Enhanced low cycle fatigue properties of selective laser melting Ti–6Al–4V with fine-tuned composition and optimized microstructure

Abstract

Improving the low-cycle fatigue (LCF) properties of additively manufactured Ti–5.6Al–3.8V alloy is critical in ensuring its service safety and represents a significant research challenge. This work discusses a solution that optimizes the alloy's microstructure and ductility by precisely controlling the over-saturated strengthening elements and heat treatment. This was accomplished using selective laser melting (SLM), heat treatment at 800 °C for 2 h, and furnace cooling on a Ti–5.6Al–3.8V alloy with tightly controlled Al, V, and O concentrations in a lower range. The results showed that the SLM-fabricated Ti–5.6Al–3.8V alloy, post-heat treatment, exhibited α laths with a width of ∼1.4 μm and β columnar grains with a diameter of ∼126 μm, without experiencing coarsening or variant selection phenomena. The alloy balanced strength and ductility post-heat treatment with a UTS of 1015 MPa and an EL of 16.5% relative to the as-deposited state (UTS of 1199 MPa and EL of 11.9%). Notably, the LCF properties of the heat-treated SLM Ti–5.6Al–3.8V alloy are superior to those of other Ti–6Al–4V alloys produced by additive manufacturing and comparable to traditional forgings. At high strain amplitudes (1–1.5%), the fatigue life of this alloy was twice that of the Ti–6Al–4V forgings. Furthermore, we comprehensively analyzed the microstructure, strength, and ductility of the SLM Ti–5.6Al–3.8V alloy to elucidate the factors influencing its LCF properties. These findings provide a solid foundation for improving the LCF properties of additively manufactured Ti–6Al–4V alloy, thereby contributing to its safe and reliable use in critical applications.