Evaluation of orientation-dependent geometry of micro triangular indentation on grain of polycrystalline α-titanium

In microindentation testing, an indentation size is smaller than the average grain size of industrial polycrystalline metals, so that the indentation shape is affected by the crystallographic orientation of grain on which the indentation is imposed. Hence, clarification of the relation between the crystal orientation and the indentation shape leads to the possibility of estimating the crystal orientation by microindentation testing. In the present study, influences of crystal orientations upon indentation shapes on grains of polycrystalline titanium were investigated. The crystal orientations of grains were measured by an electron backscattered diffraction method, and indentation tests with a triangular pyramidal indenter were performed on the grains. The indentation shapes were thus observed by a laser-scanning microscope and an optical microscope. The results revealed that the direction of the most bulged position of edges from the apex of triangular indentation agreed well with an a-axis direction. It was also found that deviation of the indentation edge from the ideal one became smaller with larger angle of inclination of c-axis for the sample surface, owing to the limited slip direction of titanium. Those results suggest the possibility to evaluate the crystal orientation of titanium grain directly from the observed indentation geometry.