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Abrasive Wear Resistance of Bulk Metallic Glasses A. Lindsay Greer1 and Wha-Nam Myung2 1Department of Materials Science & Metallurgy, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK. 2Department of Physics, Chonnam National University, Kwangju 500-757, Korea. ABSTRACT This paper reviews work on the wear of metallic glasses in general, as well as reporting recent results on the abrasive wear of bulk metallic glasses. The distinctive mechanical properties of metallic glasses make their wear resistance of fundamental interest. Metallic glasses, and the partially or fully crystalline materials derived from them, can have very good resistance to sliding and abrasive wear. Standard wear laws are followed, with behaviour similar to that of conventional hardened alloys. The microhardness and abrasive wear resistance are measured for four bulk metallic glasses (based on La, Mg, Pd or Zr). The hardness and wear resistance correlate well with the Young’s modulus of the glass.

INTRODUCTION Wear is an important failure mode in many applications, ranging from large-scale engine parts to tape-recorder heads and electronic devices such as sensors. Wear resistance is often an important secondary property. For example, in early work on soft-magnetic alloys for taperecorder heads it was found that poor wear resistance was a problem [1]. Fortunately, the alloy compositions could be tailored to retain the desirable magnetic properties while developing good wear resistance [2]. The first study of wear of metallic glasses appeared in 1979 [3], and there have since been over fifty publications on the subject. The interest in the subject has grown with the advent of bulk metallic glasses; these have removed the restriction to small sample sizes for wear tests, as well as opening up new potential applications for the materials. This review considers not just metallic glasses themselves, but also related materials such as the partially or fully crystallized alloys obtained by annealing. The geometry of these materials is varied, ranging from bulk to thin films and coatings made by such methods as sputtering, plasma spraying and laser glazing. With a wide range of actual and potential applications — microgears [4], dry bearings [5], coatings for sensors [6] and medical implants [7, 8], and hard-facing alloys [9-11], for example — it is timely to review current understanding of the wear of metallic glasses as well as characterizing the behaviour of the new bulk glasses. Metallic glasses are of particular interest from the tribological point of view because of their unique mechanical properties. They show inhomogeneous flow in the form of shear bands at ambient temperature, but viscous flow at elevated temperature [12]. The formation of shear bands is associated with a work-softening in marked contrast to normal alloy behaviour. On the other hand, metallic glasses are often not brittle in bending and can show toughnesses of ~20 MPa m1/2 [13]. Thus they have properties lying outside the normal categories of engineering materials.