Influence of phase composition on thermal expansion of Ti-0.4Al, Ti-2.2Al-2.5Zr and Ti-3Al-2.5V alloys

Abstract The influence of phase composition on the thermal expansion of Ti-0.4Al (PT-1M) and Ti-2.2Al-2.5Zr (PT-7M) titanium α-alloys, and Ti-3Al-2.5V (Grade 9/PT-3V) α + β-alloy used for pipe production was studied. The dependency of the volume fraction of β-phase (Vβ) on the heating temperature of PT-1M, PT-7M, and Ti-3Al-2.5V alloys was established by means of dilatometric analysis and thermodynamic calculations using Thermocalc software. An explanation of different Vβ values determined by these two methods was proposed. It was found out that the coefficient of thermal expansion (CTE) has a minimum at temperatures close to β-transus temperature (Tβ) of the alloy. The minimum value of CTE depends on the chemical composition of the alloy: the higher alloying degree is, the lower CTE minimum is, and it may assume negative values. This effect is associated with the redistribution of alloying elements between α- and β- phases during α + β→β − transformation in PT-1M, PT-7M, and Ti-3Al-2.5V titanium alloys.