Stress-induced amorphization at moving crack tips in NiTi

DOI PDF 被引用文献5件 オープンアクセス
  • P. R. Okamoto
    Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439
  • J. K. Heuer
    Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439
  • N. Q. Lam
    Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439
  • S. Ohnuki
    Department of Materials Engineering, Hokkaido University, Sapporo, Japan
  • Y. Matsukawa
    Department of Materials Engineering, Hokkaido University, Sapporo, Japan
  • K. Tozawa
    Department of Materials Engineering, Hokkaido University, Sapporo, Japan
  • J. F. Stubbins
    Department of Nuclear Engineering, University of Illinois, Urbana, Illinois 61801
  • United States. Department of Energy.

説明

<jats:p>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=TXmin=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.</jats:p>

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