Transformations in the Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti-17) alloy and mechanical and microstructural characteristics

The α + β type Ti–5Al–2Sn–2Zr–4Mo–4Cr (Ti-17) alloy, can be subjected to different thermal treatments of solution and aging. During the solution treatment, phase α is changed to β, until the transformation is completed upon reaching the β transus temperature (∼900 °C). The identification of the kinetics of this transformation allows to carry out different thermal treatments according to the amount of untransformed phase α. During posterior quenching from solution temperature, the phase β transforms, partially, into martensite, its amount and composition depending on the amount of untransformed phase α.Tests of thermal and dilatometric analysis, measures of electric conductivity and hardness, as well as metallographic studies have been carried out in order to analyze phase α transformation and thus to evaluate its kinetic behaviour, its characteristics and its influence in subsequent transformations. Samples of material in a mill annealed condition were heated for 1 h to temperatures between 600 and 900 °C, and then cooled in water. In addition, the samples were heated to 620 °C for 8 h.The samples were also assessed for mechanical properties: ultimate tensile strength, yield strength and elongation.The measures of conductivity, as well as the thermal and dilatometric analysis showed to be adequate methods to assess the transformation. The results support the viability of a fast and non-destructive control of thermal treatment, starting with measures of electric conductivity.