Wear behaviors of HVOF sprayed WC-12Co coatings by laser remelting under lubricated condition

Optics & Laser Technology 89 (2017) 86–91

Contents lists available at ScienceDirect

Optics & Laser Technology journal homepage: www.elsevier.com/locate/optlastec

Full length article

Wear behaviors of HVOF sprayed WC-12Co coatings by laser remelting under lubricated condition

crossmark

⁎

Kong Dejuna,b, , Sheng Tianyuana a b

College of Mechanical Engineering, Changzhou University, Changzhou 213164, China Jiangsu Key Laboratory of Materials Surface Science and Technology, Changzhou University, Changzhou 213164, China

A R T I C L E I N F O

A BS T RAC T

Keywords: Laser remelting (LR) High velocity oxygen fuel (HVOF) WC-12Co coating Lubricated friction Dry friction Friction and wear

A HVOF (high velocity oxygen fuel) sprayed WC-12Co coating was remelted with a CO2 laser. The surfaceinterface morphologies and phases were analyzed by means of SEM (scanning electron microscopy), and XRD (X-ray diffraction), respectively. The friction and wear behaviors of WC-12Co coating under the dry and lubricated conditions were investigated with a wear test. The morphologies and distributions of chemical elements on worn scar were analyzed with a SEM, and its configured EDS (energy diffusive spectrometer), respectively, and the effects of lubricated condition on COFs (coefficient of friction) and wear performance were also discussed. The results show that the adhesion between the coating and the substrate is stronger after laser remetling (LR), in which mechanical bonding, accompanying with metallurgical bonding, was found. At the load of 80 N, the average COF under the dry and lubricated friction conditions is 0.069, and 0.052, respectively, the latter lowers by 23.3% than the former, and the wear rate under the lubricated condition decreases by 302.3% than that under the dry condition. The wear mechanism under the dry and lubrication conditions is primarily composed of abrasive wear, cracking, and fatigue failure.

1. Introduction As one of the most widely used steel in the mold industry [1], H13 (i.e. 4Cr5MoSiV1) hot work mold steel has many advantages such as good toughness and thermal strength, thermal stability, antioxidant capacity and thermal fatigue, and etc., which is mainly used in the impact load of forging molds, hot extrusion mold, precision forging mold and pressure mold [2,3]. However, the H13 hot work mold steel is easily wore and failed during the usage [4,5], which is a research hotspot that how to improve wear resistance and prolong its service life [6,7]. Thermal sprayed WC-12Co coating has good wear resistance, high hardness and high temperature resistance [8,9], which has been widely used in many industrial fields. High velocity oxygen fuel (HVOF) has low flame flow temperature and high flame flow velocity characteristics [10–12], which reduces the decarburization and oxidation of sprayed WC powder particles, the coating-substrate combination after LR (laser remelting) was more closely [13,14]. However, researches on WC-12Co coating mainly focus on powder type [15,16], spraying process [17,18], microstructure [19], mechanical properties [20], and other fields, while the research on WC-12Co coating by LR is very little. Because the LR determines the distribution of surface-interface chemical elements and influences the wear resistance of the coating

⁎

[21,22], the EDS analysis of chemical elements on the worn scars under the dry and lubricated conditions has not reported. In this study, a WC12Co coating was sprayed on H13 hot work mold steel with a HVOF, and the obtained coating was processed with a LR. The morphologies of surface-interface and worn scar under the dry and lubricated conditions were analyzed by a SEM, and its configured EDS, respectively, which provided an experimental basis for the application of WC-12Co coating on the surface modification of H13 hot work mold steel. 2. Experimental The substrate was H13 hot work mold steel with the mass fraction (mass, %) as follows: C 0.32–0.45, Si 0.80–1.20, Mn 0.20–0.50, Cr 4.75–5.50, Mo 1.10–1.75, V 0.80–1.20, S, P < 0.03 and the rest was Fe. Spraying powder was a DG type WC-12Co with the mass fraction (mass, %) as follows: WC 88, Co 12. Before spraying, the sample surface was washed with alcohol, and then was treated by 200 meshes brown corundum abrasive. The spraying was conducted on a XM-8000 type supersonic spraying system, using aviation kerosene as fuel, high pressure O2 as combustion gases, and N2 as the powder feed gas. Technological parameters: fuel pressure of 1.25 MPa, O2 pressure of 1.58 MPa, water temperature of 40 °C, gun pressure of 0.95 MPa. The

Corresponding author at: College of Mechanical Engineering, Changzhou University, Changzhou 213164, China. E-mail address: [email protected] (K. Dejun).

http://dx.doi.org/10.1016/j.optlastec.2016.09.043 Received 3 August 2016; Received in revised form 15 September 2016; Accepted 26 September 2016 0030-3992/ © 2016 Elsevier Ltd. All rights reserved.

Optics & Laser Technology 89 (2017) 86–91

K. Dejun, S. Tianyuan

in a semi molten state, and the substrate was impacted by the liquid/ solid two phases, so that a large number of particles were embedded into the substrate, and the “interlocking” phenomenon appeared. The energy released during the impact occurred a part of chemical elements to diffuse. The combination between the coating and the substrate was primarily mechanical bonding, accompanied with a little metallurgical bonding. The sprayed particles enhanced bonding strength of the coating and substrate, playing a good role in the protection of the substrate. Fig. 2(a) shows the appearance of HVOF sprayed WC-12Co coating surface after LR. A part of the WC was decomposed into W and CO2, and the Co was not filled in time, therefore, the particle distribution was more obvious in the molten state. Fig. 2(b) shows the morphology of laser remelted WC-12Co coating interface with the thickness of about 200 µm, the coating texture was compact, closely jointed with the substrate. The combination mode between the coating and substrate was primarily mechanical bonding, accompanied with a certain amount of metallurgical bonding. This was because that, the chemical elements of the coating and substrate were diffused during the LR, and a certain metallurgical bonding at the interface of the coating-substrate was produced.

WC-12Co coating was remelted with a Zejin-8000 type CO2 laser, the processing parameters as follows: of 800 W, scanning speed of 500 mm/min, and the size of the spot size was 15 mm×2 mm. The wear testes were conducted on a CFT-I type multifunctional surface performance tester, and the friction mode was reciprocating, and the wear counterpart was Si3N4 ceramic ball with the diameter of 5 mm. Load was 80 N, the wear time was 30 min; the number of reciprocating was 500 mm/min; and the reciprocating length was 2 mm. After grinding and polishing, the surface-interface morphologies were observed with a JSUPRA55 type FESEM (field emission scanning electron microscope) and JSM-6363LA type SEM and, the coating microhardness was measured with a HV-1000 micro Vickers hardness tester, took five points in the coating with the load of 0.3 N, press head held time of 15 s, and the took the average of five points. After the wear test, the surface morphologies of worn scar were analyzed with a SEM and its configured EDS, and the phases of the coating was measured with a D/max2500PC type XRD (X-ray diffraction spectrometer). 3. Analysis and discussion 3.1. Surface-interface morphology

3.2. XRD analysis

Fig. 1(a) shows the morphology of HVOF sprayed WC-12Co coating. The microstructure of WC-12Co coating was compact and the porosity was low. The porosity of the coating was influenced by the coating processing, the properties of the powder, and the cooling conditions, the coating with low porosity was the main technical advantage of HVOF spraying. During the HVOF spraying, the WC particle with high melting point (2867 °C) was uniformly distributed, the binder of Co with low melting point was melted and filled between the WC particles. The WC hard phase particles with clear edges and corners were clearly visible and the coating microhardness was 1100– 1220 HV0.3 measured with a microhardness tester. The HVOF spraying time of the WC-12Co powders through the flame was short, only the binder of Co was melted, the ceramic phase of WC particles almost maintained in solid, presenting a semi molten state, and a handful of WC hard phase was spalled after cooling due to lacking of the Co binder. The cracks were caused by the solidification of Co in the process of cooling and solidification. The volume of Co decreased rapidly, the extrusion of WC solid was produced. After sandblast pretreatment, the substrate surface was uneven, prompting the substrate and sprayed coating formed a good “hooked to bite”, which helped to improve bonding strength of the coating and the substrate. Fig. 1(b) shows the interface morphology of WC-12Co coating with the thickness of about 200 µm, and the WC hard phase existed in the coating with a lamellar structure. The particles were finally presented

Fig. 3(a) shows the XRD spectrum of the HVOF sprayed WC-12Co coating, the diffraction peak of WC was very strong, the diffraction peak of Co was also strong, the coating was primarily composed of WC hard phase and a small amount of Co phase. Fig. 3(b) shows the XRD spectrum of the HVOF sprayed coating after LR, the diffraction peaks of WC at 31°, 37° and 48° were very strong, the other diffraction peaks were low, as a result, the coating composition was WC phase. The new phase of W3O was not found before and after LR from the XRD analysis results, it can be seen that there was no obvious oxidation phenomenon of W elements in the coating. Both of which appeared a few new phase of W2C, this was because that a small amount of WC appeared decarbonization reaction in the HVOF spraying, but the decarburization was not serious, showing that the component of the coating was WC and Co phases. 3.3. COFs Fig. 4(a) shows the curve of WC-12Co coating COFs vs wear time under the dry and lubricated conditions. The average COF of the coating under the dry and lubricated conditions was 0.069, and 0.052, respectively. Under the lubricated condition, the COF decreased by 24%, which significantly decreased the COFs. The wear process was

Substrate

WC-12Co coating

(a) Surface

(b) Interface

Fig. 1. Morphologies of HVOF sprayed WC-12Co coating surface-interface.

87

Optics & Laser Technology 89 (2017) 86–91

K. Dejun, S. Tianyuan

WC-12Co coating

Substrate

(a) Surface

(b) Interface

Fig. 2. Morphologies of HVOF sprayed WC-12Co coating surface-interface after LR.

3.4. Plane scans of worn scar

divided into two periods, i.e. running-in period and stable period. The COFs fluctuated greatly in the running-in period, and tended to a fixed value in the stable period. Under the dry condition, the COFs increased slowly from 0.041 to 0.076 in the running-in period (0–10 min), increased by 85%, which was mainly due to the poor contact between the coating surface and the ceramic ball. In stable period (10–30 min), the COFs were smooth, floating around a fixed value. This was primarily caused by some hard phases of the coating during the wear test. Under the lubricated condition, the COF in the running-in period (0–10 min) also increased slowly from 0.033 to 0.053, increased by 60%, which was obviously better than that under the dry condition. The COFs in stable period (10–30 min) was smooth, floating around a fixed value. Compared to that under the dry condition, the fixed value was small, indicating that the effect of hardness on the COFs was weakened, the lubricant played a significant role in reducing COFs. Fig. 4(b) shows that the width and depth of wear scar under the lubricated condition was less than that under the lubricated condition coating, The wear rate can directly reflect the wear of the coating, under the dry and lubricated conditions, the wear rate was 5.15×10−4 mm3/ s N, and 1.28×10−3 mm3/s N, respectively, the latter decreased by 302.3% than the former. In the dry and lubricated friction test, the wear width and depth under the lubricated condition was obviously less than under the dry condition, indicating that the wear rate under the lubricated condition was significantly less than that that under the dry condition, as a result, the wear under the lubricated condition was obviously better than that under the dry condition, playing a significant role of reducing wear.

Fig. 5(a) shows the morphology of the worn scar under the dry condition. The worn scar was clear with the shallow depth and the narrow width, which indicated the coating had good abrasion resistance. There was no obvious sticking phenomenon on the worn scar, the wear pattern was primarily abrasive wear. The plane scanned position of the worn scar is shown in Fig. 5(a), and the results are shown in Fig. 5(b), the mass fraction (mass, %) as follows: W 77.03, C 2.42, Co 12.74, Fe 4.39, O 3.43; and the atomic fraction (at%) as follows: W 45.35, C 16.54, Co 17.75, Fe 6.45, O 17.59. The elements of W, C and Co were evenly distributed on the coating, without enrichment phenomenon, as shown in Fig. 5(c)–(e), which proved that the coating still maintained good integrity and had good abrasion resistance after the dry friction. The Fe element was partially diffused, its plane scan is shown in Fig. 5(f). The O atom had high content on the coating surface, and its plane distribution was also relatively uniform, as shown in Fig. 5(g). Fig. 6(a) shows the plane scanned position of the worn scar. under the lubricated condition. Compared with that under the dry condition, the worn scar was relatively vague with shallower depth and narrower width, which indicated that the wear resistance of the coating was significantly improved under the lubricated condition. There was no obvious sticking phenomenon on the worn scar, and the wear pattern was mainly abrasive wear. The result of plane scans is shown in Fig. 6(b), the mass fraction (mass, %) as follows: W 76.93, C 0.40, Co 14.14, Fe 6.12. O 2.41; and the atomic fraction (at%) as follows: W

14000

30000

WC Co W 2C

12000

intensity/a.u.

W

10000

Intensity/a.u.

WC 25000

8000 6000

W

20000

Co 15000 10000 5000

4000 2000 20

W 2C

30

40

50

2

60

70

80

0 20

90

30

40

50

60

2θ /

/

(a) Before LR

o

(b) After LR

Fig. 3. XRD analysis of HVOF sprayed WC-12Co coating before and after LR.

88

70

80

90

Optics & Laser Technology 89 (2017) 86–91

K. Dejun, S. Tianyuan

0.10

0.2 Under dry condition Under lubricated condition

Wear depth/µm

0.08

0.04

Under dry condition

-0.6

0

5

10

15

20

25

30

0

50

100

Wear time/min

150

200

250

300

Wear width/ µm

(a) COFs vs wear time

(b) Wear pro les

Fig. 4. COFs vs wear time and wear profiles of HVOF sprayed WC-12Co coating before and after LR.

20000 W

A

Worn scar

16000

B

C

Counts/cps

tion

0.00

-0.2

-0.4

Under lubricated condition

0.02

Wear dir ec

COF

0.06

0.0

12000

8000 Fe Pt W O C W Co

4000

0

0

1

2

Fe Fe Fe Co 3

4

5

6

7

W 8

9

10

Energy/keV

(a) Morphology of worn scar

(c) W content

(b) Result of plane scans

(d) C content

(f) Fe content

(e) Co content

(g) O content

Fig. 5. Plane scans of HVOF sprayed WC-12Co coating by LR under dry condition.

89

350

Optics & Laser Technology 89 (2017) 86–91

K. Dejun, S. Tianyuan

W

25000

Worn scar

20000

E F

ir rd ea W

ec

Counts/cps

D

n tio

15000 10000 Fe O

5000

C 0

0

Pt W

Co W 1

Fe 2

3

4

5

W

Co 6

7

8

9

10

Energy/keV

(a) Morphology of worn scar

(c) W content

(b) Result of plane scans

(d) C content

(f) Fe content

(e) Co content

(g) O content

Fig. 6. Plane scans of HVOF sprayed WC-12Co coating by LR under lubricated condition.

Crack

(a) Abrasive wear

Fatigue spelling

(b) Crack

(c) Falling off by fatigue

Fig. 7. Wear forms of HVOF sprayed WC-12Co coating by LR under dry condition.

spraying and LR, the metallurgical combination occurred between the coating and the substrate, some Fe atoms diffused. The O element mainly came from some elements in the coating and had oxidative reaction due to the high pressure of O2 as combustion gas during the LR.

43.60, C 3.45, Co 25.00, Fe 11.39, O 15.69. The elements of W, C and Co were evenly distributed on the coating, without enrichment phenomenon, as shown in Fig. 6(c)–(e), which proved that the coating still maintained good integrity and had good abrasion resistance after the lubrication friction. The elements of Fe and O on the coating were also evenly distributed, as shown in Fig. 6(f) and (g). During the HVOF 90

Optics & Laser Technology 89 (2017) 86–91

K. Dejun, S. Tianyuan

Fatigue spelling

Crack

(a) Abrasive wear

(b) Crack

(c) Falling off by fatigue

Fig. 8. Wear forms of HVOF sprayed WC-12Co coating by LR under lubricated condition.

3.5. Wear forms [4]

Figs. 7 and 8 show the wear forms of WC-12Co coating under the dry and lubricated conditions, both were mainly abrasive wear, cracking, and fatigue falling. Compared with those under the dry friction, the abrasive wear was significantly larger than that under the lubricated condition, as shown in Figs. 7(a) and 8(a). Both of the cracks were similar, as shown in Figs. 7(b) and 8(b), this was mainly because that the coating surface oxidation was serious after LR, the reciprocating wear force made the coating produce cracks at the weak positions. But most of the cracks only existed on the coating surface, which had little effect on the coating performance. The spalled zone by fatigue under the lubricated condition was obviously less than that under the dry condition, as shown in Figs. 7(c) and 8(c). This was mainly due to the smaller COF under the lubricated condition, the ceramic ball was not easily carried over the fragile parts of the coating because of LR, and the spalling by fatigue was formed.

[5]

[6] [7]

[8]

[9]

[10]

[11]

4. Conclusions [12]

(1) The coating-substrate combination is more closely after LR, which is primarily mechanical bonding, accompanied with a little metallurgical bonding. (2) At the load of 80N, the average COF of WC-12Co coating under the dry and lubricated conditions is 0.069, and 0.052, respectively, and the latter is lowered by 23.3% than the former. (3) The wear mechanism of WC-12Co coating under the dry and lubricated conditions is primarily abrasive wear, cracking and fatigue spalling, and the wear under the lubricated condition is better than that under the dry condition.

[13]

[14]

[15]

[16]

[17]

Acknowledgments [18]

Financial support of this research by the Jiangsu Province Science and Technology Support Program (Industry) (BE2014818) is gratefully acknowledged.

[19]

References [20] [1] Ning Ma, Lei Guo, Zhenxiong Cheng, Huantao Wu, Fuxing Ye, Keke Zhang, Improvement on mechanical properties and wear resistance of HVOF sprayed WC12Co coatings by optimizing feedstock structure, Appl. Surf. Sci. 320 (2014) 364–371. [2] Jo Verwimp, Marleen Rombouts, Eric Geerinckx, Filip Motmans, Applications of laser cladded WC-Based wear resistant coatings, Phys. Procedia Part A 12 (2011) 330–337. [3] Maziar Ramezani, Timotius Pasang, Zhan Chen, Thomas Neitzert, Dominique Au,

[21]

[22]

91

Evaluation of carbon diffusion in heat treatment of H13 tool steel under different atmospheric conditions, J. Mater. Res. Technol. 4 (2015) 114–125. Q.Y. Zhang, Y. Zhou, J.Q. Liu, K.M. Chen, J.G. Mo, X.H. Cui, S.Q. Wang, Comparative research on dry sliding wear of hot-dip aluminized and uncoated AISI H13 steel, Wear 345 (2015) 22–31. S.D. Jacobsen, R. Hinrichs, I.J.R. Baumvol, G. Castellano, M.A.Z. Vasconcellos, Depth distribution of martensite in plasma nitrided AISI H13 steel and its correlation to hardness, Surf. Coat. Technol. 270 (2015) 266–271. Jing-Yuan Li, Yu-Lai Chen, Jian-Hua Huo, Mechanism of improvement on strength and toughness of H13 die steel by nitrogen, Mater. Sci. Eng.: A 640 (2015) 16–23. Marcos Pérez, Francisco Javier Belzunce, The effect of deep cryogenic treatments on the mechanical properties of an AISI H13 steel, Mater. Sci. Eng.: A 624 (2015) 32–40. M. Couto, S. Dosta, J.M. Guilemany, Comparison of the mechanical and electrochemical properties of WC-17 and 12Co coatings onto Al7075-T6 obtained by high velocity oxy-fuel and cold gas spraying, Surf. Coat. Technol. 268 (2015) 180–189. Vamsi Krishna Balla, Susmita Bose, Amit Bandyopadhyay, Microstructure and wear properties of laser deposited WC-12%Co composites, Mater. Sci. Eng.: A 527 (24– 25) (2010) 6677–6682. Mahdi Amiriyan, Houshang D. Alamdari, Carl Blais, Sylvio Savoie, Robert Schulz, Mario Gariépy, Dry sliding wear behavior of Fe3Al and Fe3Al/TiC coatings prepared by HVOF, Wear 342–343 (2015) 154–162. Wen-chao Zhang, Li-bin Liu, Guo-xing Huang, Jia-si Liang, Meng-ting Zhang, Guoxing Huang, Jia-si Liang, Xian Li, Li-gang Zhang, Comparison between WC-10Co4Cr and Cr3C2-25NiCr coatings sprayed on H13 steel by HVOF, Trans. Nonferrous Met. Soc. China 25 (2015) 3700–3707. Q. Wang, Z.H. Chen, Z.X. Ding, Performance of abrasive wear of WC-12Co coatings sprayed by HVOF, Tribol. Int. 42 (7) (2009) 1046–1051. Tao-Wang, Christoph Begau, Godehard Sutmann, Alexander Hartmaier, Large scale molecular dynamics simulation of microstructure formation during thermal spraying of pure copper, Surf. Coat. Technol. 280 (2015) 72–80. N. Makuch, A. Piasecki, P. Dziarski, M. Kulka, Influence of laser alloying with boron and niobium on microstructure and properties of nimonic 80A-alloy, Opt. Laser Technol. 75 (2015) 229–239. H. Chen, C. Xu, Q. Zhou, I.M. Hutchings, P.H. Shipway, J. Liu, Micro-scale abrasive wear behaviour of HVOF sprayed and laser-remelted conventional and nanostructured WC-Co coatings, Wear 258 (1–4) (2005) 333–338. Wojciech Żórawski, The microstructure and tribological properties of liquid-fuel HVOF sprayed nanostructured WC-12Co coatings, Surf. Coat. Technol. 220 (2013) 276–281. K. Van Acker, D. Vanhoyweghen, R. Persoons, J. Vangrunderbeek, Influence of tungsten carbide particle size and distribution on the wear resistance of laser clad WC/Ni coatings, Wear 258 (1–4) (2005) 194–202. Hongbin Liu, Daping Wan, Dejin Hu, Microstructure and wear behavior of lasertextured and micro-alloyed Co-based WC and TiC composite sintered-carbide coating, J. Mater. Process. Technol. 209 (2) (2009) 805–810. Qun-Wang, Jing-Xiang, Gen-Yu Chen, Ying-Liang Cheng, Xin-Qi Zhao, ShiQi Zhang, Propylene flow, microstructure and performance of WC–12Co coatings using a gas-fuel HVOF spray process, J. Mater. Process. Technol. 213 (2013) 1653–1660. Ning-Ma, Lei-Guo, Zhen-Xiong Cheng, Huan-Tao Wu, Fu-Xing Ye, Ke-Ke Zhang, Improvement on mechanical properties and wear resistance of HVOF sprayed WC12Co coatings by optimizing feedstock structure, Appl. Surf. Sci. 320 (2014) 364–371. A. Astarita, S. Genna, C. Leone, F. Memola Capece Minutolo, F. Rubino, A. Squillace, Study of the laser remelting of a cold sprayed titanium layer, Procedia CIRP 33 (2015) 452–457. B.S. Yilbas, S.S. Akhtar, Laser re-melting of HVOF coating with WC blend: thermal stress analysis, J. Mater. Process. Technol. 212 (2012) 2569–2577.