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The microstructure and tribological characteristics of laser-clad Ni–Cr–Al coatings on aluminium alloy
Materials Science and Engineering A290 (2000) 207 – 212 www.elsevier.com/locate/msea
The microstructure and tribological characteristics of laser-clad Ni–Cr–Al coatings on aluminium alloy G.Y. Liang *, J.Y. Su School of Mechanical Engineering, Xian Jiaotong Uni6ersity, Xian, 710049, PR China Received 22 November 1999; received in revised form 22 February 2000
Abstract Using a 5-kW CO2 laser, a Ni–Cr–Al plasma coating on Al – Si alloy surface was remelted. The microstructure of the clad zone was analysed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that some amorphous structures and crystallites exist in the laser-clad Ni – Cr – Al coating. The annealing treatment was used at 520°C in different time intervals in order to determine the content of amorphous structure in the coating. Wear tests of laser-clad samples paired with grey cast iron were carried out on a block-on-ring wear tester under oil lubricated conditions. The effect of amorphous structure on tribological characteristics of the pairs was investigated. The result showed that the wear amount of laser-clad samples was quite small. The higher the amorphous content, the smaller the wear amount of laser-clad samples and grey cast iron. The amorphous structure can prevent hard granules spalling from the matrix during the wear test and can improve wear resistance. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Aluminium alloy; Laser-cladding; Amorphous structure; Friction; Wear
1. Introduction Aluminium alloys are considered as some of the most versatile materials in the vehicle industry for their high thermal diffusion, high strength to weight ratio and low cost. However, the low hardness typical of such alloys results in poor tribological character [1]. Laser surface alloying and laser-cladding have been used to improve wear resistance and hardness on aluminium alloys. They can be combined to produce controlled modification of both the microstructure and chemical composition of the surface to meet the application requirements [2 –4]. Nickel and chromium are often used to increase the surface hardness of aluminium in laser-cladding and laser alloying [5– 7]. In a previous study, several amorphous structures which showed higher hardness were found in the laser-clad Ni – Cr coating [8] on aluminium alloys. Although the elements of the IIIA family in the periodic table together with some metalloid elements, such as B and Si, are capable of forming amorphous * Corresponding author. Fax: +86-29-3237910. E-mail address: [email protected] (G.Y. Liang).
structure, one often finds cracks in the laser-clad coating. The Ni–Cr–Al coating after laser-cladding can join with Al–Si substrate better and few cracks are found in the coating. Although aluminium is a metallic element, it also possesses some properties of metalloid elements. Hence it is possible to produce amorphous structures with transition elements Fe, Ni and Cr during fast solidification. Up to now, the research on amorphous structures in laser-clad Ni–Al coating is still scant, and the tribological properties of these amorphous structures are poorly known. As an amorphous structure exhibits higher hardness, it can be used to improve the wear resistance of aluminium alloys. Therefore, in this paper, an investigation of the tribological properties of the amorphous structure in the laser-clad Ni–Cr–Al coating has been conducted.
2. Experimental procedure The substrate sample was Al–Si cast alloy containing 8.23 wt% Si, 0.057 wt% Mg and 1.35 wt% Cu. Samples were machined into 10-mm-thick rectangular plates. After hot NaOH etching and sandblasting, the sample
0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 0 8 9 4 - 7
G.Y. Liang, J.Y. Su / Materials Science and Engineering A290 (2000) 207–212
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Table 1 Designation of samples under the different treatment conditions Sample no.
Power density (kW cm−2)
Scanning rate (mm s−1)
Treatment condition (annealing)
0 A2 A4 A6
36 36 36 36
8 8 8 8
Without 520°C/2 h 520°C/4 h 520°C/6 h
surface was sprayed with Ni – Cr – Al powder using a METCO 3MB Plasma Spray Device. The composition of the spraying powder was: Cr 16.5 wt%, Al 8.0 wt% and Ni balance. The laser-cladding process was conducted with a 5-kW continuous transverse flow CO2 laser. During the laser treatment, the samples were clad by single trace scanning, the laser beam diameter was 2.5 mm and the power density of the laser beam was 36 kW cm − 2. The samples were manipulated by mounting them on an X –Y table whose movement was controlled by a computer at a speed of 8 mm s − 1. The sample surface was protected by argon gas and cooled in air during the laser scanning. The thickness of the clad coating was from 0.3 to 0.4 mm. A cross-section of the sample was taken perpendicular to the alloyed surface, and it was polished metallographically. A foil about 0.5 mm was cut from the top of the laser-clad coating. After reducing the thickness to 0.1 mm by grinding, a TEM sample was prepared by electropolishing on a twin jet polisher. Observation and analysis of the microstructure were performed on a S-2700 scanning electron microscope (SEM) and a JEM-200CX transmission electron microscope (TEM). Laser-clad samples were annealed at 520°C at different holding time intervals to obtain different contents of amorphous structure. Designation of samples under different treatment condition is shown in Table 1. DTA was performed using DuPont 2000 DTA equipment. The semi-quantitative content of amorphous structure was obtained by comparing the area of exothermic peak of the samples on the DTA curves with a sample of full amorphous structure. The sliding wear test was carried out using a blockon-ring apparatus (Fig. 1) under oil lubricated conditions. The upper sample is a block that is made of the laser-clad sample. It was machined to a rectangular shape 15 mm in length, 3 mm in width and 3 mm in height. The laser-clad layer was the face undergoing the wear process. The lower sample was a ring composed of grey cast HT200 with hardness HB191. It was 40 mm in outer diameter and 10 mm in width, with a surface roughness of Ra =0.4 mm. The lubricant was 10 c engine oil and it was added at the rate of one drop per 15 s. A normal load of 100 N was used. The rotational speed of the ring was 200 rev. min − 1 and the total wear
distance was 5000 m. The volume losses of the laser samples were calculated from the wear weight loss and the density of the laser layer, and the volume loss of the ring samples was the wear weight loss divided by the density of grey cast iron.
3. Experimental results and discussion
3.1. Amorphous structure in the laser-clad zone Fig. 2(a) shows a TEM photograph of a bright field image in the laser-clad zone of sample A0. Fig. 2(b) is an electron diffraction pattern of Fig. 2(a). It shows that the dendritic-like structure in Fig. 2(a) is amorphous. Fig. 3(a) is another TEM photo of the laser-clad coating of sample A0. Fig. 3(b) is an electron diffraction pattern of structure B in Fig. 3(a); the diffraction pattern of structure A in Fig. 3(a) is the same as that in Fig. 2(b). It is shown that the microstructure of structure A in Fig. 3(a) is still amorphous, and the microstructure of structure B is Ni3Al crystallite by the index. This suggests that the structure of the laser-clad zone is composed of amorphous structure and some crystallites.
3.2. Annealing treatment From Figs. 2 and 3, it is known that there are some amorphous structures in the laser-clad coating. However, it is impossible to determine accurately the amount of these amorphous structures. Therefore, a semi-quantitative method to compare the amount of amorphous structure in different samples has been
Fig. 1. Schematic illustration of the block-on-ring apparatus.
G.Y. Liang, J.Y. Su / Materials Science and Engineering A290 (2000) 207–212
209
3.3. Tribological characteristics The result of the sliding wear test is shown in Fig. 7. In this figure, the upper samples were laser-cladding, and the lower samples were grey cast iron. It is seen that the wear volume of the claddings decreases from sample A6 to A0, that is, it reduces with increasing content of amorphous structure in the samples. Meanwhile, the grey cast iron sample paired with sample A0 exhibits the lowest wear volume loss, and other samples have larger wear volume losses.
Fig. 2. TEM photos in laser-clad zone of sample A0, (a) bright field image; (b) electron diffraction pattern of (a).
adopted by comparing the area of the exothermic peak in the DTA curves. Fig. 4 shows a DTA curve of the laser-clad region of sample A0 (without annealing), and Fig. 5 is a DTA curve of A4 (annealing time 4 h). The upward direction corresponds to an exothermic reaction in this figure. There is an endothermic valley (afb) caused by aluminium alloy melting, and an exothermic peak (bpc) caused by amorphous structure crystallisation in the figure. In Fig. 4, Tb is the temperature at the beginning of crystallisation process, which is about 560°C. Considering that the heating rate of DTA test is higher than that of annealing, differential areas of exothermic peak can be obtained in 520°C annealing by different holding intervals. Comparing these with the exothermic peak of full amorphous sample of Ni–Cr– Si alloy, some semi-quantitative amount of amorphous structure of samples was obtained (Table 2). Fig. 6(a) is a TEM photo of the coating of sample A4, and Fig. 6(b) is an electron diffraction pattern of Fig. 6(a). It is seen that after annealing, some amorphous structures have been changed into crystallites.
Fig. 3. TEM photos in laser melted zone of sample A0, (a) a bright field image; (b) electron diffraction pattern of point B.
Fig. 4. A DTA curve of laser-clad layer of sample A0.
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Fig. 5. A DTA curve of laser-clad layer of sample A4.
Table 2 The semi-quantitative amount of amorphous structure in the samples Sample no.
Amount of amorphous (%)
A0
A2
A4
A6
31.1
13.8
8.3
2.2
Fig. 8 shows a comparison of friction factors with sliding distance. It is found that the friction factors of all samples are similar to each other. The friction factors are smaller than 0.1 after the sliding distance exceeds 2 km. This is because the lubrication is in the mixed regime, and friction depends mainly on load and speed, not on any materials’ properties. Fig. 9(a) is a SEM photo of the worn surface of sample A0 and Fig. 9(b) is another SEM photo of the worn surface of sample A4. By comparing (a) and (b), it is found that the worn surface containing more amorphous structure appears to be smooth, and the worn surface of sample A4, which contains less amorphous structure, reveals many granules spalling off (arrow). Fig. 10 shows two SEM photographs of the crosssection of sample A0 (a) and A6 (b). In order to observe cross-section and worn surface simultaneously, the photos were taken using an electron beam oblique to the worn surface at an angle of 38°. In the figures, region A is the cross-section, and region B is the worn surface. A few holes, caused by granules spalling off, can be seen in the figures. When the amount of amor-
Fig. 7. The results of the sliding wear test.
Fig. 6. TEM photo of laser-clad zone of sample A4, (a) bright field image; (b) electron diffraction pattern of (a).
Fig. 8. A comparison of friction factor with sliding distance.
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4. Conclusion Some Ni-rich amorphous structures and Ni3Al crystallites coexist in the laser-clad Ni–Cr–Al coating on aluminium alloys. The wear volume loss of the laser-clad sample containing more amorphous structure is much lower than for samples containing less amorphous structure. When the amount of amorphous structure increases from 2.18 to 31.1%, the wear volume loss of the sample decreases about 3.6 times. Amorphous structures in the laser-cladding can reduce the granular spalling from the matrix and improve its wear resistance.
Acknowledgements This project was financially supported by the Foundation of National Natural Science Foundation of China (59871038) and the State Key Laboratory of Laser and Technology, Huazhong Science and Engineering University, China.
Fig. 9. SEM photo of worn surface of sample A0 (a) and A4 (b).
phous structure is higher, granule spalling occurs only at the surface (sample A0), and the spalling holes are smaller. The granule spalling increases with a decrease in the amount of amorphous structure (samples A4 and A6). There are many holes in the subsurface of the sample, which were caused by a few granules which were separated from the matrix during the wear test so that they were easy to pull out during the sample preparation. It is particularly obvious in sample A6. It can be noted that some granules have separated from the matrix but there are still some in it (Fig. 10(b)). During the friction process, the surface and subsurface of samples has undergone a rather large shear force. It tends to make some harder granules separate from the matrix. If granule joints are weaker than the matrix, the granules are easy to pull out during the friction. As in the sample containing less amorphous structures, the amount of granules pulled out is great, and it will also pull out easily during the friction and lead to higher wear. Therefore, some amorphous structures existing in the laser-cladding can reduce the granular spalling and improve its wear resistance.
Fig. 10. SEM photo of the cross-section of sample A0 (a) and A6 (b) (the photos were taken using an electron beam oblique to the worn surface at an angle of 38°).
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References [1] P. Vanhille, S. Tosto, J.M. Pelletier, et al., Surface Coatings Technol. 50 (1992) 295–303. [2] R. Pawlak, T. Raczynski, Mater. Sci. Eng. A168 (1993) 67 – 70. [3] W.J. Tomlinson, A.S. Bransden, Wear 185 (1995) 59– 65. [4] M. Pierantoni, J.D. Wagniere, E. Blank, Mater. Sci. Eng. A110 (1989) L17 – L21.
.
[5] Y. Liu, J. Koch, J. Mazumder, K. Shiata, Metall. Mater. Trans. B25 (1994) 425 – 434. [6] D.K. Das, K.S. Prasad, A.G. Paradkar, Mater. Sci. Eng. A174 (1994) 75 – 84. [7] Y. Fu, A.W. Batchelor, Surface Coatings Technol. 120 (1998) 119 – 126. [8] G.Y. Liang, T.T. Wong, Surface Coatings Technol. 89 (1997) 121 – 126.
The microstructure and tribological characteristics of laser-clad Ni–Cr–Al coatings on aluminium alloy G.Y. Liang *, J.Y. Su School of Mechanical Engineering, Xian Jiaotong Uni6ersity, Xian, 710049, PR China Received 22 November 1999; received in revised form 22 February 2000
Abstract Using a 5-kW CO2 laser, a Ni–Cr–Al plasma coating on Al – Si alloy surface was remelted. The microstructure of the clad zone was analysed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that some amorphous structures and crystallites exist in the laser-clad Ni – Cr – Al coating. The annealing treatment was used at 520°C in different time intervals in order to determine the content of amorphous structure in the coating. Wear tests of laser-clad samples paired with grey cast iron were carried out on a block-on-ring wear tester under oil lubricated conditions. The effect of amorphous structure on tribological characteristics of the pairs was investigated. The result showed that the wear amount of laser-clad samples was quite small. The higher the amorphous content, the smaller the wear amount of laser-clad samples and grey cast iron. The amorphous structure can prevent hard granules spalling from the matrix during the wear test and can improve wear resistance. © 2000 Elsevier Science S.A. All rights reserved. Keywords: Aluminium alloy; Laser-cladding; Amorphous structure; Friction; Wear
1. Introduction Aluminium alloys are considered as some of the most versatile materials in the vehicle industry for their high thermal diffusion, high strength to weight ratio and low cost. However, the low hardness typical of such alloys results in poor tribological character [1]. Laser surface alloying and laser-cladding have been used to improve wear resistance and hardness on aluminium alloys. They can be combined to produce controlled modification of both the microstructure and chemical composition of the surface to meet the application requirements [2 –4]. Nickel and chromium are often used to increase the surface hardness of aluminium in laser-cladding and laser alloying [5– 7]. In a previous study, several amorphous structures which showed higher hardness were found in the laser-clad Ni – Cr coating [8] on aluminium alloys. Although the elements of the IIIA family in the periodic table together with some metalloid elements, such as B and Si, are capable of forming amorphous * Corresponding author. Fax: +86-29-3237910. E-mail address: [email protected] (G.Y. Liang).
structure, one often finds cracks in the laser-clad coating. The Ni–Cr–Al coating after laser-cladding can join with Al–Si substrate better and few cracks are found in the coating. Although aluminium is a metallic element, it also possesses some properties of metalloid elements. Hence it is possible to produce amorphous structures with transition elements Fe, Ni and Cr during fast solidification. Up to now, the research on amorphous structures in laser-clad Ni–Al coating is still scant, and the tribological properties of these amorphous structures are poorly known. As an amorphous structure exhibits higher hardness, it can be used to improve the wear resistance of aluminium alloys. Therefore, in this paper, an investigation of the tribological properties of the amorphous structure in the laser-clad Ni–Cr–Al coating has been conducted.
2. Experimental procedure The substrate sample was Al–Si cast alloy containing 8.23 wt% Si, 0.057 wt% Mg and 1.35 wt% Cu. Samples were machined into 10-mm-thick rectangular plates. After hot NaOH etching and sandblasting, the sample
0921-5093/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved. PII: S 0 9 2 1 - 5 0 9 3 ( 0 0 ) 0 0 8 9 4 - 7
G.Y. Liang, J.Y. Su / Materials Science and Engineering A290 (2000) 207–212
208
Table 1 Designation of samples under the different treatment conditions Sample no.
Power density (kW cm−2)
Scanning rate (mm s−1)
Treatment condition (annealing)
0 A2 A4 A6
36 36 36 36
8 8 8 8
Without 520°C/2 h 520°C/4 h 520°C/6 h
surface was sprayed with Ni – Cr – Al powder using a METCO 3MB Plasma Spray Device. The composition of the spraying powder was: Cr 16.5 wt%, Al 8.0 wt% and Ni balance. The laser-cladding process was conducted with a 5-kW continuous transverse flow CO2 laser. During the laser treatment, the samples were clad by single trace scanning, the laser beam diameter was 2.5 mm and the power density of the laser beam was 36 kW cm − 2. The samples were manipulated by mounting them on an X –Y table whose movement was controlled by a computer at a speed of 8 mm s − 1. The sample surface was protected by argon gas and cooled in air during the laser scanning. The thickness of the clad coating was from 0.3 to 0.4 mm. A cross-section of the sample was taken perpendicular to the alloyed surface, and it was polished metallographically. A foil about 0.5 mm was cut from the top of the laser-clad coating. After reducing the thickness to 0.1 mm by grinding, a TEM sample was prepared by electropolishing on a twin jet polisher. Observation and analysis of the microstructure were performed on a S-2700 scanning electron microscope (SEM) and a JEM-200CX transmission electron microscope (TEM). Laser-clad samples were annealed at 520°C at different holding time intervals to obtain different contents of amorphous structure. Designation of samples under different treatment condition is shown in Table 1. DTA was performed using DuPont 2000 DTA equipment. The semi-quantitative content of amorphous structure was obtained by comparing the area of exothermic peak of the samples on the DTA curves with a sample of full amorphous structure. The sliding wear test was carried out using a blockon-ring apparatus (Fig. 1) under oil lubricated conditions. The upper sample is a block that is made of the laser-clad sample. It was machined to a rectangular shape 15 mm in length, 3 mm in width and 3 mm in height. The laser-clad layer was the face undergoing the wear process. The lower sample was a ring composed of grey cast HT200 with hardness HB191. It was 40 mm in outer diameter and 10 mm in width, with a surface roughness of Ra =0.4 mm. The lubricant was 10 c engine oil and it was added at the rate of one drop per 15 s. A normal load of 100 N was used. The rotational speed of the ring was 200 rev. min − 1 and the total wear
distance was 5000 m. The volume losses of the laser samples were calculated from the wear weight loss and the density of the laser layer, and the volume loss of the ring samples was the wear weight loss divided by the density of grey cast iron.
3. Experimental results and discussion
3.1. Amorphous structure in the laser-clad zone Fig. 2(a) shows a TEM photograph of a bright field image in the laser-clad zone of sample A0. Fig. 2(b) is an electron diffraction pattern of Fig. 2(a). It shows that the dendritic-like structure in Fig. 2(a) is amorphous. Fig. 3(a) is another TEM photo of the laser-clad coating of sample A0. Fig. 3(b) is an electron diffraction pattern of structure B in Fig. 3(a); the diffraction pattern of structure A in Fig. 3(a) is the same as that in Fig. 2(b). It is shown that the microstructure of structure A in Fig. 3(a) is still amorphous, and the microstructure of structure B is Ni3Al crystallite by the index. This suggests that the structure of the laser-clad zone is composed of amorphous structure and some crystallites.
3.2. Annealing treatment From Figs. 2 and 3, it is known that there are some amorphous structures in the laser-clad coating. However, it is impossible to determine accurately the amount of these amorphous structures. Therefore, a semi-quantitative method to compare the amount of amorphous structure in different samples has been
Fig. 1. Schematic illustration of the block-on-ring apparatus.
G.Y. Liang, J.Y. Su / Materials Science and Engineering A290 (2000) 207–212
209
3.3. Tribological characteristics The result of the sliding wear test is shown in Fig. 7. In this figure, the upper samples were laser-cladding, and the lower samples were grey cast iron. It is seen that the wear volume of the claddings decreases from sample A6 to A0, that is, it reduces with increasing content of amorphous structure in the samples. Meanwhile, the grey cast iron sample paired with sample A0 exhibits the lowest wear volume loss, and other samples have larger wear volume losses.
Fig. 2. TEM photos in laser-clad zone of sample A0, (a) bright field image; (b) electron diffraction pattern of (a).
adopted by comparing the area of the exothermic peak in the DTA curves. Fig. 4 shows a DTA curve of the laser-clad region of sample A0 (without annealing), and Fig. 5 is a DTA curve of A4 (annealing time 4 h). The upward direction corresponds to an exothermic reaction in this figure. There is an endothermic valley (afb) caused by aluminium alloy melting, and an exothermic peak (bpc) caused by amorphous structure crystallisation in the figure. In Fig. 4, Tb is the temperature at the beginning of crystallisation process, which is about 560°C. Considering that the heating rate of DTA test is higher than that of annealing, differential areas of exothermic peak can be obtained in 520°C annealing by different holding intervals. Comparing these with the exothermic peak of full amorphous sample of Ni–Cr– Si alloy, some semi-quantitative amount of amorphous structure of samples was obtained (Table 2). Fig. 6(a) is a TEM photo of the coating of sample A4, and Fig. 6(b) is an electron diffraction pattern of Fig. 6(a). It is seen that after annealing, some amorphous structures have been changed into crystallites.
Fig. 3. TEM photos in laser melted zone of sample A0, (a) a bright field image; (b) electron diffraction pattern of point B.
Fig. 4. A DTA curve of laser-clad layer of sample A0.
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Fig. 5. A DTA curve of laser-clad layer of sample A4.
Table 2 The semi-quantitative amount of amorphous structure in the samples Sample no.
Amount of amorphous (%)
A0
A2
A4
A6
31.1
13.8
8.3
2.2
Fig. 8 shows a comparison of friction factors with sliding distance. It is found that the friction factors of all samples are similar to each other. The friction factors are smaller than 0.1 after the sliding distance exceeds 2 km. This is because the lubrication is in the mixed regime, and friction depends mainly on load and speed, not on any materials’ properties. Fig. 9(a) is a SEM photo of the worn surface of sample A0 and Fig. 9(b) is another SEM photo of the worn surface of sample A4. By comparing (a) and (b), it is found that the worn surface containing more amorphous structure appears to be smooth, and the worn surface of sample A4, which contains less amorphous structure, reveals many granules spalling off (arrow). Fig. 10 shows two SEM photographs of the crosssection of sample A0 (a) and A6 (b). In order to observe cross-section and worn surface simultaneously, the photos were taken using an electron beam oblique to the worn surface at an angle of 38°. In the figures, region A is the cross-section, and region B is the worn surface. A few holes, caused by granules spalling off, can be seen in the figures. When the amount of amor-
Fig. 7. The results of the sliding wear test.
Fig. 6. TEM photo of laser-clad zone of sample A4, (a) bright field image; (b) electron diffraction pattern of (a).
Fig. 8. A comparison of friction factor with sliding distance.
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4. Conclusion Some Ni-rich amorphous structures and Ni3Al crystallites coexist in the laser-clad Ni–Cr–Al coating on aluminium alloys. The wear volume loss of the laser-clad sample containing more amorphous structure is much lower than for samples containing less amorphous structure. When the amount of amorphous structure increases from 2.18 to 31.1%, the wear volume loss of the sample decreases about 3.6 times. Amorphous structures in the laser-cladding can reduce the granular spalling from the matrix and improve its wear resistance.
Acknowledgements This project was financially supported by the Foundation of National Natural Science Foundation of China (59871038) and the State Key Laboratory of Laser and Technology, Huazhong Science and Engineering University, China.
Fig. 9. SEM photo of worn surface of sample A0 (a) and A4 (b).
phous structure is higher, granule spalling occurs only at the surface (sample A0), and the spalling holes are smaller. The granule spalling increases with a decrease in the amount of amorphous structure (samples A4 and A6). There are many holes in the subsurface of the sample, which were caused by a few granules which were separated from the matrix during the wear test so that they were easy to pull out during the sample preparation. It is particularly obvious in sample A6. It can be noted that some granules have separated from the matrix but there are still some in it (Fig. 10(b)). During the friction process, the surface and subsurface of samples has undergone a rather large shear force. It tends to make some harder granules separate from the matrix. If granule joints are weaker than the matrix, the granules are easy to pull out during the friction. As in the sample containing less amorphous structures, the amount of granules pulled out is great, and it will also pull out easily during the friction and lead to higher wear. Therefore, some amorphous structures existing in the laser-cladding can reduce the granular spalling and improve its wear resistance.
Fig. 10. SEM photo of the cross-section of sample A0 (a) and A6 (b) (the photos were taken using an electron beam oblique to the worn surface at an angle of 38°).
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G.Y. Liang, J.Y. Su / Materials Science and Engineering A290 (2000) 207–212
References [1] P. Vanhille, S. Tosto, J.M. Pelletier, et al., Surface Coatings Technol. 50 (1992) 295–303. [2] R. Pawlak, T. Raczynski, Mater. Sci. Eng. A168 (1993) 67 – 70. [3] W.J. Tomlinson, A.S. Bransden, Wear 185 (1995) 59– 65. [4] M. Pierantoni, J.D. Wagniere, E. Blank, Mater. Sci. Eng. A110 (1989) L17 – L21.
.
[5] Y. Liu, J. Koch, J. Mazumder, K. Shiata, Metall. Mater. Trans. B25 (1994) 425 – 434. [6] D.K. Das, K.S. Prasad, A.G. Paradkar, Mater. Sci. Eng. A174 (1994) 75 – 84. [7] Y. Fu, A.W. Batchelor, Surface Coatings Technol. 120 (1998) 119 – 126. [8] G.Y. Liang, T.T. Wong, Surface Coatings Technol. 89 (1997) 121 – 126.