passive protective film is also a time-consuming process. It has been typically observed that the presence of chloride ions in solution increases the dissolution rate of other passive metal systems by creation of locally active sites on the metal surface and increasing the rate of pit propagation [38,41–43], both of which will impair the positive effect of the passive film against corrosion. The wear morphology as observed in Fig. 7 indicates that it is the mechanical wear that dominates on the prevailing degradation mechanism. Moreover, a SEM investigation of worn specimens with high
through galvanic coupling as electrons can move between the conductive phases such as the binder and the substrate due to the heterogeneous property of PDC as depicted above. In addition, such microstructural inhomogeneities at the contact point may provide localized conditions which could promote the early stages of damage accumulation as found in the analogous hard materials (e.g. WC/Co hardmetal) [35]. Specially, the effect of chloride ions on the corrosion behavior could be interpreted as being a result of specific absorption of ions on the metal surface, and the extent of absorption depends on both metal and halide [36–38]. Undoubtedly, increased chloride concentration while abrasion would create active chemical environment for accelerated ions transfer [39], resulting in a greater degree of binder removal. At open circuit potential this preferential removal of the binderphase subsequently leads to the heavily undermining of the exposed diamond by the abrasion of debris, which will further cause much more material removal as can be inferred from the presence of cavities filled with SiC in Fig. 8. Moreover, the presence of such a mixture of fragments on the surface (shown in light green in Fig. 10) could enable the
312
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
Fig. 9. SEM images of the corresponding cross section of worn PDC as the salinity varied: (a) 0%; (b)10%; (c) 20%; (d) 20% with applied CP.
would lead to the simultaneous stripping of the protective passive film formed on the binder of the worn PDC surface, followed by an increase in electrochemical activity as the active bare binder had been
magnification further revealed the wear mode (Fig. 11). The diamond shows a heavily deformed, multiple indented wear surface with clear evidence of abrasion wear. Inevitably, such kind of abrasion wear
E
e-
A B
e-
C
D
F
E
313
Fig. 10. Schematic illustration of the tribocorrosion process between the PDC and the SiC grinding wheel (A: micro galvanic coupling between the binder and the substrate; B: passive film; C: micro galvanic coupling between the binder and the binder/agglomeration; D: corrosion of the binder; E: cracking of diamond; F: release of diamond and filled with agglomeration).
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
[5]
[6]
[7]
[8] [9]
[10] [11]
[12]
[13] [14]
Fig. 11. SEM image of a diamond grain on the worn surface of PDC.
[15]
continuously exposed to the corrosive fluid again. Consequently, further material loss turns up due to the mechanical wear accelerated corrosion.
[16] [17]
4. Conclusions
[18]
The present study reveals the tribological properties of PDC under saline solution environment and the following main conclusions can be drawn from the results:
[19] [20] [21]
(1) A new method based on three-dimensional point cloud for calculating the wear volume of PDC has been proposed and experimental results show that the measurement method is feasible with an error of no more than 5%. Further study is still necessary to improve its measurement accuracy. (2) Under salinity conditions, the wear volume of PDC increases significantly compared with that of clean water and the increased salinity causes more severe damage to the PDC cutter. Moreover, the employment of −1.0 V as the protection potential can effectively reduce the corrosion to a negligible level. (3) Degradation mechanism of PDC in abrasion-corrosion environment is complex since it is a synergistic effect between mechanical processes and electrochemical processes. Overall, the abrasion-corrosion is prominently controlled by mechanical wear since the pure abrasion provide more than 70% of the total material loss. Despite the fact that pure corrosion contributes little to the total volume loss, the corrosion attack toward the binder will result in a significant increase in material loss.
[22]
[23] [24] [25] [26] [27] [28] [29]
[30]
[31]
Acknowledgements [32]
This work was supported by the National Natural Science Foundation of China [Grant number 41872187].
[33]
References
[34] [35]
[1] R.H. Wentorf, R.C. DeVries, F.P. Bundy, Sintered superhard materials, Science 208 (4446) (1980) 873–880. [2] A. Lammer, Mechanical properties of polycrystalline diamonds, Mater. Sci. Technol. 4 (11) (1988) 949–955. [3] X. Sha, W. Yue, W. Qin, et al., Enhanced tribological behaviors of sintered polycrystalline diamond by annealing treatment under humid condition, Int. J. Refract. Met. Hard Mater. 80 (2019) 85–96. [4] S.G. Moseley, K.P. Bohn, M. Goedickemeier, Core drilling in reinforced concrete
[36] [37] [38]
314
using polycrystalline diamond (PCD) cutters: wear and fracture mechanisms, Int. J. Refract. Met. Hard Mater. 27 (2) (2009) 394–402. M. Yahiaoui, J.Y. Paris, K. Delbé, et al., Quality and wear behavior of graded polycrystalline diamond compact cutters, Int. J. Refract. Met. Hard Mater. 56 (2016) 87–95. Y. Li, X. Sha, W. Yue, et al., Effects of tribochemical reaction on tribological behaviors of Si3N4/polycrystalline diamond in hydrochloric acid, Int. J. Refract. Met. Hard Mater. 79 (2019) 197–203. T. Yue, W. Yue, J. Li, et al., Effect of vacuum annealing temperature on tribological behaviors of sintered polycrystalline diamond compact, Int. J. Refract. Met. Hard Mater. 64 (2017) 66–74. P.L. Tso, Y.G. Liu, Study on PCD machining, Int J Mach Tool Manu 42 (3) (2002) 331–334. Z.M. Akhtari, S.A.A.D. Mohammed, Z.P. Akhtari, et al., Electrochemical corrosion behavior of carbon steel pipes coated with a protective ceramic layer using plasma and HVOF thermal spray techniques for oil and gas, Ceram. Int. 42 (2) (2016) 3397–3406. J. Gu, K. Huang, Role of cobalt of polycrystalline diamond compact (PDC) in drilling process, Diam. Relat. Mater. 66 (2016) 98–101. C. Liu, Z. Kou, D. He, et al., Effect of removing internal residual metallic phases on wear resistance of polycrystalline diamond compacts, Int. J. Refract. Met. Hard Mater. 31 (2012) 187–191. L. Wang, P. Qiu, Y. Liu, et al., Corrosion behavior of thermal sprayed WC cermet coatings containing metallic binders in saline environment, Trans. Nonferrous Metals Soc. China 23 (9) (2013) 2611–2617. Patrick S.M. Dougherty, et al., Elucidating PDC rock cutting behavior in dry and aqueous conditions using tribometry, J. Pet. Sci. Eng. 133 (2015) 529–542. D. Toma, W. Brandl, G. Marginean, Wear and corrosion behaviour of thermally sprayed cermet coatings, Surf. Coat. Technol. 138 (2) (2001) 149–158. J. Berget, T. Rogne, E. Bardal, Erosion-corrosion properties of different WC-co-Cr coatings deposited by the HVOF process-influence of metallic matrix composition and spray powder size distribution, Surf. Coat. Technol. 201 (18) (2007) 7619–7625. X.F. Han, J.S. Jin, M.J. Wang, et al., A review of algorithms for filtering the 3D point cloud, Signal Process. Image Commun. 57 (2017) 103–112. N. Chen, J. Kemeny, Q. Jiang, Z. Pan, Automatic extraction of blocks from 3D point clouds of fractured rock, Comput. Geosci. 109 (2017) 149–161. Q. Zhao, Y. Wu, X. Li, et al., A method of measuring stacked objects volume based on laser sensing, Meas. Sci. Technol. 28 (10) (2017) 105002. H. Li, Y. Qian, P. Cao, et al., Calculation method of surface shape feature of rice seed based on point cloud, Comput. Electron. Agric. 142 (2017) 416–423. T. Hou, J. Liu, Y. Liu, Algorithmic clustering of LiDAR point cloud data for textural damage identifications of structural elements, Measurement 108 (2017) 77–90. Milton Stern, L. Geary Al, Electrochemical polarization I. A theoretical analysis of the shape of polarization curves, J. Electrochem. Soc. 104 (1) (1957). V.A.D. Souza, A. Neville, Corrosion and synergy in a WC-Co-Cr HVOF thermal spray coating—understanding their role in erosion-corrosion degradation, Wear 259 (1–6) (2005) 171–180. M. Reyes, A. Neville, Degradation mechanisms of Co based alloy and WC metalmatrix composites for drilling tools offshore, Wear 255 (7–12) (2003) 1143–1156. V.A. De Souza, A. Neville, Corrosion and erosion damage mechanisms during erosion-corrosion of WC-Co-Cr cermet coatings, Wear 255 (1–6) (2003) 146–156. ASTM, ASTM G119-2003(1998) Standard Guide for Determining Synergism between Wear and Corrosion, (2003). C. Hodge, M.M. Stack, Tribo-corrosion mechanisms of stainless steel in soft drinks, Wear 270 (1) (2010) 104–114. K.R. Trethewey, J. Chamberlain, Corrosion for Students of Science and Engineering, Longman Sc & Tech, 1988. S. Mischler, A. Spiegel, M. Stemp, et al., Influence of passivity on the tribocorrosion of carbon steel in aqueous solutions, Wear 251 (1) (2001) 1295–1307. P.E. Sinnett-Jones, J.A. Wharton, R.J.K. Wood, Micro-abrasion-corrosion of a CoCrMo alloy in simulated artificial hip joint environments, Wear 259 (7) (2005) 898–909. M.R. Thakare, J.A. Wharton, R.J.K. Wood, C. Menger, Investigation of micro-scale abrasion–corrosion of WC-based sintered hardmetal and sprayed coating using in situ electrochemical current-noise measurements, Wear 267 (11) (2009) 1967–1977. J.O. Bello, R.J.K. Wood, J.A. Wharton, Synergistic effects of micro-abrasion-corrosion of UNS S30403, S31603 and S32760 stainless steels, Wear 263 (1) (2007) 149–159. F. Ferrer, H. Idrissi, H. Mazille, et al., A study of abrasion-corrosion of AISI 304L austenitic stainless steel in saline solution using acoustic emission technique, Ndt & E Int. 33 (6) (2000) 363–371. A.J. Gant, M.G. Gee, A.T. May, The evaluation of tribo-corrosion synergy for WC–co hardmetals in low stress abrasion, Wear 256 (5) (2004) 500–516. A.J. Gant, M.G. Gee, A.T. May, Microabrasion of WC–Co hardmetals in corrosive media, Wear 256 (9) (2004) 954–962. A.J. Gant, M.G. Gee, D.D. Gohil, et al., Use of FIB/SEM to assess the tribo-corrosion of WC/Co hardmetals in model single point abrasion experiments, Tribol. Int. 68 (6) (2013) 56–66. S.M. Sharland, A review of the theoretical modelling of crevice and pitting corrosion, Corros. Sci. 27 (3) (1987) 289–323. T.P. Hoar, The production and breakdown of the passivity of metals, Corros. Sci. 7 (6) (1967) 341–355. F. Al-Kharafi, W. Badawy, J. Al-Ajmi, Effect of chloride ions on the corrosion and passivation behaviours of cobalt in neutral solutions, Indian J. Chem. Technol. 6 (4)
International Journal of Refractory Metals & Hard Materials 81 (2019) 307–315
L. Peng, et al.
[41] H. Jung, A. Alfantazi, Corrosion properties of electrodeposited cobalt in sulfate solutions containing chloride ions, Electrochim. Acta 55 (3) (2010) 865–869. [42] S.S. Abd El Rehim, A.A. El Basosi, M.M. Osman, The influence of halide ions on the corrosion and passivity of cobalt in an alkaline medium, J. Electroanal. Chem. 348 (1–2) (1993) 99–106. [43] O.J. Murphy, Bockris J.M. Pou, Chloride ion penetration of passive films on iron, J. Electrochem. Soc. 8 (130) (1983) 1792–1794.
(1999) 194–201. [39] K.M. Emran, A.K. Al-Harbi, Comparison of the corrosion resistance behaviour for two metal-metal glassy alloys in neutral solution with chloride impact, J. Alloys Compd. 767 (2018) 753–762. [40] Robert J.K. Wood, Stephen Herd, R. Mandar, A critical review of the tribocorrosion of cemented and thermal sprayed tungsten carbide, Tribol. Int. 119 (2018) 491–509.
315