日本金属学会誌

J. Japan Inst. Metals, Vol. 60, No. 6 (1996),
pp. 577-581

Stress Corrosion Behavior of Ni-Ti Shape Memory Alloys in High Temperature Water

Shinobu Matsushima, Han-Choel Choe,Shigeo Ohashi and Tadao Ishihara

National Research Institute for Metals, Tsukuba

Abstract:

The effects of composition, heat treatment, test temperature and dissolved oxygen (DO) concentration on the stress corrosion cracking (SCC) behavior of Ni-Ti and Ni-Ti-Cu shape memory alloys in high temperature pure water were examined. The tests were conducted by using slow strain rate test machine.
The 50{~}50.9 at%Ni-Ti and 40{~}41.5 at%Ni-Ti-10 at%Cu shape memory alloys were subjected to SCC in air saturated water of 561 K, except for the annealed 50 at%Ni-Ti alloy. The annealed 50 at%Ni-Ti was immune to SCC, but the SCC susceptibilities of the other Ni-Ti alloys were not affected by nickel concentration and heat treatment. In the case of Ni-Ti-Cu alloys both low nickel concentration and aging promoted SCC. SCC of Ni-Ti and Ni-Ti-Cu alloys initiated from the scratches and propagated transgranularly.

At 473 K, SCC occurred and the susceptibilities were not largely different from those at 561 K. In the case of a stainless steel shape memory alloy, the martensite phase specimens were susceptible to SCC in deaerated low temperature water. On the contrary, the martensitic Ni-Ti alloys did not crack in the deaerated water at 287 K.

The susceptibilities to SCC of Ni-Ti and Ni-Cu-Ti alloys in deaerated water of 561 K were the same as those in aerated water of the same temperature. Dissolved oxygen did not accelerate nor prevent SCC in high temperature water.


(Received December 22, 1995)

Keywords:

stress corrosion cracking, nitinol shape memory alloy, high temperature water, nickel content, heat treatment, test temperatue, dissolved oxygen


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