Evolution of microstructure and mechanical properties of Ti65 high-temperature titanium alloy after additive manufacturing and annealing

Abstract

Ti65 was prepared by Laser Direct Energy Deposition (LDED) and subjected to Annealing Heat Treatment (AHT). The microstructure and mechanical properties of different specimens were evaluated. The results indicated that the prior β columnar crystals had a strong [0001] texture along the grain growth direction. The coarsening or spheroidization of α lath was attributed to the splitting of lamellar α, subsequent non-directional growth, element migration, and Ostwald ripening. The isotropy of the specimen annealed at 950 °C was caused by trimodal microstructure, discontinuous grain boundary α (αGB), precipitates dissolution, and low-angle grain boundary. A mathematical model was established to predict yield strength (YS) and microhardness based on the α lath thickness. The microhardness-strength correlation of LDED Ti65 followed an empirically derived model (Tabor's relationship). Improvements to the original models of the microhardness-strength relationship for Ti65, in conjunction with the strain-hardening effect and α orientation, made it possible to use these models to predict the strength of LDED Ti65 parts and improve the accuracy of the predicted values. Simultaneously, the model can provide data support for the industrial application of Ti65 or, where appropriate, provide a reference for other technical production (material applications).