Deformation induced transformation of ω phase in aged Ti-14 mass%Mo alloy

Ti-14 mass%Mo alloys aged for 1 × 10⁶ s at 623 K were deformed by means of a tensile test at 300, 523, 623 and 723 K in Ar atmosphere or of rolling at room temperature in order to investigate the brittle fracture mechanism related to the ω phase. These deformed specimens were observed by optical and transmission electron microscopy. Both deformed structures consisted of many band-like products. In the products, very few ω particles could be found. Instead, zones having a structure different from ω, β and α phases existed. It was found that these zones possessed a body centered triclinic structure, which was newly named β″ on account of the structural similarity to the β phase. The β″ was transformed from ω by deformation. In the transformation process to β″, one ω variant changed into two types of β″; one was closely related to the β matrix, and the other had a {112}〈111〉 twin relation to the former. It is suggested that the band products act as a path of crack propagation prior to the brittle fracture in the aged Ti-Mo alloy.