Transformation-mismatch plasticity of NiAl/ZrO2 composites—finite-element modeling

A coupled thermo-mechanical finite-element model was developed to describe transformation-mismatch plasticity resulting from mismatch stresses produced by allotropic particles within a creeping matrix. A composite consisting of a NiAl matrix with 10 vol.% zirconia allotropic particles was modeled in two dimensions for a range of externally-applied stress values. The instantaneous composite strain developed during the zirconia transformation is found to increase linearly with the applied stress, in agreement with continuum-mechanical, closed-form models for transformation-mismatch plasticity. This instantaneous strain is smaller than the total strain accumulated over a half temperature cycle, indicating that mismatch stresses produced during the transformation relax by matrix creep long after the particles have transformed. Also, the total composite strain calculated after a full temperature cycle is in good agreement with strains determined experimentally on a NiAl–10% ZrO2 composite. Finally, the internal stress distribution within the transforming composite is determined numerically and compared to simple analytical averages.