Wear-resistance and hardness: Are they directly related for nanostructured hard materials?

Abstract

The major challenge in the field of cemented carbides and other hard materials is to obtain their better combination of hardness, wear-resistance and fracture toughness. It is well known that the dependence of abrasion wear on fracture toughness for WC–Co cemented carbides is represented by a relatively narrow band and it is hardly possible to “break away” out from it by the use of conventional approaches based on varying the WC mean grain size and Co content. Also, it is well known that the wear-resistance of conventional cemented carbides depends mainly on their hardness. The major objective of this paper is to establish what will happen with the wear-resistance of hard materials as a result of their nanostructuring when the hardness is nearly the same as for conventional WC–Co cemented carbides. The results obtained provide clear evidence that, if one enters the region of nanostructured materials with the mean grain size of less than 10nm, traditional wisdom indicating that the wear-resistance is directly related to the hardness appears not to be valid. In some cases of such nanostructured materials, it can be possible to achieve the dramatically improved wear-resistance compared to that of conventional WC–Co cemented carbides at nearly the same level of hardness and fracture toughness. The abovementioned is based on considering hard nanomaterials of the following four types: (1) WC–Co cemented carbides with nanograin reinforced binder, (2) near-nano WC–Co cemented carbides, (3) cemented carbides of the W–C–Cr–Si–Fe system for hard-facing having a nanostructured Fe-based binder, and (4) CVD hard materials consisting of nanostructured W2C grains embedded in a tungsten metal binder.