Thermal analysis of precipitation reactions in a Ti-25Nb-3Mo-3Zr-2Sn alloy

A study was undertaken on a Ti-25Nb-3Mo-3Zr-2Sn alloy using differential scanning calorimetry (DSC) in order to improve understanding of the precipitation reactions occurring during aging heat treatments. The investigation showed that isothermal omega phase can be formed in the cast and solution treated alloy at low aging temperatures. An exothermic peak in the temperature range of 300 to 400A degrees C was detected for precipitation of the omega phase, with approximate activation energy of 176 kJ/mol. The omega phase begins to dissolve at temperatures around 400A degrees C and precipitation of the alpha phase is favoured at higher temperatures between 400A degrees C and 600A degrees C. An exothermic peak with activation energy of 197 kJ/mol was measured for precipitation of the alpha phase. Deformation resulting in the formation of the stress induced alpha aEuro(3) phase altered the DSC heating profile for the solution treated alloy. The exothermic peak associated with precipitation of the omega phase was not detected during heating of the deformed material and increased endothermic heating associated with recovery and recrystallisation was observed.