Controlling the tensile and fatigue properties of selective laser melted Ti–6Al–4V alloy by post treatment

Abstract

The microstructure, phase composition, tensile and fatigue properties of Ti–6Al–4V samples produced by selective laser melting (SLM), SLM followed by heat treatment (HT), and SLM followed by hot isostatic pressing (HIP) were investigated to explore a simpler approach to improve the mechanical performances by post treatment at minimum cost in our work. Results showed that the tensile and fatigue properties of the as-SLMed samples were far below the level of wrought counterpart. Heat treatment and HIP can more obviously enhance tensile properties and fatigue performances, respectively. The microstructure consisted of the lamellar or acicular α and grain boundary α within prior β columnar grain boundaries in the SLMed samples after solution treatment at 850 °C followed by water quenching, whose tensile properties were improved to be 1085 MPa, 859 MPa, 14.0%. A tri-modal microstructure including lamellar α, polygonal α and acicular nanoscale α+β phase formed in the samples after 850 °C solution treatment and 550 °C aging treatment. Their corresponding tensile properties were enhanced to be 1192 MPa, 1054 MPa, 11.4%. The microstructure was composed of lamellar α+β phases for the SLMed sample after HIP treatment, which improved the tensile (>1000 MPa, >850 MPa, and >10%) and fatigue (105∼6 at the stress amplitude of 500 MPa) properties. Therefore, solution treatment at 850 °C followed by water quenching or HIP treatment is a simpler method to control the performances of the SLMed Ti–6Al–4V alloy.