| Abstract Scope |
NiTi alloys have been extensively used because of excellent functional properties. NiTi alloys fabricated by LENS have good formability and adjustable size and shape. The precipitates in NiTi alloys have influence on performance. In this work, we induce and change states of Ni4Ti3 and NiTi2 precipitates by heat treatment to achieved the recovery rate of 93.44%, the tensile strength of ~700 MPa and the strain of ~11% . Fundamentally, the Ni4Ti3 precipitates with smaller size and larger aspect ratio (width/length) promote the mechanical properties of NiTi alloys. The more NiTi2 precipitates have an unfavorable effect on the strength. Besides, precipitates near grain boundaries and precipitates free regions in grain interiors and this microstructure shows a three step (multiple step) transformation or a two-step transformation. This relates to inhomogeneity between grain boundary region and grain interior and local stress and composition inhomogeneity around Ni4Ti3 precipitates. |