Decomposition processes of β phase in a Ti-15Zr-4Nb-4Ta alloy

Abstract

Decomposition processes of β phase in a Ti-15Zr-4Nb-4Ta alloy during isothermal holding have been examined mainly by transmission electron microscopy. Specimens solution-treated at 1000°C in β phase field were held at temperatures between 400 and 600°C. α phase lath formed in β phase during isothermal holding at 600°C. After holding at 600°C for a short duration, remaining β phase, untransformed β phase into α phase at 600°C, was transformed into α′ martensite during quenching into ice-brine. As increasing holding time at 600°C, remaining β phase was transformed into α″ or athermal ω phases during quenching. After prolonged holding at 600°C, remaining β phase was not transformed during quenching. Enrichment of Nb, Ta and Zr into remaining β phase occurred with increasing holding time at 600°C, resulting in the variation of transformation of remaining β phase during quenching. Microstructures evolved at 400 and 500°C were almost same as those at 600°C.