2019 Volume 66 Issue 1 Pages 9-16
In order to improve the controllability of the mechanical properties of powder metallurgy (PM) titanium (Ti) -nickel (Ni) super-elastic alloys, cobalt (Co) powder was added to the alloys up to 2.0 at.%. In particular, the dependence of plateau stress and recovery rate in tensile hysteresis test on Co content was investigated by considering microstructures analysis results. XRD and TEM-EDS analysis clarified Co elements existed as substitutional solution atoms in Ni atom sites of Ti-Ni alloys. It was confirmed that PM Ti-Ni-Co alloys with the Co content of 1.0 at.% Co or less showed a high shape recovery rate of around 90% or more. In addition, the increment of the plateau stress of Ti-Ni-Co alloys was almost constant regardless of the holding time in heat treatment. That is, the Co solution content had no effect on the amount and morphological size of Ti3Ni4 precipitates. Therefore, it was possible to independently control the plateau stress without affecting sliding critical strain by adding Co element to Ti-Ni alloys.
