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Abrasive wear behaviour of Fe, Co and Ni based metallic glasses
Wear 258 (2005) 217–224
Abrasive wear behaviour of Fe, Co and Ni based metallic glasses Braham Prakash∗ Lule˚a University of Technology, Lule˚a SE-97187, Sweden Received 22 December 2003 Available online 13 October 2004
Abstract Metallic glasses are a different category of materials that are characterized by their amorphous structure and metallic bonds. Owing to their disordered structure, metallic glasses possess several unique properties that make them attractive for tribological applications. This paper deals with an in depth investigation into the two-body abrasive wear behaviour of several compositions of Fe, Co and Ni based metallic glasses while rubbing against metallographic grade SiC abrasive papers. Identical studies have also been carried out on crystalline cold-rolled AISI 304 stainless steel for comparison. Two-body abrasive wear results indicate that wear characteristics of different metallic glasses are marginally superior or similar to that of stainless steel. The wear in Ni based metallic glass MBF 35 is significantly higher than that in stainless steel. This is inspite of the fact that metallic glasses are considerably harder than stainless steel. Scratch indentation and acoustic emission studies (AE) were carried out with a view to understanding the mechanisms of occurrence of two-body abrasive wear in metallic glasses. Scratched surfaces of metallic glasses indicated the presence of arc-like features that in some cases extend well beyond the scratched groove edges. In the case of Ni based metallic glass MBF 35, cracking on the surface was clearly visible. In stainless steel, the grooves formed were neatly cut out and were free from the arc-like features. During scratch tests on metallic glasses, AE signals were obtained but no AE signals were generated during scratch tests on steel. Presence of arc-like features on scratched surfaces in metallic glasses are tensile micro-cracks formed due to brittle fracture owing to their poor ductility in tension. These results revealed that the abrasive wear of metallic glasses is not commensurate to their high hardness and occurrence of micro-cracking results in their poor abrasive wear resistance. © 2004 Elsevier B.V. All rights reserved. Keywords: Abrasive wear; Scratch tests; Acoustic emission; Metallic glasses
1. Introduction Metallic glasses are a different category of materials that are characterized by their amorphous structure and interatomic metallic bonds. Owing to their disordered or amorphous structure, metallic glasses possess some unique characteristics like high magnetic permeability, electrical resistivity, hardness and tensile strength, resistance to gamma radiation damage and corrosion [1]. A combination of these properties in metallic glasses makes them attractive for various technological applications. Their high hardness coupled with high strength and corrosion resistance indicates their potential in tribological applications. The magnetic, electri∗
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0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.09.010
cal, mechanical and chemical properties of metallic glasses have been studied extensively but only a few studies have been undertaken concerning their tribological properties. The interest in tribological properties of metallic glasses is in view of their potential applications as audio/video recording heads, foil bearings, electric razors and razor blades [2–3]. The sliding friction and wear characteristics of various metallic glasses have been studied by Miyoshi et al. and several other researchers [4–9]. Recently, Greer et al. have reviewed the wear resistance of amorphous metallic alloys and related materials [10]. The two-body abrasive wear studies have earlier been carried out by Boswell et al. and others on different metallic glasses [11–15]. Most of these studies have been aimed at measuring the abrasive wear resistance of different metallic glasses. In some cases the mechanisms of two-body abra-
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B. Prakash / Wear 258 (2005) 217–224
Table 1 Experimental materials Alloy designation
Nominal composition (at.%)
Thickness (m)
Density (g/cm3 )
Crystallization temperature (◦ C)
Vickers microhardness at 100 g
Fe based metallic glasses 2605 SC 2605 S2 2826 MB 2605 S3A 2605 CO
Fe81 B13.5 Si3.5 C2 Fe78 B13 Si9 Fe40 Ni38 Mo4 B18 Fe77 Cr2 B16 Si5 Fe66 Co18 B15 Si1
32 25 20 22 23
7.32 7.18 8.02 7.29 7.56
480 550 410 535 430
858a 851a 885a 858a 825a
Co based metallic glass 2714 A
Co66 Fe4 Ni1 B14 Si15
20
7.6
550
888a
Ni based metallic glass MBF 50 MBF 35
Ni72.5 Cr18.5 Si7.5 B1.5 Ni91 Si7 B2
40 32
7.85 6.59
– –
790a 776a
Stainless steel sheet (cold-rolled) AISI 304 Standard a
100
520
These hardness values listed here were obtained from the bright side of metallic glass ribbons.
sion process have also been analyzed. These investigations are mostly material specific and no clear evidence of occurrence of a particular mechanism has been presented. It is thus felt that there is a need to characterize the wear behaviour of some of the commonly available metallic glasses and understand the mechanisms that contribute towards occurrence of two-body abrasive wear. In this work, two-body abrasive wear characteristics of different Fe, Co and Ni based metallic glasses have been studied under unidirectional as well as reciprocating sliding conditions. Further investigations aimed at identifying the contributing mechanisms towards occurrence of two-body abrasive wear process in Fe, Co and Ni based metallic glasses have also been undertaken by employing single pass scratch tests. Single pass scratch tests simulate the abrading action of a hard asperity or hard particles against the counterface material. Identical studies have been conducted on 304 stainless steel to compare the wear behaviour of metallic glasses visa-vis crystalline 304 stainless steel. AISI 304 stainless steel was chosen as a reference material as the idea was to have a crystalline Fe based material available in the form of thin sheets as majority of metallic glasses were Fe based in the form of thin ribbons. 2. Experimental materials Several alloy compositions of Fe, Co and Ni based metallic glasses have been investigated for their wear behaviour in two-body abrasive wear situations. The experimental metallic glass materials used in these studies were 20–40 m thick ribbons. The crystalline material samples were cut out from thin sheet of cold-rolled stainless steel (AISI 304). The designation, nominal composition and some physical and mechanical properties of different materials are listed in Table 1. Metallographic grade SiC abrasive papers of different grit sizes were used in two-body abrasion experiments.
It has earlier been reported that the dull side of metallic glass ribbons are harder than the bright side. It has also been found that the average surface roughness values of the bright sides of most metallic glass ribbons are slightly higher than that of the dull side. For these reasons, all tests have been carried out by using the bright sides of all metallic glass ribbons so as to obtain their minimum wear performance.
3. Test techniques and experimental work The two-body abrasive wear characteristics of different materials were studied under unidirectional and reciprocating sliding conditions. Two-body abrasive wear studies under reciprocating sliding conditions were conducted on a Suga abrasion tester while those under unidirectional sliding conditions were conducted on CSEM Revetest scratch adhesion tester. These testers were suitably adapted to enable tests on metallic glass ribbons and thin stainless steel sheets. A Revetest scratch adhesion tester incorporating acoustic emission detector was also utilized for fundamental investigations into the twobody abrasion process. These test techniques along with the experimental approach adopted are briefly described below. 3.1. Two-body abrasive wear studies during reciprocating sliding conditions For two-body abrasive wear studies during reciprocating sliding conditions, glass ribbons were cut into thin rectangular sheets of 40 mm × 25 mm and bonded to an Al alloy plate by using Loctite 415 adhesive. The abrasive papers were cut into 12 mm × 158 mm sheets and fixed to the circumferential surface of an Al alloy wheel (50 mm diameter) by means of double sided adhesive tape. Two-body abrasion studies on different materials were carried out by loading the abrasive
B. Prakash / Wear 258 (2005) 217–224
219
Fig. 2. Test configuration for two-body abrasive wear studies under unidirectional sliding conditions by using Revetest scratch adhesion tester. Fig. 1. Test configuration for two-body abrasive wear studies under reciprocating sliding conditions by using Suga abrasion tester.
paper wheel against the reciprocating flat surface of the test material in a line contact configuration (Fig. 1). The abrasive paper wheel turns by 0.9◦ angle at the end of each stroke to bring fresh abrasive paper in contact with the test material with a view to eliminate the influence of degradation of abrasive paper during rubbing on abrasive wear results. A constant velocity of 0.04 m/s and stroke length of 30 mm were employed in all experiments. The influence of sliding distance, load and abrasive grit size on abrasive wear behaviour of different metallic glasses and 304 stainless steel have been investigated. Tests were conducted up to a maximum sliding distance of 120 m and at loads of 1, 3, 5 and 7 N, respectively. SiC abrasive papers of #150, #220, #280, #320 and #400 mesh sizes were used to study the abrasive particle size effect on abrasive wear in two-body abrasion. 3.2. Two-body abrasive wear studies during unidirectional sliding conditions For two-body abrasive wear studies under unidirectional sliding conditions, metallic glass ribbons and stainless steel thin sheets were cut into small rectangular sheets of dimensions 16 mm × 9 mm. They were then fixed to the curved surface of the specimen holder by using Loctite 415 adhesive. The specimen holder with the test material on its curved surface was then mounted on the scratch adhesion tester in place of Rockwell C indenter. SiC abrasive papers of different grit sizes were cut into rectangular sheets of dimensions 60 mm × 30 mm. They were fixed to the flat surface of an Al alloy plate by a double-sided adhesive tape. This Al plate with abrasive paper on its top surface was then clamped to the specimen table of the scratch adhesion tester. The test configuration for two-body abrasive wear studies by using scratch adhesion tester is shown in Fig. 2. Test material samples were loaded against the abrasive paper at various test loads (10–40 N) and rubbed against it at a speed of 10 mm/min. A stroke of 12 mm was used in all experiments. At the completion of each stroke, the position of abrasive paper was shifted slightly with a view to bring the fresh abrasive paper surface for rubbing against the test specimen. This ensured that rubbing during two abrasion process always occurred against the fresh abrasive paper surface and
the influence of damaged abrasive paper on wear results is eliminated. In two-body abrasive wear studies under unidirectional as well as reciprocating sliding conditions; three to five experiments were repeated to ensure good reproducibility of wear results. 3.3. SEM examination of worn surfaces The worn surfaces of metallic glass and stainless steel specimens from reciprocating as well as unidirectional sliding tests were examined by using a scanning electron microscope (SEM) with a view to understanding the wear mechanisms. 3.4. Scratch indentation and acoustic emission (AE) studies Revetest scratch adhesion tester was also employed for investigations into the two-body abrasive wear process of metallic glasses and stainless steel by employing the test configuration shown in Fig. 3. These tests involved scratching the specimen surface with a Rockwell C indenter at a constant load. A resonant AE transducer (type 8313, 200 KHz, B&K) provides the AE signal during scratch indentation tests. Metallic glass ribbons and stainless steel thin sheets were cut and bonded to steel disc surfaces by using an adhesive. Scratches on test samples were generated at loads of 10, 20, 30 and 40 N. A sliding velocity of 10 mm/min and scratch length of 12 mm were used in all the tests. The scratched surfaces were examined by using scanning electron microscopy
Fig. 3. Test configuration for scratch indentation tests by using Revetest scratch adhesion tester.
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Fig. 4. Specific wear of Fe, Co based metallic glasses and stainless steel as a function of sliding distance during two-body abrasion under reciprocating conditions (load: 5 N; sliding velocity: 0.04 m/s; SiC abrasive paper: #400).
(SEM) technique to characterize the mode of surface damage.
4. Results and discussion The abrasive wear characteristics of different metallic glasses and 304 stainless steel have been obtained for reciprocating sliding and unidirectional sliding conditions. Further, scratch indentation tests have also been carried out with a view to obtaining an insight into occurrence of two-body abrasive wear in metallic glasses vis-a-vis 304 stainless steel. Some of the salient results from all these studies have been described below. 4.1. Two-body abrasive wear under reciprocating sliding conditions The specific wear results of metallic glasses and stainless steel as a function of sliding distance are given in Figs. 4 and 5. The specific wear in Fe and Co based metallic glasses is somewhat higher (∼0.7 × 10−2 mm3 /N m) during the initial sliding distance of 24 m and thereafter it becomes almost constant at ∼0.5 × 10−2 to 0.6 × 10−2 mm3 /N m (Fig. 4). In Ni
Fig. 5. Specific wear of Ni based metallic glasses and stainless steel as a function of sliding distance during two-body abrasion under reciprocating conditions (load: 5 N; sliding velocity: 0.04 m/s; SiC abrasive paper: #400).
Fig. 6. Specific wear of Fe, Co based metallic glasses and stainless steel as a function of load during two-body abrasion under reciprocating sliding conditions (sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive paper: #400).
based metallic glasses, specific wear is almost constant as a function of sliding distance with Ni based alloy MBF 35 showing higher wear (∼0.8 × 10−2 mm3 /N m) as compared to MBF 50 Ni based metallic glass (∼0.6 × 10−2 mm3 /N m), Fig. 5. The overall wear in 304 stainless steel is relatively higher, 1.1 × 10−2 mm3 /N m during the initial sliding distance of 24 m and then it gradually decreases to ∼0.7 × 10−2 mm3 /N m. The increase in load in two-body abrasion under reciprocating sliding conditions also results in an increase in wear of metallic glasses and the 304 stainless steel. However, the specific wear results as function of load did not indicate any clear trend as can be seen from Figs. 6 and 7. The effect of abrasive grit size on specific wear of different metallic glasses during two-body abrasion under reciprocating sliding conditions is also anomalous and does not indicate any particular trend as can be seen from Fig. 8. 4.2. Abrasive wear under unidirectional sliding conditions A comparison of specific wear at a load of 20 N after 18 rubbing strokes for different metallic glasses and cold-rolled 304 stainless steel have been made in Fig. 9. It can be seen
Fig. 7. Specific wear of Ni based metallic glasses and stainless steel as a function of load during two-body abrasion under reciprocating sliding conditions (sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive paper: #400).
B. Prakash / Wear 258 (2005) 217–224
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Fig. 8. Specific wear of Fe, Co based metallic glasses and stainless steel as a function of abrasive grit size in two-body abrasion under reciprocating sliding conditions (load: 5 N; sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive paper: #400).
that specific wear in most metallic glasses (except Ni based alloy MBF 35) is ∼1.0 × 10−2 to 1.5 × 10−2 mm3 /N m. The specific wear of 304 stainless steel is ∼1.5 × 10−3 mm3 /N m. The specific wear of Ni based MBF 35 is ∼2.1 × 10−2 mm3 /N m and is higher as compared to other metallic glasses and 304 stainless steel. The wear of most Fe and Co based metallic glasses is lower than that of 304 stainless steel. Overall, the abrasive wear results under unidirectional sliding conditions indicate that the wear behaviour of various metallic glasses and stainless steel is quite similar to that obtained under reciprocating sliding conditions. The effect of abrasive particle size on wear of metallic glasses under unidirectional sliding conditions is quite anomalous as has been the case in reciprocating conditions and no clear trend has been observed. 4.3. SEM observation of worn surfaces The worn surfaces of metallic glass and stainless steel specimens from reciprocating as well as unidirectional sliding tests were analyzed by using scanning electron microscope (SEM). Typical SEM micrographs of worn surfaces of
Fig. 9. Comparative specific wear of different metallic glasses and 304 stainless steel in two-body abrasion under unidirectional conditions (load: 20 N; sliding velocity: 10 mm/min; sliding distance: 0.216 m; SiC abrasive grit size: #400).
Fig. 10. SEM micrograph of worn surface of 2826 MB metallic glass from two-body abrasion studies under reciprocating sliding conditions (load: 7 N; sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive grit size: #400).
2826 MB metallic glass and 304 stainless steel specimens are shown in Figs. 10 and 11, respectively. The microcutting action is clearly evident in both metallic glass and stainless steel. Further, in stainless steel, the microcutting is accompanied by significant microploughing action. However, in the case of metallic glass specimen, some spalling, possibly owing to cracking of material at the wear groove edges can be clearly seen. The precise cause of this damage is not clear from the SEM examination. 4.4. Scratch indentation and acoustic emission measurement results The two-body abrasive wear results presented above indicate that the wear characteristics of most metallic glasses are only marginally superior to that of crystalline 304 stainless
Fig. 11. SEM micrograph of worn surface of 304 stainless steel from twobody abrasion studies under reciprocating sliding conditions (load: 7 N; sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive grit size: #400).
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Fig. 12. Specific wear of different metallic glasses and stainless steel vs. Vickers microhardness (load: 20 N; sliding velocity: 10 mm/min; sliding distance: 0.216 m; SiC abrasive grit size: #400).
and are not commensurate with their high hardness. It can be clearly seen from Fig. 12 that specific wear rates of different metallic glasses do not indicate a clear trend with respect to their hardness. Further, the SEM micrograph of metallic glass worn surfaces have indicated some kind of cracking/spalling type of damage (Fig. 10) but its cause is not clear. The scratch indentation and acoustic emission studies have been mainly aimed at understanding the mechanisms contributing towards two-body abrasive wear in metallic glasses. These studies were carried out on different Fe, Co and Ni based metallic glasses but only some representative results have been presented here. The SEM micrograph of the scratched surface of Fe based metallic glass 2826 MB as shown in Fig. 13 is characterized by arc-like features which extend well beyond the groove edges. In some cases, complete cracking of metallic glass material (MBF 50 Ni based metallic glass) has also been observed (Fig. 14). The arc-like features in metallic glasses are tensile microcracks formed due to brittle fracture and are similar to those
Fig. 13. SEM micrograph showing the tensile micro-cracks on scratched surface of Fe based Metglas 2826 MB from scratch indentation test at 40 N load.
Fig. 14. SEM micrograph showing cracking on scratch surface of Ni based Metglas MBF 50 from scratch indentation test at 30 N load.
seen in brittle solids such as glasses and ceramics. During scratch indentation, the stress system is quite complex due to the action of normal and tangential forces. The maximum tensile stress occurs at the trailing edge of the indenter. If this maximum tensile stress exceeds the ultimate strength of the material, tensile micro-cracks are formed. The tensile microcracks have been observed in all the metallic glasses even at the lowest test load of 10 N whereas no such cracks have been observed in 304 stainless steel even at 50 N load. The formation of tensile micro-cracks can be attributed to low ductility of metallic glasses in tension. Scoring marks in the direction of sliding and some material pileup ahead of the indenter at the end of the sliding stroke are also seen indicating the possibility of some microcutting and microploughing action. In stainless steel, the grooves formed are neatly cut out and are completely free from the arc-like features or microcracks (Fig. 15), which were observed on the scratched surfaces of metallic glasses. The presence of some material flow,
Fig. 15. SEM micrograph showing the scratched surface of 304 stainless steel from scratch indentation test at 50 N load.
B. Prakash / Wear 258 (2005) 217–224
Fig. 16. AE intensity during scratching of Fe based Metglas 2826 MB at 40 N load.
shear lips and material pile up at the end of sliding stroke are however seen in stainless steel indicating the occurrence of microcutting and microploughing action. AE measurements also indicated the distinct behaviour of metallic glasses during scratch indentation vis-a-vis 304 stainless steel. The results show that AE signals are obtained during scratch tests on all metallic glasses (Fig. 16) but in the case of stainless steel no AE signals are generated even at the highest test load (Fig. 17). Also, in the case of metallic glasses, the AE signal intensity increased with an increase in load. The generation of AE signals during scratch indentation is indicative of formation of cracks. Therefore the generation of AE signals during scratch tests on metallic glasses is due to the formation of tensile micro-cracks. In scratch tests on 304 stainless steel, no micro-cracks have been observed and accordingly no AE signals are generated. In actual two-body abrasive wear, each hard abrasive wear particle acts as an indenter. So the metallic glass material surface is subjected to indentation by several hard abrasive particles thereby forming a network of micro-cracks during sliding. Some of these adjoining micro-cracks join and even-
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tually result in material removal. The combined action of micro-cracking along with microcutting and microploughing action is attributed to high abrasive wear of metallic glasses despite their high hardness. The scratch indentation studies and subsequent examination of scratched surfaces have clearly indicated that microcutting, microploughing (although to a smaller extent) and micro-cracking are the important mechanisms that contribute towards occurrence of two-body abrasive wear in metallic glasses. On the other hand, the material removal mechanism during two-body abrasive wear in crystalline 304 stainless is primarily a result of microcutting and microploughing action. It may be pertinent to point out that some scratch indentation and AE tests were also conducted on crystalline AISI 52100 bearing steel (hardness ∼1030 HV at 100 g load) which is harder than all the metallic glass specimens. The behaviour of AISI 52100 bearing steel was quite similar to that of crystalline 304 stainless steel as no micro-cracks could be seen on the scratched surfaces inspite of its high hardness.
5. Conclusions (I) Two-body abrasive wear characteristics of most metallic glasses are marginally superior to that of crystalline 304 stainless steel and their specific wear rates are ∼1.0 × 10−2 to 1.5 × 10−2 mm3 /N m. Highest wear is observed in Ni based metallic glass MBF 35 and its wear rate is ∼2.0 × 10−2 to 2.5 × 10−2 mm3 /N m. (II) The two-body abrasive wear characteristics of different metallic glasses under reciprocating and unidirectional sliding conditions are similar. (III) The wear resistance of metallic glasses is not commensurate to their high hardness. This may be attributed to occurrence of micro-cracking as revealed by scratch indentation and acoustic emission measurements. During abrasive wear process, the material experiences high tensile stresses and in metallic glasses, micro-cracks are caused due to their poor ductility in tension. (IV) The dominant wear mechanisms contributing towards two-body abrasive wear in metallic glasses are microcutting and micro-cracking. In the case of 304 stainless steel, the material removal in two-body abrasion is through microcutting and microploughing mechanisms. (V) This work indicates the potential of acoustic emission (AE) technique in investigating the abrasive wear process.
References
Fig. 17. AE intensity during scratching of crystalline 304 stainless steel at 40 N load.
[1] F.E. Lubrosky (Ed.), Amorphous Metallic Alloys, Butterworths Monographs in Materials, 1983. [2] T. Masumoto, Present status and prospects of rapidly quenched metals, in: Proceedings of the 4th International Conference on Rapidly Quenched Metals, Sendai, Japan, 1981, pp. 5–10.
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[3] F.H. Froes, R. Carbonara, Applications of rapid solidification, J. Met. (1988) 20–27. [4] K. Miyoshi, D.H. Buckley, Friction and wear of some ferrous base metallic glasses, ASLE Trans. 27 (4) (1983) 295–304. [5] R. Klinger, H.G. Feller, Sliding friction and wear resistance of the metallic glass Fe40 Ni40 B20 , Wear 86 (1983) 287–297. [6] R. Moreton, J.K. Lancaster, The friction and wear behaviour of various metallic glasses, J. Mater. Sci. Lett. 4 (1985) 133–137. [7] G. Girerd, P. Guiraldenq, N. Nu, Surface fatigue during dry friction of a ferrous metallic glass Fe40 Ni40 P14 B20 , Wear 102 (1985) 233–240. [8] B. Prakash, K. Hiratsuka, Sliding wear behaviour of some Fe, Co and Ni based metallic glasses during rubbing against bearing steel, Tribol. Lett. 8 (2000) 153–160. [9] K. Hiratsuka, S. Norose, T. Sasada, B. Prakash, N. Takahashi, Wear of amorphous alloys rubbed against pure metals, in: Proceedings
[10]
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of the 29th Japan Congress on Material Research, 1986, pp. 105– 110. A.L. Greer, K.L. Rutherford, I.M. Hutchings, Wear resistance of amorphous alloys and related materials, Int. Mater. Rev. 47 (2) (2002) 87–112. P.G. Boswell, Wear resistance of liquid quenched metallic glass, J. Mater. Sci. Lett. 14 (1979) 1505–1507. K.H. Zum Gahr, H. Nocker, Abrasive wear of metallic glasses, Metallurgy 35 (10) (1981) 988–995. C.J. Wong, J.C.M. Li, Wear behaviour of an amorphous alloy, Wear 98 (1984) 45–61. F. vom Wege, B. Skrotzki, E. Hornbogen, Abrasive wear of a meltspun and subsequently annealed Co-base alloy, Z. Metall. 79 (8) (1988) 492–498. B. Prakash, V.D. Vankar, Abrasive wear behaviour of some ferrous and nickel based metallic glasses, J. Adv. Sci. 3 (2) (1991) 64–68.
Abrasive wear behaviour of Fe, Co and Ni based metallic glasses Braham Prakash∗ Lule˚a University of Technology, Lule˚a SE-97187, Sweden Received 22 December 2003 Available online 13 October 2004
Abstract Metallic glasses are a different category of materials that are characterized by their amorphous structure and metallic bonds. Owing to their disordered structure, metallic glasses possess several unique properties that make them attractive for tribological applications. This paper deals with an in depth investigation into the two-body abrasive wear behaviour of several compositions of Fe, Co and Ni based metallic glasses while rubbing against metallographic grade SiC abrasive papers. Identical studies have also been carried out on crystalline cold-rolled AISI 304 stainless steel for comparison. Two-body abrasive wear results indicate that wear characteristics of different metallic glasses are marginally superior or similar to that of stainless steel. The wear in Ni based metallic glass MBF 35 is significantly higher than that in stainless steel. This is inspite of the fact that metallic glasses are considerably harder than stainless steel. Scratch indentation and acoustic emission studies (AE) were carried out with a view to understanding the mechanisms of occurrence of two-body abrasive wear in metallic glasses. Scratched surfaces of metallic glasses indicated the presence of arc-like features that in some cases extend well beyond the scratched groove edges. In the case of Ni based metallic glass MBF 35, cracking on the surface was clearly visible. In stainless steel, the grooves formed were neatly cut out and were free from the arc-like features. During scratch tests on metallic glasses, AE signals were obtained but no AE signals were generated during scratch tests on steel. Presence of arc-like features on scratched surfaces in metallic glasses are tensile micro-cracks formed due to brittle fracture owing to their poor ductility in tension. These results revealed that the abrasive wear of metallic glasses is not commensurate to their high hardness and occurrence of micro-cracking results in their poor abrasive wear resistance. © 2004 Elsevier B.V. All rights reserved. Keywords: Abrasive wear; Scratch tests; Acoustic emission; Metallic glasses
1. Introduction Metallic glasses are a different category of materials that are characterized by their amorphous structure and interatomic metallic bonds. Owing to their disordered or amorphous structure, metallic glasses possess some unique characteristics like high magnetic permeability, electrical resistivity, hardness and tensile strength, resistance to gamma radiation damage and corrosion [1]. A combination of these properties in metallic glasses makes them attractive for various technological applications. Their high hardness coupled with high strength and corrosion resistance indicates their potential in tribological applications. The magnetic, electri∗
Tel.: +46 920 493055; fax: +46 920 491047. E-mail address: [email protected].
0043-1648/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.wear.2004.09.010
cal, mechanical and chemical properties of metallic glasses have been studied extensively but only a few studies have been undertaken concerning their tribological properties. The interest in tribological properties of metallic glasses is in view of their potential applications as audio/video recording heads, foil bearings, electric razors and razor blades [2–3]. The sliding friction and wear characteristics of various metallic glasses have been studied by Miyoshi et al. and several other researchers [4–9]. Recently, Greer et al. have reviewed the wear resistance of amorphous metallic alloys and related materials [10]. The two-body abrasive wear studies have earlier been carried out by Boswell et al. and others on different metallic glasses [11–15]. Most of these studies have been aimed at measuring the abrasive wear resistance of different metallic glasses. In some cases the mechanisms of two-body abra-
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B. Prakash / Wear 258 (2005) 217–224
Table 1 Experimental materials Alloy designation
Nominal composition (at.%)
Thickness (m)
Density (g/cm3 )
Crystallization temperature (◦ C)
Vickers microhardness at 100 g
Fe based metallic glasses 2605 SC 2605 S2 2826 MB 2605 S3A 2605 CO
Fe81 B13.5 Si3.5 C2 Fe78 B13 Si9 Fe40 Ni38 Mo4 B18 Fe77 Cr2 B16 Si5 Fe66 Co18 B15 Si1
32 25 20 22 23
7.32 7.18 8.02 7.29 7.56
480 550 410 535 430
858a 851a 885a 858a 825a
Co based metallic glass 2714 A
Co66 Fe4 Ni1 B14 Si15
20
7.6
550
888a
Ni based metallic glass MBF 50 MBF 35
Ni72.5 Cr18.5 Si7.5 B1.5 Ni91 Si7 B2
40 32
7.85 6.59
– –
790a 776a
Stainless steel sheet (cold-rolled) AISI 304 Standard a
100
520
These hardness values listed here were obtained from the bright side of metallic glass ribbons.
sion process have also been analyzed. These investigations are mostly material specific and no clear evidence of occurrence of a particular mechanism has been presented. It is thus felt that there is a need to characterize the wear behaviour of some of the commonly available metallic glasses and understand the mechanisms that contribute towards occurrence of two-body abrasive wear. In this work, two-body abrasive wear characteristics of different Fe, Co and Ni based metallic glasses have been studied under unidirectional as well as reciprocating sliding conditions. Further investigations aimed at identifying the contributing mechanisms towards occurrence of two-body abrasive wear process in Fe, Co and Ni based metallic glasses have also been undertaken by employing single pass scratch tests. Single pass scratch tests simulate the abrading action of a hard asperity or hard particles against the counterface material. Identical studies have been conducted on 304 stainless steel to compare the wear behaviour of metallic glasses visa-vis crystalline 304 stainless steel. AISI 304 stainless steel was chosen as a reference material as the idea was to have a crystalline Fe based material available in the form of thin sheets as majority of metallic glasses were Fe based in the form of thin ribbons. 2. Experimental materials Several alloy compositions of Fe, Co and Ni based metallic glasses have been investigated for their wear behaviour in two-body abrasive wear situations. The experimental metallic glass materials used in these studies were 20–40 m thick ribbons. The crystalline material samples were cut out from thin sheet of cold-rolled stainless steel (AISI 304). The designation, nominal composition and some physical and mechanical properties of different materials are listed in Table 1. Metallographic grade SiC abrasive papers of different grit sizes were used in two-body abrasion experiments.
It has earlier been reported that the dull side of metallic glass ribbons are harder than the bright side. It has also been found that the average surface roughness values of the bright sides of most metallic glass ribbons are slightly higher than that of the dull side. For these reasons, all tests have been carried out by using the bright sides of all metallic glass ribbons so as to obtain their minimum wear performance.
3. Test techniques and experimental work The two-body abrasive wear characteristics of different materials were studied under unidirectional and reciprocating sliding conditions. Two-body abrasive wear studies under reciprocating sliding conditions were conducted on a Suga abrasion tester while those under unidirectional sliding conditions were conducted on CSEM Revetest scratch adhesion tester. These testers were suitably adapted to enable tests on metallic glass ribbons and thin stainless steel sheets. A Revetest scratch adhesion tester incorporating acoustic emission detector was also utilized for fundamental investigations into the twobody abrasion process. These test techniques along with the experimental approach adopted are briefly described below. 3.1. Two-body abrasive wear studies during reciprocating sliding conditions For two-body abrasive wear studies during reciprocating sliding conditions, glass ribbons were cut into thin rectangular sheets of 40 mm × 25 mm and bonded to an Al alloy plate by using Loctite 415 adhesive. The abrasive papers were cut into 12 mm × 158 mm sheets and fixed to the circumferential surface of an Al alloy wheel (50 mm diameter) by means of double sided adhesive tape. Two-body abrasion studies on different materials were carried out by loading the abrasive
B. Prakash / Wear 258 (2005) 217–224
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Fig. 2. Test configuration for two-body abrasive wear studies under unidirectional sliding conditions by using Revetest scratch adhesion tester. Fig. 1. Test configuration for two-body abrasive wear studies under reciprocating sliding conditions by using Suga abrasion tester.
paper wheel against the reciprocating flat surface of the test material in a line contact configuration (Fig. 1). The abrasive paper wheel turns by 0.9◦ angle at the end of each stroke to bring fresh abrasive paper in contact with the test material with a view to eliminate the influence of degradation of abrasive paper during rubbing on abrasive wear results. A constant velocity of 0.04 m/s and stroke length of 30 mm were employed in all experiments. The influence of sliding distance, load and abrasive grit size on abrasive wear behaviour of different metallic glasses and 304 stainless steel have been investigated. Tests were conducted up to a maximum sliding distance of 120 m and at loads of 1, 3, 5 and 7 N, respectively. SiC abrasive papers of #150, #220, #280, #320 and #400 mesh sizes were used to study the abrasive particle size effect on abrasive wear in two-body abrasion. 3.2. Two-body abrasive wear studies during unidirectional sliding conditions For two-body abrasive wear studies under unidirectional sliding conditions, metallic glass ribbons and stainless steel thin sheets were cut into small rectangular sheets of dimensions 16 mm × 9 mm. They were then fixed to the curved surface of the specimen holder by using Loctite 415 adhesive. The specimen holder with the test material on its curved surface was then mounted on the scratch adhesion tester in place of Rockwell C indenter. SiC abrasive papers of different grit sizes were cut into rectangular sheets of dimensions 60 mm × 30 mm. They were fixed to the flat surface of an Al alloy plate by a double-sided adhesive tape. This Al plate with abrasive paper on its top surface was then clamped to the specimen table of the scratch adhesion tester. The test configuration for two-body abrasive wear studies by using scratch adhesion tester is shown in Fig. 2. Test material samples were loaded against the abrasive paper at various test loads (10–40 N) and rubbed against it at a speed of 10 mm/min. A stroke of 12 mm was used in all experiments. At the completion of each stroke, the position of abrasive paper was shifted slightly with a view to bring the fresh abrasive paper surface for rubbing against the test specimen. This ensured that rubbing during two abrasion process always occurred against the fresh abrasive paper surface and
the influence of damaged abrasive paper on wear results is eliminated. In two-body abrasive wear studies under unidirectional as well as reciprocating sliding conditions; three to five experiments were repeated to ensure good reproducibility of wear results. 3.3. SEM examination of worn surfaces The worn surfaces of metallic glass and stainless steel specimens from reciprocating as well as unidirectional sliding tests were examined by using a scanning electron microscope (SEM) with a view to understanding the wear mechanisms. 3.4. Scratch indentation and acoustic emission (AE) studies Revetest scratch adhesion tester was also employed for investigations into the two-body abrasive wear process of metallic glasses and stainless steel by employing the test configuration shown in Fig. 3. These tests involved scratching the specimen surface with a Rockwell C indenter at a constant load. A resonant AE transducer (type 8313, 200 KHz, B&K) provides the AE signal during scratch indentation tests. Metallic glass ribbons and stainless steel thin sheets were cut and bonded to steel disc surfaces by using an adhesive. Scratches on test samples were generated at loads of 10, 20, 30 and 40 N. A sliding velocity of 10 mm/min and scratch length of 12 mm were used in all the tests. The scratched surfaces were examined by using scanning electron microscopy
Fig. 3. Test configuration for scratch indentation tests by using Revetest scratch adhesion tester.
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Fig. 4. Specific wear of Fe, Co based metallic glasses and stainless steel as a function of sliding distance during two-body abrasion under reciprocating conditions (load: 5 N; sliding velocity: 0.04 m/s; SiC abrasive paper: #400).
(SEM) technique to characterize the mode of surface damage.
4. Results and discussion The abrasive wear characteristics of different metallic glasses and 304 stainless steel have been obtained for reciprocating sliding and unidirectional sliding conditions. Further, scratch indentation tests have also been carried out with a view to obtaining an insight into occurrence of two-body abrasive wear in metallic glasses vis-a-vis 304 stainless steel. Some of the salient results from all these studies have been described below. 4.1. Two-body abrasive wear under reciprocating sliding conditions The specific wear results of metallic glasses and stainless steel as a function of sliding distance are given in Figs. 4 and 5. The specific wear in Fe and Co based metallic glasses is somewhat higher (∼0.7 × 10−2 mm3 /N m) during the initial sliding distance of 24 m and thereafter it becomes almost constant at ∼0.5 × 10−2 to 0.6 × 10−2 mm3 /N m (Fig. 4). In Ni
Fig. 5. Specific wear of Ni based metallic glasses and stainless steel as a function of sliding distance during two-body abrasion under reciprocating conditions (load: 5 N; sliding velocity: 0.04 m/s; SiC abrasive paper: #400).
Fig. 6. Specific wear of Fe, Co based metallic glasses and stainless steel as a function of load during two-body abrasion under reciprocating sliding conditions (sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive paper: #400).
based metallic glasses, specific wear is almost constant as a function of sliding distance with Ni based alloy MBF 35 showing higher wear (∼0.8 × 10−2 mm3 /N m) as compared to MBF 50 Ni based metallic glass (∼0.6 × 10−2 mm3 /N m), Fig. 5. The overall wear in 304 stainless steel is relatively higher, 1.1 × 10−2 mm3 /N m during the initial sliding distance of 24 m and then it gradually decreases to ∼0.7 × 10−2 mm3 /N m. The increase in load in two-body abrasion under reciprocating sliding conditions also results in an increase in wear of metallic glasses and the 304 stainless steel. However, the specific wear results as function of load did not indicate any clear trend as can be seen from Figs. 6 and 7. The effect of abrasive grit size on specific wear of different metallic glasses during two-body abrasion under reciprocating sliding conditions is also anomalous and does not indicate any particular trend as can be seen from Fig. 8. 4.2. Abrasive wear under unidirectional sliding conditions A comparison of specific wear at a load of 20 N after 18 rubbing strokes for different metallic glasses and cold-rolled 304 stainless steel have been made in Fig. 9. It can be seen
Fig. 7. Specific wear of Ni based metallic glasses and stainless steel as a function of load during two-body abrasion under reciprocating sliding conditions (sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive paper: #400).
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Fig. 8. Specific wear of Fe, Co based metallic glasses and stainless steel as a function of abrasive grit size in two-body abrasion under reciprocating sliding conditions (load: 5 N; sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive paper: #400).
that specific wear in most metallic glasses (except Ni based alloy MBF 35) is ∼1.0 × 10−2 to 1.5 × 10−2 mm3 /N m. The specific wear of 304 stainless steel is ∼1.5 × 10−3 mm3 /N m. The specific wear of Ni based MBF 35 is ∼2.1 × 10−2 mm3 /N m and is higher as compared to other metallic glasses and 304 stainless steel. The wear of most Fe and Co based metallic glasses is lower than that of 304 stainless steel. Overall, the abrasive wear results under unidirectional sliding conditions indicate that the wear behaviour of various metallic glasses and stainless steel is quite similar to that obtained under reciprocating sliding conditions. The effect of abrasive particle size on wear of metallic glasses under unidirectional sliding conditions is quite anomalous as has been the case in reciprocating conditions and no clear trend has been observed. 4.3. SEM observation of worn surfaces The worn surfaces of metallic glass and stainless steel specimens from reciprocating as well as unidirectional sliding tests were analyzed by using scanning electron microscope (SEM). Typical SEM micrographs of worn surfaces of
Fig. 9. Comparative specific wear of different metallic glasses and 304 stainless steel in two-body abrasion under unidirectional conditions (load: 20 N; sliding velocity: 10 mm/min; sliding distance: 0.216 m; SiC abrasive grit size: #400).
Fig. 10. SEM micrograph of worn surface of 2826 MB metallic glass from two-body abrasion studies under reciprocating sliding conditions (load: 7 N; sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive grit size: #400).
2826 MB metallic glass and 304 stainless steel specimens are shown in Figs. 10 and 11, respectively. The microcutting action is clearly evident in both metallic glass and stainless steel. Further, in stainless steel, the microcutting is accompanied by significant microploughing action. However, in the case of metallic glass specimen, some spalling, possibly owing to cracking of material at the wear groove edges can be clearly seen. The precise cause of this damage is not clear from the SEM examination. 4.4. Scratch indentation and acoustic emission measurement results The two-body abrasive wear results presented above indicate that the wear characteristics of most metallic glasses are only marginally superior to that of crystalline 304 stainless
Fig. 11. SEM micrograph of worn surface of 304 stainless steel from twobody abrasion studies under reciprocating sliding conditions (load: 7 N; sliding velocity: 0.04 m/s; sliding distance: 24 m; SiC abrasive grit size: #400).
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Fig. 12. Specific wear of different metallic glasses and stainless steel vs. Vickers microhardness (load: 20 N; sliding velocity: 10 mm/min; sliding distance: 0.216 m; SiC abrasive grit size: #400).
and are not commensurate with their high hardness. It can be clearly seen from Fig. 12 that specific wear rates of different metallic glasses do not indicate a clear trend with respect to their hardness. Further, the SEM micrograph of metallic glass worn surfaces have indicated some kind of cracking/spalling type of damage (Fig. 10) but its cause is not clear. The scratch indentation and acoustic emission studies have been mainly aimed at understanding the mechanisms contributing towards two-body abrasive wear in metallic glasses. These studies were carried out on different Fe, Co and Ni based metallic glasses but only some representative results have been presented here. The SEM micrograph of the scratched surface of Fe based metallic glass 2826 MB as shown in Fig. 13 is characterized by arc-like features which extend well beyond the groove edges. In some cases, complete cracking of metallic glass material (MBF 50 Ni based metallic glass) has also been observed (Fig. 14). The arc-like features in metallic glasses are tensile microcracks formed due to brittle fracture and are similar to those
Fig. 13. SEM micrograph showing the tensile micro-cracks on scratched surface of Fe based Metglas 2826 MB from scratch indentation test at 40 N load.
Fig. 14. SEM micrograph showing cracking on scratch surface of Ni based Metglas MBF 50 from scratch indentation test at 30 N load.
seen in brittle solids such as glasses and ceramics. During scratch indentation, the stress system is quite complex due to the action of normal and tangential forces. The maximum tensile stress occurs at the trailing edge of the indenter. If this maximum tensile stress exceeds the ultimate strength of the material, tensile micro-cracks are formed. The tensile microcracks have been observed in all the metallic glasses even at the lowest test load of 10 N whereas no such cracks have been observed in 304 stainless steel even at 50 N load. The formation of tensile micro-cracks can be attributed to low ductility of metallic glasses in tension. Scoring marks in the direction of sliding and some material pileup ahead of the indenter at the end of the sliding stroke are also seen indicating the possibility of some microcutting and microploughing action. In stainless steel, the grooves formed are neatly cut out and are completely free from the arc-like features or microcracks (Fig. 15), which were observed on the scratched surfaces of metallic glasses. The presence of some material flow,
Fig. 15. SEM micrograph showing the scratched surface of 304 stainless steel from scratch indentation test at 50 N load.
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Fig. 16. AE intensity during scratching of Fe based Metglas 2826 MB at 40 N load.
shear lips and material pile up at the end of sliding stroke are however seen in stainless steel indicating the occurrence of microcutting and microploughing action. AE measurements also indicated the distinct behaviour of metallic glasses during scratch indentation vis-a-vis 304 stainless steel. The results show that AE signals are obtained during scratch tests on all metallic glasses (Fig. 16) but in the case of stainless steel no AE signals are generated even at the highest test load (Fig. 17). Also, in the case of metallic glasses, the AE signal intensity increased with an increase in load. The generation of AE signals during scratch indentation is indicative of formation of cracks. Therefore the generation of AE signals during scratch tests on metallic glasses is due to the formation of tensile micro-cracks. In scratch tests on 304 stainless steel, no micro-cracks have been observed and accordingly no AE signals are generated. In actual two-body abrasive wear, each hard abrasive wear particle acts as an indenter. So the metallic glass material surface is subjected to indentation by several hard abrasive particles thereby forming a network of micro-cracks during sliding. Some of these adjoining micro-cracks join and even-
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tually result in material removal. The combined action of micro-cracking along with microcutting and microploughing action is attributed to high abrasive wear of metallic glasses despite their high hardness. The scratch indentation studies and subsequent examination of scratched surfaces have clearly indicated that microcutting, microploughing (although to a smaller extent) and micro-cracking are the important mechanisms that contribute towards occurrence of two-body abrasive wear in metallic glasses. On the other hand, the material removal mechanism during two-body abrasive wear in crystalline 304 stainless is primarily a result of microcutting and microploughing action. It may be pertinent to point out that some scratch indentation and AE tests were also conducted on crystalline AISI 52100 bearing steel (hardness ∼1030 HV at 100 g load) which is harder than all the metallic glass specimens. The behaviour of AISI 52100 bearing steel was quite similar to that of crystalline 304 stainless steel as no micro-cracks could be seen on the scratched surfaces inspite of its high hardness.
5. Conclusions (I) Two-body abrasive wear characteristics of most metallic glasses are marginally superior to that of crystalline 304 stainless steel and their specific wear rates are ∼1.0 × 10−2 to 1.5 × 10−2 mm3 /N m. Highest wear is observed in Ni based metallic glass MBF 35 and its wear rate is ∼2.0 × 10−2 to 2.5 × 10−2 mm3 /N m. (II) The two-body abrasive wear characteristics of different metallic glasses under reciprocating and unidirectional sliding conditions are similar. (III) The wear resistance of metallic glasses is not commensurate to their high hardness. This may be attributed to occurrence of micro-cracking as revealed by scratch indentation and acoustic emission measurements. During abrasive wear process, the material experiences high tensile stresses and in metallic glasses, micro-cracks are caused due to their poor ductility in tension. (IV) The dominant wear mechanisms contributing towards two-body abrasive wear in metallic glasses are microcutting and micro-cracking. In the case of 304 stainless steel, the material removal in two-body abrasion is through microcutting and microploughing mechanisms. (V) This work indicates the potential of acoustic emission (AE) technique in investigating the abrasive wear process.
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Fig. 17. AE intensity during scratching of crystalline 304 stainless steel at 40 N load.
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