Do cracks melt their way through solids?

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Real-time, in situ fracture studies in the high-voltage electron microscope (HVEM) show that microscopically thin regions of amorphous NiTi form ahead of moving crack tips in the B2-NiTi intermetallic compound during tensile straining at temperatures equal to or below 600K. The upper cutoff temperature of 600K for this stress-induced melting (or amorphization) is identical to the upper cutoff temperatures reported in the literature for both heavy-ion-induced amorphization of the intermetallic NiTi and ion-beam-mixing-induced amorphization of Ni and Ti multilayer. These results, together with the fact that the higher crystallization temperatures ({approximately}800K)of unrelaxed amorphous NiTi alloys obtained by rapid quenching can ... continued below

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23 p.

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Okamoto, P. R. December 1, 1998.

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Description

Real-time, in situ fracture studies in the high-voltage electron microscope (HVEM) show that microscopically thin regions of amorphous NiTi form ahead of moving crack tips in the B2-NiTi intermetallic compound during tensile straining at temperatures equal to or below 600K. The upper cutoff temperature of 600K for this stress-induced melting (or amorphization) is identical to the upper cutoff temperatures reported in the literature for both heavy-ion-induced amorphization of the intermetallic NiTi and ion-beam-mixing-induced amorphization of Ni and Ti multilayer. These results, together with the fact that the higher crystallization temperatures ({approximately}800K)of unrelaxed amorphous NiTi alloys obtained by rapid quenching can also be reduced to, but not lower than 600K, by heavy-ion irradiation, strongly suggest that structural relaxation processes enhanced or induced by dynamic atomic disordering allow the formation of a unique, fully-relaxed glassy state which is characterized by a unique isothermal crystallization temperature. We believe that this unique temperature is the Kauzmann glass-transition temperature, corresponding to the ideal glass having the same entropy as the crystalline state. As the glassy state with the lowest global free energy, the preferential formation of this ideal glass by disorder-induced amorphization processes can be understood as the most energetically-favored, kinetically-constrained melting response of crystalline materials driven far from equilibrium at low temperatures.

Physical Description

23 p.

Notes

INIS; OSTI as DE00011168

Medium: P; Size: 23 pages

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  • Symposium on High Voltage Microscopy for 21st Century and its Application to Frontier Materials Study, Sapporo (JP), 10/15/1998--10/17/1998

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  • Report No.: ANL/MSD/CP-97852
  • Grant Number: W-31109-ENG-38
  • Office of Scientific & Technical Information Report Number: 11168
  • Archival Resource Key: ark:/67531/metadc626384

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  • December 1, 1998

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  • June 16, 2015, 7:43 a.m.

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  • April 10, 2017, 3:45 p.m.

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Okamoto, P. R. Do cracks melt their way through solids?, article, December 1, 1998; Illinois. (digital.library.unt.edu/ark:/67531/metadc626384/: accessed September 22, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.