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

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 so-lution 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 ℃ 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 bal-anced 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 manu-facturing 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 mi-crostructure,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.