On the fcc to hcp transformation in a Co-Ru alloy: Variant selection and intervariant boundary character
Ehsan Farabi, N. Haghdadi, Christoph Czettl, Julia Pachlhofer, Gregory S. Rohrer, Simon P. Ringer, Sophie Primig
Abstract
Ru is a common addition to the Co-binder in WCCo hardmetals for advanced cutting tool applications. Internal Co-Co interfaces control many properties such as hot-hardness, toughness, and creep resistance. Hence, phase transformations determining the internal interface character can be harnessed to achieve superior properties. We investigate the γ (face-centred cubic) to α (hexagonally closed packed) martensitic phase transformation of a model Co-Ru binder alloy. We describe the crystallography of γ to α phase transformations and the resulting α/γ and α/α interface character distributions. The stabilisation of the γ-phase results in the formation of low energy (0 0 0 1) α/γ interphase boundary planes. Preferred formation of α/α intervariant and twin-related boundaries with symmetrical tilt configurations are also observed. We discuss how crystallographic constraints of the transformation promote the formation of grain boundary planes other than those of the lowest energy configurations.