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Dependence of wear behavior on sintering mechanism for Iron-Alumina Metal Matrix Nanocomposites
Accepted Manuscript Dependence of Wear Behavior on Sintering Mechanism for Iron-Alumina Metal Matrix Nanocomposites
Pallav Gupta, Devendra Kumar, Om Parkash, A.K. Jha PII:
S0254-0584(18)30744-2
DOI:
10.1016/j.matchemphys.2018.08.079
Reference:
MAC 20922
To appear in:
Materials Chemistry and Physics
Received Date:
27 November 2017
Accepted Date:
24 August 2018
Please cite this article as: Pallav Gupta, Devendra Kumar, Om Parkash, A.K. Jha, Dependence of Wear Behavior on Sintering Mechanism for Iron-Alumina Metal Matrix Nanocomposites, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.08.079
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Graphical Abstract
Ball Milling
Fe
[Dextrin used as Binder]
(Metal Powder)
& Compaction
1) XRD Characterizations 2) SEM (As Prepared)
Sintering
+ Al2O3
(Ceramic Reinforcement)
3) Wear Argon Atmosphere
Green Specimen
Sintered Specimen
4) Microstrcuture (Worn Surface)
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Dependence of Wear Behavior on Sintering Mechanism for Iron-Alumina Metal Matrix Nanocomposites Pallav Gupta1*, Devendra Kumar2, Om Parkash2 and A. K. Jha3 1Department
of Mechanical Engineering, A.S.E.T.,
Amity University, Uttar Pradesh, Noida-201313 (INDIA) 2Department
of Ceramic Engineering, Indian Institute of Technology
(Banaras Hindu University), Varanasi-221005 (INDIA) 3Department
of Mechanical Engineering, Indian Institute of Technology
(Banaras Hindu University), Varanasi-221005 (INDIA) Abstract The present paper reports the dependence of wear behavior on sintering mechanism for iron (Fe) – alumina (Al2O3) metal matrix nanocomposites fabricated via Powder Metallurgy (P/M) technique. Nanocomposite composition was taken as 10 wt. % Al2O3 and 90 wt. % Fe. Synthesized green specimens were sintered in an argon atmosphere in the temperature range of 900 - 1100C for 1 to 3 h. XRD pattern of sintered nanocomposite reveals the formation of iron aluminate phase (FeAl2O4) beside presence of Iron (Fe) and trace amount of aluminium oxide (Al2O3). Iron aluminate phase is formed as a result of reactive sintering between iron and alumina particles. Wear and coefficient of friction behavior of nanocomposite specimens was investigated under a load of 0.5, 1.0 and 2.0 kg with a constant sliding velocity of 4 m/s and sliding time of 1 hour. It is found from these studies that the wear properties in nanocomposite specimen depend on the sintering temperature and sintering time respectively. Keywords: Metal Matrix Nanocomposites (MMNCs); Sintering; X-Ray Diffraction (XRD); Wear; Scanning Electron Microscopy (SEM) *Corresponding
Author E-mail Id: [email protected]
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1. Introduction Metal Matrix Nanocomposites (MMNCs) refer to a class of material in which hard ceramic reinforcements are dispersed in a ductile metal or alloy matrix [1]. MMNCs act as a bridge between metallic properties like ductility, toughness and ceramic properties like high strength and modulus, finally leading to greater strength in shear and compression and to higher service temperature capabilities [2]. Improvements in various properties such as density, hardness, wear resistance, abrasion resistance, compressive and tensile strength etc. have been reported extensively [3]. These improvements in the properties are dependent upon various factors such as particle size, particle size distribution and processing route [4-5]. Several fabrication techniques such as Stir Casting, Powder Metallurgy (P/M), Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD), Liquid Infiltration etc. are put forth for the fabrication of quality MMNCs [6]. Powder Metallurgy is a technique which is used to develop product with unique and distinguished homogeneity [7-8]. There have been several tribological studies on MMCs with aluminium, copper and magnesium as the matrix material. Unfortunately there are only a few reports using iron as the matrix phase [9-12]. Naplocha and Granat [13] studied the tribological behavior of Al/Saffil/C hybrid composites with varying percentage of graphite and alumina, produced via squeeze casting technique. The main results reported in their investigations include; (i) Dispersing of Al2O3 fibres in the composite prevents the adhesion and seizure effect, especially under high pressure of 1 MPa and (ii) Addition of graphite clearly improves co-operation of the friction force leading to the generation of couple which reduces the wear depending on content of reinforcement and the applied pressure. Rosenberger et al. [14] also carried investigations on AA1060 aluminum matrix dispersed with 15 vol. % of alumina particles in a load range of 4.9 to 91.2 N using a pin-on-ring machine at a 2
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sliding velocity of 2.7 m/s. It was found that at load lower than 80 N a mild wear mechanism is present and at higher loads the mechanism changes to severe mode. During mild wear regime, a mechanically mixed layer (MML), with iron from the counterface and material of the composite was formed. This MML was responsible for the wear resistance of the composite. Two mechanisms were observed for increasing the wear resistance of the MML; (i) hardening by mechanical alloying and strain hardening (ii) an increase in thickness. At a higher load the conditions produced large instabilities which prevented the formation of a protective mechanically mixed layer. Akhtar et al. [15] studied the processing, microstructure, mechanical properties, electrical conductivity and wear behavior of high volume titanium carbide reinforced copper matrix composites. It was reported that hardness and strength of the composite increased with titanium carbide content and alloying elements in the matrix phase. Wear resistance of composites was studied against high speed steel. Microploughing of copper base matrix was found to be the dominant wear mechanism. Less microploughing and wear loss was observed at lower loads and for high vol. % of TiC particles. Heavy microploughing effect was observed under 300 N wear load caused by very rapid removal of material from the worn surface. Rajkumar and Aravindan studied the copper-TiC (5-15 vol %) - graphite (5-10 vol. %) hybrid composites fabricated through a novel microwave processing technique. Pin on disc tester was used to evaluate the tribological properties under testing parameters of normal loads 12 - 48 N and sliding speed of 1.25 – 2.51 m/s. It was observed that there is an increase in coefficient of friction with increasing normal load. It was also found that hybrid composites exhibited lower coefficient of friction compared with unreinforced copper. Higher coefficient of friction was
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exhibited by unreinforced copper under all the loading conditions. Adhesive nature of tribo contact leads to the transfer of soft copper matrix to harder counter surface [16]. Franco et al. have studied the wear performance of Mg-AZ91 alloy and TiC as reinforcement processed by pressure less infiltration technique. Results indicated that the wear resistance of alloy Mg AZ91 showed best behavior when the pin sample are worn over the AISI 4140 steel and the worst results with the AISIH13 steel. Therefore, at this TiC particulate concentration, the composite exhibits a low favorable response for the projected automotive application, since the obtained wear rates are higher in comparison with the unreinforced alloy [17-18]. In the last few years, our research group has carried out some important investigations on FeAl2O3 and Fe-ZrO2 metal matrix composites fabricated via powder metallurgy technique. Due to the reactive sintering process a nano iron aluminate (FeAl2O4) phase forms in Fe-Al2O3 composite system, whereas in Fe-ZrO2 composite system a nano iron zirconium oxide (Zr6Fe3O) phase forms. Due to these phases, the various properties such as density, hardness, wear, compression, deformation and corrosion were found to improve [19-23]. The formation of these nano iron aluminate and iron zirconium oxide phases depend on processing parameters. Mechanical properties also depend on processing parameters. Fe-Al2O3 nanocomposites are potential candidate for applications in heavy duty components such as railway wagon wheels, braking system etc. where pure iron cannot give the desired tribological properties. The present paper reports the wear behavior of 10% Al2O3 reinforced iron based nanocomposite synthesized via powder metallurgy technique as a function of sintering parameters i.e. temperature and time. The wear measurement of nanocomposite pins was carried out under a
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load of 0.5, 1.0 and 2.0 kg respectively for a fixed sliding velocity of 4 m/sec and time 1 hour. Worn surface analysis of the specimens was also done in order to study the type of wear. 2. Experimental Work In the present work 90% Fe (electrolytic grade with 99.5% purity and particle size in the range of 49-58 µm) and 10% Al2O3 (active; particle size in the range of 63-210 µm) was taken as the starting materials. Composite powder in desired composition was ball milled dry using powder to ball ratio of 1:2. Zirconia balls were used as the grinding and mixing media. 2 wt%. of dextrin was used as binder for providing green strength to the specimen. Composite powder was compacted at a load of 7 tons. Composite pins were sintered in argon atmosphere in the temperature range of 900-1100°C for 1 to 3 hours respectively. Heating and cooling rate of the furnace has been kept as 5°C/min during the sintering process. Specimens of size 12 mm diameter and 20 mm height were obtained after sintering. Nomenclature of specimens along with density and hardness is illustrated in Table 1 below. Surface of the specimen was polished using various grades of emery paper. X-ray diffraction (XRD) pattern of the synthesized specimen was studied using Rigaku High Resolution Powder X-Ray diffractometer with Cu-Kα radiation and Ni-filter. Acceleration voltage was kept as 30kV, acceleration current as 15mA and step size of 0.02° was used in the present phase analysis study. Micrograph of worn specimens was studied using Inspect S-50, FP 2017/12 scanning electron microscope. Wear characterization of the cylindrical pin specimens of 12 mm diameter was carried out using pin on disc wear and friction testing machine (Magnum Engineers, Bangalore, India). Wear characterization was carried out using standardized steps. Prior to the test the disc (hardened steel disc with a hardness of HRC 60) was ground using alumina wheel and then polished using various grades of emery papers to remove the erosion 5
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marks. Initially, the nanocomposite pin was loaded against a rotating disc, and was made to run under a load of 2.0 kg for 2h so that the worn surface of the specimen pin becomes parallel to the disc. Sliding velocity is kept as 4 m/sec and the test is performed for a time interval of 1h. Wear characteristics of the specimens were studied using a load of 0.5, 1.0 and 2.0 kg in dry sliding condition. Wear debris were removed from the surface of the plate intermittently using tissue paper moist with acetone. Two readings were taken for each load. Weight loss of the nanocomposite pin was measured at an interval of 1h in an analytical balance of 10-4 g precision. Wear volume was then calculated from the weight loss values. Worn surfaces of the nanocomposite pins were observed in a scanning electron microscope to study the nature of wear. 3. Results and Discussions 3.1 XRD X-Ray diffraction pattern of representative nanocomposite specimen sintered at 1100C for 2h (10AFe1100(2)) is shown in Fig.1. Diffraction peaks of XRD patterns were matched with JCPDS files of cubic α-Fe (file no. 06-0696), Al2O3 (file no. 11-0517) and FeAl2O4 (file no. 34-0192). It was found from matching that Fe, Al2O3 and FeAl2O4 phases were present in the present specimen. This iron aluminate (FeAl2O4) phase forms due to reactive sintering between iron and alumina particles [17]. Amount of dispersed (Al2O3 and FeAl2O4) and matrix (Fe) phases in the nanocomposite and the properties thereof depend on sintering temperature and time. Presence of this iron aluminate phase was found in all the specimens of this system. It was also found that 3 hour of sintered specimen showed more amount of iron aluminate phase and trace amount of alumina particles. It was concluded that the peak
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intensity of iron aluminate phase was higher in the specimen reinforced with 10% Al2O3 in comparison to 5% Al2O3 reinforcement [24]. 3.2 Microstructure (As Prepared) Detailed microstructure of Fe-Al2O3 metal matrix nanocomposites specimens was described in our earlier publication [24]. Figure 2 shows the SEM of specimen 10AFe1100(1) (a) 5000X and (b) 20000X magnification. Fig. 2(a) shows highly dense phase composite specimen containing negligible amount of porosity. These microstructures show grains of Fe, Al2O3 and FeAl2O4. The dark black grains are of iron white ones are of aluminium oxide. Remaining grey coloured grains are of iron aluminate. Fig. 2(b) shows micrograph of the same specimens at 20,000X magnification. Present microstructure shows the micron and nanometer size grains of iron aluminate phase. The particle size lies in the range of 14 – 135 nm respectively. 3.3 Wear Characterization Fig. 3(a) shows the wear rate vs. load plots for specimen sintered for 1h. Specimen 10AFe900(1) shows the wear rate of 0.69x10-3 mm3/s under a load of 0.5 kg. On increasing the load to 1.0 and to 2.0 kg the wear rate increases significantly from 0.73x10-3 mm3/s to 2.02x10-3 mm3/s. For the specimen 10AFe1000(1) under 0.5 and 1.0 kg load the wear rate was found to be reduced in comparison to specimen 10AFe900(1). At 2.0 kg load the wear rate was found to increase in comparison to specimen 10AFe900(1). Specimen 10AFe1100(1) shows lower wear rate values at all loads. It was found from the study that the specimen sintered at low temperature showed high amount of wear. On increasing the sintering temperature the wear rate was reduced significantly. At higher sintering temperature a more amount of iron aluminate phase is formed.
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In a similar manner Fig. 3(b) shows the wear rate vs. load plots for specimens sintered for 2h. Wear rate for specimen 10AFe900(2) was found to be 0.54x10-3 mm3/s, 1.06x10-3 mm3/s and 2.20x10-3 mm3/s under 0.5 kg, 1.0 kg and 2.0 kg load respectively. Specimen 10AFe1000(2) showed a lower values of wear rate at a load of 0.5 and 1.0 kg load whereas wear rate was found to be high at a load of 2.0 kg as compared to specimen 10AFe900(2). Upon increasing the sintering temperature to 1100C for 2 hour of sintering time, specimen 10AFe1100(2) showed lower values of wear rate at a load of 0.5 and 1.0 kg whereas it showed a higher wear rate value at a load of 2.0 kg when compared to specimen 10AFe900(2) and 10AFe1000(2). Fig. 3(c) shows wear rate vs. load plots for specimens sintered for 3h. Specimen 10AFe900(3) shows a wear rate of 0.20x10-3 mm3/s under a load of 0.5 kg. Further increase of load to1.0 kg and 2.0 kg increased the wear rate to 0.40 x10-3 mm3/s and 1.94x10-3 mm3/s respectively. Wear rate values at different loads for specimen 10AFe900(3) was found to be reduced in comparison to specimen 10AFe900(1) and 10AFe900(2). For specimen 10AFe1000(3) the wear rate was found to be lowest at all loads in comparison to all other specimens. Upon increasing the sintering temperature to 1100C for 3 hours of sintering time the specimen 10AFe1100(3) showed a higher wear rate at a load of 0.5 and 1.0 kg in comparison to specimen 10AFe900(3). Fig. 4(a) shows the coefficient of friction vs. load plot for specimens sintered for 1h. Specimen 10AFe900(1) shows the coefficient of friction value of 19 N under 0.5 kg load, whereas the same specimen showed friction force value of 13.5 N under 1.0 kg load. On further increasing the load to 2.0 kg the same specimen showed friction force value of 10.25 N. The specimen which is sintered at 1000°C for 1 hour i.e. specimen 10AFe1000(1) showed higher coefficient of friction values at all loads in comparison to specimen 10AFe900(1). On further increasing the sintering
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temperature to 1100°C and for 1 hour i.e. for specimen 10AFe1100(1) the coefficient of friction values were found to be higher at all loads in comparison to specimen 10AFe900(1) and 10AFe1000(1). Fig. 4(b) shows the coefficient of friction vs. load plot for specimens sintered for 2h. Specimen 10AFe900(2) shows the coefficient of friction value of 16.0 N under 0.5 kg load, whereas the same specimen showed friction force value of 14.0 N under 1.0 kg load. On further increasing the load to 2.0 kg the same specimen showed friction force value of 10.25 N. Specimen which is sintered at 1000°C for 2 hour i.e. specimen 10AFe1000(2) showed higher coefficient of friction values at all loads in comparison to specimen 10AFe900(2). On further increasing the sintering temperature to 1100°C for 2 hour i.e. for specimen 10AFe1100(2) the coefficient of friction value was reduced in comparison to specimen 10AFe900(2) and 10AFe1100(2). In the similar manner Fig. 4(c) shows the coefficient of friction vs. load plot for specimens sintered for 3h. Specimen 10AFe900(3) shows the friction force value of 13.0 N under 0.5 kg load, whereas the same specimen showed friction force value of 13.5 N under 1.0 kg load. On further increasing the load to 2.0 kg the same specimen showed friction force value of 9.0 N. Specimen which is sintered at 1000°C for 3 hour i.e. specimen 10AFe1000(3) showed higher coefficient of friction values at a load of 0.5 and 1.0 kg whereas for 2.0 kg load it was almost same as compared to specimen 10AFe900(3). On further increasing the sintering temperature to 1100°C and for 3 hour i.e. for specimen 10AFe1100(3) the coefficient of friction values were reduced in comparison to specimen 10AFe900(3) and 10AFe1000(3). It could be seen from the above interpretation that specimen 10AFe1000(3) shows the lowest value of wear rate. However, at lower load i.e. 0.5 kg the specimen shows high value of 9
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coefficient of friction whereas at high load the coefficient of friction value reduces. At high temperature and time values a more amount of iron aluminate phase forms thus the wear rate values are reduced significantly. Iron aluminate phase formation depends on the percentage of alumina along with sintering parameters i.e. temperature and time respectively. In our earlier articles, it has been shown that the sintering and in turn hardness and wear characteristics of the nancomposite Fe-Al2O3 specimens varies in complex manner due to reaction between iron and alumina during consolidation and sintering. Formation of iron aluminate phase will enhance the hardness and wear characteristics only when there is good binding between iron grains encompassing the alumina ceramic and reactive iron aluminate phase. The formation of iron aluminate phase depends on sintering temperature and time. Therefore, with increasing sintering temperature and time its content increases, which in turn increases hardness and decreases wear rate. However, the increase in iron aluminate phase decreases the consolidation or binding between different grains. Thus, there shall always be an optimum sintering temperature for good binding between the grains with sufficient ceramic phase, thereby leading to good mechanical characteristics. Secondly, the wear and friction force depend on the wear mechanism operative at a particular load. It has also been shown that adhesive or micro- ploughing wear mechanism operates at low loads and at high loads due to entrapment of hard ceramic debris between pin and disc abrasive wears starts dominating. Abrasive wear increases the wear rate and decreases the frictional forces [19, 22, and 24]. 3.4 Microstructure (Worn Surface) SEM analysis of the worn surface formed during the dry sliding wear test was carried out in order to study the wear mechanism maps in the nanocomposite pins. Fig. 5 shows the worn 10
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surface analysis of specimen 10AFe900(1) at (a) 200X (b) 500X and (c) 10000X after wear measurement under 2.0 kg load. Specimen 10AFe900(1) shows the micrograph after wear testing under 2.0 kg load (Fig. 5(a)). Microstructure shows the wear marks generated during the dry sliding contact between the steel disc and the composite pins. Initially the interaction of asperities on the disc and steel pin leads to the fragmentation and fracture at some asperities. Uneven removal of debris from the specimen surface indicates sharp edges of the ceramic reinforcement particles which stand proud of the nanocomposite surface. These may cut into the specimen surface and can generate the grooves. Even when the test load on the specimen is 2.0 kg the amount of wear from the surface is not too much which in turn suggests the improved hardness of the nanocomposite pins. Fig. 5(b) shows the higher magnification micrograph of same specimen which depict removal of material as well as smoothing of specimen surface. This smoothing takes place by the removal of the material which comes in contact between the disc and specimen surface thereby forming tribo film between the two. In the present image nano size formation of iron aluminate (FeAl2O4) phase with the presence of some sub micron sized particles of iron as well as aluminium oxide can also be seen. Fig. 6 shows the worn surface analysis of specimen 10AFe900(2) at (a) 200X (b) 500X and (c) 10000X magnification after wear measurement under 2.0 kg load. Fig. 6(a) shows the micrograph of specimen after wear testing under 2.0 kg load for specimen 10AFe900(2). This micrograph shows the wear marks generated in a regular fashion and the generated grooves are more or less equal to the wear marks generated in the specimen 10AFe900(1). Micrograph also shows some grains of aluminium oxide being embedded in the bed of iron matrix. Fig. 6(b) shows that wear in the present case takes place by smoothing as well as by the microploughing
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effect on the specimen by the eroded particles. It also reveals some sub micron sized and nano range particles of iron aluminate phase. Fig. 7 shows the worn surface analysis of specimen 10AFe1100(1) at (a) 200X (b) 500X and (c) 10000X magnification after wear measurement under 2.0 kg load. Fig. 7(a) shows the micrograph after wear testing under 2.0 kg load for specimen 10AFe1100(1). Specimen shows wear grooves and also intense wear marks generated due to the entrapment of hard aluminium oxide particles between the disc and specimen. In this micrograph a big amount of material is removed from the specimen contact surface which has caused progressive wear by the action of the detached particles. This results in ploughing and the creation of surface grooves. Fig. 7(b) shows the higher magnification worn micrograph of the specimen 10AFe1100(1) under 2.0 kg load, specimen is abraded heavily by the hard ceramic reinforcement which is removed from the specimen surface thereby forming tribo film between the disc and the specimen itself. Image also revealed the formation of iron aluminate phase with some micron and sub micron size particles of iron and aluminium oxide respectively. Presence of iron aluminate phase was also seen in the X-ray diffraction pattern of representative nanocomposite specimen. 3.5 Discussion On the basis of the above results and interpretations it can be concluded that at lower values of load i.e. under 0.5 kg the wear from the pin is mainly due to removal of debris material which is due to cutting and flowability of penetrated hard debris material into the softer surface. It is found that after some interval (i.e. after completing some interval),a higher amount of stress is expected to act on the debris, due to the higher values of hardness of the nanocomposite specimens. Because of this high value of stress levels at these points, the removed debris gets
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deformed plastically by getting entrapped in between disc and pin surface and some of the sharp removed particles get fractured due to combined effect of normal and shear stress. Initially it is also seen that the wear mapping of the nanocomposites shows a considerable high amount of energy which is generally spent in generating a high amount of frictional force. This leads to an increase in the heating between the specimen surface and the disc. Therefore, it is observed that initially the temperature of the contact surface is less and hence the debris materials are expected to be in stronger and in more rigid form. With passage of time there is increase in the value of wear from the pin surface which is removed in a linear manner and the temperature of the intermittent surface is also increased significantly. Due to the increase in the temperature of the contact surface, the debris formed is mild and small in the nature. At higher loads i.e. under 2.0 kg the initial wearing is similar to that of the wear which takes place at lower loads but as the time passes, the value of frictional heating increases. This leads to higher temperature and softening of the surface materials. When there is a sliding action, a 100% amount of the frictional force acts between the two intermittent surfaces, which causes a large amount of frictional heating between the disc and pin i.e. at the contact point. Since the two counter acting surfaces i.e. disc and pin surface are in relative motion with respect to each other, the dissipation of frictional heat from the surface in dry sliding test is regular because of insufficient time for removal of heat. In the initial stage the debris are stronger and sharper due to which the frictional heating takes place at a higher rate. After a certain period of time, because of the increase in the removal of the material from the specimen surface, slipping action is higher leading to the decrease in the amount of frictional heating. There is also a possibility of adhesion between the counter surfaces which leads to higher degree of friction. Because of these counter actions, frictional heating remains almost constant. 13
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The values of wear rate in all the specimen increases with an increase in the applied load values. Increase in the values of applied load leads to increase in the penetration of the hard debris material from the disc surface to the surface of the nanocomposite pins. As the value of the load increases beyond the critical value, the wear from the surface of the nanocomposite pins increases in an abrupt manner. Load at which the value of wear rate increases abruptly is called the transition load. When applied load is greater than the transition load, the wear rate of the nanocomposite pins shoots up to significantly higher value. This effect is due to significantly higher frictional heating and thus the localized adhesion of the nanocomposite pin surface with the counter surface. This effect leads to the softening of the pin surface thus leads to more penetration of the debris material. Therefore, the material removal due to the delamination of adhered areas, micro cutting and micro fracturing increases significantly [25-26]. Overall variation of the wear rate and frictional force values were quite low and were found to depend on the iron aluminate phase formation which in turn depends upon the sintering temperature and time respectively. 4. Conclusions A systematic study of dependence of wear behavior on sintering mechanism for Iron-Alumina Metal Matrix Nanocomposites prepared by Powder Metallurgy has been reported in this paper. The experimental results have been discussed critically and the following important conclusions have been drawn: 1) XRD results show the formation of iron aluminate phase due to the reactive sintering between iron and aluminium oxide particles.
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2) At lower loads, the removal of the material is due to fragmentation of asperities and removal of material is due to slipping actions of penetrated hard asperities into the softer surface. 3) Wear mechanism maps in the present case lead to the microploughing effect. 4) All the synthesized nanocomposite specimen showed improved wear rate in comparison to pure iron specimen. The wear rate of pure iron specimen at a load of 0.5, 1.0 and 2.0 kg was found out to be 0.80x10-3 mm3/s, 1.31x10-3 mm3/s and 3.65x10-3 mm3/s. It is expected that the results of these investigations will be useful in developing technology for producing better quality MMNC at competitive rates.
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[18] Rastogi R B, Maurya J L, Jaiswal V. Phosphorous free antiwear formulations: Zinc thiosemicarbazones–borate ester mixtures. Proc Inst Mech Eng, Part J: J Engg Trib 2013; 227 (3): 220-233. [19] Gupta P, Kumar D, Parkash O and Jha A K. Structural and mechanical behavior of 5%Al2O3 reinforced Fe metal matrix composites (MMC) produced by powder metallurgy(P/M) route. Bull Mater Sci 2013; 36 (5): 859-868. [20] Gupta P, Kumar D, Quraishi M A and Parkash O. Corrosion Behavior of Al2O3 Reinforced Fe Metal Matrix Nanocomposites Produced by Powder Metallurgy Technique. Adv Sci Engg Med2013; 5(4): 366-370. [21] Jha P, Gupta P, Kumar D and Parkash O. Synthesis and characterization of Fe–ZrO2 metal matrix composites. J Comp Mater 2014; 48 (17): 2107-2115. [22] Gupta P, Kumar D, Parkash O and Jha A K. Effect of Sintering on Wear Characteristics of Fe-Al2O3 Metal Matrix Composites. Proc Inst Mech Eng, Part J: J Engg Trib 2014; 228(3): 362368. [23] Kumar U J P, Gupta P, Jha A K and Kumar D. Closed Die Deformation Behavior of Cylindrical Iron-Alumina Metal Matrix Composites During Cold Sinter Forging. J Inst Eng India: Series D 2016; 97(2): 135-151. [24] Gupta P, Kumar D, Parkash O. and Jha A K. Sintering and Hardness Behavior of Fe-Al2O3 Metal Matrix Nanocomposites (MMNCs) prepared by Powder Metallurgy. J Comp 2014; Article ID 145973: 1-10.
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[25] Mazahery A. and Shabani M O. Study on microstructure and abrasive wear behavior of sintered Al matrix composites. Cer Intl 2012; 38: 4263-4269. [26] Kumar D, Himadri R. and Show B K. Tribological Behavior of an Aluminum Matrix Composite with Al4SiC4 Reinforcement under Dry Sliding Condition. Trib Trans 2015; 58: 518526.
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LIST OF FIGURE CAPTIONS Fig. 1 X-Ray Diffraction pattern of 10AFe1100(2). Fig. 2 SEM of specimen 10AFe1100(1) (a) 5000X and (b) 20000X magnification [24]. Fig. 3 Wear Rate vs. Load for specimens sintered for (a) 1h (b) 2h and (c) 3h. Fig. 4 Coefficient of friction vs. Load for specimens sintered (a) 1h (b) 2h and (c) 3h. Fig. 5 Worn surface analysis of specimen 10AFe900(1) at (a) 200X and (b) 10000X after wear measurement under 2.0 kg load. Fig. 6 Worn surface analysis of specimen 10AFe900(2) at (a) 200X and (b) 10000X after wear measurement under 2.0 kg load. Fig. 7 Worn surface analysis of specimen 10AFe1100(1) at (a) 200X and (b) 10000X after wear measurement under 2.0 kg load.
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LIST OF TABLE CAPTIONS Table 1 Nomenclature of Specimens along with density and hardness
21
20 30 40 50
2 (degree)
Figure 1
FeAl2O4 (311)
60 70
FeAl2O4 (533)
FeAl2O4 (620)
FeAl2O4 (440) Fe (200)
FeAl2O4 (511)
FeAl2O4 (422)
Al2O3 (104)
FeAl2O4 (220)
Fe (110)
Intensity (arbt. units)
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10AFe1100(2)
80
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(a)
(b)
Fe
Al2O3 FeAl2O4 Nanosize FeAl2O4
Figure 2
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10% Al2O3 + 90 % Fe o
900 C(1h) o 1000 C(1h) o 1100 C(1h)
2.5
3
Wear Rate x 10 (mm /sec)
3.0
-3
2.0 1.5 1.0 0.5 0.0 0.0
0.5
1.0
1.5
2.0
2.5
2.0
2.5
2.0
2.5
Load (kg)
(a) 3.5
10% Al2O3 + 90 % Fe o
900 C(2h) o 1000 C(2h) o 1100 C(2h)
2.5
3
Wear Rate x 10 (mm /sec)
3.0
-3
2.0 1.5 1.0 0.5 0.0 0.0
0.5
1.0 1.5 Load (kg)
(b) 3.5
10% Al2O3 + 90 % Fe
2.5
o
900 C(3h) o 1000 C(3h) o 1100 C(3h)
3
Wear Rate x 10 (mm /sec)
3.0
-3
2.0 1.5 1.0 0.5 0.0 0.0
0.5
1.0 1.5 Load (Kg)
(c) Figure 3
35
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900 C(1h) o 1000 C(1h) o 1100 C(1h)
Coefficient of Friction (N)
30 25 20 15 10 5 0 0.0
0.5
1.0
1.5
2.0
2.5
Load (kg)
(a) 35
10% Al2O3 + 90 % Fe o
900 C(2h) o 1000 C(2h) o 1100 C(2h)
Coefficient of Friction (N)
30 25 20 15 10 5 0 0.0
0.5
1.0
1.5
2.0
2.5
Load (kg)
(b) 35
10% Al2O3 + 90 % Fe o
900 C(3h) o 1000 C(3h) o 1100 C(3h)
Coefficient of Friction (N)
30 25 20 15 10 5 0 0.0
0.5
1.0
1.5
Load (kg)
(c) Figure 4
2.0
2.5
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(a)
Figure 5
(b)
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(a) Microploughing
Figure 6
(b)
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(a)
(b)
Figure 7
(c)
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RESEARCH HIGHLIGHTS
Present paper investigates the wear behavior of Fe - 10% Al2O3 MMCs.
The wear properties are dependent on densification and hardness of the specimen.
Wear behavior of the specimens varies with the iron aluminate phase formation.
Wear mechanism maps in the present case lead to the microploughing effect.
All the synthesized nanocomposite specimen showed improved wear rate in comparison to pure iron specimen.
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Table 1
S.
Sintering
Sintering
Specimen
No.
Temperature
Time (h)
Code
(°C)
Green Density
Sintered Density
(g/cm3)
(g/cm3)
Hardness (HRH)
1.
900
1
10AFe900(1)
3.8119
3.9421
55
2.
900
2
10AFe900(2)
3.7730
4.0713
42
3.
900
3
10AFe900(3)
3.8250
4.4977
40
4.
1000
1
10AFe1000(1)
3.9196
3.9330
39
5.
1000
2
10AFe1000(2)
3.9031
4.2577
40
6.
1000
3
10AFe1000(3)
3.8967
4.5055
43
7.
1100
1
10AFe1100(1)
3.8852
4.4707
40
8.
1100
2
10AFe1100(2)
3.8909
4.6008
54
9.
1100
3
10AFe1100(3)
3.9233
4.9806
42
Pallav Gupta, Devendra Kumar, Om Parkash, A.K. Jha PII:
S0254-0584(18)30744-2
DOI:
10.1016/j.matchemphys.2018.08.079
Reference:
MAC 20922
To appear in:
Materials Chemistry and Physics
Received Date:
27 November 2017
Accepted Date:
24 August 2018
Please cite this article as: Pallav Gupta, Devendra Kumar, Om Parkash, A.K. Jha, Dependence of Wear Behavior on Sintering Mechanism for Iron-Alumina Metal Matrix Nanocomposites, Materials Chemistry and Physics (2018), doi: 10.1016/j.matchemphys.2018.08.079
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Graphical Abstract
Ball Milling
Fe
[Dextrin used as Binder]
(Metal Powder)
& Compaction
1) XRD Characterizations 2) SEM (As Prepared)
Sintering
+ Al2O3
(Ceramic Reinforcement)
3) Wear Argon Atmosphere
Green Specimen
Sintered Specimen
4) Microstrcuture (Worn Surface)
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Dependence of Wear Behavior on Sintering Mechanism for Iron-Alumina Metal Matrix Nanocomposites Pallav Gupta1*, Devendra Kumar2, Om Parkash2 and A. K. Jha3 1Department
of Mechanical Engineering, A.S.E.T.,
Amity University, Uttar Pradesh, Noida-201313 (INDIA) 2Department
of Ceramic Engineering, Indian Institute of Technology
(Banaras Hindu University), Varanasi-221005 (INDIA) 3Department
of Mechanical Engineering, Indian Institute of Technology
(Banaras Hindu University), Varanasi-221005 (INDIA) Abstract The present paper reports the dependence of wear behavior on sintering mechanism for iron (Fe) – alumina (Al2O3) metal matrix nanocomposites fabricated via Powder Metallurgy (P/M) technique. Nanocomposite composition was taken as 10 wt. % Al2O3 and 90 wt. % Fe. Synthesized green specimens were sintered in an argon atmosphere in the temperature range of 900 - 1100C for 1 to 3 h. XRD pattern of sintered nanocomposite reveals the formation of iron aluminate phase (FeAl2O4) beside presence of Iron (Fe) and trace amount of aluminium oxide (Al2O3). Iron aluminate phase is formed as a result of reactive sintering between iron and alumina particles. Wear and coefficient of friction behavior of nanocomposite specimens was investigated under a load of 0.5, 1.0 and 2.0 kg with a constant sliding velocity of 4 m/s and sliding time of 1 hour. It is found from these studies that the wear properties in nanocomposite specimen depend on the sintering temperature and sintering time respectively. Keywords: Metal Matrix Nanocomposites (MMNCs); Sintering; X-Ray Diffraction (XRD); Wear; Scanning Electron Microscopy (SEM) *Corresponding
Author E-mail Id: [email protected]
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1. Introduction Metal Matrix Nanocomposites (MMNCs) refer to a class of material in which hard ceramic reinforcements are dispersed in a ductile metal or alloy matrix [1]. MMNCs act as a bridge between metallic properties like ductility, toughness and ceramic properties like high strength and modulus, finally leading to greater strength in shear and compression and to higher service temperature capabilities [2]. Improvements in various properties such as density, hardness, wear resistance, abrasion resistance, compressive and tensile strength etc. have been reported extensively [3]. These improvements in the properties are dependent upon various factors such as particle size, particle size distribution and processing route [4-5]. Several fabrication techniques such as Stir Casting, Powder Metallurgy (P/M), Chemical Vapor Deposition (CVD) and Physical Vapor Deposition (PVD), Liquid Infiltration etc. are put forth for the fabrication of quality MMNCs [6]. Powder Metallurgy is a technique which is used to develop product with unique and distinguished homogeneity [7-8]. There have been several tribological studies on MMCs with aluminium, copper and magnesium as the matrix material. Unfortunately there are only a few reports using iron as the matrix phase [9-12]. Naplocha and Granat [13] studied the tribological behavior of Al/Saffil/C hybrid composites with varying percentage of graphite and alumina, produced via squeeze casting technique. The main results reported in their investigations include; (i) Dispersing of Al2O3 fibres in the composite prevents the adhesion and seizure effect, especially under high pressure of 1 MPa and (ii) Addition of graphite clearly improves co-operation of the friction force leading to the generation of couple which reduces the wear depending on content of reinforcement and the applied pressure. Rosenberger et al. [14] also carried investigations on AA1060 aluminum matrix dispersed with 15 vol. % of alumina particles in a load range of 4.9 to 91.2 N using a pin-on-ring machine at a 2
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sliding velocity of 2.7 m/s. It was found that at load lower than 80 N a mild wear mechanism is present and at higher loads the mechanism changes to severe mode. During mild wear regime, a mechanically mixed layer (MML), with iron from the counterface and material of the composite was formed. This MML was responsible for the wear resistance of the composite. Two mechanisms were observed for increasing the wear resistance of the MML; (i) hardening by mechanical alloying and strain hardening (ii) an increase in thickness. At a higher load the conditions produced large instabilities which prevented the formation of a protective mechanically mixed layer. Akhtar et al. [15] studied the processing, microstructure, mechanical properties, electrical conductivity and wear behavior of high volume titanium carbide reinforced copper matrix composites. It was reported that hardness and strength of the composite increased with titanium carbide content and alloying elements in the matrix phase. Wear resistance of composites was studied against high speed steel. Microploughing of copper base matrix was found to be the dominant wear mechanism. Less microploughing and wear loss was observed at lower loads and for high vol. % of TiC particles. Heavy microploughing effect was observed under 300 N wear load caused by very rapid removal of material from the worn surface. Rajkumar and Aravindan studied the copper-TiC (5-15 vol %) - graphite (5-10 vol. %) hybrid composites fabricated through a novel microwave processing technique. Pin on disc tester was used to evaluate the tribological properties under testing parameters of normal loads 12 - 48 N and sliding speed of 1.25 – 2.51 m/s. It was observed that there is an increase in coefficient of friction with increasing normal load. It was also found that hybrid composites exhibited lower coefficient of friction compared with unreinforced copper. Higher coefficient of friction was
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exhibited by unreinforced copper under all the loading conditions. Adhesive nature of tribo contact leads to the transfer of soft copper matrix to harder counter surface [16]. Franco et al. have studied the wear performance of Mg-AZ91 alloy and TiC as reinforcement processed by pressure less infiltration technique. Results indicated that the wear resistance of alloy Mg AZ91 showed best behavior when the pin sample are worn over the AISI 4140 steel and the worst results with the AISIH13 steel. Therefore, at this TiC particulate concentration, the composite exhibits a low favorable response for the projected automotive application, since the obtained wear rates are higher in comparison with the unreinforced alloy [17-18]. In the last few years, our research group has carried out some important investigations on FeAl2O3 and Fe-ZrO2 metal matrix composites fabricated via powder metallurgy technique. Due to the reactive sintering process a nano iron aluminate (FeAl2O4) phase forms in Fe-Al2O3 composite system, whereas in Fe-ZrO2 composite system a nano iron zirconium oxide (Zr6Fe3O) phase forms. Due to these phases, the various properties such as density, hardness, wear, compression, deformation and corrosion were found to improve [19-23]. The formation of these nano iron aluminate and iron zirconium oxide phases depend on processing parameters. Mechanical properties also depend on processing parameters. Fe-Al2O3 nanocomposites are potential candidate for applications in heavy duty components such as railway wagon wheels, braking system etc. where pure iron cannot give the desired tribological properties. The present paper reports the wear behavior of 10% Al2O3 reinforced iron based nanocomposite synthesized via powder metallurgy technique as a function of sintering parameters i.e. temperature and time. The wear measurement of nanocomposite pins was carried out under a
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load of 0.5, 1.0 and 2.0 kg respectively for a fixed sliding velocity of 4 m/sec and time 1 hour. Worn surface analysis of the specimens was also done in order to study the type of wear. 2. Experimental Work In the present work 90% Fe (electrolytic grade with 99.5% purity and particle size in the range of 49-58 µm) and 10% Al2O3 (active; particle size in the range of 63-210 µm) was taken as the starting materials. Composite powder in desired composition was ball milled dry using powder to ball ratio of 1:2. Zirconia balls were used as the grinding and mixing media. 2 wt%. of dextrin was used as binder for providing green strength to the specimen. Composite powder was compacted at a load of 7 tons. Composite pins were sintered in argon atmosphere in the temperature range of 900-1100°C for 1 to 3 hours respectively. Heating and cooling rate of the furnace has been kept as 5°C/min during the sintering process. Specimens of size 12 mm diameter and 20 mm height were obtained after sintering. Nomenclature of specimens along with density and hardness is illustrated in Table 1 below. Surface of the specimen was polished using various grades of emery paper. X-ray diffraction (XRD) pattern of the synthesized specimen was studied using Rigaku High Resolution Powder X-Ray diffractometer with Cu-Kα radiation and Ni-filter. Acceleration voltage was kept as 30kV, acceleration current as 15mA and step size of 0.02° was used in the present phase analysis study. Micrograph of worn specimens was studied using Inspect S-50, FP 2017/12 scanning electron microscope. Wear characterization of the cylindrical pin specimens of 12 mm diameter was carried out using pin on disc wear and friction testing machine (Magnum Engineers, Bangalore, India). Wear characterization was carried out using standardized steps. Prior to the test the disc (hardened steel disc with a hardness of HRC 60) was ground using alumina wheel and then polished using various grades of emery papers to remove the erosion 5
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marks. Initially, the nanocomposite pin was loaded against a rotating disc, and was made to run under a load of 2.0 kg for 2h so that the worn surface of the specimen pin becomes parallel to the disc. Sliding velocity is kept as 4 m/sec and the test is performed for a time interval of 1h. Wear characteristics of the specimens were studied using a load of 0.5, 1.0 and 2.0 kg in dry sliding condition. Wear debris were removed from the surface of the plate intermittently using tissue paper moist with acetone. Two readings were taken for each load. Weight loss of the nanocomposite pin was measured at an interval of 1h in an analytical balance of 10-4 g precision. Wear volume was then calculated from the weight loss values. Worn surfaces of the nanocomposite pins were observed in a scanning electron microscope to study the nature of wear. 3. Results and Discussions 3.1 XRD X-Ray diffraction pattern of representative nanocomposite specimen sintered at 1100C for 2h (10AFe1100(2)) is shown in Fig.1. Diffraction peaks of XRD patterns were matched with JCPDS files of cubic α-Fe (file no. 06-0696), Al2O3 (file no. 11-0517) and FeAl2O4 (file no. 34-0192). It was found from matching that Fe, Al2O3 and FeAl2O4 phases were present in the present specimen. This iron aluminate (FeAl2O4) phase forms due to reactive sintering between iron and alumina particles [17]. Amount of dispersed (Al2O3 and FeAl2O4) and matrix (Fe) phases in the nanocomposite and the properties thereof depend on sintering temperature and time. Presence of this iron aluminate phase was found in all the specimens of this system. It was also found that 3 hour of sintered specimen showed more amount of iron aluminate phase and trace amount of alumina particles. It was concluded that the peak
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intensity of iron aluminate phase was higher in the specimen reinforced with 10% Al2O3 in comparison to 5% Al2O3 reinforcement [24]. 3.2 Microstructure (As Prepared) Detailed microstructure of Fe-Al2O3 metal matrix nanocomposites specimens was described in our earlier publication [24]. Figure 2 shows the SEM of specimen 10AFe1100(1) (a) 5000X and (b) 20000X magnification. Fig. 2(a) shows highly dense phase composite specimen containing negligible amount of porosity. These microstructures show grains of Fe, Al2O3 and FeAl2O4. The dark black grains are of iron white ones are of aluminium oxide. Remaining grey coloured grains are of iron aluminate. Fig. 2(b) shows micrograph of the same specimens at 20,000X magnification. Present microstructure shows the micron and nanometer size grains of iron aluminate phase. The particle size lies in the range of 14 – 135 nm respectively. 3.3 Wear Characterization Fig. 3(a) shows the wear rate vs. load plots for specimen sintered for 1h. Specimen 10AFe900(1) shows the wear rate of 0.69x10-3 mm3/s under a load of 0.5 kg. On increasing the load to 1.0 and to 2.0 kg the wear rate increases significantly from 0.73x10-3 mm3/s to 2.02x10-3 mm3/s. For the specimen 10AFe1000(1) under 0.5 and 1.0 kg load the wear rate was found to be reduced in comparison to specimen 10AFe900(1). At 2.0 kg load the wear rate was found to increase in comparison to specimen 10AFe900(1). Specimen 10AFe1100(1) shows lower wear rate values at all loads. It was found from the study that the specimen sintered at low temperature showed high amount of wear. On increasing the sintering temperature the wear rate was reduced significantly. At higher sintering temperature a more amount of iron aluminate phase is formed.
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In a similar manner Fig. 3(b) shows the wear rate vs. load plots for specimens sintered for 2h. Wear rate for specimen 10AFe900(2) was found to be 0.54x10-3 mm3/s, 1.06x10-3 mm3/s and 2.20x10-3 mm3/s under 0.5 kg, 1.0 kg and 2.0 kg load respectively. Specimen 10AFe1000(2) showed a lower values of wear rate at a load of 0.5 and 1.0 kg load whereas wear rate was found to be high at a load of 2.0 kg as compared to specimen 10AFe900(2). Upon increasing the sintering temperature to 1100C for 2 hour of sintering time, specimen 10AFe1100(2) showed lower values of wear rate at a load of 0.5 and 1.0 kg whereas it showed a higher wear rate value at a load of 2.0 kg when compared to specimen 10AFe900(2) and 10AFe1000(2). Fig. 3(c) shows wear rate vs. load plots for specimens sintered for 3h. Specimen 10AFe900(3) shows a wear rate of 0.20x10-3 mm3/s under a load of 0.5 kg. Further increase of load to1.0 kg and 2.0 kg increased the wear rate to 0.40 x10-3 mm3/s and 1.94x10-3 mm3/s respectively. Wear rate values at different loads for specimen 10AFe900(3) was found to be reduced in comparison to specimen 10AFe900(1) and 10AFe900(2). For specimen 10AFe1000(3) the wear rate was found to be lowest at all loads in comparison to all other specimens. Upon increasing the sintering temperature to 1100C for 3 hours of sintering time the specimen 10AFe1100(3) showed a higher wear rate at a load of 0.5 and 1.0 kg in comparison to specimen 10AFe900(3). Fig. 4(a) shows the coefficient of friction vs. load plot for specimens sintered for 1h. Specimen 10AFe900(1) shows the coefficient of friction value of 19 N under 0.5 kg load, whereas the same specimen showed friction force value of 13.5 N under 1.0 kg load. On further increasing the load to 2.0 kg the same specimen showed friction force value of 10.25 N. The specimen which is sintered at 1000°C for 1 hour i.e. specimen 10AFe1000(1) showed higher coefficient of friction values at all loads in comparison to specimen 10AFe900(1). On further increasing the sintering
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temperature to 1100°C and for 1 hour i.e. for specimen 10AFe1100(1) the coefficient of friction values were found to be higher at all loads in comparison to specimen 10AFe900(1) and 10AFe1000(1). Fig. 4(b) shows the coefficient of friction vs. load plot for specimens sintered for 2h. Specimen 10AFe900(2) shows the coefficient of friction value of 16.0 N under 0.5 kg load, whereas the same specimen showed friction force value of 14.0 N under 1.0 kg load. On further increasing the load to 2.0 kg the same specimen showed friction force value of 10.25 N. Specimen which is sintered at 1000°C for 2 hour i.e. specimen 10AFe1000(2) showed higher coefficient of friction values at all loads in comparison to specimen 10AFe900(2). On further increasing the sintering temperature to 1100°C for 2 hour i.e. for specimen 10AFe1100(2) the coefficient of friction value was reduced in comparison to specimen 10AFe900(2) and 10AFe1100(2). In the similar manner Fig. 4(c) shows the coefficient of friction vs. load plot for specimens sintered for 3h. Specimen 10AFe900(3) shows the friction force value of 13.0 N under 0.5 kg load, whereas the same specimen showed friction force value of 13.5 N under 1.0 kg load. On further increasing the load to 2.0 kg the same specimen showed friction force value of 9.0 N. Specimen which is sintered at 1000°C for 3 hour i.e. specimen 10AFe1000(3) showed higher coefficient of friction values at a load of 0.5 and 1.0 kg whereas for 2.0 kg load it was almost same as compared to specimen 10AFe900(3). On further increasing the sintering temperature to 1100°C and for 3 hour i.e. for specimen 10AFe1100(3) the coefficient of friction values were reduced in comparison to specimen 10AFe900(3) and 10AFe1000(3). It could be seen from the above interpretation that specimen 10AFe1000(3) shows the lowest value of wear rate. However, at lower load i.e. 0.5 kg the specimen shows high value of 9
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coefficient of friction whereas at high load the coefficient of friction value reduces. At high temperature and time values a more amount of iron aluminate phase forms thus the wear rate values are reduced significantly. Iron aluminate phase formation depends on the percentage of alumina along with sintering parameters i.e. temperature and time respectively. In our earlier articles, it has been shown that the sintering and in turn hardness and wear characteristics of the nancomposite Fe-Al2O3 specimens varies in complex manner due to reaction between iron and alumina during consolidation and sintering. Formation of iron aluminate phase will enhance the hardness and wear characteristics only when there is good binding between iron grains encompassing the alumina ceramic and reactive iron aluminate phase. The formation of iron aluminate phase depends on sintering temperature and time. Therefore, with increasing sintering temperature and time its content increases, which in turn increases hardness and decreases wear rate. However, the increase in iron aluminate phase decreases the consolidation or binding between different grains. Thus, there shall always be an optimum sintering temperature for good binding between the grains with sufficient ceramic phase, thereby leading to good mechanical characteristics. Secondly, the wear and friction force depend on the wear mechanism operative at a particular load. It has also been shown that adhesive or micro- ploughing wear mechanism operates at low loads and at high loads due to entrapment of hard ceramic debris between pin and disc abrasive wears starts dominating. Abrasive wear increases the wear rate and decreases the frictional forces [19, 22, and 24]. 3.4 Microstructure (Worn Surface) SEM analysis of the worn surface formed during the dry sliding wear test was carried out in order to study the wear mechanism maps in the nanocomposite pins. Fig. 5 shows the worn 10
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surface analysis of specimen 10AFe900(1) at (a) 200X (b) 500X and (c) 10000X after wear measurement under 2.0 kg load. Specimen 10AFe900(1) shows the micrograph after wear testing under 2.0 kg load (Fig. 5(a)). Microstructure shows the wear marks generated during the dry sliding contact between the steel disc and the composite pins. Initially the interaction of asperities on the disc and steel pin leads to the fragmentation and fracture at some asperities. Uneven removal of debris from the specimen surface indicates sharp edges of the ceramic reinforcement particles which stand proud of the nanocomposite surface. These may cut into the specimen surface and can generate the grooves. Even when the test load on the specimen is 2.0 kg the amount of wear from the surface is not too much which in turn suggests the improved hardness of the nanocomposite pins. Fig. 5(b) shows the higher magnification micrograph of same specimen which depict removal of material as well as smoothing of specimen surface. This smoothing takes place by the removal of the material which comes in contact between the disc and specimen surface thereby forming tribo film between the two. In the present image nano size formation of iron aluminate (FeAl2O4) phase with the presence of some sub micron sized particles of iron as well as aluminium oxide can also be seen. Fig. 6 shows the worn surface analysis of specimen 10AFe900(2) at (a) 200X (b) 500X and (c) 10000X magnification after wear measurement under 2.0 kg load. Fig. 6(a) shows the micrograph of specimen after wear testing under 2.0 kg load for specimen 10AFe900(2). This micrograph shows the wear marks generated in a regular fashion and the generated grooves are more or less equal to the wear marks generated in the specimen 10AFe900(1). Micrograph also shows some grains of aluminium oxide being embedded in the bed of iron matrix. Fig. 6(b) shows that wear in the present case takes place by smoothing as well as by the microploughing
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effect on the specimen by the eroded particles. It also reveals some sub micron sized and nano range particles of iron aluminate phase. Fig. 7 shows the worn surface analysis of specimen 10AFe1100(1) at (a) 200X (b) 500X and (c) 10000X magnification after wear measurement under 2.0 kg load. Fig. 7(a) shows the micrograph after wear testing under 2.0 kg load for specimen 10AFe1100(1). Specimen shows wear grooves and also intense wear marks generated due to the entrapment of hard aluminium oxide particles between the disc and specimen. In this micrograph a big amount of material is removed from the specimen contact surface which has caused progressive wear by the action of the detached particles. This results in ploughing and the creation of surface grooves. Fig. 7(b) shows the higher magnification worn micrograph of the specimen 10AFe1100(1) under 2.0 kg load, specimen is abraded heavily by the hard ceramic reinforcement which is removed from the specimen surface thereby forming tribo film between the disc and the specimen itself. Image also revealed the formation of iron aluminate phase with some micron and sub micron size particles of iron and aluminium oxide respectively. Presence of iron aluminate phase was also seen in the X-ray diffraction pattern of representative nanocomposite specimen. 3.5 Discussion On the basis of the above results and interpretations it can be concluded that at lower values of load i.e. under 0.5 kg the wear from the pin is mainly due to removal of debris material which is due to cutting and flowability of penetrated hard debris material into the softer surface. It is found that after some interval (i.e. after completing some interval),a higher amount of stress is expected to act on the debris, due to the higher values of hardness of the nanocomposite specimens. Because of this high value of stress levels at these points, the removed debris gets
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deformed plastically by getting entrapped in between disc and pin surface and some of the sharp removed particles get fractured due to combined effect of normal and shear stress. Initially it is also seen that the wear mapping of the nanocomposites shows a considerable high amount of energy which is generally spent in generating a high amount of frictional force. This leads to an increase in the heating between the specimen surface and the disc. Therefore, it is observed that initially the temperature of the contact surface is less and hence the debris materials are expected to be in stronger and in more rigid form. With passage of time there is increase in the value of wear from the pin surface which is removed in a linear manner and the temperature of the intermittent surface is also increased significantly. Due to the increase in the temperature of the contact surface, the debris formed is mild and small in the nature. At higher loads i.e. under 2.0 kg the initial wearing is similar to that of the wear which takes place at lower loads but as the time passes, the value of frictional heating increases. This leads to higher temperature and softening of the surface materials. When there is a sliding action, a 100% amount of the frictional force acts between the two intermittent surfaces, which causes a large amount of frictional heating between the disc and pin i.e. at the contact point. Since the two counter acting surfaces i.e. disc and pin surface are in relative motion with respect to each other, the dissipation of frictional heat from the surface in dry sliding test is regular because of insufficient time for removal of heat. In the initial stage the debris are stronger and sharper due to which the frictional heating takes place at a higher rate. After a certain period of time, because of the increase in the removal of the material from the specimen surface, slipping action is higher leading to the decrease in the amount of frictional heating. There is also a possibility of adhesion between the counter surfaces which leads to higher degree of friction. Because of these counter actions, frictional heating remains almost constant. 13
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The values of wear rate in all the specimen increases with an increase in the applied load values. Increase in the values of applied load leads to increase in the penetration of the hard debris material from the disc surface to the surface of the nanocomposite pins. As the value of the load increases beyond the critical value, the wear from the surface of the nanocomposite pins increases in an abrupt manner. Load at which the value of wear rate increases abruptly is called the transition load. When applied load is greater than the transition load, the wear rate of the nanocomposite pins shoots up to significantly higher value. This effect is due to significantly higher frictional heating and thus the localized adhesion of the nanocomposite pin surface with the counter surface. This effect leads to the softening of the pin surface thus leads to more penetration of the debris material. Therefore, the material removal due to the delamination of adhered areas, micro cutting and micro fracturing increases significantly [25-26]. Overall variation of the wear rate and frictional force values were quite low and were found to depend on the iron aluminate phase formation which in turn depends upon the sintering temperature and time respectively. 4. Conclusions A systematic study of dependence of wear behavior on sintering mechanism for Iron-Alumina Metal Matrix Nanocomposites prepared by Powder Metallurgy has been reported in this paper. The experimental results have been discussed critically and the following important conclusions have been drawn: 1) XRD results show the formation of iron aluminate phase due to the reactive sintering between iron and aluminium oxide particles.
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2) At lower loads, the removal of the material is due to fragmentation of asperities and removal of material is due to slipping actions of penetrated hard asperities into the softer surface. 3) Wear mechanism maps in the present case lead to the microploughing effect. 4) All the synthesized nanocomposite specimen showed improved wear rate in comparison to pure iron specimen. The wear rate of pure iron specimen at a load of 0.5, 1.0 and 2.0 kg was found out to be 0.80x10-3 mm3/s, 1.31x10-3 mm3/s and 3.65x10-3 mm3/s. It is expected that the results of these investigations will be useful in developing technology for producing better quality MMNC at competitive rates.
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[9] Lee C S, Kim Y H, HanK Sand Lim T. Wear behaviour of alurninium matrix composite Materials. J Mater Sci 1992; 27: 793-800. [10] Tjong S C and Lau K C. Microstructural and mechanical characteristics of in situ metal matrix composites. Mater Let 2000; 43: 274–280. [11] Lim C Y H, Leo D K, Ang J J Sand Gupta M. Wear of magnesium composites reinforced with nano-sized alumina particulates. Wear 2005; 259: 620-625. [12] Bhattacharjee D, Muthusamy K. and Ramanujam S. “Effect of Load and Composition on Friction and Dry Sliding Wear Behavior of Tungsten Carbide Particle-Reinforced Iron Composites. Trib Trans 2014; 57: 292-299. [13] Naplocha K and Granat K. Dry sliding wear of Al/Saffil/C hybrid metal matrix composites.Wear2008; 265: 1734-1740. [14] Rosenberger M R, Forlerer E and Schvezova C E. Wear behavior of AA1060 reinforced with alumina under different loads. Wear 2009; 266: 356-359. [15] Akhtar F, Askari S J, Shah K A, Du X, Guo S. Microstructure, mechanical properties, electrical conductivity and wear behavior of high volume TiC reinforced Cu-matrix composites. Mater Char 2009; 60: 327-336. [16] Deaquino-Lara R. et al. Tribological characterization of Al7075-graphite composites fabricated by mechanical alloying and hot extrusion, Mater Des 2015; 67: 224-231. [17] Franco LF, Becerril E B, Ruiz J L, Rodríguez J G G, Guardian R and Rosales I. Wear performance of TiC as reinforcement of a magnesium alloy matrix composite. Comp: Part B 2011;42: 275-279. 17
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[18] Rastogi R B, Maurya J L, Jaiswal V. Phosphorous free antiwear formulations: Zinc thiosemicarbazones–borate ester mixtures. Proc Inst Mech Eng, Part J: J Engg Trib 2013; 227 (3): 220-233. [19] Gupta P, Kumar D, Parkash O and Jha A K. Structural and mechanical behavior of 5%Al2O3 reinforced Fe metal matrix composites (MMC) produced by powder metallurgy(P/M) route. Bull Mater Sci 2013; 36 (5): 859-868. [20] Gupta P, Kumar D, Quraishi M A and Parkash O. Corrosion Behavior of Al2O3 Reinforced Fe Metal Matrix Nanocomposites Produced by Powder Metallurgy Technique. Adv Sci Engg Med2013; 5(4): 366-370. [21] Jha P, Gupta P, Kumar D and Parkash O. Synthesis and characterization of Fe–ZrO2 metal matrix composites. J Comp Mater 2014; 48 (17): 2107-2115. [22] Gupta P, Kumar D, Parkash O and Jha A K. Effect of Sintering on Wear Characteristics of Fe-Al2O3 Metal Matrix Composites. Proc Inst Mech Eng, Part J: J Engg Trib 2014; 228(3): 362368. [23] Kumar U J P, Gupta P, Jha A K and Kumar D. Closed Die Deformation Behavior of Cylindrical Iron-Alumina Metal Matrix Composites During Cold Sinter Forging. J Inst Eng India: Series D 2016; 97(2): 135-151. [24] Gupta P, Kumar D, Parkash O. and Jha A K. Sintering and Hardness Behavior of Fe-Al2O3 Metal Matrix Nanocomposites (MMNCs) prepared by Powder Metallurgy. J Comp 2014; Article ID 145973: 1-10.
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[25] Mazahery A. and Shabani M O. Study on microstructure and abrasive wear behavior of sintered Al matrix composites. Cer Intl 2012; 38: 4263-4269. [26] Kumar D, Himadri R. and Show B K. Tribological Behavior of an Aluminum Matrix Composite with Al4SiC4 Reinforcement under Dry Sliding Condition. Trib Trans 2015; 58: 518526.
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LIST OF FIGURE CAPTIONS Fig. 1 X-Ray Diffraction pattern of 10AFe1100(2). Fig. 2 SEM of specimen 10AFe1100(1) (a) 5000X and (b) 20000X magnification [24]. Fig. 3 Wear Rate vs. Load for specimens sintered for (a) 1h (b) 2h and (c) 3h. Fig. 4 Coefficient of friction vs. Load for specimens sintered (a) 1h (b) 2h and (c) 3h. Fig. 5 Worn surface analysis of specimen 10AFe900(1) at (a) 200X and (b) 10000X after wear measurement under 2.0 kg load. Fig. 6 Worn surface analysis of specimen 10AFe900(2) at (a) 200X and (b) 10000X after wear measurement under 2.0 kg load. Fig. 7 Worn surface analysis of specimen 10AFe1100(1) at (a) 200X and (b) 10000X after wear measurement under 2.0 kg load.
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LIST OF TABLE CAPTIONS Table 1 Nomenclature of Specimens along with density and hardness
21
20 30 40 50
2 (degree)
Figure 1
FeAl2O4 (311)
60 70
FeAl2O4 (533)
FeAl2O4 (620)
FeAl2O4 (440) Fe (200)
FeAl2O4 (511)
FeAl2O4 (422)
Al2O3 (104)
FeAl2O4 (220)
Fe (110)
Intensity (arbt. units)
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10AFe1100(2)
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(a)
(b)
Fe
Al2O3 FeAl2O4 Nanosize FeAl2O4
Figure 2
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10% Al2O3 + 90 % Fe o
900 C(1h) o 1000 C(1h) o 1100 C(1h)
2.5
3
Wear Rate x 10 (mm /sec)
3.0
-3
2.0 1.5 1.0 0.5 0.0 0.0
0.5
1.0
1.5
2.0
2.5
2.0
2.5
2.0
2.5
Load (kg)
(a) 3.5
10% Al2O3 + 90 % Fe o
900 C(2h) o 1000 C(2h) o 1100 C(2h)
2.5
3
Wear Rate x 10 (mm /sec)
3.0
-3
2.0 1.5 1.0 0.5 0.0 0.0
0.5
1.0 1.5 Load (kg)
(b) 3.5
10% Al2O3 + 90 % Fe
2.5
o
900 C(3h) o 1000 C(3h) o 1100 C(3h)
3
Wear Rate x 10 (mm /sec)
3.0
-3
2.0 1.5 1.0 0.5 0.0 0.0
0.5
1.0 1.5 Load (Kg)
(c) Figure 3
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900 C(1h) o 1000 C(1h) o 1100 C(1h)
Coefficient of Friction (N)
30 25 20 15 10 5 0 0.0
0.5
1.0
1.5
2.0
2.5
Load (kg)
(a) 35
10% Al2O3 + 90 % Fe o
900 C(2h) o 1000 C(2h) o 1100 C(2h)
Coefficient of Friction (N)
30 25 20 15 10 5 0 0.0
0.5
1.0
1.5
2.0
2.5
Load (kg)
(b) 35
10% Al2O3 + 90 % Fe o
900 C(3h) o 1000 C(3h) o 1100 C(3h)
Coefficient of Friction (N)
30 25 20 15 10 5 0 0.0
0.5
1.0
1.5
Load (kg)
(c) Figure 4
2.0
2.5
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(a)
Figure 5
(b)
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(a) Microploughing
Figure 6
(b)
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(a)
(b)
Figure 7
(c)
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RESEARCH HIGHLIGHTS
Present paper investigates the wear behavior of Fe - 10% Al2O3 MMCs.
The wear properties are dependent on densification and hardness of the specimen.
Wear behavior of the specimens varies with the iron aluminate phase formation.
Wear mechanism maps in the present case lead to the microploughing effect.
All the synthesized nanocomposite specimen showed improved wear rate in comparison to pure iron specimen.
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Table 1
S.
Sintering
Sintering
Specimen
No.
Temperature
Time (h)
Code
(°C)
Green Density
Sintered Density
(g/cm3)
(g/cm3)
Hardness (HRH)
1.
900
1
10AFe900(1)
3.8119
3.9421
55
2.
900
2
10AFe900(2)
3.7730
4.0713
42
3.
900
3
10AFe900(3)
3.8250
4.4977
40
4.
1000
1
10AFe1000(1)
3.9196
3.9330
39
5.
1000
2
10AFe1000(2)
3.9031
4.2577
40
6.
1000
3
10AFe1000(3)
3.8967
4.5055
43
7.
1100
1
10AFe1100(1)
3.8852
4.4707
40
8.
1100
2
10AFe1100(2)
3.8909
4.6008
54
9.
1100
3
10AFe1100(3)
3.9233
4.9806
42