Influence of crystallographic orientation upon microscopic indentation shape on pure titanium

A micro indentation testing has been used to investigate the local mechanical properties of engineering materials. Since the size of indentation becomes much smaller than the average grain size of ordinary metallic materials by that testing, the results must be influenced more or less by the characteristics of each grain in which the indentation is imposed. However, the influences of crystal orientation of the grain upon the indentation results have scarcely been investigated for polycrystalline metals. In the present study, the micro indentation tests were performed on the grains of commercially pure titanium, of which the crystal orientations were evaluated beforehand by an electron back scattering diffraction technique. The relationships between the crystal orientation and the resultant indentation shapes as well as the indentation hardness values were then experimentally investigated. The results showed clear orientation dependences of the indentation shape and indentation hardness for the titanium grains. The anisotropy and the distortion of indentation profile tended to increase, while the obtained indentation hardness tended to decrease with increase in the angle between <0001> direction and the surface normal direction. The distortion of the indentation shape was found to appear due to the pile-up of materials in the limited area around the indentation by the restricted plastic flow with regard to the crystal orientation. These results are supposed to indicate the possibility to use an indentation made on grain's surface for the identification of its crystal orientation in polycrystalline titanium.