Nanoindentation Measurement for a Tungsten(001)Single Crystal

Abstract

Nanoindentation measurement for tungsten(001)single crystal was conducted with an AFM ultra-micro hardness tester. For electrolytically polished tungsten(001)single crystal, sudden increase of penetration by around 50 nm occurred at 1.3 mN with a three-sided pyramidal indenter of an apical angle of 115°, and 0.24 mN with an indenter of 60°. Deformation was purely elastic under this critical force. However, these behaviors did not occur for mechanically polished surface, where a deformed layer of no more than 6 μm thickness exists. These facts lead an idea that such phenomena come from the same source of upper and lower yield points in tensile tests for B.C.C.crystals. Normalized shear stress τ_max/G at upper yield point was estimated as 0.22 and 0.24. Also, curvature radius of indenters, that is of great importance in nanoindentation, was estimated from both force-penetration depth curves and AFM topographic images.