Microstructure and transformation behavior of Ni50Ti45Ta5 shape memory alloy
摘要
The microstructure and transformation behavior of Ni50 Ti45 Ta5 shape memory alloy were investigated using optical microscope, EPMA, X-ray diffraction and DSC methods. The microstructures are primary NiTi dendrite and net-like eutectic. The room temperature phases of this alloy are B2 austenite with lattice parameter a=0. 302 5nm, B19' martensite with lattice parameters a=0. 290 nm, b=0. 412 nm and c=0. 473 nm, β= 98.2° and a body center cubic β-Ta with lattice parameter a' =0. 330 4 nm. A maximal shape memory recovery strain of 5.6% is obtained after deformation to 6.4%. The reverse transformation temperatures increase and the forward transformation temperatures decrease in the first heating/cooling cycle after deformation. The reverse transformation heat also increases with increasing deformation. The phenomenon disappears in the second heating/cooling cycle. It is closely related to the variation of elastic energy and irreversible energies during deformation.