The Effect of Heat Treatment on Ti64-1.2Cu Deposits Fabricated by Wire-arc Directed Energy Deposition: Process Optimization, Microstructures, and Mechanical Properties

This study employed the Gleeble high-throughput test to optimize the heat treatment condition of the modified Ti64-1.2Cu alloy, aiming to enhance its mechanical properties. The optimal heat treatment condition was determined to be: warm preservation at 883°C for 0.5 h followed by water quenching to room temperature. With this condition, the microhardness significantly increased from 346.8 HV to 395.1 HV, the yield strength increased from 934 MPa to 990 MPa, and the ultimate tensile strength increased from 991 MPa to 1043 MPa. Despite the tensile fracture elongation reduced from 10.66% to 7.46%, it is still higher than traditional Ti64 deposits (6.35%, as a reference group). The enhancement of microhardness and tensile strength is mainly contributed by the precipitation hardening effect caused by the formation of ~20 nm Ti 2 Cu precipitates. However, those brittle nano Ti 2 Cu particles, the widening of α laths (from 1.91 µm/6.90 µm 2 to 2.76 µm/10.95 µm 2 ), as well as the coarsening of prior β grains (from 1.05 mm/0.44 mm 2 to 2.52 mm/1.64 mm 2 ), commonly contributed to increased brittleness, leading to a decreased tensile fracture elongation. Overall, under the premise that the tensile fracture elongation does not decrease much and is still within the desirable application range, such heat treatment optimization methods and conditions have a positive sense for improving the performance of Ti64-1.2Cu alloy.