Reverse effect of hot isostatic pressing on high-speed selective laser melted Ti-6Al-4V alloy

Abstract

Despite recent progress in achieving high mechanical properties of 3D printed metal products, the low productivity still remains a major limitation for their cost-effective feasibility in practical applications. To achieve high-speed printing with affordable mechanical properties, we increased the scanning speed of selective laser melting process with Ti-6Al-4V up to 1800 mm/s and applied a hot isostatic pressing (HIP) process to compensate for the porosity. In these high-speed printed specimens, the HIP process led to a microstructural change from alpha'-lath martensite to a Widmanstatten a-lamellar structure, which deteriorated their tensile properties due to the segregation of beta-stabilizing atoms and caused inter-lamellar fracture. The deterioration phenomenon of high-speed printed Ti-6Al-4V specimens after the HIP process was found to be critically affected by the surface roughness of as-built state, which can be efficiently controlled with a build angle set-up.