Phase changes, such as carbide precipitation or formation of intermetallic compounds, are accompanied by changes in specific volume/density. This fact has long been known and it is one of the fundamental principles that the dilatometry technique exploits for monitoring phase change kinetics.
Under isotropic conditions, the volumetric changes due to phase changes introduce lattice-scale misfit strains and stresses, but should not induce mesoscopic or macroscopic residual stresses. Exceptions occur where materials are constrained and hydrostatic stresses increase. This may contribute to localized cracking, particularly in thermally activated materials (in the creep range). The linear strains associated with phase changes are of the order of 0.01-0.1 %.
The scope of this project is the development of a generic volume contraction model with solid thermodynamic and kinetic foundation. The model shall describe volumetric change as a function of precipitation for varying degrees of deformation (cold work/dislocation density/hardness), alloying element content for the forming phase, temperature, time, solution treatment, microstructural parameters such as grain size, or other relevant parameters. The model is focused on FCC materials in the 300 stainless steel family, the alloy 800 family, and the Ni-base alloy 600 family.
