Two-phase materials for high-temperature service

The structures and properties of two families of lattice-coherent composites, those based on γ/γ′ Ni3Al and those based on TiAl/Ti3Al, are shown to have strong similarities. The coherent system of cubic/tetragonal Y2O3–stabilized ZrO2 is then described, and shown to have strong similarities to the system TiAl/Ti3Al. The phases γ TiAℓ (L1o) and α2 Ti3Aℓ (DO19) are not cubic, and their anisotropic thermal expansion may lead to ratcheting creep under conditions of thermal cycling.