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Graphite on 9Cr18 Stainless Steel Surface
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JOURNAL OF IRON
ScienceDirect
AND STEEL RESEARCH,
INTERNATIONAL. 2007, 14(3) : 69-72
Laser Alloyed Coatings of TiBJGraphite on 9Cr18 Stainless Steel Surface YING Li-xia'
,
W A N G Li-qin'
,
JIA Xiao-mei' ,
GU Le2
( I . School of Mechatronics Engineering, Harbin Engineering University, Harbin 150001, Heilongjiang, China ; 2. School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China) Abstract: Modified coatings including carbide of iron, nickel, chromium, silicon, and titanium are obtained on 9Cr18 stainless steel surface by laser alloying. The processing method, the microstructure, the interface, the tribological properties, and the forming mechanisms of the coatings are analyzed. The results show that the microstructure of the alloyed coatings is mainly irregular FeC crystals. Carbides of chromium and iron are around the FeC crystals. Small granular TiC disperses in the alloyed coatings, The microhardness of the alloyed coatings is greatly improved because of the occurrence of carbide with high hardness. At the same time, the wear resistance of the alloyed coatings are higher than that of 9Cr18 stainless steel. Key words: laser alloying; Ti& ; graphite: carbide
A t present, ion beam deposition, plasma nitriding, surface carburizing, and ion implantation are the main methods of surface modification t o improve the antiwear and self-lubricating properties of 9Cr18 stainless steel, However, the thickness of the thin films obtained using these methods is only micron or submicro grades and t h u s it is difficult to meet the requirements of the long-term elevated temperature working conditionc1]. Laser alloying is a n available surface modification technology, which can evidently improve the antiwear and anticorrosion properties of material^[^-^'. T h e present study has been carried out on the laser alloying coatings of TiB,/graphite. In-situ metallic carbide and ceramic T i c are expected t o be synthesized on the alloyed coating. Metallic carbide with high hardness, elevated-temperature stability, and low density can greatly improve the hardness and the antiwear property of the substrate 9Cr18.
1
Experimental Materials and Methods
In the experiment , the substrate is 9Cr18 stainless steel in quenched and tempered state. TiB, and graphite are used a s the main ingredients of the composite. T h e addition of a small quantity of Ni6OA is done to improve the wettability of the coating on the
substrate. T h e mass percent of the powders used for laser alloying is Ti& : graphite : Ni60A=81 : 4 : 15. T h e mixture is preplaced on the clean substrate surface to provide a thickness of about 0. 1 mm. Laser alloying experiments were done on a 5 kW continuous wave CO, laser t o produce a series of single alloyed tracks without overlap. Through screening and optimizingc6], the processing parameters are obtained as follows: laser power 2. 5 kW and beam diameter 5 mm. Three different scanning speeds of 4 m m / s , 5 m m / s , and 6 mm/s were respectively adopted. Cross-sections of the specimen were deeply corroded by HF solution after grinding and polishing. T h e microstructure of the alloyed coatings was observed using a scanning electron microscope (SEMI and an optical microscope (OM). T h e distribution of elements and the phases in the coatings were identified using an energy dispersive X-ray detector (EDX) and X-ray diffraction (XRD). Vickers hardness was measured to analyze the microhardness variation along the depth of the cross-section. T h e friction coefficient and the wear-resistant property were tested on block-on-ring tribo tester MM-200 at room temperature. For the tribological test, the outer ring radius was 40 mm. T h e load and the rotational
Foundation Item: Item Sponsored by Youth Science Foundation of Heilongjiang (QC06C023) Biography: YING Li-xia(1978-), Female, Doctor; E-mail: ylxhit@hit. edu. cn; Revised Date: November 9 , 2005
70
-
Journal of Iron and Steel Research, International
speed were fixed at 50 N and 200 r/min, respectively. For the investigation of the wear mechanism, the worn surfaces of the coatings were observed by SEM.
2
Results and Discussion
Microstructure The coating of TiBz/graphite, which is free of cracks and pores, can be obtained by laser alloying. It is seen from Fig. 1 that the alloyed coating is composed of martensite, austenite, CrZ3Cs , TiB, , TIC, and graphite. The microstructure of the alloyed coatings is mainly erose white crystals, as shown in Fig. 2 (a). The results of the EDX analyses, as shown in Table 1, indicate that the erose white crystals mainly consist of FeC. Carbides of chromium and iron are around the FeC, and ceramic TIC grains uniformly disperse
2.1
800
600
{ 400 2g
200
0 20
60
40
80
100
2ey)
Fig. 1 X-ray diffraction pattern of alloyed coating
Fig. 2
Vol. 14
across the whole coating. Hence, it is known that TiB, decomposes on the melted pool. There are strong chemical reactions and metallurgical processes among the titanium, graphite, and the molten metal. Thus, vast scale hard antiwear phases of carbides are synthesized after the melt pool rapidly solidifies, and multiphase antiwear composite materials, which are strengthened by ceramic T i c , TiB, , and carbide, are obtained as expected. Furthermore, regular CrZ3C6 is precipitated because chromium is prone to synthesize carbide and there is a higher content of Cr-C on the melted pool. Simultaneously, titanium is also a kind of element, which inclines to synthesize carbide. A small quantity of grains Tic is synthesized. Fig. 2 ( b ) shows that the alloyed coatings have metallurgical bonding with the substrate. When these are closer t o the surface, there are more white carbides, that is, there are more carbides of iron near the surface and more Tic near the interface. When the laser power is 2.5 kW and the scanning speed is 4 mm/s, 5 mm/s, and 6 mm/s, respectively, the optical microstructure of the alloyed coatings of samples 1, 2 , and 3 are shown in Fig. 3. T h e results indicate that the lower the scanning speed, the higher is the energy density and there are more white carbides on the alloyed coatings. When the
SEM micrographs of sample 1
Table 1 Content of elements at different points Phase b
Phase a
Phase c
Element Mass percent/%
Atomic percent/%
Mass percent/%
Atomic percent/%
Mass percent/%
Atomic percent/%
C
18.51
50. 93
19.16
48.83
16.04
46.32
Si Ti Cr Fe
1. 48
1. 74
0
0
0
0
0
0
75.24
48.09
0
0
0
0
0. 3 1
0. 18
18.93
12.78
80. 0
47.33
5. 29
2. 90
65.03
40.90
No. 3
Laser Alloyed Coatings of Ti&/Graphite on 9Cr18 Stainless Steel Surface
( b ) V = 5 mrn/si
(a) V = 4 mm/s;
Fig. 3
Microhardness Fig. 4 illustrates the hardness variation of the
cross-section. T h e results show that the hardness of the alloyed coatings is greatly improved, which can be ascribed to the hard antiwear phase carbides. O n the surface layer, the microhardness is the highest and reaches HV950. T h e in-situ dendritic carbides are firmly embedded on the alloyed coating and are expected to have excellent antiwear property. T h e
lOOOh
0 0.5
1.5
2.5
V=6 mm/s
3.5
4.5
thickness of the alloyed coatings is about 0. 6 mm. T h e hardness is the lowest near the interface because the substrate is tempered.
2.3
Tribological properties
T h e friction and wear properties were evaluated on a block-on-ring tribo-tester MM-200 under dry condition. T h e counterpart ring is 9Crl8 stainless steel in quenched and tempered state. T h e experiments include two groups for comparison: alloyed coating on ring 9Cr18 and block 9Cr18 on ring 9Cr18. T h e friction coefficient of the alloyed coating is about 0. 74, which is slightly lower than that of the substrate 0. 78. It is seen from the SEM photographs of the worn surface, as shown in Fig. 5 , that the alloyed coatings have the typical feature of wear debris peeling. T h e wear mechanisms are mainly the brittle carbide peeling off, abrasive wear. peeling layer wear, and adhesion wear. T h e alloyed coating is slightly worn. Yet, there are serious adhesion peeling pits and furrows on the surface of the block 9Cr18. Since hard carbide dispersing in the soft matrix improves the hardness of the coatings and reduces the micro-cutting process, the alloyed coatings that include hard carbide have excellent antiwear property. Furthermore, in situ hard grains have high
5.5
Distance from surfacdmm (a)
Fig. 4
.
Optical microstructuresof alloyed coatings of samples 1 , 2 , and 3
scanning speed is increased to 6 m m / s , the microstructure of the alloyed coatings is mainly coarse nickel-based alloy dendrites and hardly has any carbide. T h u s , the microstructures of the alloyed coatings are strongly affected by the processing parameters of laser alloying. When the other parameters are fixed, the lower the scanning speed, the longer is the interactive time between the substrate and the preplaced composite material. Accordingly, more carbon and titanium enter the molten substrate, and more FeC and TIC are synthesized before the melted pool rapidly solidifies. T h e alloyed coatings have more volume fraction of carbide. Hence, when the scanning speeding is 4 m m / s , the alloyed coating must have high hardness and antiwear properties.
2.2
(c)
71
Microhardnessof alloyed coatings
Fig. 5
Alloyed coating;
( b ) 9Ci-18
SEM photographs of worn surfaces
72
-
Journal of Iron and Steel Research, International
bonding strength with the matrix. These form a good carrier capacity system together, while distinctively reduce the load intensity carried by the grains, and effectively restrain the forming and development of micro-cutting, and improve the antiwear and antifriction properties of the coatingsc7’.
3
Conclusions
The composite alloyed coatings of Ti& /graphite, which are free of cracks and pores, can be obtained by laser alloying with suitable processing parameters on the 9Cr18 stainless steel. T h e coatings have a large amount of high hardness carbides of iron, nickel, chromium, silicon, and titanium. The hardness and the antiwear properties of the alloying coating have been greatly improved. References:
113
ZENG Zhao-ming, TANG Bao-yin, WANG Song-yan. Improvement of Tribological Properties of 9Cr18 Steel by Metal
Vol. 14
Plasma Immersion Ion Implantation [JJ. Vacuum Science and Technology, 2000, 2 I 77-80 (in Chinese). Agarwal Arvind, Dahotre Narendra B. Comparative Wear in Titanium Diboride Coatings on Steel Using High Energy Density Processes [JJ. Wear Volume, 2000, 240(1-2): 144-151. Katipelli Lalitha R, Agarwal Arvind, Dahotre Narendra B. Laser Surface Engineered Tic Coating on 6061 Al Alloy: Microstructure and Wear [JJ. Applied Surface Science, 2000, 153(23) : 65-78. Thawari G , Sundarararjan G , Joshi S V. Laser Surface Alloying of Medium Carbon Steel With SiC(p) [JJ. Thin Solid Films, 2003, (423)$ 41-53. HUANG Chong-cheng, TSAI Wen-ta, LEE Ju-tung. Microstructural Aspects and Oxidation Behavior of Laser Surface Clad Silicon-Containing Stainless Steels [J]. Scripta Metallur gica et Materiala, 1995, 32(9): 1465-1470. YING Li-xia, WANG Li-qin, CHEN Guan-ci. Simulation and Calculation of 3D Laser Cladding Temperature Field of Ceramic Metal Composite Coatings by FEM [JJ. Heat Treatment of Metals, 2004, 29(323): 24-28 (in Chinese). WANG Hui, XIA Wei-ming, YIN Yuan-sheng. Study on Abrasive Resistance of Ni-Based Coatings Containing WC Hard Phase [J]. Tribology, 1995, 3: 211-217 (in Chinese).
JOURNAL OF IRON
ScienceDirect
AND STEEL RESEARCH,
INTERNATIONAL. 2007, 14(3) : 69-72
Laser Alloyed Coatings of TiBJGraphite on 9Cr18 Stainless Steel Surface YING Li-xia'
,
W A N G Li-qin'
,
JIA Xiao-mei' ,
GU Le2
( I . School of Mechatronics Engineering, Harbin Engineering University, Harbin 150001, Heilongjiang, China ; 2. School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China) Abstract: Modified coatings including carbide of iron, nickel, chromium, silicon, and titanium are obtained on 9Cr18 stainless steel surface by laser alloying. The processing method, the microstructure, the interface, the tribological properties, and the forming mechanisms of the coatings are analyzed. The results show that the microstructure of the alloyed coatings is mainly irregular FeC crystals. Carbides of chromium and iron are around the FeC crystals. Small granular TiC disperses in the alloyed coatings, The microhardness of the alloyed coatings is greatly improved because of the occurrence of carbide with high hardness. At the same time, the wear resistance of the alloyed coatings are higher than that of 9Cr18 stainless steel. Key words: laser alloying; Ti& ; graphite: carbide
A t present, ion beam deposition, plasma nitriding, surface carburizing, and ion implantation are the main methods of surface modification t o improve the antiwear and self-lubricating properties of 9Cr18 stainless steel, However, the thickness of the thin films obtained using these methods is only micron or submicro grades and t h u s it is difficult to meet the requirements of the long-term elevated temperature working conditionc1]. Laser alloying is a n available surface modification technology, which can evidently improve the antiwear and anticorrosion properties of material^[^-^'. T h e present study has been carried out on the laser alloying coatings of TiB,/graphite. In-situ metallic carbide and ceramic T i c are expected t o be synthesized on the alloyed coating. Metallic carbide with high hardness, elevated-temperature stability, and low density can greatly improve the hardness and the antiwear property of the substrate 9Cr18.
1
Experimental Materials and Methods
In the experiment , the substrate is 9Cr18 stainless steel in quenched and tempered state. TiB, and graphite are used a s the main ingredients of the composite. T h e addition of a small quantity of Ni6OA is done to improve the wettability of the coating on the
substrate. T h e mass percent of the powders used for laser alloying is Ti& : graphite : Ni60A=81 : 4 : 15. T h e mixture is preplaced on the clean substrate surface to provide a thickness of about 0. 1 mm. Laser alloying experiments were done on a 5 kW continuous wave CO, laser t o produce a series of single alloyed tracks without overlap. Through screening and optimizingc6], the processing parameters are obtained as follows: laser power 2. 5 kW and beam diameter 5 mm. Three different scanning speeds of 4 m m / s , 5 m m / s , and 6 mm/s were respectively adopted. Cross-sections of the specimen were deeply corroded by HF solution after grinding and polishing. T h e microstructure of the alloyed coatings was observed using a scanning electron microscope (SEMI and an optical microscope (OM). T h e distribution of elements and the phases in the coatings were identified using an energy dispersive X-ray detector (EDX) and X-ray diffraction (XRD). Vickers hardness was measured to analyze the microhardness variation along the depth of the cross-section. T h e friction coefficient and the wear-resistant property were tested on block-on-ring tribo tester MM-200 at room temperature. For the tribological test, the outer ring radius was 40 mm. T h e load and the rotational
Foundation Item: Item Sponsored by Youth Science Foundation of Heilongjiang (QC06C023) Biography: YING Li-xia(1978-), Female, Doctor; E-mail: ylxhit@hit. edu. cn; Revised Date: November 9 , 2005
70
-
Journal of Iron and Steel Research, International
speed were fixed at 50 N and 200 r/min, respectively. For the investigation of the wear mechanism, the worn surfaces of the coatings were observed by SEM.
2
Results and Discussion
Microstructure The coating of TiBz/graphite, which is free of cracks and pores, can be obtained by laser alloying. It is seen from Fig. 1 that the alloyed coating is composed of martensite, austenite, CrZ3Cs , TiB, , TIC, and graphite. The microstructure of the alloyed coatings is mainly erose white crystals, as shown in Fig. 2 (a). The results of the EDX analyses, as shown in Table 1, indicate that the erose white crystals mainly consist of FeC. Carbides of chromium and iron are around the FeC, and ceramic TIC grains uniformly disperse
2.1
800
600
{ 400 2g
200
0 20
60
40
80
100
2ey)
Fig. 1 X-ray diffraction pattern of alloyed coating
Fig. 2
Vol. 14
across the whole coating. Hence, it is known that TiB, decomposes on the melted pool. There are strong chemical reactions and metallurgical processes among the titanium, graphite, and the molten metal. Thus, vast scale hard antiwear phases of carbides are synthesized after the melt pool rapidly solidifies, and multiphase antiwear composite materials, which are strengthened by ceramic T i c , TiB, , and carbide, are obtained as expected. Furthermore, regular CrZ3C6 is precipitated because chromium is prone to synthesize carbide and there is a higher content of Cr-C on the melted pool. Simultaneously, titanium is also a kind of element, which inclines to synthesize carbide. A small quantity of grains Tic is synthesized. Fig. 2 ( b ) shows that the alloyed coatings have metallurgical bonding with the substrate. When these are closer t o the surface, there are more white carbides, that is, there are more carbides of iron near the surface and more Tic near the interface. When the laser power is 2.5 kW and the scanning speed is 4 mm/s, 5 mm/s, and 6 mm/s, respectively, the optical microstructure of the alloyed coatings of samples 1, 2 , and 3 are shown in Fig. 3. T h e results indicate that the lower the scanning speed, the higher is the energy density and there are more white carbides on the alloyed coatings. When the
SEM micrographs of sample 1
Table 1 Content of elements at different points Phase b
Phase a
Phase c
Element Mass percent/%
Atomic percent/%
Mass percent/%
Atomic percent/%
Mass percent/%
Atomic percent/%
C
18.51
50. 93
19.16
48.83
16.04
46.32
Si Ti Cr Fe
1. 48
1. 74
0
0
0
0
0
0
75.24
48.09
0
0
0
0
0. 3 1
0. 18
18.93
12.78
80. 0
47.33
5. 29
2. 90
65.03
40.90
No. 3
Laser Alloyed Coatings of Ti&/Graphite on 9Cr18 Stainless Steel Surface
( b ) V = 5 mrn/si
(a) V = 4 mm/s;
Fig. 3
Microhardness Fig. 4 illustrates the hardness variation of the
cross-section. T h e results show that the hardness of the alloyed coatings is greatly improved, which can be ascribed to the hard antiwear phase carbides. O n the surface layer, the microhardness is the highest and reaches HV950. T h e in-situ dendritic carbides are firmly embedded on the alloyed coating and are expected to have excellent antiwear property. T h e
lOOOh
0 0.5
1.5
2.5
V=6 mm/s
3.5
4.5
thickness of the alloyed coatings is about 0. 6 mm. T h e hardness is the lowest near the interface because the substrate is tempered.
2.3
Tribological properties
T h e friction and wear properties were evaluated on a block-on-ring tribo-tester MM-200 under dry condition. T h e counterpart ring is 9Crl8 stainless steel in quenched and tempered state. T h e experiments include two groups for comparison: alloyed coating on ring 9Cr18 and block 9Cr18 on ring 9Cr18. T h e friction coefficient of the alloyed coating is about 0. 74, which is slightly lower than that of the substrate 0. 78. It is seen from the SEM photographs of the worn surface, as shown in Fig. 5 , that the alloyed coatings have the typical feature of wear debris peeling. T h e wear mechanisms are mainly the brittle carbide peeling off, abrasive wear. peeling layer wear, and adhesion wear. T h e alloyed coating is slightly worn. Yet, there are serious adhesion peeling pits and furrows on the surface of the block 9Cr18. Since hard carbide dispersing in the soft matrix improves the hardness of the coatings and reduces the micro-cutting process, the alloyed coatings that include hard carbide have excellent antiwear property. Furthermore, in situ hard grains have high
5.5
Distance from surfacdmm (a)
Fig. 4
.
Optical microstructuresof alloyed coatings of samples 1 , 2 , and 3
scanning speed is increased to 6 m m / s , the microstructure of the alloyed coatings is mainly coarse nickel-based alloy dendrites and hardly has any carbide. T h u s , the microstructures of the alloyed coatings are strongly affected by the processing parameters of laser alloying. When the other parameters are fixed, the lower the scanning speed, the longer is the interactive time between the substrate and the preplaced composite material. Accordingly, more carbon and titanium enter the molten substrate, and more FeC and TIC are synthesized before the melted pool rapidly solidifies. T h e alloyed coatings have more volume fraction of carbide. Hence, when the scanning speeding is 4 m m / s , the alloyed coating must have high hardness and antiwear properties.
2.2
(c)
71
Microhardnessof alloyed coatings
Fig. 5
Alloyed coating;
( b ) 9Ci-18
SEM photographs of worn surfaces
72
-
Journal of Iron and Steel Research, International
bonding strength with the matrix. These form a good carrier capacity system together, while distinctively reduce the load intensity carried by the grains, and effectively restrain the forming and development of micro-cutting, and improve the antiwear and antifriction properties of the coatingsc7’.
3
Conclusions
The composite alloyed coatings of Ti& /graphite, which are free of cracks and pores, can be obtained by laser alloying with suitable processing parameters on the 9Cr18 stainless steel. T h e coatings have a large amount of high hardness carbides of iron, nickel, chromium, silicon, and titanium. The hardness and the antiwear properties of the alloying coating have been greatly improved. References:
113
ZENG Zhao-ming, TANG Bao-yin, WANG Song-yan. Improvement of Tribological Properties of 9Cr18 Steel by Metal
Vol. 14
Plasma Immersion Ion Implantation [JJ. Vacuum Science and Technology, 2000, 2 I 77-80 (in Chinese). Agarwal Arvind, Dahotre Narendra B. Comparative Wear in Titanium Diboride Coatings on Steel Using High Energy Density Processes [JJ. Wear Volume, 2000, 240(1-2): 144-151. Katipelli Lalitha R, Agarwal Arvind, Dahotre Narendra B. Laser Surface Engineered Tic Coating on 6061 Al Alloy: Microstructure and Wear [JJ. Applied Surface Science, 2000, 153(23) : 65-78. Thawari G , Sundarararjan G , Joshi S V. Laser Surface Alloying of Medium Carbon Steel With SiC(p) [JJ. Thin Solid Films, 2003, (423)$ 41-53. HUANG Chong-cheng, TSAI Wen-ta, LEE Ju-tung. Microstructural Aspects and Oxidation Behavior of Laser Surface Clad Silicon-Containing Stainless Steels [J]. Scripta Metallur gica et Materiala, 1995, 32(9): 1465-1470. YING Li-xia, WANG Li-qin, CHEN Guan-ci. Simulation and Calculation of 3D Laser Cladding Temperature Field of Ceramic Metal Composite Coatings by FEM [JJ. Heat Treatment of Metals, 2004, 29(323): 24-28 (in Chinese). WANG Hui, XIA Wei-ming, YIN Yuan-sheng. Study on Abrasive Resistance of Ni-Based Coatings Containing WC Hard Phase [J]. Tribology, 1995, 3: 211-217 (in Chinese).