Influence of copper on the microstructure and mechanical properties of titanium ortho-alloy produced by selective laser melting

Abstract

This study explores an intermetallic orthorhombic titanium alloy produced by incorporating varying copper concentrations ranging from 0 to 6 wt. % through in-situ doping during selective laser melting (SLM) fabrication, coupled with simultaneous substrate preheating. The investigation delves into the influence of copper introduction on grain refinement within the primary B2/β-phase and subsequent alterations in mechanical properties. Through X-ray diffraction analysis and scanning electron microscopy, the microstructure characterized by the presence of the B2/β-phase and orthorhombic phase precipitates was identified. Additionally, the detection of a minor quantity of the α2-Ti3Al-phase was noted, with its proportion increasing proportionally with the augmentation of copper content. Differential scanning calorimetry revealed a shift in the phase transformation temperatures towards higher temperatures and a constricted α2-Ti3Al + B2/β + Ti2AlNb region, attributed to the inclusion of copper. The addition of copper, up to 6 wt. %, resulted in the softening and embrittlement of the orthorhombic alloy, forming a fine-grained microstructure with an average grain size of 8.3 μm. Energy dispersive X-ray spectroscopy confirmed the presence of an intermetallic O-phase along the grain boundaries, contributing to a 12 % increase in hardness compared to the orthorhombic alloy without copper after SLM with substrate heating at 850 °C. An alloy containing 4 wt. % copper exhibited superior plastic properties and a tensile strength of 1080 MPa, comparable to the strength of the orthorhombic alloy obtained via SLM followed by hot isostatic pressing.