Microstructure, crystal structure and mechanical properties of the new ternary intermetallic alloy phase Zr2TiAl

Zr3Al is an intermetallic compound with a cubic structure whereas the isoelectronic compound Ti3Al is hexagonal. Crystallographic, microstructural and mechanical study of an alloy containing all the three elements is use in advancing our knowledge of the phase behavior across this pseudobinary alloy. A nominal composition of the Zr2TiAl alloy was prepared by arc melting and subsequently vacuum annealed at 1050 °C for 30 days and 1000 °C for 20 days. Scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDAX) showed the presence of three phases in the material. Among the three phases, the major phase was the stoichiometric Zr2TiAl alloy. From the SEM micrograph, it was seen that the major phase grains varied in size from 10 μm to 50 μm. Of the two minor phases present in the specimen, one is rich in Ti and the other in Al. In order to identify the peaks due to individual phases, micro-beam XRD was carried out, enabling the identification of all the three unambiguously. The stoichiometric alloy (Zr2TiAl) has L21 structure (space group Fm3m), the Ti-rich phase has DO19 structure (space group P63/mmc) and the Al-rich phase has Aa structure (space group I4/mmm) Further, mechanical characterization of this alloy was carried out using nano-indentation and the typical hardness was found to be 8.5 GPa on the grain and 7.4 GPa at the grain boundary.