2015 年 56 巻 10 号 p. 1747-1755
The compositions of β type Ti alloys having shape-memory ability above 400 K were proposed by alloying parameters used in the d-electrons concept. They were both Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo which were designed for improvement of thermal stability in shape memory behavior of Ti-6Mo base alloy, preserving the tensile strength of 700 MPa. Their ingots without contamination from the used crucible were produced by cold crucible levitation melting. They consisted of β and α′′ phases after the cold roll and heat treatment, and their amounts were depended on values in the alloying parameters. The shape recovery rate of 40 and 25% was measured after 4 cycles in the loading-unloading tests in Ti-6Mo-2Al-1Sn and Ti-6Nb-3Mo, respectively. They showed the As temperature above 490 K and improvement of thermal stability because of a much smaller amount of ω phase than Ti-6Mo. The alloys showed tensile strength of 682 to 718 MPa. These results were caused by exactly prediction of the phase stability, shape memory ability and tensile strength, using alloying parameters.
