The hardness of α-Ti grains as a function of both indentation depth and orientation was assessed using nano-indentation. Direct observations and analyses of the dislocation sub-structures were achieved by cutting thin-foil membranes exactly through given indents with a dual-beam focused-ion-beam instrument and from diffraction-contrast experiments in a transmission electron microscope. It was found, as expected, that the hardness varied with the depth of indentation. Regarding the orientation dependence of hardness, the nature of the statistically stored dislocations as well as that of the geometrically necessary dislocations was identified. Thus, the occurrence of the majority of the former dislocations could be predicted on the basis of Schmid’s law, while noting the presence of minor densities of other dislocations required presumably because of the arbitrary shape change imposed by the nano-indenter. The geometrically necessary dislocations were identified as the appropriate combinations of slip dislocations such that an overall displacement parallel to the direction of the indentation results.

Direct Observations and Analyses of Dislocation Substructures in the α Phase of an α/β Ti-Alloy Formed by Nano-Indentation. G.B.Viswanathan, E.Lee, D.M.Maher, S.Banerjee, H.L.Fraser: Acta Materialia, 2005, 53[19], 5101-15