Stress-induced amorphization at moving crack tips in NiTi

Abstract

The sui3mmed th be ted by the Universifl?~h\p~o*as &aae& of Argonne National Laboratory under Contract No. W-31-109-E J??& the U.S. Department of Ener y. The U.S. f Government retains for itsel, and others acting on its behalf, a paid-up, non exclusive,irrevocable worldiwde hcense in said article to reproduce, prepare derivative works, distribute c ies to the public, and 7' perform publiclyan dwplay publicly, by or on behalf of the Government.

Effect of constituent phase of Ni–Ti shape memory alloy on susceptibility to hydrogen embrittlement

“…It is likely that some interactions between hydrogen and defects created during dynamic process is concerned with the enhanced susceptibility. In a Ni-Ti alloy, amorphization at the crack tip has been reported by Okamoto et al [37], which is an expected consequence of lattice instability due to an increased density of vacancies [38]. Amorphization associated with ductile crack growth has been shown recently in a hydrogen-charged ferritic steel [39].…”

Do cracks melt their way through solids?

“…NiTi [11]. The temperature dependence of stress-induced amorphization and the isothermal crystallization behavior of the resulting glass were compared with those associated with irradiationinduced amorphization of crystalline NITi [12] and with ion-beam mixing of Ni and Ti mukilayers [13].…”

“…The second is that T~represents an absolute upper-limiting cutoff temperature for all disorder-driven crystal-to-glass transformations. This conclusion follows from the fact there is no thermodynamic driving force for arnorphization for any disordered or stressed crystalline state that has a melting temperature higher than TK In the following section recent experimental observations [11] supporting this simple thermodynamic picture of disorder-driven melting at crack tips are examined.…”

Structural transformation, amorphization, and fracture in nanowires: A multimillion-atom molecular dynamics study

“…A similar phenomenon-crack propagation preceded by melting-has been observed in intermetallic compounds and alloys. [15][16][17] In summary, multimillion-atom MD simulations of 128and 1204-chain SiSe 2 nanowires with circular cross sections were performed in order to study structural characteristics under strain and the dynamics of strain-induced amorphization and fracture. The SiSe 2 unit cell transformed from a body-centered orthorhombic structure to a body-centered tetragonal structure under strain, so that the overall cross sectional shape of the wires became elliptical.…”