Evidence of an Orthorhombic Transition Phase in a Ti-44Al-3Mo (at.%) Alloy Using in Situ Synchrotron Diffraction and Transmission Electron Microscopy

Alloying of a binary system with an additional clement often leads to the formation of new phases. In this work, a gamma-TiAl based alloy with 3 at.% molybdenum was investigated, which was quenched from 1450 degrees C. Upon reheating, the formation of an orthorhombic phase was observed with the help of in situ high-energy X-ray diffraction. This phase formed at 600 degrees C and vanished again at 720 degrees C, and acts as a transition phase between the alpha(2) and the gamma phase. Such a transition phase has not been observed before in this type of alloy. Additionally, transmission electron microscopy was used to study the microstructure of selected sample states on a sub-micrometer level. The orthorhombic phase formed fine lamellae inside the alpha(2) phase and the alpha(2)' martensite.