Crystallography and microstructure of TaRu

The solid-state phase transformations and crystallography of equiatomic TaRu were examined by conventional and in-situ high-temperature transmission electron microscopy, with complementary experiments using X-ray diffraction and dilatometry. This alloy undergoes two displacive phase transformations on cooling from the high-temperature B2-ordered cubic phase. The high-temperature cubic-to-tetragonal transformation produces a highly twinned microstructure similar to that observed in many shape memory effect alloys. The phase produced by the low-temperature transformation was shown by detailed microdiffraction to have a monoclinic symmetry rather than the orthorhombic symmetry which had been previously reported. The structure of this monoclinic lattice indicates the possibility of an omega-like transformation in this alloy.