The frictional component in microhardness testing of intermetallics

It has been recognized for quite a long time that Vickers (and Knoop) microhardness of many metallic and non-metallic materials becomes greater at lower loads (so-called indentation size effect or ISE). One group of investigators attributed this peculiar phenomenon to an operator factor, or simply speaking to an experimental error, rather than to intrinsic material properties. However, an alternative analysis takes a more physical approach in which two factors, namely, the surface energy contribution and the volume energy contribution are suggested. The former represents the work needed to create the new surface while the latter represents the work needed to produce the volume deformation. It has recently been shown that L12 titanium and zirconium trialuminides (based on Al3Ti and Al3Zr intermetallics) exhibit a very strong ISE. In the present paper it is shown that the ISE is very characteristic for many other intermetallics and the PSR (proportional specimen resistance) model by Li et al. can be applied to explain the origin of ISE in intermetallics, as being fundamentally attributed to the frictional component of indentation testing