Phase transformation and lattice stresses in ni-based superalloys and tial-based intermetallics

This article firstly emphasizes that a solid phase transformation always results in lattice distortions associated with "coherency" stresses. Then, it identifies four possible mechanisms of complete or partial stress relaxation, i.e. (a) plastic deformation; (b) crystal shape optimization; (c) selection of favorable crystallographic variants and (d) alteration of phase equilibrium. Lastly, some examples are given relative to the precipitation, dissolution and "rafting" of gamma' phase in single-crystal nickel-based superalloys (mechanisms b and d), then to the lamellar alpha -> alpha 2 -gamma transformation in TiAl-based intermetallic alloys (mechanism c).