Martensitic alpha and omega phases as deformation products in a titanium-15% molybdenum alloy

Abstract

The structure of omega phase and its formation by heat treatments in certain titanium alloys are well established. Formation of this phase during cold deformation of β-phase alloys, although claimed by some investigators, has not been studied extensively and conflicting evidence has been published. The effect of compressive stresses on coarse and fine grained specimens of a Ti-15% Mo alloy in the retained beta phase condition has been examined. Specimens have plastically deformed initially by formation of martensitic alpha phase and subsequently by slip. In coarse grained specimens some alpha phase plates have been observed to restrict their own growth by generating slip across the growth direction. Analysis of slip line separation magnitudes in one of these instances indicated that a maximum stress, of the order of 10 10 dyn/cm 2, is present at a plate tip and that stress decreases linearly with distance from the point in the direction of propagation of the plate. X-ray diffraction results have established that omega phase in this alloy forms in greater quantities as cold deformation proceeds, at least until about 40 per cent strain has been effected. The phase originates on octahedral planes in the lattice of the beta matrix and appears to grow on these planes.