Meaning
Structural integrity at a phase boundary depends on the elastic energy stored when atoms maintain a continuous lattice across an interface. Presence of coherency strain alters the total energy of a precipitate system and influences the morphology of strengthening phases. This strain occurs when the mismatch between the solvent and solute lattices is small enough to be accommodated without forming dislocations.
Mechanical Hardening
Impediment of dislocation motion results from the internal stress fields surrounding coherent particles. While a material undergoes thermal aging, the coherency strain contributes to the yield strength by creating a barrier that moving line defects must overcome. Shearable precipitates provide hardening because the elastic field interacts with the glide planes of the matrix.
Phase Stability
Elastic energy density limits the maximum size a coherent particle can reach before relaxing. Excessive coherency strain triggers the formation of interfacial dislocations that transform the boundary from coherent to semi-coherent.
Directional Coarsening
Alignment of precipitates during high-temperature service follows the path of least elastic resistance. An external load interacts with the coherency strain to produce a rafted structure where the particles elongate perpendicular or parallel to the stress axis. Such morphological changes determine the remaining life of components operating in high-stress environments.
Periodic inspection of the grain structure reveals whether the lattice has undergone this type of permanent reconfiguration.
