Stress-induced amorphization at moving crack tips in NiTi
- Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
- Department of Materials Engineering, Hokkaido University, Sapporo (Japan)
- Department of Nuclear Engineering, University of Illinois, Urbana, Illinois 61801 (United States)
{ital 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, T{sub C{endash}A}{sup max}, 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, T{sub A{endash}C}{sup min}, for radiation-induced crystallization of initially-unrelaxed amorphous NiTi and the lowest isothermal annealing temperature, T{sub X}{sup min}, at which stress-induced amorphous NiTi crystallizes. Since T{sub X}{sup min} should be T{sub K}, the ideal glass transition temperature, the discovery that T{sub C{endash}A}{sup max}=T{sub A{endash}C}{sup min}=T{sub X}{sup min}=T{sub K} 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. {copyright} {ital 1998 American Institute of Physics.}
- OSTI ID:
- 639049
- Journal Information:
- Applied Physics Letters, Vol. 73, Issue 4; Other Information: PBD: Jul 1998
- Country of Publication:
- United States
- Language:
- English
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