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Dry sliding wear behavior of in situ Al–Al4C3 metal matrix composite produced by mechanical alloying technique
Materials & Design Materials and Design 27 (2006) 799–804 www.elsevier.com/locate/matdes
Short communication
Dry sliding wear behavior of in situ Al–Al4C3 metal matrix composite produced by mechanical alloying technique Halil Arik *, Yusuf Ozcatalbas, Mehmet Turker Metallurgy Department, Technical Education Faculty, Gazi University, 06500-Besevler, Ankara, Turkey Received 23 September 2004; accepted 19 January 2005 Available online 21 April 2005
Abstract Dry sliding wear behavior of in situ Al–Al4C3 composite produced by mechanical alloying technique was examined. Mechanically alloyed Al–C powders were compacted at 650 MPa to produce the blanks with the size of ø10 · 25 mm. These blanks were then sintered at 650 C for 20 h and MMC samples with the density of 92% and the hardness of 314 Hv were produced. Dry sliding behavior of the produced Al–Al4C3 composite was examined by using pin-on-disk technique. In the case of low applying force, Fe based stable mechanical mixed layer was formed on the pin surface and which decreased the wear rate. However, high applied force resulted in the formation of mechanical deformed layer on the surface of samples which facilities the wear rate. 2005 Elsevier Ltd. All rights reserved. Keywords: Metal matrix composite; Al–Al4C3 composites; In situ; Mechanical alloyed; Sliding wear
1. Introduction Aluminum alloys is an important material for tribological applications due to its low density and high thermal conductivity. Therefore, the investigation of tribological behavior of aluminum based materials is becoming increasingly important. In the recent past, another class of material, namely the metal matrix composite (MMC), is becoming increasingly important [1]. The need for new materials able to match increasingly stringent engineering requirements has led to the development of MMC for aerospace and automotive applications. Properties such as friction and wear resistance in lubricated or unlubricated conditions are of particular importance for the development, for example, of brakes or engine pistons etc. [2,3]. Recently, a number of Al alloys have also been developed as light-weight materials for such uses as bearings. Although Al alloys meet many *
Corresponding author. Tel.: +90 312 212 6820; fax: +90 312 212 0059. E-mail address: [email protected] (H. Arik). 0261-3069/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.01.024
requirements for such applications, their poor resistance to seizure make them vulnerable under poor lubricating conditions [3]. In order to improve the tribological behavior of Al alloys, hypereutectic alloys containing 14–20% Si, have been used for the above-mentioned applications. Internal-combustion-engine cylinder bores made from these alloys do perform well under favorable conditions; however, with limited running-in, poor lubrication, and cold starts, scuffing can occur between the bore and the skirt of the aluminum positions. An alternative approach is to develop a composite incorporating a solid lubricant, such as graphite [3]. The graphite could display a very low coefficient of friction on sliding due to the fact that its crystal structure contains weakly bonded sheets although the bondings within these are quite strong. These Al–graphite alloy composites have been proven to possess better gall resistance, improved wear resistance, high damping capacity, and good machinability [4], however, the strength of the resultant composites are weakened by the effect of graphite particle dispersion.
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H. Arik et al. / Materials and Design 27 (2006) 799–804
Techniques for producing Al–graphite particle composites by various casting routes have been developed. The major difficulty in the preparation of cast Al–graphite particle composites by liquid metallurgy process is the apparent non-wetability of graphite by liquid Al alloy and the density difference between the two materials [3]. However, the dispersion strengthened Al alloy Al– Al4C3 prepared by mechanical alloying (MA) using powder metallurgy (PM) technique are promising structural materials enabling significant cuts of weight [5], for use first in aircraft and car industry, also at elevated temperatures [6,7]. It was thought that producing parts containing carbon by PM technique not only increase the strength but also increase the dry sliding behavior due to residual carbon, which act as a binder, in the matrix. The aim of this study was to produce in situ A1– Al4C3 composite from Al–C powders by MA technique and examining the dry sliding behavior of produced composite.
Table 2 Properties of composite materials [8] Sintered density (%)
Al/Al4C3
Hardness (HV)
Transverse rupture strength (MPa)
92
92/8
284
157
block was lightly ground and polished to remove any irregularity or debris. Then hardness of sample was measured by the Vickers hardness method and mean of at least five readings was taken. In order to determine the formation of Al4C3 particles, samples were analyzed by using X-Ray diffraction (XRD) and scanning electron microscopy (SEM). Some important properties of produced composite material to be used in wear tests are given in Table 2. 2.2. Wear tests
2. Experimental procedures 2.1. Production and characterizations of composite material In this study, gas atomized Al powders with the maximum particle size of 150 lm powders were produced at Gazi University PM Lab. from 99% pure Al ingots which were supplied from ETIBANK (Turkish Aluminum Producing Co.). Carbon black with 99% purity and mean particle size (agglomerate size) of 2.4 lm were obtained from YARPET (Turkish Petrochemical Trade Co.) Powders were mechanical alloyed with the parameters given in Table 1. Mechanically alloyed powders were compacted at 1000 MPa pressure to produce blanks with ø10 · 25 mm in size. Blanks were put in graphite boat which was placed in an atmosphere controlled tube furnace and heated to test temperature in a flowing argon atmosphere for predetermined durations. Heating rate of the furnace to the desired temperature was approximately 5 C min 1. The furnace was held at that temperature with the accuracy of ±5 C, and then cooled to room temperature at 5 C min 1. Sintering process was performed at 650 C for 20 h. The surfaces of sintered
The wear tests were performed using a pin on-disc wear tester under dry sliding condition (Fig. 1). Composite specimens with the dimensions of ø10 mm · 20 mm were sliced on a SAE 5190 steel disc having a hardness of 62 HRc. The disc, 180 mm in diameter and 20 mm thick, was ground to a 1200 grit finish prior to testing. Tests were carried out at 1.41 m s 1 sliding velocity and at applied loads of 20, 50, and 80 N. Sliding distance was 2538 m, track diameter 90 mm and sliding time was 30 min. Specimens were weighted before and after each wear test by using a digital balance with a precision of 10 4 g. Weight loses were obtained by determining the masses of the samples before and after wear tests. The wear results then were expressed in terms of wear rates after conversion of the weight loss into volume loss using a density of 2.41 g cm 3. Each test was performed on a new disc surface, and for each test condition, three runs were performed. Scanning electron microscope and optical microscope were used to examine the wear surface of the MMC.
Table 1 Condition of mechanical alloying Vessel volume (cm3)
750
Mass of aluminum powder (g) Mass of carbon black (g) Charge ratio (mass of grinding balls:mass of powder in mill) Steel ball diameter (mm)
48.5 1.5 6:1
Rotor speed (rev min 1) MA atmosphere Cooling Milling time (h)
Argon Water 20
10
PCA (%)
2
450
Fig. 1. Schematic illustration of wear device.
H. Arik et al. / Materials and Design 27 (2006) 799–804
801
Fig. 2 shows the wear rates of MMC as a function of the applied load. In general with increasing the applied load, wear rate increased, although it was not a proportional to the applied load. Wear rate was found to be very low (0.73 mm3 m 1) at 20 N load. With increasing the load to 50 N a clear increase was observed on the wear rate and which reached to 19.67 mm3 m 1. However, considerable amount of wear rate was observed (187.35 mm3 m 1) on the sample examined at 80 N. This results were similar to those seen by Straffelini and Narayan [2,9] in respect to the load–wear rate although they used different materials. Fig. 3(a) and (b) depicts the SEM and light microscopes images of the perpendicular section of the worn surface at 20 N load. As seen in the pictures the surface of MMC is rough and irregular in appearance. Worn surface of pin was found to be perfectly coated with a mechanical mixed layer (white areas in Fig. 3(a)) of 5–8 lm thickness. Frictional surface of this layer (contact to mounting material in Fig. 3(a)) to counterface appeared flat and smooth. Surface of MMC was rough
but this was filled with the formed layer and flattened. Rough subsurface indicates that wearing occurs on both disc and pin surface before formation of the mechanical mixed layer. The layer formed on the pin surface covered about the 85% of the pin surface (Fig. 4). Energy dispersive X-Ray (EDAX) analysis result of this layer is given in Fig. 5. Although this layer mainly consisted of Al, it contained small amount of Fe, Ti, Cr, Mn and O which came from the counter surface. However, the light brownish appearance of this layer with naked eye indicates that this layer is mainly iron oxide. This result shows that during the wearing of MMC, counter face wears and consequently Fe based oxide film forms on the MMC pin surface. Similar result was reported by Setraffelini et al. [2] who studied the sliding behavior of Al2O3 reinforced Al matrix composite. It is believed that formation of such layer on the pin surface acts as a lubricant and protects the MMC pin against wear and thus reduced the wear rate [1,2]. Figs. 6 and 7 show the microstructures of worn surface of MMC under 50 N load. Here, mechanical deformed layer (MDL) about 20 lm thick formed between the pin and the counter face
Fig. 2. The effect of applied load on wear rate of MMC material.
Fig. 4. FeO layer on the wear surface of pin at 20 N load.
3. Results and discussion
Fig. 3. Cross-section perpendicular to worn surface tested at 20 N load, (a) SEM, (b) optical microscopy.
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Fig. 7. FeO layer on the wear surface of pin at 20 N load. Fig. 5. EDAX analysis of layer material on the pin.
Fig. 6. Cross-section perpendicular to worn surface tested at 50 N load, (a) optical microscopy, (b) SEM.
(Fig. 6(a)). Increasing of high mechanical deformation layer towards the pin surface is clearly visible. Furthermore, a discontinuous layer formed on the surface but it was not as smooth as the Fe oxide layer formed on the surface of sample worn under 20 N. This layer was not continuous (Fig. 6(b)) and consisted of fragments and contained some porosity (Fig. 7). EDAX analyses indicate that this layer mainly consists of Al and C but contained small amount of counterface elements (Fig. 8). The blackish appearance of this layer was attributed to the effect of residual carbon. High deformed pin surface resulted in wear debris which could not completely cover the surface. During experiments, formation of small amount of vibration and noise indicate the interruption of sliding. This may result in the formation of discontinuous Al and C based surface film. For this reason sample tested under 50 N exhibited more severe wear compared to those seen under 20 N. In this case, only small amount of wearing was observed on counter face. However, high amount of wear on the pin surface resulted in the formation of wear debris and discontinues surface film instead of forming FeO based contin-
Fig. 8. EDAX analysis of layer material on the pin.
uous layer. Wear behavior of MMC at 80 N is shown in Figs. 9 and 10. MDL layer about 40 lm in thick is seen in Fig. 9(a) and (b). This layer formed
H. Arik et al. / Materials and Design 27 (2006) 799–804
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Fig. 9. Cross-section perpendicular to worn surface tested at 80 N load, (a) MDL formation and cracking of MMC on the pin surface, (b) MDL on the pin surface.
Fig. 10. SEM micrographs of worn surfaces at 80 N load.
on MMC pin sometimes contains crack or defects as shown in Fig. 9 with a white arrow. However, wear debris based layer was not visible on this surface. In this loading condition occurring of considerable amount of vibration and noise resulted in an unstable experiment condition. Cracking and spalling of the MDL layer were attributed to this unstable experimental condition. Fig. 10(a) and (b) show the SEM micrographs of worn surface containing deep groves and highly deformed colonized MMC particles. In the case of 50 N load, the worn surface is characterized by the presence of micro-plowing scars parallel to the sliding direction and brittle scales which were prone to detachment. The reason for high wear rate at higher wear load, especially at 80 N, was due to the sliding of surfaces to each other without formation of protective oxide layer. At this load, high deformation occurs on MMC pin surface which resulting the formation of crack or spallation on the heavily work hardened MDL.
4. Conclusion From the present study, the following can be inferred (1) Formation of stable iron based mechanical mixed layer on the surface of Al–Al4C3 composite during the dry sliding at low applied loads resulted in low wear of MMC. (2) At high loads instead of formation of a stable MML, mechanically deformed layer formed on the MMC surface due to high deformation. Due to the cracking or spallation of this layer increased the wear rate considerably.
Acknowledgment The authors thank Gazi University Research Fund for the financial support of this research work (No: 07/2000-06).
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H. Arik et al. / Materials and Design 27 (2006) 799–804
References [1] Venkataraman B, Sundararajan G. Correlation between the characteristics of the mechanically mixed layer and wear behaviour of aluminum, Al-7075 alloy and Al-MMCs. Wear 2000;245:22–38. [2] Straffelini G, Bonollo F, Molinari A, Tiziani A. Influence of matrix hardness on the dry sliding behaviour of 20 vol.% Al2O3-particulate-reinforced 6061 Al metal matrix composite. Wear 1997;211: 192–7. [3] Chu HS, Liu KS, Yeh JW. An in situ composite of Al (graphite, Al4C3) produced by reciprocating extrusion. Mater Sci Eng A 2000;227:25–32. [4] Ozcatalbas Y. Investigation of the machinability behaviour of Al4C3 reinforced Al-based composite produced by
[5]
[6] [7] [8]
[9]
mechanical alloying technique. Compos Sci Technol 2003;63:53–61. Besterci M, Slesar M, Kovac L. Influence of strain rate on fracture of dispersion strengthened Al–Al4C3 systems. Scripta Mater 1997;37:1077–80. Suryanarayana C. Mechanical alloying and milling. Prog Mater Sci 2001;46:1–184. Zhang DL. Processing of advanced materials using high-energy mechanical milling. Prog Mater Sci 2004;49:537–60. Arik H. Production and characterization of in situ Al4C3 reinforced aluminium-based composite produced by mechanical alloying technique. Mater Des 2004;25:31–40. Narayan M, Surappa M, Pramila Bai K. Dry sliding wear of Al alloy 2024-Al2O3 particle metal matrix composites. Wear 1995;181–183:563–70.
Short communication
Dry sliding wear behavior of in situ Al–Al4C3 metal matrix composite produced by mechanical alloying technique Halil Arik *, Yusuf Ozcatalbas, Mehmet Turker Metallurgy Department, Technical Education Faculty, Gazi University, 06500-Besevler, Ankara, Turkey Received 23 September 2004; accepted 19 January 2005 Available online 21 April 2005
Abstract Dry sliding wear behavior of in situ Al–Al4C3 composite produced by mechanical alloying technique was examined. Mechanically alloyed Al–C powders were compacted at 650 MPa to produce the blanks with the size of ø10 · 25 mm. These blanks were then sintered at 650 C for 20 h and MMC samples with the density of 92% and the hardness of 314 Hv were produced. Dry sliding behavior of the produced Al–Al4C3 composite was examined by using pin-on-disk technique. In the case of low applying force, Fe based stable mechanical mixed layer was formed on the pin surface and which decreased the wear rate. However, high applied force resulted in the formation of mechanical deformed layer on the surface of samples which facilities the wear rate. 2005 Elsevier Ltd. All rights reserved. Keywords: Metal matrix composite; Al–Al4C3 composites; In situ; Mechanical alloyed; Sliding wear
1. Introduction Aluminum alloys is an important material for tribological applications due to its low density and high thermal conductivity. Therefore, the investigation of tribological behavior of aluminum based materials is becoming increasingly important. In the recent past, another class of material, namely the metal matrix composite (MMC), is becoming increasingly important [1]. The need for new materials able to match increasingly stringent engineering requirements has led to the development of MMC for aerospace and automotive applications. Properties such as friction and wear resistance in lubricated or unlubricated conditions are of particular importance for the development, for example, of brakes or engine pistons etc. [2,3]. Recently, a number of Al alloys have also been developed as light-weight materials for such uses as bearings. Although Al alloys meet many *
Corresponding author. Tel.: +90 312 212 6820; fax: +90 312 212 0059. E-mail address: [email protected] (H. Arik). 0261-3069/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2005.01.024
requirements for such applications, their poor resistance to seizure make them vulnerable under poor lubricating conditions [3]. In order to improve the tribological behavior of Al alloys, hypereutectic alloys containing 14–20% Si, have been used for the above-mentioned applications. Internal-combustion-engine cylinder bores made from these alloys do perform well under favorable conditions; however, with limited running-in, poor lubrication, and cold starts, scuffing can occur between the bore and the skirt of the aluminum positions. An alternative approach is to develop a composite incorporating a solid lubricant, such as graphite [3]. The graphite could display a very low coefficient of friction on sliding due to the fact that its crystal structure contains weakly bonded sheets although the bondings within these are quite strong. These Al–graphite alloy composites have been proven to possess better gall resistance, improved wear resistance, high damping capacity, and good machinability [4], however, the strength of the resultant composites are weakened by the effect of graphite particle dispersion.
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H. Arik et al. / Materials and Design 27 (2006) 799–804
Techniques for producing Al–graphite particle composites by various casting routes have been developed. The major difficulty in the preparation of cast Al–graphite particle composites by liquid metallurgy process is the apparent non-wetability of graphite by liquid Al alloy and the density difference between the two materials [3]. However, the dispersion strengthened Al alloy Al– Al4C3 prepared by mechanical alloying (MA) using powder metallurgy (PM) technique are promising structural materials enabling significant cuts of weight [5], for use first in aircraft and car industry, also at elevated temperatures [6,7]. It was thought that producing parts containing carbon by PM technique not only increase the strength but also increase the dry sliding behavior due to residual carbon, which act as a binder, in the matrix. The aim of this study was to produce in situ A1– Al4C3 composite from Al–C powders by MA technique and examining the dry sliding behavior of produced composite.
Table 2 Properties of composite materials [8] Sintered density (%)
Al/Al4C3
Hardness (HV)
Transverse rupture strength (MPa)
92
92/8
284
157
block was lightly ground and polished to remove any irregularity or debris. Then hardness of sample was measured by the Vickers hardness method and mean of at least five readings was taken. In order to determine the formation of Al4C3 particles, samples were analyzed by using X-Ray diffraction (XRD) and scanning electron microscopy (SEM). Some important properties of produced composite material to be used in wear tests are given in Table 2. 2.2. Wear tests
2. Experimental procedures 2.1. Production and characterizations of composite material In this study, gas atomized Al powders with the maximum particle size of 150 lm powders were produced at Gazi University PM Lab. from 99% pure Al ingots which were supplied from ETIBANK (Turkish Aluminum Producing Co.). Carbon black with 99% purity and mean particle size (agglomerate size) of 2.4 lm were obtained from YARPET (Turkish Petrochemical Trade Co.) Powders were mechanical alloyed with the parameters given in Table 1. Mechanically alloyed powders were compacted at 1000 MPa pressure to produce blanks with ø10 · 25 mm in size. Blanks were put in graphite boat which was placed in an atmosphere controlled tube furnace and heated to test temperature in a flowing argon atmosphere for predetermined durations. Heating rate of the furnace to the desired temperature was approximately 5 C min 1. The furnace was held at that temperature with the accuracy of ±5 C, and then cooled to room temperature at 5 C min 1. Sintering process was performed at 650 C for 20 h. The surfaces of sintered
The wear tests were performed using a pin on-disc wear tester under dry sliding condition (Fig. 1). Composite specimens with the dimensions of ø10 mm · 20 mm were sliced on a SAE 5190 steel disc having a hardness of 62 HRc. The disc, 180 mm in diameter and 20 mm thick, was ground to a 1200 grit finish prior to testing. Tests were carried out at 1.41 m s 1 sliding velocity and at applied loads of 20, 50, and 80 N. Sliding distance was 2538 m, track diameter 90 mm and sliding time was 30 min. Specimens were weighted before and after each wear test by using a digital balance with a precision of 10 4 g. Weight loses were obtained by determining the masses of the samples before and after wear tests. The wear results then were expressed in terms of wear rates after conversion of the weight loss into volume loss using a density of 2.41 g cm 3. Each test was performed on a new disc surface, and for each test condition, three runs were performed. Scanning electron microscope and optical microscope were used to examine the wear surface of the MMC.
Table 1 Condition of mechanical alloying Vessel volume (cm3)
750
Mass of aluminum powder (g) Mass of carbon black (g) Charge ratio (mass of grinding balls:mass of powder in mill) Steel ball diameter (mm)
48.5 1.5 6:1
Rotor speed (rev min 1) MA atmosphere Cooling Milling time (h)
Argon Water 20
10
PCA (%)
2
450
Fig. 1. Schematic illustration of wear device.
H. Arik et al. / Materials and Design 27 (2006) 799–804
801
Fig. 2 shows the wear rates of MMC as a function of the applied load. In general with increasing the applied load, wear rate increased, although it was not a proportional to the applied load. Wear rate was found to be very low (0.73 mm3 m 1) at 20 N load. With increasing the load to 50 N a clear increase was observed on the wear rate and which reached to 19.67 mm3 m 1. However, considerable amount of wear rate was observed (187.35 mm3 m 1) on the sample examined at 80 N. This results were similar to those seen by Straffelini and Narayan [2,9] in respect to the load–wear rate although they used different materials. Fig. 3(a) and (b) depicts the SEM and light microscopes images of the perpendicular section of the worn surface at 20 N load. As seen in the pictures the surface of MMC is rough and irregular in appearance. Worn surface of pin was found to be perfectly coated with a mechanical mixed layer (white areas in Fig. 3(a)) of 5–8 lm thickness. Frictional surface of this layer (contact to mounting material in Fig. 3(a)) to counterface appeared flat and smooth. Surface of MMC was rough
but this was filled with the formed layer and flattened. Rough subsurface indicates that wearing occurs on both disc and pin surface before formation of the mechanical mixed layer. The layer formed on the pin surface covered about the 85% of the pin surface (Fig. 4). Energy dispersive X-Ray (EDAX) analysis result of this layer is given in Fig. 5. Although this layer mainly consisted of Al, it contained small amount of Fe, Ti, Cr, Mn and O which came from the counter surface. However, the light brownish appearance of this layer with naked eye indicates that this layer is mainly iron oxide. This result shows that during the wearing of MMC, counter face wears and consequently Fe based oxide film forms on the MMC pin surface. Similar result was reported by Setraffelini et al. [2] who studied the sliding behavior of Al2O3 reinforced Al matrix composite. It is believed that formation of such layer on the pin surface acts as a lubricant and protects the MMC pin against wear and thus reduced the wear rate [1,2]. Figs. 6 and 7 show the microstructures of worn surface of MMC under 50 N load. Here, mechanical deformed layer (MDL) about 20 lm thick formed between the pin and the counter face
Fig. 2. The effect of applied load on wear rate of MMC material.
Fig. 4. FeO layer on the wear surface of pin at 20 N load.
3. Results and discussion
Fig. 3. Cross-section perpendicular to worn surface tested at 20 N load, (a) SEM, (b) optical microscopy.
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H. Arik et al. / Materials and Design 27 (2006) 799–804
Fig. 7. FeO layer on the wear surface of pin at 20 N load. Fig. 5. EDAX analysis of layer material on the pin.
Fig. 6. Cross-section perpendicular to worn surface tested at 50 N load, (a) optical microscopy, (b) SEM.
(Fig. 6(a)). Increasing of high mechanical deformation layer towards the pin surface is clearly visible. Furthermore, a discontinuous layer formed on the surface but it was not as smooth as the Fe oxide layer formed on the surface of sample worn under 20 N. This layer was not continuous (Fig. 6(b)) and consisted of fragments and contained some porosity (Fig. 7). EDAX analyses indicate that this layer mainly consists of Al and C but contained small amount of counterface elements (Fig. 8). The blackish appearance of this layer was attributed to the effect of residual carbon. High deformed pin surface resulted in wear debris which could not completely cover the surface. During experiments, formation of small amount of vibration and noise indicate the interruption of sliding. This may result in the formation of discontinuous Al and C based surface film. For this reason sample tested under 50 N exhibited more severe wear compared to those seen under 20 N. In this case, only small amount of wearing was observed on counter face. However, high amount of wear on the pin surface resulted in the formation of wear debris and discontinues surface film instead of forming FeO based contin-
Fig. 8. EDAX analysis of layer material on the pin.
uous layer. Wear behavior of MMC at 80 N is shown in Figs. 9 and 10. MDL layer about 40 lm in thick is seen in Fig. 9(a) and (b). This layer formed
H. Arik et al. / Materials and Design 27 (2006) 799–804
803
Fig. 9. Cross-section perpendicular to worn surface tested at 80 N load, (a) MDL formation and cracking of MMC on the pin surface, (b) MDL on the pin surface.
Fig. 10. SEM micrographs of worn surfaces at 80 N load.
on MMC pin sometimes contains crack or defects as shown in Fig. 9 with a white arrow. However, wear debris based layer was not visible on this surface. In this loading condition occurring of considerable amount of vibration and noise resulted in an unstable experiment condition. Cracking and spalling of the MDL layer were attributed to this unstable experimental condition. Fig. 10(a) and (b) show the SEM micrographs of worn surface containing deep groves and highly deformed colonized MMC particles. In the case of 50 N load, the worn surface is characterized by the presence of micro-plowing scars parallel to the sliding direction and brittle scales which were prone to detachment. The reason for high wear rate at higher wear load, especially at 80 N, was due to the sliding of surfaces to each other without formation of protective oxide layer. At this load, high deformation occurs on MMC pin surface which resulting the formation of crack or spallation on the heavily work hardened MDL.
4. Conclusion From the present study, the following can be inferred (1) Formation of stable iron based mechanical mixed layer on the surface of Al–Al4C3 composite during the dry sliding at low applied loads resulted in low wear of MMC. (2) At high loads instead of formation of a stable MML, mechanically deformed layer formed on the MMC surface due to high deformation. Due to the cracking or spallation of this layer increased the wear rate considerably.
Acknowledgment The authors thank Gazi University Research Fund for the financial support of this research work (No: 07/2000-06).
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H. Arik et al. / Materials and Design 27 (2006) 799–804
References [1] Venkataraman B, Sundararajan G. Correlation between the characteristics of the mechanically mixed layer and wear behaviour of aluminum, Al-7075 alloy and Al-MMCs. Wear 2000;245:22–38. [2] Straffelini G, Bonollo F, Molinari A, Tiziani A. Influence of matrix hardness on the dry sliding behaviour of 20 vol.% Al2O3-particulate-reinforced 6061 Al metal matrix composite. Wear 1997;211: 192–7. [3] Chu HS, Liu KS, Yeh JW. An in situ composite of Al (graphite, Al4C3) produced by reciprocating extrusion. Mater Sci Eng A 2000;227:25–32. [4] Ozcatalbas Y. Investigation of the machinability behaviour of Al4C3 reinforced Al-based composite produced by
[5]
[6] [7] [8]
[9]
mechanical alloying technique. Compos Sci Technol 2003;63:53–61. Besterci M, Slesar M, Kovac L. Influence of strain rate on fracture of dispersion strengthened Al–Al4C3 systems. Scripta Mater 1997;37:1077–80. Suryanarayana C. Mechanical alloying and milling. Prog Mater Sci 2001;46:1–184. Zhang DL. Processing of advanced materials using high-energy mechanical milling. Prog Mater Sci 2004;49:537–60. Arik H. Production and characterization of in situ Al4C3 reinforced aluminium-based composite produced by mechanical alloying technique. Mater Des 2004;25:31–40. Narayan M, Surappa M, Pramila Bai K. Dry sliding wear of Al alloy 2024-Al2O3 particle metal matrix composites. Wear 1995;181–183:563–70.