The fabrication of ultrahigh strength Ti-4Cu-6Al alloy using laser additive manufacturing

Abstract

In this paper, we reported an ultrahigh strength Ti-4Cu-6Al (wt.%) alloy fabricated by selective laser melting (SLM), and the microstructure and mechanical behavior of as-SLMed and heat-treated alloys were systematically investigated. Findings indicate that the as-SLMed specimen consists of an ultrafine acicular α′ structure, averaging a spacing of ∼0.07 μm. The ultrafine acicular α′ decomposes into α and Ti₂Cu after heat treatment at 700 °C and 800 °C for 1 h. The Ti₂Cu precipitate phase became invisible, while a small number of β_t Cu-enriched structure formed when the heat treatment temperature is raised to 900 °C. The as-SLMed sample exhibits an ultra-high ultimate tensile strength of 1578 MPa, while a low elongation of 1.7 %. The heat treatment temperature at 700 °C decreases the ultimate tensile strength to 1299 MPa, while it hardly improves tensile elongation. A good balance between strength and elongation is achieved when the specimens were subjected to thermal processing at 800 °C or 900 °C for 1 h. The specimen subjected to heat treatment at 900 °C demonstrated superior mechanical performance, evidenced by a notable increase in tensile elongation from 1.7 % to 10.3 % and a slight decrease in ultimate tensile strength from 1578 MPa to 1254 MPa. At last, the reasons for the microstructure evolution during heat treatments and the strengthening mechanisms in the as-prepared samples were discussed.