Investigation of the Influence of Cr on the Microstructure and Properties of Ti6Al4VxCr Alloys with a Combinatorial Approach

A combinatorial approach has been applied to investigate the influence of Cr on the microstructure and properties of Ti6Al4VxCr alloys. A diffusion couple was manufactured with Ti6Al4V and Ti6Al4V20Cr alloys and annealed at 1000 °C for 600 h to obtain a wide range of compositions. It was heated to 1050 °C (above β transus) for 6 h, quenched to room temperature and subsequently aged at 600 °C for 6 h to achieve the typical α + β two-phase microstructures. Combining electron probe microanalysis, scanning electron microscope and nanoindentation, the relationships between the composition and microstructure as well as hardness of the diffusion couple were determined. By calculating the volume fractions using Thermo-Calc, it was found that after aging the Ti6Al4V6Cr sample contained a reasonable (~57 vol%) content of fine α phase and showed peak hardness among the Ti6Al4VxCr alloys. HAADF-STEM and XRD revealed that after solution treatment above the β transus temperature and quenching, the metastable α″ lamellar formed in the Ti6Al4V6Cr alloy. Subsequent isothermal aging of the α″ lamellar became coarse acting as precursors/preferential nucleation sites for the stable α phase.