Stress-induced amorphization at moving crack tips in NiTi

P. R. Okamoto, J. K. Heuer, N. Q. Lam, S. Ohnuki, Y. Matsukawa, K. Tozawa, J. F. Stubbins

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In situ fracture studies have been carried out on thin films of the NiTi intermetallic compound under plane stress, tensile loading conditions in the high-voltage electron microscope. Local stress-induced amorphization of regions directly in front of moving crack tips has been observed. The upper cutoff temperature, TC-Amax, for the stress-induced crystalline-to-amorphous transformation was found to be 600 K, identical to that for heavy ion-induced amorphization of NiTi and for ion-beam mixing-induced amorphization of Ni and Ti multilayer specimens. 600 K is also both the lower cutoff temperature, TA-Cmin, for radiation-induced crystallization of initially-unrelaxed amorphous NiTi and the lowest isothermal annealing temperature, TXmin, at which stress-induced amorphous NiTi crystallizes. Since TXmin should be TK, the ideal glass transition temperature, the discovery that TC-Amax=TA-Cmin=TX min=TK implies that disorder-driven crystalline-to-amorphous transformations result in the formation of the ideal glass, i.e., the glassy state that has the same entropy as that of the defect-free crystal. As the glassy state with the lowest free energy, its formation can be understood as the most energetically-favored, kinetically-constrained response of crystalline alloys driven far from equilibrium.

Original languageEnglish (US)
Pages (from-to)473-475
Number of pages3
JournalApplied Physics Letters
Issue number4
StatePublished - 1998

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)


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