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In situ production of Fe–VC and Fe–TiC surface composites by cast-sintering
Composites: Part A 32 (2001) 281–286 www.elsevier.com/locate/compositesa
Short Communication
In situ production of Fe–VC and Fe–TiC surface composites by cast-sintering Yisan Wang*, Xinyuan Zhang, Guangting Zeng, Fengchun Li Metal Materials Department, Sichuan University, Sichuan Chengdu 610065, People’s Republic of China Received 5 August 1999; revised 5 April 2000; accepted 7 June 2000
Abstract Using a new cast-sintering technique, iron-base surface composites reinforced by VC and TiC particles which were produced in situ and consisting of self-lubricant graphite and chromium-carbide, were sintered on the surface of cast steel during casting. The structure and composition of the surface composites were studied with the help of a SEM, an electron probe and XRD. From the outside in of the ironbased surface composites, the concentration of V and Ti was relatively stable and consistently retained a high level, while the concentration of Cr and Ni took on a gradient distribution and decreased gradually. The fine particles of VC and TiC measuring between 1 and 3 mm in diameter were uniformly dispersed in their matrices, and there was a perfect metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping with a heavy load, the Fe–VC and Fe–TiC surface composites offer virtually unique wearresistance. 䉷 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Metal–matrix composites (MMCs); A. Particle-reinforcement; B. Microstructure; B. Wear
1. Introduction Ceramic particles of TiC and VC have high hardness and thermal stability and can be used to reinforce iron-based composites. Fe–TiC composites are produced mainly by powder metallurgy routes involving the addition of TiC powders to iron alloy powders. The advantages of powder metallurgy are that the surface quality and precision of products are very good, but carry a high production cost, while their shape and size are restricted. In recent years there has been an interest in liquid-based routes involving the in situ formation of the TiC and VC particles in ironbased composites. The advantage of an in situ route is that the surfaces of reinforcements generated by liquid reaction tend to remain clean, i.e. free from gas absorption, oxidation or other detrimental surface reactions, and the matrix–filler interface bond therefore tends to be stronger. In addition, this route may be more economical as the reinforcements are not manufactured and handled separately. In the previous works, all the produced Fe–TiC and Fe–VC composites are monolithic composites [1–4]. However, from the point of view of the application, the service life of components usually relies on their surface wear-
* Corresponding author.
resistance, and it is desirable that the surface layer of casting is reinforced by TiC or VC particles to offer high wearresistance to them whilst they retain the high toughness and strength of the bulk of casting [5–7]. Materials with such a structure characteristic, being referred to as surface composites, will be produced in situ in the present work using a novel cast-sintering technique, which utilizes the heat of the liquid steel during casting to sinter the metal– ceramic composite layer consisting of TiC or VC particles on a surface of cast steel. According to the liquid-phase sintering theory of powder metallurgy, the sintering densification process can be accelerated in the presence of a liquid phase [8]. In order to finish the sintering densification of press block in a few minutes during pouring and solidifying, the liquid content in the press block should be higher than a certain critical level, and therefore the press block consists of a low-melt-point component and a carbide forming component. The former component which forms the liquid-phase during sintering consists of Cr, Ni, Si, C and Fe mainly, whilst the latter component consists of Ti–Fe or V–Fe powder mainly. From the previous work [5–7], it can be found that the reaction times of complete conversion of the added Ti or V to carbides, in the presence of a liquid phase, were very short at 1500–1600⬚C, thereby during casting, it is possible to sinter and generate carbides simultaneously. In consideration of further improving
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Table 1 Composition of raw materials Low-melting-point component Carbide-forming component 1 Carbide-forming component 2
Cr; 25–28% V; 51.65% Ti; 27.90%
Ni; 15–30% Si; 0.36% Si; 1.025
wear-resistance, it is better that, in addition to TiC or VC particles, the surface composites consist of chromium carbides and self-lubricant graphite in a matrix of Martensite. Therefore, the Cr, Ni and Si contents in the press block should be carefully adjusted. The cast-sintering technique combines the advantages of powder metallurgy and casting, and provides the opportunity of producing near-net-shape final components with metal–ceramic surface composite layer during casting so the production process is simple and offers a virtually unique combination of low cost and good wear-resistance. The aim of the work reported here
Si; 5–7% Al; 0.10 Al; 2.12%
C; 3–5%
Fe; balance Fe; balance Fe; balance
was to provide an initial assessment of the structure, composition distribution and wear-resistance of the Fe–TiC and Fe–VC surface composites.
2. Experimental procedure The compositions of the low-melting-point component and the carbide-forming component were presented in Table 1. The ratio of low-melting-point component to the carbide-forming component was 1:1 and 1:1.5 for Fe–VC
Fig. 1. SEM micrographs: (a) Line-scanning patterns of V and C; (b) microstructure of the Fe–VC surface composite.
Fig. 2. SEM micrographs: (a) coexistence of VC and Martensite reliefs; (b) coexistence of VC and chrome-carbides; (c) line-scanning pattern of Cr.
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The presence of vanadium carbide and graphite flakes in the Fe–VC surface composite layer is confirmed by wavespectrum line-scanning mapping as shown in Fig. 1a. The
formation of graphite in the surface composite layer is due to the fact that Si partially neutralized the disadvantageous effect of Cr and V on graphitization. In the surface layer of the sample, as shown in Fig. 1b, uniform vanadium carbide dispersions of between 24.7 and 33.4% by weight were achieved with particle sizes in the range 1–3 mm. Fig. 2a shows the coexistence of vanadium carbide and Martensite reliefs which was the result of a shear transformation in the matrix, and Fig. 2b shows the coexistence of vanadium carbide and black chunks in an etched sample. The microzone constituent analysis (in Table 2) and the wave-spectrum line-scanning mapping (in Fig. 2c) showed that these black chunks were chromium-carbides. The X-ray diffraction pattern of the Fe–VC surface composite layer, as shown in Fig. 3, confirms that the surface composite holds VC and (Fe, Cr)7C3 in a matrix of Martensite. The concentration distribution of elements in the surface layer is shown in Fig. 4. The concentration of V is relatively stable and consistently retains a high level in the thickness range of the surface composite layer, but the concentration of Cr and Ni, after retaining a high level in a shorter distance from outside, took on a gradient distribution, i.e. with the distance from the outside increasing, their concentration decreased gradually. The results of the micro-zone constituent analysis of matrix of the Fe–VC surface composite indicate that the amounts of Ni, Cr and V in the matrix are 20.03, 9.58 and 1.43%, respectively. The difference in the distribution profiles of V with other two elements is due to the fact that Ni and Cr dissolve in the matrix while V forms VC. The elements that dissolve in the matrix also diffuse into it by solid state diffusion. In the Fe–TiC surface composite, as shown in Fig. 5a, there are many small white particles (with sizes in the range 1–3 mm) on the matrix. The wavespectrum line-scanning mapping, as shown in Fig. 5b, showed that they are TiC, and the mass balance calculations indicated that uniform TiC dispersions of between 15.1 and 16.4% by weight could be achieved. Fig. 5c showed the coexistence of TiC and graphite flakes which were facilitated by the presence of Ni and Si in the press blocks. The X-ray diffraction pattern, as shown in Fig. 6, confirms that the surface composite layer consisted of TiC and
Fig. 3. X-ray diffraction pattern of the Fe–VC surface composite.
Fig. 4. Concentration distribution of V, Cr and Ni in Fe–VC surface composite.
Table 2 Composition of zone A in Fig. 2b Cr
Si
V
Mn
Fe
58.97%
6.99%
3.06%
3.86%
27.12%
and Fe–TiC surface composite, respectively. Elemental powders were mixed in a ball mill for 24 h and pressed into pellets with dimensions of 30 × 20 × 3 mm 3 using a steel pressure die. The pellets were bonded to the wall of a casting mould, which was made from PVA sand. After baking at 433⬚K for 4 h, liquid steel at 1873⬚K was poured into the mould. The melting procedure was carried out using a MgO-lined medium-frequency induction furnace. After solidification and cooling, samples were removed, cut and polished for observation under a SEM. From the outside in of the samples, micro-zone compositions were analysed with the help of an electron probe energy-spectrometer. An XRD and an electron probe with a wave-spectrum were used to confirm the presence of TiC and VC. The bond strength between the surface composite layer and the alloy was assessed by using a three-point curve test. Dry slipping wear tests were carried out against a hardened alloy-steel with a hardness of HRC 55 using a MM-200 wear-testing machine. Loads of 196, 392 and 588 N were used, a rotative velocity of 400 r.p.m. and a wear stroke of 2000 m were used. The average width of the wear trail was measured with the help of a tool-microscope, and the wear volume was calculated using the following formula: V B{r 2 sin⫺1 b=2r ⫺ b=2 r2 ⫺ b2 =41=2 } Bb3 =12r mm3 where B, width of wear ring (mm); b, width of wear trail (mm); and r, out radius of wear ring (mm). 3. Results and discussion
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Fig. 5. SEM micrographs: (a) microstructure of the Fe–TiC surface composite; (b) line-scanning patterns of Ti and C; (c) coexistence of TiC and graphite flakes.
Fig. 6. X-ray diffraction pattern of Fe–TiC surface composite.
Fig. 7. Concentration distribution of Ti, Cr and Ni in Fe–TiC surface composite.
chromium-carbide in the Martensitic and Austenitic matrices. The results of the micro-zone constituent analysis of the Fe–TiC surface composite are shown in Fig. 7. The concentration of Ti consistently retained a high level in the thickness range 3 mm and the concentration of Cr and Ni took on a gradient distribution. The micro-zone composition of the matrix of the Fe–TiC surface composite was checked with the help of an electron probe energy-spectrometer. The amounts of Ni, Cr and Ti in the matrix are 8.05, 6.37 and 0.81%, respectively. This fact indicates that Ti forms TiC while Ni and Cr dissolve in the matrix. The same argument as with vanadium will probably apply to explain the difference in the distribution profiles of Ti with the other two
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is shown in Fig. 10. The Fe–TiC and Fe–VC surface composites possess great wear-resistance which is 10.5times and 10.0-times less than that of the hardening medium-carbon steel under a 588 N load, respectively. The wear-resistance of Fe–TiC and Fe–VC surface composites is attributed to the hard TiC or VC particles and chromium-carbide that reinforce the matrix and protect it from serious abrasion. Meanwhile the graphite flakes act as a solid lubricant to eliminate serious adhesive wear.
4. Conclusions
Fig. 8. Fracture morphology of three points curve test of Fe–TiC surface composite.
elements. The fracture morphology of the three point curve test of Fe–TiC surface composite is shown in Fig. 8. There are no cracks or tears at the interface of the surface composite layer and the master alloy, indicating that the bond strength is very strong. The interface micrographs of the Fe–TiC and Fe–VC surface composites are shown in Fig. 9, There was a good metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping wear with loads of 196, 392 and 588 N, respectively, the wear-volumes of the Fe–TiC, Fe– VC surface composites and the hardening medium-carbon steel are presented in Table 3. The relative wear-resistance which was expressed as a ratio of wear-volume of the hardening medium-carbon steel and that of the surface composites
Using a new cast-sintering technique, iron base surface composites, reinforced by VC and TiC particles were produced in situ. The surface quality of the Fe–TiC and Fe–VC surface composites produced by cast-sintering was very good, and the thickness of the surface composite layer can be accurately controlled by the thickness of a press block. The VC and TiC generated in situ during cast-sintering were uniformly dispersed in the matrix with particle sizes in the range 1–3 mm. There was a perfect metallurgy-bond between the surface composite layer and the master-alloy, and the bond strength was very strong. In the surface composite layer, the concentrations of V and Ti were relatively stable and consistently retained a high level. However, the concentration of Cr and Ni in the surface composites took on a gradient distribution and decreased gradually. In addition to VC and TiC particles, the cast-sintered iron base surface composites consist of chromium-carbides and graphite flakes. Under the condition of dry slipping with heavy loads, the Fe–TiC and Fe–VC surface composites offer a high wear-resistance.
Fig. 9. Interface micrographs: (a) Interface of Fe–VC surface composite layer and master-alloy; (b) interface of Fe–TiC surface composite layer and masteralloy.
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Table 3 Wear volume of Fe–VC, Fe–TiC surface composites and hardening medium-carbon steel Wear volume (mm 3)
Hardening medium-carbon steel Fe–VC surface composite Fe–TiC surface composite
Under 196 N
Under 392 N
Under 588 N
9.71 2.06 1.68
32.38 4.04 3.51
121.43 12.09 11.56
Fig. 10. Comparison of wear-resistance of Fe–VC, Fe–TiC surface composites and hardening medium-carbon steel.
References [1] Kattamis TZ, et al. Solidification processing and tribological behaviour of particulate TiC–ferrous matrix composite. Mater Sci Engng 1990;A128:241–52. [2] Raghunath C, Bhat MS, Rohatgi PK. In situ technique for synthesizing Fe–TiC composites. Scripta Metallurgica Materialia 1995;4: 577–82. [3] Terry BS, Chinyamakobvu OS. In situ production of Fe–TiC composites by reaction in liquid iron alloy. J Mater Lett 1991;10:628–9.
[4] Chrysanthou A, Davies NW, et al. Reaction synthesis of carbidereinforced cast iron. J Mater Lett 1996;15:473–4. [5] Wang Yisan, Huang Wen. Structure and properties of an iron based selflubricant wear-resistant gradient layer. Mater Design 1998;6:109–12. [6] Wang Yisan, Li Fengchun, et al. Structure and wear-resistance of an Fe– VC surface composite produced in situ. Mater Design 1999;1:19–22. [7] Wang Yisa, Zhang Xinyuan, et al. Study on an Fe–TiC surface composite produced in situ. Mater Design 1998;5:233–6. [8] Kingery WD. Densification during sintering in the presence of a liquid phase. J Appl Phys 1959;30:301–10.
Short Communication
In situ production of Fe–VC and Fe–TiC surface composites by cast-sintering Yisan Wang*, Xinyuan Zhang, Guangting Zeng, Fengchun Li Metal Materials Department, Sichuan University, Sichuan Chengdu 610065, People’s Republic of China Received 5 August 1999; revised 5 April 2000; accepted 7 June 2000
Abstract Using a new cast-sintering technique, iron-base surface composites reinforced by VC and TiC particles which were produced in situ and consisting of self-lubricant graphite and chromium-carbide, were sintered on the surface of cast steel during casting. The structure and composition of the surface composites were studied with the help of a SEM, an electron probe and XRD. From the outside in of the ironbased surface composites, the concentration of V and Ti was relatively stable and consistently retained a high level, while the concentration of Cr and Ni took on a gradient distribution and decreased gradually. The fine particles of VC and TiC measuring between 1 and 3 mm in diameter were uniformly dispersed in their matrices, and there was a perfect metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping with a heavy load, the Fe–VC and Fe–TiC surface composites offer virtually unique wearresistance. 䉷 2001 Elsevier Science Ltd. All rights reserved. Keywords: A. Metal–matrix composites (MMCs); A. Particle-reinforcement; B. Microstructure; B. Wear
1. Introduction Ceramic particles of TiC and VC have high hardness and thermal stability and can be used to reinforce iron-based composites. Fe–TiC composites are produced mainly by powder metallurgy routes involving the addition of TiC powders to iron alloy powders. The advantages of powder metallurgy are that the surface quality and precision of products are very good, but carry a high production cost, while their shape and size are restricted. In recent years there has been an interest in liquid-based routes involving the in situ formation of the TiC and VC particles in ironbased composites. The advantage of an in situ route is that the surfaces of reinforcements generated by liquid reaction tend to remain clean, i.e. free from gas absorption, oxidation or other detrimental surface reactions, and the matrix–filler interface bond therefore tends to be stronger. In addition, this route may be more economical as the reinforcements are not manufactured and handled separately. In the previous works, all the produced Fe–TiC and Fe–VC composites are monolithic composites [1–4]. However, from the point of view of the application, the service life of components usually relies on their surface wear-
* Corresponding author.
resistance, and it is desirable that the surface layer of casting is reinforced by TiC or VC particles to offer high wearresistance to them whilst they retain the high toughness and strength of the bulk of casting [5–7]. Materials with such a structure characteristic, being referred to as surface composites, will be produced in situ in the present work using a novel cast-sintering technique, which utilizes the heat of the liquid steel during casting to sinter the metal– ceramic composite layer consisting of TiC or VC particles on a surface of cast steel. According to the liquid-phase sintering theory of powder metallurgy, the sintering densification process can be accelerated in the presence of a liquid phase [8]. In order to finish the sintering densification of press block in a few minutes during pouring and solidifying, the liquid content in the press block should be higher than a certain critical level, and therefore the press block consists of a low-melt-point component and a carbide forming component. The former component which forms the liquid-phase during sintering consists of Cr, Ni, Si, C and Fe mainly, whilst the latter component consists of Ti–Fe or V–Fe powder mainly. From the previous work [5–7], it can be found that the reaction times of complete conversion of the added Ti or V to carbides, in the presence of a liquid phase, were very short at 1500–1600⬚C, thereby during casting, it is possible to sinter and generate carbides simultaneously. In consideration of further improving
1359-835X/01/$ - see front matter 䉷 2001 Elsevier Science Ltd. All rights reserved. PII: S1359-835 X( 00)00 118-4
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Y. Wang et al. / Composites: Part A 32 (2001) 281–286
Table 1 Composition of raw materials Low-melting-point component Carbide-forming component 1 Carbide-forming component 2
Cr; 25–28% V; 51.65% Ti; 27.90%
Ni; 15–30% Si; 0.36% Si; 1.025
wear-resistance, it is better that, in addition to TiC or VC particles, the surface composites consist of chromium carbides and self-lubricant graphite in a matrix of Martensite. Therefore, the Cr, Ni and Si contents in the press block should be carefully adjusted. The cast-sintering technique combines the advantages of powder metallurgy and casting, and provides the opportunity of producing near-net-shape final components with metal–ceramic surface composite layer during casting so the production process is simple and offers a virtually unique combination of low cost and good wear-resistance. The aim of the work reported here
Si; 5–7% Al; 0.10 Al; 2.12%
C; 3–5%
Fe; balance Fe; balance Fe; balance
was to provide an initial assessment of the structure, composition distribution and wear-resistance of the Fe–TiC and Fe–VC surface composites.
2. Experimental procedure The compositions of the low-melting-point component and the carbide-forming component were presented in Table 1. The ratio of low-melting-point component to the carbide-forming component was 1:1 and 1:1.5 for Fe–VC
Fig. 1. SEM micrographs: (a) Line-scanning patterns of V and C; (b) microstructure of the Fe–VC surface composite.
Fig. 2. SEM micrographs: (a) coexistence of VC and Martensite reliefs; (b) coexistence of VC and chrome-carbides; (c) line-scanning pattern of Cr.
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The presence of vanadium carbide and graphite flakes in the Fe–VC surface composite layer is confirmed by wavespectrum line-scanning mapping as shown in Fig. 1a. The
formation of graphite in the surface composite layer is due to the fact that Si partially neutralized the disadvantageous effect of Cr and V on graphitization. In the surface layer of the sample, as shown in Fig. 1b, uniform vanadium carbide dispersions of between 24.7 and 33.4% by weight were achieved with particle sizes in the range 1–3 mm. Fig. 2a shows the coexistence of vanadium carbide and Martensite reliefs which was the result of a shear transformation in the matrix, and Fig. 2b shows the coexistence of vanadium carbide and black chunks in an etched sample. The microzone constituent analysis (in Table 2) and the wave-spectrum line-scanning mapping (in Fig. 2c) showed that these black chunks were chromium-carbides. The X-ray diffraction pattern of the Fe–VC surface composite layer, as shown in Fig. 3, confirms that the surface composite holds VC and (Fe, Cr)7C3 in a matrix of Martensite. The concentration distribution of elements in the surface layer is shown in Fig. 4. The concentration of V is relatively stable and consistently retains a high level in the thickness range of the surface composite layer, but the concentration of Cr and Ni, after retaining a high level in a shorter distance from outside, took on a gradient distribution, i.e. with the distance from the outside increasing, their concentration decreased gradually. The results of the micro-zone constituent analysis of matrix of the Fe–VC surface composite indicate that the amounts of Ni, Cr and V in the matrix are 20.03, 9.58 and 1.43%, respectively. The difference in the distribution profiles of V with other two elements is due to the fact that Ni and Cr dissolve in the matrix while V forms VC. The elements that dissolve in the matrix also diffuse into it by solid state diffusion. In the Fe–TiC surface composite, as shown in Fig. 5a, there are many small white particles (with sizes in the range 1–3 mm) on the matrix. The wavespectrum line-scanning mapping, as shown in Fig. 5b, showed that they are TiC, and the mass balance calculations indicated that uniform TiC dispersions of between 15.1 and 16.4% by weight could be achieved. Fig. 5c showed the coexistence of TiC and graphite flakes which were facilitated by the presence of Ni and Si in the press blocks. The X-ray diffraction pattern, as shown in Fig. 6, confirms that the surface composite layer consisted of TiC and
Fig. 3. X-ray diffraction pattern of the Fe–VC surface composite.
Fig. 4. Concentration distribution of V, Cr and Ni in Fe–VC surface composite.
Table 2 Composition of zone A in Fig. 2b Cr
Si
V
Mn
Fe
58.97%
6.99%
3.06%
3.86%
27.12%
and Fe–TiC surface composite, respectively. Elemental powders were mixed in a ball mill for 24 h and pressed into pellets with dimensions of 30 × 20 × 3 mm 3 using a steel pressure die. The pellets were bonded to the wall of a casting mould, which was made from PVA sand. After baking at 433⬚K for 4 h, liquid steel at 1873⬚K was poured into the mould. The melting procedure was carried out using a MgO-lined medium-frequency induction furnace. After solidification and cooling, samples were removed, cut and polished for observation under a SEM. From the outside in of the samples, micro-zone compositions were analysed with the help of an electron probe energy-spectrometer. An XRD and an electron probe with a wave-spectrum were used to confirm the presence of TiC and VC. The bond strength between the surface composite layer and the alloy was assessed by using a three-point curve test. Dry slipping wear tests were carried out against a hardened alloy-steel with a hardness of HRC 55 using a MM-200 wear-testing machine. Loads of 196, 392 and 588 N were used, a rotative velocity of 400 r.p.m. and a wear stroke of 2000 m were used. The average width of the wear trail was measured with the help of a tool-microscope, and the wear volume was calculated using the following formula: V B{r 2 sin⫺1 b=2r ⫺ b=2 r2 ⫺ b2 =41=2 } Bb3 =12r mm3 where B, width of wear ring (mm); b, width of wear trail (mm); and r, out radius of wear ring (mm). 3. Results and discussion
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Fig. 5. SEM micrographs: (a) microstructure of the Fe–TiC surface composite; (b) line-scanning patterns of Ti and C; (c) coexistence of TiC and graphite flakes.
Fig. 6. X-ray diffraction pattern of Fe–TiC surface composite.
Fig. 7. Concentration distribution of Ti, Cr and Ni in Fe–TiC surface composite.
chromium-carbide in the Martensitic and Austenitic matrices. The results of the micro-zone constituent analysis of the Fe–TiC surface composite are shown in Fig. 7. The concentration of Ti consistently retained a high level in the thickness range 3 mm and the concentration of Cr and Ni took on a gradient distribution. The micro-zone composition of the matrix of the Fe–TiC surface composite was checked with the help of an electron probe energy-spectrometer. The amounts of Ni, Cr and Ti in the matrix are 8.05, 6.37 and 0.81%, respectively. This fact indicates that Ti forms TiC while Ni and Cr dissolve in the matrix. The same argument as with vanadium will probably apply to explain the difference in the distribution profiles of Ti with the other two
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is shown in Fig. 10. The Fe–TiC and Fe–VC surface composites possess great wear-resistance which is 10.5times and 10.0-times less than that of the hardening medium-carbon steel under a 588 N load, respectively. The wear-resistance of Fe–TiC and Fe–VC surface composites is attributed to the hard TiC or VC particles and chromium-carbide that reinforce the matrix and protect it from serious abrasion. Meanwhile the graphite flakes act as a solid lubricant to eliminate serious adhesive wear.
4. Conclusions
Fig. 8. Fracture morphology of three points curve test of Fe–TiC surface composite.
elements. The fracture morphology of the three point curve test of Fe–TiC surface composite is shown in Fig. 8. There are no cracks or tears at the interface of the surface composite layer and the master alloy, indicating that the bond strength is very strong. The interface micrographs of the Fe–TiC and Fe–VC surface composites are shown in Fig. 9, There was a good metallurgy-bond between the surface composite layer and the master-alloy. Under the condition of dry slipping wear with loads of 196, 392 and 588 N, respectively, the wear-volumes of the Fe–TiC, Fe– VC surface composites and the hardening medium-carbon steel are presented in Table 3. The relative wear-resistance which was expressed as a ratio of wear-volume of the hardening medium-carbon steel and that of the surface composites
Using a new cast-sintering technique, iron base surface composites, reinforced by VC and TiC particles were produced in situ. The surface quality of the Fe–TiC and Fe–VC surface composites produced by cast-sintering was very good, and the thickness of the surface composite layer can be accurately controlled by the thickness of a press block. The VC and TiC generated in situ during cast-sintering were uniformly dispersed in the matrix with particle sizes in the range 1–3 mm. There was a perfect metallurgy-bond between the surface composite layer and the master-alloy, and the bond strength was very strong. In the surface composite layer, the concentrations of V and Ti were relatively stable and consistently retained a high level. However, the concentration of Cr and Ni in the surface composites took on a gradient distribution and decreased gradually. In addition to VC and TiC particles, the cast-sintered iron base surface composites consist of chromium-carbides and graphite flakes. Under the condition of dry slipping with heavy loads, the Fe–TiC and Fe–VC surface composites offer a high wear-resistance.
Fig. 9. Interface micrographs: (a) Interface of Fe–VC surface composite layer and master-alloy; (b) interface of Fe–TiC surface composite layer and masteralloy.
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Table 3 Wear volume of Fe–VC, Fe–TiC surface composites and hardening medium-carbon steel Wear volume (mm 3)
Hardening medium-carbon steel Fe–VC surface composite Fe–TiC surface composite
Under 196 N
Under 392 N
Under 588 N
9.71 2.06 1.68
32.38 4.04 3.51
121.43 12.09 11.56
Fig. 10. Comparison of wear-resistance of Fe–VC, Fe–TiC surface composites and hardening medium-carbon steel.
References [1] Kattamis TZ, et al. Solidification processing and tribological behaviour of particulate TiC–ferrous matrix composite. Mater Sci Engng 1990;A128:241–52. [2] Raghunath C, Bhat MS, Rohatgi PK. In situ technique for synthesizing Fe–TiC composites. Scripta Metallurgica Materialia 1995;4: 577–82. [3] Terry BS, Chinyamakobvu OS. In situ production of Fe–TiC composites by reaction in liquid iron alloy. J Mater Lett 1991;10:628–9.
[4] Chrysanthou A, Davies NW, et al. Reaction synthesis of carbidereinforced cast iron. J Mater Lett 1996;15:473–4. [5] Wang Yisan, Huang Wen. Structure and properties of an iron based selflubricant wear-resistant gradient layer. Mater Design 1998;6:109–12. [6] Wang Yisan, Li Fengchun, et al. Structure and wear-resistance of an Fe– VC surface composite produced in situ. Mater Design 1999;1:19–22. [7] Wang Yisa, Zhang Xinyuan, et al. Study on an Fe–TiC surface composite produced in situ. Mater Design 1998;5:233–6. [8] Kingery WD. Densification during sintering in the presence of a liquid phase. J Appl Phys 1959;30:301–10.