Deformation Twinning Arising in Single-Crystal, Bicrystal and Polycrystal on Commercially Pure Titanium Plate

Background Deformation twinning plays a dominant role in the mechanical behavior of an important group of (e.g., hexagonal close packed) polycrystalline metals. A better understanding of this mechanism is necessary for fabricating these materials with high strength and ductility. Objective This study was conducted to elucidate deformation twinning and slip plasticity in polycrystalline commercial-pure titanium (CP-Ti) at several scales. Methods Micropillar specimens of two types were fabricated from a CP-Ti plate that is first characterized by EBSD orientation mapping. The first type comprises single-crystal and bicrystal micropillar specimens of 5 mu m x 5 mu m x 10 mu m, fabricated using focused ion beam (FIB) technique. The other type includes larger polycrystalline micropillar specimens of 70 mu m x 70 mu m x 140 mu m to 200 mu m x 200 mu m x 400 mu m, fabricated using in-house processing. Then microcompression tests were performed using in-house fixtures for single-crystal, bicrystal and polycrystalline micropillar specimens. Acoustic emission (AE) monitoring was used to measure the nucleation behavior of deformation twinning for polycrystalline micropillar specimens under uniaxial compressive loading. Results From single-crystal experiments, marked differences of stress-strain curves are observed for crystallographic orientation specimens of five kinds. The results of polycrystalline micropillar specimen show that 70 mu m micropillar specimens demonstrate splitting stress-strain curves. By contrast, results obtained for a 200 mu m micropillar specimen present matching stress-strain curves. Conclusions Deformation twinning is not readily induced in 5 mu m x 5 mu m x 10 mu m single-crystal micropillar specimens. Deformation twinning is induced at a low stress level by basal slip in neighboring grains for bicrystal micropillar specimen. The existence of a small number of grains where prism slip has a higher probability of occurring affects the macroscopic stress-strain curve for polycrystal micropillar specimen.