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Sliding tribological characteristics of Zr-based bulk metallic glass under lubricated conditions
Intermetallics 18 (2010) 1251e1253
Contents lists available at ScienceDirect
Intermetallics journal homepage: www.elsevier.com/locate/intermet
Short communication
Sliding tribological characteristics of Zr-based bulk metallic glass under lubricated conditions Mustafa Bakkal* Department of Mechanical Engineering, Istanbul Technical University, Istanbul 34437, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 June 2008 Received in revised form 31 January 2010 Accepted 2 February 2010 Available online 19 March 2010
This paper presents the effect of lubricant, SAE EP 90, on tribological properties of Zr-based bulk metallic glass. The coefficient of friction and wear rate values were evaluated for the wide range of applied normal loads (5e40 N) and contact sliding speeds (0.15e1.60 m/s). Wear and friction properties of tribolayers were strongly affected by both parameters throughout the study. Overall average coefficient of friction values were less than 0.1 in the range of study. No sliding induced crystallization was detected by X-Ray analysis. The results of wear characteristics of BMG were also compared with well-known structural materials, AISI 6061-T6 and AISI 304. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: B. Glasses, metallic B. Tribological properties B. Surface properties G. Wear-resistant applications
1. Introduction Due to their unusual mechanical, physical and chemical properties, amorphous alloys are accepted to be promising materials for tribological applications [1]. Earlier tribological tests had been performed on ribbon shape amorphous alloys, due to the requirement of extreme cooling rates for production of bulk form of materials. First results produced promising outcomes for further research. In mid-80s Miyoshi [2] reported that amorphous alloys had higher wear resistance than AISI 304 stainless steel materials. After the discovery of low critical cooling rate amorphous alloys [3,4], it became easier to manufacture in bulk formed samples for more realistic fundamental tribological analysis. The tribological potential of bulk amorphous metals has been under investigation in recent years [1,5e8], most of which focused on wear and friction characteristics of amorphous alloys under dry conditions [1,5,7,8]. However, liquid lubrication conditions are more common for practical engineering applications like gear and engine parts [6]. Selection of accurate lubricant in order to protect precise machine parts in running is one the most crucial steps in engineering design [9]. In recent studies about wear on bulk metallic glasses, microcrack formation was reported in all nano-scratch tests in critical loads [1]. Formation and subsequent peeling-off of oxygen rich tribolayers
* Tel.: þ90 212 2931300/2775; fax: þ90 212 245 0795. E-mail address: [email protected] 0966-9795/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2010.02.003
was defined as the main wear mechanism of Zr-based bulk metallic glass materials during sliding tests by Jin et al. [7]. Fu [5] compared wear characteristics of the same metallic glass material under air and vacuum conditions. According to Fu, vacuum condition causes lower coefficient of friction and less wear. Coefficient of friction range of Zr-based bulk metallic glass material was stated as 0.35e0.45 in dry sliding tests by Parlar et al. [8]. They also stated that Zr-based bulk metallic glass has better friction characteristics than AISI 6061-T6 and AISI 304. The goal of this research is to study the effect of lubricant on wear and friction characteristics of Zr-based bulk metallic glass material under different loading and sliding speed conditions. The bulk metallic glass examined in this study is Zr52.5Ti5Cu17.9Ni14.6Al10 [3], hereafter denoted as BMG. The effect of normal load and sliding speed on the coefficient of friction and wear analysis were presented. Finally, wear analysis results were presented to extract the distinctive wear characteristics of BMG under boundary lubrication regimes. 2. Experimental setup An amorphous Zr-based metallic glass rod 6.35-mm in diameter was produced through the rapid casting technique, detailed elsewhere [8]. The counter surface material was an AISI 8660 water quenched to HV 677 hardness. Ra value of the counter surface was 0.55 mm. Contact surfaces of the test specimen were machined to the same radius of curvature as the counter surface cylinder for better conformity between both surfaces.
M. Bakkal / Intermetallics 18 (2010) 1251e1253
3. Results and discussion 3.1. Sliding tests The coefficient of friction (m) vs. sliding speed (v) results for BMG are shown in Fig. 1. Low m values to some extent are recorded for the duration of the test interval. This result is also suggested by Mang [10] due to the excellent resistance to contact pressure of extreme pressure gear oils. The values of coefficient of friction show linear behavior until 0.5 m/s sliding speed. Under 0.5 m/s sliding speed, m values confirm the independence of sliding speed for all normal forces. Average friction coefficients for different normal forces until 0.5 m/s sliding speed were within the range of 0.01e0.06 and 0.04e0.07. In higher sliding speeds, m values slightly increase e except for 5 and 10 N e and reaches up to 0.09. On the other hand, lower forces, 5 and 10 N, show somehow inconsistent increase on coefficient of friction results. According to Kargelsky [11], normal load and the sliding speed strongly affect the behavior of the lubricant film and any mismatch on these parameters may cause severe wear on the rubbing surfaces. Corresponding to this clarification, lower loading forces lead to unexpected increase in m values in higher sliding speeds. Higher normal loads were more stable m values even in lower sliding speeds. As indicated by Blau [6], m value was 0.20 in condition of 4.95 N applied normal load and 0.25 m/s sliding speed for 10W40 oil. In this study, 0.025 coefficient of friction value were recorded under same condition. As indicated in Blau's paper, different formulation of friction- and wear-modifying additives would be better for metallic glass material. As a consequence of this analysis, formulations of gear oil is more suitable for metallic glass material than that of 10W40 diesel oil. Effectiveness of extreme pressure gear oil lubricant in boundary condition friction is also reported by Mang [10]. According to Mang,
Table 1 Properties of lubricant used in sliding and wear tests.
0,3
BMG - EP90
Coefficient of Friction
Sliding friction and wear tests under lubricated conditions were conducted by using a Plint brand multi-purpose friction and wear tester, with a block-on-ring geometry, according to procedure outlined in ASTM standard G77. A commercially extreme pressure gear oil, EP 90 (OPET Orsa brand) were selected to obtain boundary lubrication conditions during all sliding tests. General properties of lubricant is given in Table 1. Configuration of the experimental setup and a picture of the BMG disc clamping and contact point of the counter surface are given in elsewhere [8]. The frictional force exerted on the test specimen during sliding was measured by a force transducer placed on the pin holder. The force transducer has a load range 200 N with a sensitivity of 2 mV, which is equivalent to 0.1 N maximum measurement error. The experiments were carried out in 20 C environment and 40e50% relative humidity. The wear was quantified by the mass-loss measured using a scale with 0.0001 g accuracy. Worn surface and wear track analysis were carried out on gear oil using lubricated wear test surface. Test sets between 0.15 and 1.60 m/s at seven different sliding speeds and eight different normal loads from 5 to 40 N (in 5 N increments) were selected to study the coefficient of friction of test materials under lubricated conditions. Constant sliding speed, 0.5 m/s, and sliding distance, 100 m, were preferred on wear tests.
0,2 0,15 0,1 0,05
Density at 15 C [kg/lt]
Viscosity at 40 C [cst]
Viscosity Index
Gear Oil-SAE EP90
0.898
197.9
95
0
0,5
1
1,5
2
Sliding Speed (m/s) Fig. 1. The coefficient of friction (m) vs. sliding speed (v) results for BMG under gear oil lubricated condition.
extreme pressure lubricant prevents the metal contacts by means of metal soap formation between surfaces as a slider layer. Fig. 2 presents the relation between the normal load and coefficient of friction for BMG at different sliding speeds. The effect of applied normal loads may be evaluated prior and subsequent to 10 N normal loads due to the entirely different aspect of results under gear oil lubricant conditions in Fig. 2. Various authors also went behind the similar evaluation method [1,12]. Friction values varied in huge intervals in lower normal loads. On the other hand friction results were more consistent in higher normal loads for all sliding speeds. The m values were high in the broader range of 0.06e0.16 at lower normal loads, but then shrink in the range of 0.01e0.08 for the rest of the test interval, as a result of the higher loading conditions. The mismatch between applied normal load and contact sliding speeds lead to that result. According to the general test results, no distinctive effect of normal loads and trend in coefficient of friction values were determined. Although average m values in tests intervals varied, this pattern of behavior matched with common behavior of metals in sliding tests [13], [14].
3.2. Wear tests Fig. 3 presents and compares the wear analysis results of the test materials with two well-known structural materials, Al6061 and SS304, under same loading and lubricated conditions. Wear rate of BMG surface increases until 30 N normal loads. After that point, wear rate diminishes about 10% and maintains its value for the rest of the test. Other two test materials were alike in respect of wear characteristics with each other under test conditions. Wear rate values for Al6061 and SS304 were almost the same during the test interval for the higher normal loads. On the other
0,3 BMG - EP90 0,25
0,15 m/s 0,30 m/s
0,2
0,60 m/s
0,15
0,90 m/s
0,1
1,20 m/s
0,05
1,40 m/s
0
Lubricant
5N 10 N 15 N 20 N 25 N 30 N 35 N 40 N
0,25
0
Coefficient of Friction
1252
1,60 m/s 0
10
20 Normal Force (N)
30
40
Fig. 2. The coefficient of friction (m) vs. normal load (N) results for BMG under gear oil lubricated condition.
M. Bakkal / Intermetallics 18 (2010) 1251e1253
Wear Rate (gr/Nm.m)x10 -6
60
Acknowledgements
EP 90 BMG
40
The author would like to thank Dr. C.T. Liu for providing the bulk metallic glass sample and Dr. Zeynep Parlar for helping with the experiments.
Al 6061
20
SS 304 0
1253
0
10
20 Normal Load (N)
30
40
Fig. 3. Wear rate vs. normal load for BMG, Al6061 and SS304 (0.5 m/s sliding speed), (a) EP90, gear oil used wear test results show opposite wear behavior between BMG and structural materials.
hand, SS304 wear rate values were slightly higher than Al6061 due to the higher chemical affinity of steel-to-steel contact [14]. Similar wear characteristics for both materials were reported earlier under dry sliding conditions [8]. X-ray analysis result of worn surface indicated that there is no wear induced crystallization trace. Two broad peaks at 38 and 64 also confirmed fully amorphous structure. 4. Concluding remarks In this study sliding tribological characteristics of Zr-based bulk metallic glass under boundary lubrication conditions were investigated. Wear and friction properties of tribolayers were strongly affected by both parameters throughout the study. Lower normal loads and higher sliding speeds always led to higher friction coefficients under lubrication conditions. Critical normal load was determined as 10 N.
References [1] Wang JG, Choi BW, Nieh TG, Liu CT. Nano-scratch behavior of a bulk Zre10Ale5Tie17.9Cue14.6Ni amorphous alloy. J Mater Res 2000;15 (4):913e22. [2] Miyoshi K, Buckley DH. Friction and wear of some ferrous-base metallic glasses. Tribol Trans:295e304, http://www.informaworld.com/smpp/ title~content¼t713669620~db¼all~tab¼issueslist~branches¼27-v2727(4); 1984. [3] Liu CT, Heatherly L, Easton DS, Carmichael CA, Schneibel JH, Chen CH, et al. Test environments and mechanical properties of Zr-base bulk amorphous alloys. Metall Mater Trans 1998;A29:1811e20. [4] Peker A, Johnson WL. A highly processable metallic glass: Zr41Ti14Cu125Ni10Be22.5. Appl Phys Lett 1993;63:2342e4. [5] Fu X-Y, Kasai T, Falk ML, Rigney DA. Sliding behavior of metallic glass e part I. Experimental investigations. Wear 2001;250:409e19. [6] Blau PJ. Friction and wear of a Zr-based amorphous metal alloy under dry and lubricated conditions. Wear 2001;250:431e4. [7] Jin HW, Ayer R, Koo JY, Raghavan R, Ramamurty U. Reciprocating wear mechanisms in a Zr-based bulk metallic glass. J Mater Res 2007;22 (2):264e73. [8] Parlar Z, Bakkal M, Shih AJ. Sliding tribological characteristics of Zr-based bulk metallic glass. Intermetallics 2008;16(1):34e41. [9] Bayer RG. Wear analysis for engineers. HNB Publishing; 2001. [10] Mang T, Dresel W. Lubricants and lubrication. Wiley-VCH; 2001. [11] Kargelsky IV, Alisin VV. Tribology-lubriction, friction, and wear. Professional Engineering Publishing; 2001. [12] Chen M, Kato K, Adachi K. The comparisons of sliding speed and normal load effect on friction coefficients of self-mated Si3N4 and SiC under water lubrication. Tribol Int 2002;35(3):129e35. [13] Bhushan B. Introduction to tribology. New York: John Wiley & Sons; 2002. [14] Jisheng E, Gawne DT. Influence of lubrication regime on the sliding wear behavior of an alloy steel. Wear 1997;211:1e8.
Contents lists available at ScienceDirect
Intermetallics journal homepage: www.elsevier.com/locate/intermet
Short communication
Sliding tribological characteristics of Zr-based bulk metallic glass under lubricated conditions Mustafa Bakkal* Department of Mechanical Engineering, Istanbul Technical University, Istanbul 34437, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history: Received 18 June 2008 Received in revised form 31 January 2010 Accepted 2 February 2010 Available online 19 March 2010
This paper presents the effect of lubricant, SAE EP 90, on tribological properties of Zr-based bulk metallic glass. The coefficient of friction and wear rate values were evaluated for the wide range of applied normal loads (5e40 N) and contact sliding speeds (0.15e1.60 m/s). Wear and friction properties of tribolayers were strongly affected by both parameters throughout the study. Overall average coefficient of friction values were less than 0.1 in the range of study. No sliding induced crystallization was detected by X-Ray analysis. The results of wear characteristics of BMG were also compared with well-known structural materials, AISI 6061-T6 and AISI 304. Ó 2010 Elsevier Ltd. All rights reserved.
Keywords: B. Glasses, metallic B. Tribological properties B. Surface properties G. Wear-resistant applications
1. Introduction Due to their unusual mechanical, physical and chemical properties, amorphous alloys are accepted to be promising materials for tribological applications [1]. Earlier tribological tests had been performed on ribbon shape amorphous alloys, due to the requirement of extreme cooling rates for production of bulk form of materials. First results produced promising outcomes for further research. In mid-80s Miyoshi [2] reported that amorphous alloys had higher wear resistance than AISI 304 stainless steel materials. After the discovery of low critical cooling rate amorphous alloys [3,4], it became easier to manufacture in bulk formed samples for more realistic fundamental tribological analysis. The tribological potential of bulk amorphous metals has been under investigation in recent years [1,5e8], most of which focused on wear and friction characteristics of amorphous alloys under dry conditions [1,5,7,8]. However, liquid lubrication conditions are more common for practical engineering applications like gear and engine parts [6]. Selection of accurate lubricant in order to protect precise machine parts in running is one the most crucial steps in engineering design [9]. In recent studies about wear on bulk metallic glasses, microcrack formation was reported in all nano-scratch tests in critical loads [1]. Formation and subsequent peeling-off of oxygen rich tribolayers
* Tel.: þ90 212 2931300/2775; fax: þ90 212 245 0795. E-mail address: [email protected] 0966-9795/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.intermet.2010.02.003
was defined as the main wear mechanism of Zr-based bulk metallic glass materials during sliding tests by Jin et al. [7]. Fu [5] compared wear characteristics of the same metallic glass material under air and vacuum conditions. According to Fu, vacuum condition causes lower coefficient of friction and less wear. Coefficient of friction range of Zr-based bulk metallic glass material was stated as 0.35e0.45 in dry sliding tests by Parlar et al. [8]. They also stated that Zr-based bulk metallic glass has better friction characteristics than AISI 6061-T6 and AISI 304. The goal of this research is to study the effect of lubricant on wear and friction characteristics of Zr-based bulk metallic glass material under different loading and sliding speed conditions. The bulk metallic glass examined in this study is Zr52.5Ti5Cu17.9Ni14.6Al10 [3], hereafter denoted as BMG. The effect of normal load and sliding speed on the coefficient of friction and wear analysis were presented. Finally, wear analysis results were presented to extract the distinctive wear characteristics of BMG under boundary lubrication regimes. 2. Experimental setup An amorphous Zr-based metallic glass rod 6.35-mm in diameter was produced through the rapid casting technique, detailed elsewhere [8]. The counter surface material was an AISI 8660 water quenched to HV 677 hardness. Ra value of the counter surface was 0.55 mm. Contact surfaces of the test specimen were machined to the same radius of curvature as the counter surface cylinder for better conformity between both surfaces.
M. Bakkal / Intermetallics 18 (2010) 1251e1253
3. Results and discussion 3.1. Sliding tests The coefficient of friction (m) vs. sliding speed (v) results for BMG are shown in Fig. 1. Low m values to some extent are recorded for the duration of the test interval. This result is also suggested by Mang [10] due to the excellent resistance to contact pressure of extreme pressure gear oils. The values of coefficient of friction show linear behavior until 0.5 m/s sliding speed. Under 0.5 m/s sliding speed, m values confirm the independence of sliding speed for all normal forces. Average friction coefficients for different normal forces until 0.5 m/s sliding speed were within the range of 0.01e0.06 and 0.04e0.07. In higher sliding speeds, m values slightly increase e except for 5 and 10 N e and reaches up to 0.09. On the other hand, lower forces, 5 and 10 N, show somehow inconsistent increase on coefficient of friction results. According to Kargelsky [11], normal load and the sliding speed strongly affect the behavior of the lubricant film and any mismatch on these parameters may cause severe wear on the rubbing surfaces. Corresponding to this clarification, lower loading forces lead to unexpected increase in m values in higher sliding speeds. Higher normal loads were more stable m values even in lower sliding speeds. As indicated by Blau [6], m value was 0.20 in condition of 4.95 N applied normal load and 0.25 m/s sliding speed for 10W40 oil. In this study, 0.025 coefficient of friction value were recorded under same condition. As indicated in Blau's paper, different formulation of friction- and wear-modifying additives would be better for metallic glass material. As a consequence of this analysis, formulations of gear oil is more suitable for metallic glass material than that of 10W40 diesel oil. Effectiveness of extreme pressure gear oil lubricant in boundary condition friction is also reported by Mang [10]. According to Mang,
Table 1 Properties of lubricant used in sliding and wear tests.
0,3
BMG - EP90
Coefficient of Friction
Sliding friction and wear tests under lubricated conditions were conducted by using a Plint brand multi-purpose friction and wear tester, with a block-on-ring geometry, according to procedure outlined in ASTM standard G77. A commercially extreme pressure gear oil, EP 90 (OPET Orsa brand) were selected to obtain boundary lubrication conditions during all sliding tests. General properties of lubricant is given in Table 1. Configuration of the experimental setup and a picture of the BMG disc clamping and contact point of the counter surface are given in elsewhere [8]. The frictional force exerted on the test specimen during sliding was measured by a force transducer placed on the pin holder. The force transducer has a load range 200 N with a sensitivity of 2 mV, which is equivalent to 0.1 N maximum measurement error. The experiments were carried out in 20 C environment and 40e50% relative humidity. The wear was quantified by the mass-loss measured using a scale with 0.0001 g accuracy. Worn surface and wear track analysis were carried out on gear oil using lubricated wear test surface. Test sets between 0.15 and 1.60 m/s at seven different sliding speeds and eight different normal loads from 5 to 40 N (in 5 N increments) were selected to study the coefficient of friction of test materials under lubricated conditions. Constant sliding speed, 0.5 m/s, and sliding distance, 100 m, were preferred on wear tests.
0,2 0,15 0,1 0,05
Density at 15 C [kg/lt]
Viscosity at 40 C [cst]
Viscosity Index
Gear Oil-SAE EP90
0.898
197.9
95
0
0,5
1
1,5
2
Sliding Speed (m/s) Fig. 1. The coefficient of friction (m) vs. sliding speed (v) results for BMG under gear oil lubricated condition.
extreme pressure lubricant prevents the metal contacts by means of metal soap formation between surfaces as a slider layer. Fig. 2 presents the relation between the normal load and coefficient of friction for BMG at different sliding speeds. The effect of applied normal loads may be evaluated prior and subsequent to 10 N normal loads due to the entirely different aspect of results under gear oil lubricant conditions in Fig. 2. Various authors also went behind the similar evaluation method [1,12]. Friction values varied in huge intervals in lower normal loads. On the other hand friction results were more consistent in higher normal loads for all sliding speeds. The m values were high in the broader range of 0.06e0.16 at lower normal loads, but then shrink in the range of 0.01e0.08 for the rest of the test interval, as a result of the higher loading conditions. The mismatch between applied normal load and contact sliding speeds lead to that result. According to the general test results, no distinctive effect of normal loads and trend in coefficient of friction values were determined. Although average m values in tests intervals varied, this pattern of behavior matched with common behavior of metals in sliding tests [13], [14].
3.2. Wear tests Fig. 3 presents and compares the wear analysis results of the test materials with two well-known structural materials, Al6061 and SS304, under same loading and lubricated conditions. Wear rate of BMG surface increases until 30 N normal loads. After that point, wear rate diminishes about 10% and maintains its value for the rest of the test. Other two test materials were alike in respect of wear characteristics with each other under test conditions. Wear rate values for Al6061 and SS304 were almost the same during the test interval for the higher normal loads. On the other
0,3 BMG - EP90 0,25
0,15 m/s 0,30 m/s
0,2
0,60 m/s
0,15
0,90 m/s
0,1
1,20 m/s
0,05
1,40 m/s
0
Lubricant
5N 10 N 15 N 20 N 25 N 30 N 35 N 40 N
0,25
0
Coefficient of Friction
1252
1,60 m/s 0
10
20 Normal Force (N)
30
40
Fig. 2. The coefficient of friction (m) vs. normal load (N) results for BMG under gear oil lubricated condition.
M. Bakkal / Intermetallics 18 (2010) 1251e1253
Wear Rate (gr/Nm.m)x10 -6
60
Acknowledgements
EP 90 BMG
40
The author would like to thank Dr. C.T. Liu for providing the bulk metallic glass sample and Dr. Zeynep Parlar for helping with the experiments.
Al 6061
20
SS 304 0
1253
0
10
20 Normal Load (N)
30
40
Fig. 3. Wear rate vs. normal load for BMG, Al6061 and SS304 (0.5 m/s sliding speed), (a) EP90, gear oil used wear test results show opposite wear behavior between BMG and structural materials.
hand, SS304 wear rate values were slightly higher than Al6061 due to the higher chemical affinity of steel-to-steel contact [14]. Similar wear characteristics for both materials were reported earlier under dry sliding conditions [8]. X-ray analysis result of worn surface indicated that there is no wear induced crystallization trace. Two broad peaks at 38 and 64 also confirmed fully amorphous structure. 4. Concluding remarks In this study sliding tribological characteristics of Zr-based bulk metallic glass under boundary lubrication conditions were investigated. Wear and friction properties of tribolayers were strongly affected by both parameters throughout the study. Lower normal loads and higher sliding speeds always led to higher friction coefficients under lubrication conditions. Critical normal load was determined as 10 N.
References [1] Wang JG, Choi BW, Nieh TG, Liu CT. Nano-scratch behavior of a bulk Zre10Ale5Tie17.9Cue14.6Ni amorphous alloy. J Mater Res 2000;15 (4):913e22. [2] Miyoshi K, Buckley DH. Friction and wear of some ferrous-base metallic glasses. Tribol Trans:295e304, http://www.informaworld.com/smpp/ title~content¼t713669620~db¼all~tab¼issueslist~branches¼27-v2727(4); 1984. [3] Liu CT, Heatherly L, Easton DS, Carmichael CA, Schneibel JH, Chen CH, et al. Test environments and mechanical properties of Zr-base bulk amorphous alloys. Metall Mater Trans 1998;A29:1811e20. [4] Peker A, Johnson WL. A highly processable metallic glass: Zr41Ti14Cu125Ni10Be22.5. Appl Phys Lett 1993;63:2342e4. [5] Fu X-Y, Kasai T, Falk ML, Rigney DA. Sliding behavior of metallic glass e part I. Experimental investigations. Wear 2001;250:409e19. [6] Blau PJ. Friction and wear of a Zr-based amorphous metal alloy under dry and lubricated conditions. Wear 2001;250:431e4. [7] Jin HW, Ayer R, Koo JY, Raghavan R, Ramamurty U. Reciprocating wear mechanisms in a Zr-based bulk metallic glass. J Mater Res 2007;22 (2):264e73. [8] Parlar Z, Bakkal M, Shih AJ. Sliding tribological characteristics of Zr-based bulk metallic glass. Intermetallics 2008;16(1):34e41. [9] Bayer RG. Wear analysis for engineers. HNB Publishing; 2001. [10] Mang T, Dresel W. Lubricants and lubrication. Wiley-VCH; 2001. [11] Kargelsky IV, Alisin VV. Tribology-lubriction, friction, and wear. Professional Engineering Publishing; 2001. [12] Chen M, Kato K, Adachi K. The comparisons of sliding speed and normal load effect on friction coefficients of self-mated Si3N4 and SiC under water lubrication. Tribol Int 2002;35(3):129e35. [13] Bhushan B. Introduction to tribology. New York: John Wiley & Sons; 2002. [14] Jisheng E, Gawne DT. Influence of lubrication regime on the sliding wear behavior of an alloy steel. Wear 1997;211:1e8.