Affiliation:
1. Department of Mechanical Engineering, Isfahan University of Technology, Isfahan, Iran
Abstract
In this paper, effect of the external surface layer on low pressure phase (LPP)-high pressure phase (HPP) transformation in a single crystal is investigated using a phase field model. It consists of a kinetic equation to represent the LPP-HPP transformation and another one to introduce the external surface layer between the bulk and surrounding phase within which the surface energy is properly distributed. After resolving a stationary layer, the coupled elasticity and phase field equations are solved to capture the HHP evolution. The variation of the critical thermal driving force ([Formula: see text]) versus the ratio of the external surface layer width to the HPP-LPP interface width ([Formula: see text]) is found for different boundary conditions, uniaxial pressures and transformation strains. The external surface layer reveals a similar nonlinear increase of [Formula: see text] versus [Formula: see text], in agreement with previous numerical and experimental data on thermal induced transformation/melting at the nanoscale. Without vertical constraint, [Formula: see text] nonlinearly increases versus [Formula: see text] and remains constant for [Formula: see text]. It also linearly reduces versus the pressure/transformation strain, independent of [Formula: see text]. With vertical constraint, [Formula: see text] is larger and weakly dependent on [Formula: see text]. Under applied pressure, the transformation work linearly increases with the transformation strain for [Formula: see text] and consequently, [Formula: see text] reduces. The obtained results help to understand the effect of the external surface layer on the HPP evolution in relation to other key parameters depending on its width.
Funder
Iran National Science Foundation
Isfahan University of Technology