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NiSi metal silicide composite coatings
Journal of Alloys and Compounds 359 (2003) 287–291
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www.elsevier.com / locate / jallcom
Microstructure and dry sliding wear properties of laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings X.D. Lu, H.M. Wang* Laboratory of Laser Materials Processing and Surface Engineering, School of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, PR China Received 30 September 2002; received in revised form 23 January 2003; accepted 23 January 2003
Abstract Mo 2 Ni 3 Si / NiSi wear-resistant metal silicide matrix composite coatings were fabricated on a substrate of an austenitic stainless steel 1Cr18Ni9Ti by laser cladding using Ni–Mo–Si elemental powder blends. The laser clad Mo 2 Ni 3 Si / NiSi composite coatings have a fine microstructure consisting of Mo 2 Ni 3 Si primary dendrites and the interdendritic Mo 2 Ni 3 Si / NiSi eutectics. Wear resistance of the laser clad coatings is evaluated under dry sliding wear test conditions. Influences of wear testing parameters on the wear resistance of laser clad coatings were studied and the wear mechanisms were discussed based on observations of worn surface morphology and subsurface microstructure. Results showed that laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings have excellent dry sliding wear resistance and low friction coefficient. Increasing test load has little influence on the wear mass loss of laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings. 2003 Elsevier B.V. All rights reserved. Keywords: Transition metal silicides; Composite coatings; Wear; Laser cladding; Microstructure
1. Introduction Transition metal silicides such as MoSi 2 , Ti 5 Si 3 , Cr 3 Si, etc., are considered as a new class of alternative hightemperature structural materials for the aerospace and energy-processing industries owing to their outstanding combinations of high melting point, low density, excellent high-temperature oxidation and creep resistance. Serious room-temperature brittleness is the main obstacle preventing the materials from industrial applications as structural components [1–3]. However, from a tribological point of view, these transition metal silicides are also anticipated to have both excellent abrasive and adhesive wear resistance because of their very high hardness and their unique covalent-dominant atomic bonding characteristics. Preliminary results [4–6] demonstrated that these transition metal silicide-based materials do exhibit excellent tribological properties and are likely a new class of abrasion
*Corresponding author. Tel.: 186-10-8231-7102; fax: 186-10-82328041. E-mail address: [email protected] (H.M. Wang). 0925-8388 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00192-0
and adhesion wear-resistant materials for tribological components working under high-temperature or aggressive service conditions. The binary metal silicide MoSi 2 has been widely studied, because of its high melting point (2020 8C), low density and excellent high-temperature oxidation resistance [7–13]. Because of its serious room temperature brittleness and intermediate temperature catastrophic pest oxidation, it is still difficult for the singlephase binary metal silicide alloys to be utilized as thick wear-resistant coatings. Multi-phase strengthening and toughening is one of the most efficient means to improve the toughness of intermetallic alloys. Compared to the binary metal molybdenum silicides (e.g., MoSi 2 , Mo 5 Si 3 ), the ternary metal silicide Mo 2 Ni 3 Si with hP12 Laves crystal structure possessing better toughness while still keeping the high hardness and its inherent strong interatomic bonds, is expected to be an ideal novel wearresistant coating material or a wear-resistant reinforcement. In this paper, Mo 2 Ni 3 Si / NiSi wear-resistant metal silicide matrix composite coatings were fabricated on a substrate of an austenitic stainless steel 1Cr18Ni9Ti by laser cladding using Ni–Mo–Si elemental powder blends and the wear resistance was evaluated under room temperature dry sliding wear test conditions.
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X.D. Lu, H.M. Wang / Journal of Alloys and Compounds 359 (2003) 287–291
2. Experimental procedures The commercial austenitic stainless steel 1Cr18Ni9Ti, 50320310 mm in size, was selected as the substrate material. The starting powder precursor materials used for laser cladding are commercial pure molybdenum, silicon and nickel elemental powder blends (particle size, 70–140 mm). The nominal chemical compositions (wt.%) of the Ni–Mo–Si elemental powder blends are 40Ni–36Mo– 24Si. The powder blends are preplaced on the surface of the austenitic stainless steel samples before laser cladding, with a powder bed thickness of approximately 1.8 mm. The powder-bedded specimens were preheated in a furnace at approximately 400 8C before laser cladding treatment and were, after laser cladding, cooled down slowly on a carbon steel ‘hot-plate’ preheated on a 2-kW electric stove to avoid thermal cracking. The laser cladding was conducted on a 5-kW transverse-flow continuous-wave CO 2 laser materials processing system equipped with a fouraxis computer numerical controlled (CNC) laser materials processing machine under atmospheric environment. Laser processing parameters have a notable influence on the coating features. If the laser scanning speed is too high, the substrate will be melted excessively, leading to excessive dilution of the coating by the substrate. If the laser scanning speed is too low, the substrate will be inadequately melted, leading to no metallurgical bonding to substrate of the coating. The final laser cladding parameters optimized on the basis of experimental trials are: laser outpower 3.2 kW, laser beam size 1731 mm and beam traverse speed 100 mm / min. Metallographic cross-sections, both transverse and longitudinal, of the laser clad composite coatings are prepared using conventional mechanical polishing procedures and are chemically etched in a solution of HF, HNO 3 and H 2 O in volume ratio of 1:6:7. The microstructure of the laser clad composite coatings was analyzed by the Nephot II optical microscope (OM) and KYKY-2800 scanning electron microscope (SEM). The phase presented in the laser clad composite coating was identified by X-ray diffraction (XRD) method using a Rigaku D/ max2200 using Cu Ka radiation with a scanning rate of 58 / min. The chemical composition of the phases was analyzed by energy dispersive spectroscopy (EDS) on Noran vantage DSI. Hardness profiles along the depth direction of the laser clad composite coatings were measured using an MH-6 semi-automatic Vickers microhardness tester with a test load of 1.96 N and a load dwelling time of 15 s. Wear resistance of the coatings were evaluated on a block-on-wheel dry sliding wear tester at room-temperature environment, where the laser clad composite coating specimen, 10310310 mm in size, was pressed under applied load against the outer periphery of a rotating wheel of hardened 0.45%C steel (HRc53). The dry sliding wear were conducted at applied loads of 49, 98 and 147 N, and sliding speeds of 0.43 and 0.86 m / s, respectively. The total wear sliding distance was 3096 m.
Fig. 1. OM micrograph showing the overview transverse cross-section of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
Austenitic stainless steel 1Cr18Ni9Ti was selected as the reference material for all the wear tests. Wear mass loss was measured using a Sartorius 110S precision electronic balance with an accuracy of 0.1 mg and specific wear rate, i.e., wear mass loss of unit sliding distance was used to characterize the wear resistance of laser clad composite coatings. Friction coefficient was calculated from the friction torque recorded during the dry sliding wear process.
Fig. 2. SEM micrograph showing the bonding of the laser clad Mo 2 Ni 3 Si / NiSi composite coating to the substrate.
X.D. Lu, H.M. Wang / Journal of Alloys and Compounds 359 (2003) 287–291
289
Fig. 3. XRD pattern of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
Fig. 5. Hardness profile of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
3. Results and discussion
Mo 2 Ni 3 Si ternary metal silicide and the interdendritic lamellar structure is the Mo 2 Ni 3 Si / NiSi eutectics, as shown in Fig. 4. Volume fraction of the Mo 2 Ni 3 Si primary dendrite of laser clad Mo 2 Ni 3 Si / NiSi composite coating is approximately 60%. As indicated in Fig. 5, the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings have a high and uniform hardness distribution within the coatings except in the coating / substrate bonding zone where the hardness has a gradient decrease to the substrate.
As shown in Fig. 1, microstructure of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings is fine, uniform, free from pores and cracks and with high-quality metallurgical bonding to the substrate (Fig. 2). Laser clad Mo–Ni–Si coatings have a dendritic structure with interdendritic eutectics. Results of XRD (Fig. 3) and EDS analysis indicate that the primary dendrites are the
Fig. 4. OM (a) and SEM (b) micrographs showing microstructure of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
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Fig. 6. Specific wear rate of laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings under different test load.
Result of dry sliding wear test at room temperature showed that the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings have excellent wear resistance and low friction coefficient, as indicated in Figs. 6 and 7. Both the wear mass loss and the friction coefficient are much lower than that of the austenitic stainless steel 1Cr18Ni9Ti. It is interesting, as indicated in Fig. 6, that wear mass loss of the laser clad composite coatings is very insensitive to the increased applied test load and increases very slowly as the applied load increases. On the contrary, the wear mass loss of the reference material 1Cr18Ni9Ti increases drastically with the increasing applied load. This phenomenon implies that the laser clad metal silicides are most preferable for working under heavy load sliding wear service conditions. The friction coefficient for the sliding friction couple between the laser clad Mo 2 Ni 3 Si / NiSi metal silicide
composite coating and the hardened 0.45%C steel is very low and fluctuates between approximately 0.32 and 0.38, while that between reference stainless steel 1Cr18Ni9Ti and the hardened 0.45%C steel fluctuates between approximately 0.60 and 0.68. The excellent wear resistance, low friction coefficient and very sluggish response of wear mass loss to test load of the laser clad Mo 2 Ni 3 Si / NiSi intermetallic composite coatings are primarily attributed to its microstructure characteristics and its unique chemical and physical properties inherent to the transition metal silicides. Because all the microstructural constituent phases, i.e., Mo 2 Ni 3 Si and NiSi, are metal silicides having high hardness and abnormal hardness–temperature relations, the laser clad Mo 2 Ni 3 Si / NiSi composite coatings exhibited excellent abrasive wear resistance due to their outstanding resistance to microcutting and plowing during dry sliding wear process, which is evidenced by the very smooth worn surface with no noticeable grooves and scratches visible, as shown in Fig. 8a. Because of the strong intermetallic atomic bonds of the metal silicide Mo 2 Ni 3 Si and NiSi, the laser clad Mo 2 Ni 3 Si / NiSi composite coatings have very outstanding abilities for metallic adhesion when sliding on the surface of the 0.45%C steel wheel. This is demonstrated by the extremely smooth worn surface morphology having no metallic adhesion features, as shown in Fig. 8a. The worn surface is so smooth that the microstructural constituent phases are clearly revealed, similar to the polished-and-etched metallographic sections. To the knowledge of the authors, no such worn surface morphology was reported in the open literature under metallic dry sliding wear test conditions. Careful examination of worn subsurface microstructure indicates clearly that no selective wear and plastic deformation occurred during the dry sliding wear process for the laser clad metal silicide composite coating, as shown in Fig. 8b.
Fig. 7. Variation of friction coefficients versus test time for the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings and the reference stainless steel 1Cr18Ni9Ti under dry sliding wear test conditions.
X.D. Lu, H.M. Wang / Journal of Alloys and Compounds 359 (2003) 287–291
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Fig. 8. SEM micrographs showing the worn surface (a) and the worn subsurface (b) of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings.
4. Conclusions
References
Wear-resistant Mo 2 Ni 3 Si / NiSi metal silicide composite coatings consisting of Mo 2 Ni 3 Si primary dendrites and interdendritic Mo 2 Ni 3 Si / NiSi eutectics are fabricated on a substrate of an austenitic stainless steel 1Cr18Ni9Ti by laser cladding using 40Ni–36Mo–24Si (wt.%) elemental powder blends. Because of the high hardness and strong atomic bonds, the laser clad Mo 2 Ni 3 Si / NiSi composite coatings have excellent abrasive and adhesive wear resistance under dry sliding wear test conditions.
[1] J.J. Petrovic, A.K. Vasudevan, Mater. Sci. Eng. A261 (1999) 1. [2] A.K. Vasudevan, Mater. Sci. Eng. A155 (1992) 1. [3] D.M. Shah, D. Berczik, D.L. Anton, R. Hecht, Mater. Sci. Eng. A155 (1992) 45. [4] G. Duan, H.M. Wang, Scripta Mater. 146 (2002) 107. [5] H.M. Wang, G. Duan, Mater. Sci. Eng. A336 (2002) 117. [6] H.M. Wang, Y.F. Liu, Mater. Sci. Eng. A338 (2002) 126. [7] A. Hidouci, J.M. Pelletier, Mater. Sci. Eng. A252 (1998) 17. [8] K. Ghosh, M.H. McCay, N.B. Dahotre, J. Mater. Proc. Tech. 88 (1999) 169. [9] S. Ignat, P. Sallamand, A. Nichici, A.B. Vannes, D. Grevey, E. Cicala, Optics Laser Tech. 33 (2001) 461. [10] A. Newman, S. Sampath, H. Herman, Mater. Sci. Eng. A261 (1999) 252. [11] M. Akinc, M.K. Meyer, M.J. Kramer, A.J. Thom, J.J. Huebsch, B. Cook, Mater. Sci. Eng. A261 (1999) 16. [12] S.A. Maloy, J.J. Lewandowski, A.H. Heuer, J.J. Petrovic, Mater. Sci. Eng. A155 (1992) 159. [13] T.A. Kircher, E.L. Courtright, Mater. Sci. Eng. A155 (1992) 67.
Acknowledgements The research was supported by the National High-Tech R&D Program (Contract No. 2002AA331030), the National Natural Science Foundation of China (Grant No. 50071004), the Trans-Century Training Program for Outstanding Talents of the Ministry of Education of China, the Beijing Natural Science Foundation (Grant No. 2022012) and the Science Funds Office of AVIC (02H51007).
L
www.elsevier.com / locate / jallcom
Microstructure and dry sliding wear properties of laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings X.D. Lu, H.M. Wang* Laboratory of Laser Materials Processing and Surface Engineering, School of Materials Science and Engineering, Beijing University of Aeronautics and Astronautics, Beijing 100083, PR China Received 30 September 2002; received in revised form 23 January 2003; accepted 23 January 2003
Abstract Mo 2 Ni 3 Si / NiSi wear-resistant metal silicide matrix composite coatings were fabricated on a substrate of an austenitic stainless steel 1Cr18Ni9Ti by laser cladding using Ni–Mo–Si elemental powder blends. The laser clad Mo 2 Ni 3 Si / NiSi composite coatings have a fine microstructure consisting of Mo 2 Ni 3 Si primary dendrites and the interdendritic Mo 2 Ni 3 Si / NiSi eutectics. Wear resistance of the laser clad coatings is evaluated under dry sliding wear test conditions. Influences of wear testing parameters on the wear resistance of laser clad coatings were studied and the wear mechanisms were discussed based on observations of worn surface morphology and subsurface microstructure. Results showed that laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings have excellent dry sliding wear resistance and low friction coefficient. Increasing test load has little influence on the wear mass loss of laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings. 2003 Elsevier B.V. All rights reserved. Keywords: Transition metal silicides; Composite coatings; Wear; Laser cladding; Microstructure
1. Introduction Transition metal silicides such as MoSi 2 , Ti 5 Si 3 , Cr 3 Si, etc., are considered as a new class of alternative hightemperature structural materials for the aerospace and energy-processing industries owing to their outstanding combinations of high melting point, low density, excellent high-temperature oxidation and creep resistance. Serious room-temperature brittleness is the main obstacle preventing the materials from industrial applications as structural components [1–3]. However, from a tribological point of view, these transition metal silicides are also anticipated to have both excellent abrasive and adhesive wear resistance because of their very high hardness and their unique covalent-dominant atomic bonding characteristics. Preliminary results [4–6] demonstrated that these transition metal silicide-based materials do exhibit excellent tribological properties and are likely a new class of abrasion
*Corresponding author. Tel.: 186-10-8231-7102; fax: 186-10-82328041. E-mail address: [email protected] (H.M. Wang). 0925-8388 / 03 / $ – see front matter 2003 Elsevier B.V. All rights reserved. doi:10.1016 / S0925-8388(03)00192-0
and adhesion wear-resistant materials for tribological components working under high-temperature or aggressive service conditions. The binary metal silicide MoSi 2 has been widely studied, because of its high melting point (2020 8C), low density and excellent high-temperature oxidation resistance [7–13]. Because of its serious room temperature brittleness and intermediate temperature catastrophic pest oxidation, it is still difficult for the singlephase binary metal silicide alloys to be utilized as thick wear-resistant coatings. Multi-phase strengthening and toughening is one of the most efficient means to improve the toughness of intermetallic alloys. Compared to the binary metal molybdenum silicides (e.g., MoSi 2 , Mo 5 Si 3 ), the ternary metal silicide Mo 2 Ni 3 Si with hP12 Laves crystal structure possessing better toughness while still keeping the high hardness and its inherent strong interatomic bonds, is expected to be an ideal novel wearresistant coating material or a wear-resistant reinforcement. In this paper, Mo 2 Ni 3 Si / NiSi wear-resistant metal silicide matrix composite coatings were fabricated on a substrate of an austenitic stainless steel 1Cr18Ni9Ti by laser cladding using Ni–Mo–Si elemental powder blends and the wear resistance was evaluated under room temperature dry sliding wear test conditions.
288
X.D. Lu, H.M. Wang / Journal of Alloys and Compounds 359 (2003) 287–291
2. Experimental procedures The commercial austenitic stainless steel 1Cr18Ni9Ti, 50320310 mm in size, was selected as the substrate material. The starting powder precursor materials used for laser cladding are commercial pure molybdenum, silicon and nickel elemental powder blends (particle size, 70–140 mm). The nominal chemical compositions (wt.%) of the Ni–Mo–Si elemental powder blends are 40Ni–36Mo– 24Si. The powder blends are preplaced on the surface of the austenitic stainless steel samples before laser cladding, with a powder bed thickness of approximately 1.8 mm. The powder-bedded specimens were preheated in a furnace at approximately 400 8C before laser cladding treatment and were, after laser cladding, cooled down slowly on a carbon steel ‘hot-plate’ preheated on a 2-kW electric stove to avoid thermal cracking. The laser cladding was conducted on a 5-kW transverse-flow continuous-wave CO 2 laser materials processing system equipped with a fouraxis computer numerical controlled (CNC) laser materials processing machine under atmospheric environment. Laser processing parameters have a notable influence on the coating features. If the laser scanning speed is too high, the substrate will be melted excessively, leading to excessive dilution of the coating by the substrate. If the laser scanning speed is too low, the substrate will be inadequately melted, leading to no metallurgical bonding to substrate of the coating. The final laser cladding parameters optimized on the basis of experimental trials are: laser outpower 3.2 kW, laser beam size 1731 mm and beam traverse speed 100 mm / min. Metallographic cross-sections, both transverse and longitudinal, of the laser clad composite coatings are prepared using conventional mechanical polishing procedures and are chemically etched in a solution of HF, HNO 3 and H 2 O in volume ratio of 1:6:7. The microstructure of the laser clad composite coatings was analyzed by the Nephot II optical microscope (OM) and KYKY-2800 scanning electron microscope (SEM). The phase presented in the laser clad composite coating was identified by X-ray diffraction (XRD) method using a Rigaku D/ max2200 using Cu Ka radiation with a scanning rate of 58 / min. The chemical composition of the phases was analyzed by energy dispersive spectroscopy (EDS) on Noran vantage DSI. Hardness profiles along the depth direction of the laser clad composite coatings were measured using an MH-6 semi-automatic Vickers microhardness tester with a test load of 1.96 N and a load dwelling time of 15 s. Wear resistance of the coatings were evaluated on a block-on-wheel dry sliding wear tester at room-temperature environment, where the laser clad composite coating specimen, 10310310 mm in size, was pressed under applied load against the outer periphery of a rotating wheel of hardened 0.45%C steel (HRc53). The dry sliding wear were conducted at applied loads of 49, 98 and 147 N, and sliding speeds of 0.43 and 0.86 m / s, respectively. The total wear sliding distance was 3096 m.
Fig. 1. OM micrograph showing the overview transverse cross-section of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
Austenitic stainless steel 1Cr18Ni9Ti was selected as the reference material for all the wear tests. Wear mass loss was measured using a Sartorius 110S precision electronic balance with an accuracy of 0.1 mg and specific wear rate, i.e., wear mass loss of unit sliding distance was used to characterize the wear resistance of laser clad composite coatings. Friction coefficient was calculated from the friction torque recorded during the dry sliding wear process.
Fig. 2. SEM micrograph showing the bonding of the laser clad Mo 2 Ni 3 Si / NiSi composite coating to the substrate.
X.D. Lu, H.M. Wang / Journal of Alloys and Compounds 359 (2003) 287–291
289
Fig. 3. XRD pattern of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
Fig. 5. Hardness profile of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
3. Results and discussion
Mo 2 Ni 3 Si ternary metal silicide and the interdendritic lamellar structure is the Mo 2 Ni 3 Si / NiSi eutectics, as shown in Fig. 4. Volume fraction of the Mo 2 Ni 3 Si primary dendrite of laser clad Mo 2 Ni 3 Si / NiSi composite coating is approximately 60%. As indicated in Fig. 5, the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings have a high and uniform hardness distribution within the coatings except in the coating / substrate bonding zone where the hardness has a gradient decrease to the substrate.
As shown in Fig. 1, microstructure of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings is fine, uniform, free from pores and cracks and with high-quality metallurgical bonding to the substrate (Fig. 2). Laser clad Mo–Ni–Si coatings have a dendritic structure with interdendritic eutectics. Results of XRD (Fig. 3) and EDS analysis indicate that the primary dendrites are the
Fig. 4. OM (a) and SEM (b) micrographs showing microstructure of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coating.
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Fig. 6. Specific wear rate of laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings under different test load.
Result of dry sliding wear test at room temperature showed that the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings have excellent wear resistance and low friction coefficient, as indicated in Figs. 6 and 7. Both the wear mass loss and the friction coefficient are much lower than that of the austenitic stainless steel 1Cr18Ni9Ti. It is interesting, as indicated in Fig. 6, that wear mass loss of the laser clad composite coatings is very insensitive to the increased applied test load and increases very slowly as the applied load increases. On the contrary, the wear mass loss of the reference material 1Cr18Ni9Ti increases drastically with the increasing applied load. This phenomenon implies that the laser clad metal silicides are most preferable for working under heavy load sliding wear service conditions. The friction coefficient for the sliding friction couple between the laser clad Mo 2 Ni 3 Si / NiSi metal silicide
composite coating and the hardened 0.45%C steel is very low and fluctuates between approximately 0.32 and 0.38, while that between reference stainless steel 1Cr18Ni9Ti and the hardened 0.45%C steel fluctuates between approximately 0.60 and 0.68. The excellent wear resistance, low friction coefficient and very sluggish response of wear mass loss to test load of the laser clad Mo 2 Ni 3 Si / NiSi intermetallic composite coatings are primarily attributed to its microstructure characteristics and its unique chemical and physical properties inherent to the transition metal silicides. Because all the microstructural constituent phases, i.e., Mo 2 Ni 3 Si and NiSi, are metal silicides having high hardness and abnormal hardness–temperature relations, the laser clad Mo 2 Ni 3 Si / NiSi composite coatings exhibited excellent abrasive wear resistance due to their outstanding resistance to microcutting and plowing during dry sliding wear process, which is evidenced by the very smooth worn surface with no noticeable grooves and scratches visible, as shown in Fig. 8a. Because of the strong intermetallic atomic bonds of the metal silicide Mo 2 Ni 3 Si and NiSi, the laser clad Mo 2 Ni 3 Si / NiSi composite coatings have very outstanding abilities for metallic adhesion when sliding on the surface of the 0.45%C steel wheel. This is demonstrated by the extremely smooth worn surface morphology having no metallic adhesion features, as shown in Fig. 8a. The worn surface is so smooth that the microstructural constituent phases are clearly revealed, similar to the polished-and-etched metallographic sections. To the knowledge of the authors, no such worn surface morphology was reported in the open literature under metallic dry sliding wear test conditions. Careful examination of worn subsurface microstructure indicates clearly that no selective wear and plastic deformation occurred during the dry sliding wear process for the laser clad metal silicide composite coating, as shown in Fig. 8b.
Fig. 7. Variation of friction coefficients versus test time for the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings and the reference stainless steel 1Cr18Ni9Ti under dry sliding wear test conditions.
X.D. Lu, H.M. Wang / Journal of Alloys and Compounds 359 (2003) 287–291
291
Fig. 8. SEM micrographs showing the worn surface (a) and the worn subsurface (b) of the laser clad Mo 2 Ni 3 Si / NiSi metal silicide composite coatings.
4. Conclusions
References
Wear-resistant Mo 2 Ni 3 Si / NiSi metal silicide composite coatings consisting of Mo 2 Ni 3 Si primary dendrites and interdendritic Mo 2 Ni 3 Si / NiSi eutectics are fabricated on a substrate of an austenitic stainless steel 1Cr18Ni9Ti by laser cladding using 40Ni–36Mo–24Si (wt.%) elemental powder blends. Because of the high hardness and strong atomic bonds, the laser clad Mo 2 Ni 3 Si / NiSi composite coatings have excellent abrasive and adhesive wear resistance under dry sliding wear test conditions.
[1] J.J. Petrovic, A.K. Vasudevan, Mater. Sci. Eng. A261 (1999) 1. [2] A.K. Vasudevan, Mater. Sci. Eng. A155 (1992) 1. [3] D.M. Shah, D. Berczik, D.L. Anton, R. Hecht, Mater. Sci. Eng. A155 (1992) 45. [4] G. Duan, H.M. Wang, Scripta Mater. 146 (2002) 107. [5] H.M. Wang, G. Duan, Mater. Sci. Eng. A336 (2002) 117. [6] H.M. Wang, Y.F. Liu, Mater. Sci. Eng. A338 (2002) 126. [7] A. Hidouci, J.M. Pelletier, Mater. Sci. Eng. A252 (1998) 17. [8] K. Ghosh, M.H. McCay, N.B. Dahotre, J. Mater. Proc. Tech. 88 (1999) 169. [9] S. Ignat, P. Sallamand, A. Nichici, A.B. Vannes, D. Grevey, E. Cicala, Optics Laser Tech. 33 (2001) 461. [10] A. Newman, S. Sampath, H. Herman, Mater. Sci. Eng. A261 (1999) 252. [11] M. Akinc, M.K. Meyer, M.J. Kramer, A.J. Thom, J.J. Huebsch, B. Cook, Mater. Sci. Eng. A261 (1999) 16. [12] S.A. Maloy, J.J. Lewandowski, A.H. Heuer, J.J. Petrovic, Mater. Sci. Eng. A155 (1992) 159. [13] T.A. Kircher, E.L. Courtright, Mater. Sci. Eng. A155 (1992) 67.
Acknowledgements The research was supported by the National High-Tech R&D Program (Contract No. 2002AA331030), the National Natural Science Foundation of China (Grant No. 50071004), the Trans-Century Training Program for Outstanding Talents of the Ministry of Education of China, the Beijing Natural Science Foundation (Grant No. 2022012) and the Science Funds Office of AVIC (02H51007).