Microstructural evolution during post-heat treatment and its effect on the mechanical properties of directed energy deposited near titanium alloy

In this work, the microstructural evolution of a directed energy deposited near beta titanium alloy, Ti5Al2Sn2Zr4Mo4Cr, during post-heat treatment was investigated, and its effect on the mechanical prop-erties was evaluated. The results showed that the equilibrium volume fraction of the alpha phase was reached in the first 30 min over a temperature range of 720-840 degrees C. Fine basketweave alpha laths (alpha BW) were homo-genously distributed within the prior beta grains at 840 degrees C. Both fine alpha BW and alpha colonies developed from the grain boundary alpha layers (alpha GBW) were obtained in the sample solutions treated at 720, 760, and 800 degrees C. Water-quenching and air-cooling were employed to retain the beta phase at room temperature. The alpha phase volume fraction increased significantly and reached the equilibrium volume fraction during the furnace -cooling process. In addition, the manner in which the samples were subjected to isothermal temperatures can strongly affect the evolution of the alpha phase. The homogenized specimen containing a single beta phase exhibited the lowest strength and the highest plasticity. The strength increased and the ductility decreased after subtransus solution treatment. The difference in the mechanical properties can be attributed to the differences in the alpha and beta phases caused by the various heat treatments. The modified rule of mixtures appropriately described the relationship between the yield strength and microstructure characteristics. (c) 2022 Elsevier B.V. All rights reserved.