Mobility of the β₁-γ ₁ ^′ martensitic interface in Cu-Al-Ni: Part II. Model calculations

The interaction of the twinned β _-1-γ ₁ ^′, martensitic interface with various experimentally observed obstacle particles is analyzed using a specific dislocation model for the interface. The strain interaction of particles with simple shears and tetragonal distortions and their modulus interactions are treated as functions of particle crystallographic orientation, particle position with respect to interfacial intersection, and particle size. Differences from previous predictions of a simple general interface model arise primarily from differences in the assumed interfacial trajectory relative to the particles. The finite-particle calculations indicate that the point-particle approximation is valid for a particle radius less than one-tenth the interfacial twin period. Overall agreement with the experimentally measured interfacial mobility behavior is greatly improved over the previous simple model prediction. The measured athermal component of the driving force for interfacial motion is consistent with the strain and modulus interaction with 2H-phase particles. The activation-energy /driving-force relations obtained from the thermally activated component are reasonably represented by the strain interaction with the fine-scale atomic displacements of the tweed structure.