Phase Transformation Control of Powder Metallurgy Super-Elastic Ti–Ni Alloy by Adding Co Element

• Published in: MATERIALS TRANSACTIONS Vol. 60; no. 8; pp. 1583 - 1590
• Main Authors: Eda, Tomoki, Khantachawana, Anak, Umeda, Junko, Kondoh, Katsuyoshi
• Format: Journal Article
• Language: English
• Published: Sendai The Japan Institute of Metals and Materials 01-08-2019; Japan Science and Technology Agency
• Subjects: Alloy powders; Alloying additive; Alloying elements; Cobalt; Cobalt plating; Controllability; Dependence; Heat treatment; Mechanical properties; Nickel base alloys; Phase transitions; Powder metallurgy; Precipitates; precipitation; Recovery; shape memory property; Stability; super-elastic; Titanium base alloys; titanium-nickel-cobalt alloy
• ISSN: 1345-9678; 1347-5320
• DOI: 10.2320/matertrans.Y-M2019821

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 cobalt content was investigated by considering microstructures analysis results. XRD and TEM-EDS analysis clarified cobalt 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 cobalt 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 cobalt solution content had no effect on the amount and size of Ti3Ni4 precipitates. Therefore, it was possible to independently control the plateau stress without affecting the critical slip strain by adding cobalt element to Ti–Ni alloys. This Paper was Originally Published in Japanese in J. Jpn. Soc. Powder Powder Metallurgy 66 (2019) 9–16.