Effects of elemental vaporization and condensation during heat treatment of single crystal superalloys

Vaporization and subsequent condensation of Ni and Al is shown to play a dominant role in the evolution of microstructure during heat treatment of an Re-containing single crystal superalloy. Thus the traditional view that matter is not exchanged with the environment – so that the thermodynamic system is closed – is shown to be incorrect. The extent of depletion of Ni and Al alters the surface chemistry, causing formation of refractory-rich precipitates and destabilization of the matrix phase, γ.