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Effect of oxidation on transformation and deformation behavior in Ni-Ti alloy

Kwang K. Jee 1Kyu S. Kim 1,2Yoon B. Kim 1Seung H. Han 1W. Y. Jang 3

1. Korea Institute of Science and Technology, Material Science and Engineering Division, Seoul, Korea, South
2. Hongik University, Jochiwon, Jochiwon 339-800, Korea, South
3. Dept. of Metallurgical Engineering, Chosun University, #375 Seosuk-Dong, Dong-Gu, Gwangju 501-759, Korea, South


Since Ti reacts preferably with oxygen to form titanium oxide, Ni content increases between the matrix and the oxide, forming compounds and Ni-rich region. Because transformation temperature of Ni-Ti alloy depends strongly on Ni contents, the Ni-rich region affects transformation as well as deformation behavior. It is found out that the oxidation resultant including Ni-rich region lowers Ms and As temperatures in the alloys undergoing B2⇋ M transformation. In case of alloy of B2→R→M transformation, a significant decrease in B2→R transformation temperature is observed near surface. Besides, no R→M transformation is observed when it is cooled to 123K, while Ms of the matrix is 250K. The Ni-rich region experiences more plastic deformation than the matrix during superelastic deformation, since slip occurs instead of formation of stress-induced martensite. It is summarized that increase in Ni content near surface by oxidation retards martensitic transformation and prevents SIM deformation by lowering enormously transformation temperature.


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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium E, by Kwang K. Jee
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 02:51
Revised:   2009-06-07 00:44