Continuum analysis of dispersed-phase martensitic transformation toughening of two-phase metallic materials

Abstract

Finite element analysis was used to study the martensitic transformation toughening in a two-phase metallic system consisting of a transforming metallic phase embedded in the form of small particles in a stable (non-transforming) metallic matrix phase. The material constitutive model for dispersed-phase transformation plasticity recently developed by Grujicic and Sankaran [1] was used for continuum description of the material behavior. Transient crack growth was simulated in the finite element mesh by a nodal release technique. The remote crack-opening tensile load was adjusted to mantain the near-tip energy release rate at the level necessary for crack advance. The transformation zone surrounding the crack tip and the resistance curves were computed for several levels of thermodynamic stability of the transforming phase. An optimum level of thermodynamic stability of the dispersed phase which gives rise to a maximum enhancement in material fracture toughness has been identified. Finally, the analysis was used to rationalize a nearly 100 percent increase in the fracture toughness observed by Grujicic and Dang [2] in a material system consisting of the gamma TiAl matrix and a 10vol.% of a Ti-Al-V-Fe beta phase dispersion.