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

Highlights: • The influence of phase composition on CTE of titanium alloys (Ti-0.4Al, Ti-2.2Al-2.5Zr and Ti-3Al-2.5V) has been studied. • The dependency of the volume fraction of β-phase (V_β) on the heating temperature has been established by different methods. • The CTE of alloys has a minimum at temperatures close to β-transus temperature of the alloy. • The minimum value of CTE depends on the chemical composition of the alloy and it may assume negative values. • This effect is associated with the redistribution of alloying elements between α- and β- phases during α→β-transformation. -- 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 (V_β) 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 V_β 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 (T_β) 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.