Investigation of the influence of the conditions during recrystallization annealing on the plasticity of molybdenum-base alloys with low concentrations of additives

Abstract

An investigation was made of the conditions during recrystallization annealing on the plasticity and the nature of fracture of Mo-base alloys containing zirconium or titanium (TSM-4, TsM-6, Mo-Ti-C) and alloys free of active oxide-forming elements (TSM-3). Annealing at T > Trecr took place under traditional conditions employed in heat treatments (in ∼10−4−10−6 torr vacuum, in hydrogen-filled furnaces) or under conditions ensuring minimal saturation of the alloys with oxygen during heat treatments (this involved preliminary outgassing vacuum furnaces and wrapping of the samples in molybdenum foil) or under conditions of controlled partial oxygen pressure (in the presence of the Al2O3 powder in the annealing zone). The degree of saturation of the alloys with oxygen was deduced from the appearance of zirconium or titanium oxide in the surface layers of the alloys containing these elements. The results indicated that the conditions during heat treatment and alloying of molybdenum with zirconium and titanium had an important influence on the plasticity and fracture of the Mo-base alloys. The results obtained were analyzed on the basis of the ideas on intergranular brittleness in bcc materials because of segregation of oxygen at grain boundaries and a refining influence of zirconium and titanium on the Mo alloys saturated with oxygen, involving binding of the oxygen in oxides and thus preventing its segregation at grain boundaries.