DEFORMATION-INDUCED TRANSFORMATION OF OMEGA-PHASE IN AGED TI-14 MASS-PERCENT-MO ALLOY

Ti-14 mass%Mo alloys aged for 1x10(6) 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 omega 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 omega particles could be found. Instead, zones having a structure different from omega, beta and alpha phases existed. It was found that these zones possessed a body centered triclinic structure, which was newly named beta '' on account of the structural similarity to the beta phase. The beta '' was transformed from omega by deformation. In the transformation process to beta '', one omega variant changed into two types of beta ''; one was closely related to the beta 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.