Effect of tantalum ion implantation on deformation behavior and fracture of TiNi SMA. Part I. quasi-static tension

Abstract

The effect of high dose implantation of Ta+ ions (Dion = 5′1016 cm−2) into samples from a TiNi shape memory alloy (SMA) on patterns of deformation and fracture mechanisms under quasi-static uniaxial tensile loads was studied. Using X-ray diffractometry, transmission electron microscopy, and scanning electron microscopy, it was shown that ion implantation resulted in amorphization of the surface layer with a thickness of ∼100 nm due to the formation of a chemical composition of approximately Ti36Ni41Ta23 (at.%), thermodynamically corresponding to the highest glass forming ability in the Ti–Ni–Ta system. In the implanted surface layer, both the microstructure and crystal structure defects subsystem were modified at a depth of ∼5 mm. Using the digital image correlation (DIC) method, the dynamics of changes in the integral and local (εyy longitudinal, εxy shear and εxx transverse) strain components were investigated in the tensile tests of both as-received and implanted TiNi SMA samples. On the basis of the obtained results, both integral and local stress–strain diagrams were plotted. In all studied cases, the main contribution to strain accumulation was made by the εyy and εxx strains, which differed significantly for the as-received and implanted TiNi SMA samples. It was concluded that the positive effect of ion implantation was manifested in loading ranges close to the martensitic yield stress (at strain range of 1–6%), despite a noticeable decrease in the ultimate tensile strength and plasticity of the implanted TiNi samples.