Knoop microhardness anisotropy and the indentation size effect on the (100) of single crystal NiAl

The Knoop microhardness anisotropy of the B2 intermetallic compound NiAl in single crystal form was investigated on the (100) plane. Indentation test loads from 25 to 500 g were applied and the indentation size effect (ISE) was analyzed by an energy balance. The Knoop microhardness profile confirmed the 〈011〉{100} primary slip system for NiAl. The load independent, orientation independent Knoop microhardness was determined to be 218.6±5.8 kg mm −2 for the NiAl (100) plane. Additional Knoop indentation experiments were completed with a lubricant applied to the specimen surface. The load independent, orientation independent Knoop microhardness for the lubricated microhardness measurements was 220.3±5.0 kg mm −2, essentially the same. However, the extent of the ISE was significantly reduced. Based on these results, it is evident that the ISE can be attributed primarily to frictional effects between the indenter facets and the test specimen surface.