Phase transformations in beta isomorphous titanium alloys

Influence of phase transformation kinetics on the formation of α in a β-quenched Ti–5Al–5Mo–5V–3Cr–1Zr alloy

“…Furthermore, investigations with Zr-Al based alloys showed that cuboidal x particles were formed between compositional fluctuations along h1 0 0i b during subsequent long-term ageing [18,27]. These findings together with the results presented in the current study support an influence of spinodal decomposition in the formation of x as it was also suggested by other studies with titanium alloys [29,54,61].…”

“…This effect leads to the formation of a composition-modulated structure across h1 0 0i b directions, which are elastically soft directions for bcc titanium and zirconium alloys [18,27]. In agreement with the present results, the spinodal decomposition mechanism was suggested to explain the homogeneous precipitation of fine a plates from the metastable b matrix of the analogous Ti-5Al-5Mo-5V-3Cr-0.5Fe, a Timetal 21S and Ti-V alloys [52][53][54]. These works state that the transformation is controlled by small compositional fluctuations in b, where lean and rich regions in solute evolve towards the equilibrium as the temperature increases.…”

Effect of Nb on Microstructural Characteristics of Ti-Nb-Ta-Zr Alloy for Biomedical Applications

“…After ageing treatment for relatively short time (two days), definite evidence of α phase and isothermal ω phase was not observed from bright field TEM image of the high Nb alloy. Instead, precipitation similar to the formation of a β +β structure 25,26) was found in these aged specimens (see Fig. 6(a)).…”

On the decomposition of the beta phase in titanium alloys

“…The most important observation is that the omega phase forms spontaneously on quenching in lowsolute alloys, and that ageing is necessary to produce omega if the solute content is increased [2,3,5]. Furthermore it is found that there exists a maximum solute content above which omega has not been found under any circumstances [3,4]. These facts taken together prove that the minimum in the free energy curve for the omega phase must be on the solute-lean side of a minimum in the free energy curve for the beta phase.…”

“…Several investigations dealing with the formation of the alpha and the omega phase from the metastable beta phase in titanium and zirconium base alloys have made reference to free energy diagrams or equilibrium phase diagrams [1][2][3][4], but the diagrams have been used mainly to rationalise the results obtained, rather than to predict further possible properties of the systems. In this paper a systematic analysis is made of the free energy diagrams for a binary titanium alloy consisting of a metastable beta phase that tends to form either the alpha or the omega phase or both.…”