Hot isostatic pressing of MRI compatible Zr-1Mo components manufactured by laser powder bed fusion

Abstract

To avoid the “susceptibility artifacts” in magnetic resonance imaging (MRI) and realize patient-specific medical devices with complicated shapes, a novel MRI compatible Zr-1Mo alloy with low porosity (c.a. 0.4%) were manufactured by laser powder bed fusion process(L-PBF) using gas-atomized Zr-1Mo(wt%) alloy powder. However, as-built Zr-1Mo(wt%) components using optimized process parameters show relatively high mechanical performance(elongation of 6.4%, UTS of 1175 MPa), but contain 0.4 vol% defects which show a spherical morphology and distribute in the builds randomly. These defects definitely deteriorate the mechanical performance(especially ductility, fatigue behavior) of Zr-1Mo components manufactured by L-PBF. In order to eliminate defects in as-built Zr-1Mo components, hot isostatic pressing(HIP), which has been known as an effective process to decrease the porosity of additive manufactured products, was executed. Due to the elevated temperature and high pressure during HIP treatment, the randomly distributed defects were eliminated after the HIP process. Moreover, the α-martensite structure in the as-built alloy was transformed into a basketweave α + β structure at low HIP temperature(1023 K and 1073 K) or lamellar α + β structure at relatively high HIP temperature(1173 K and 1273 K). In the meantime, the elongation of HIP-treated Zr-1Mo components significantly increased, but the strength shows the opposite trend. From the viewpoint of mechanical property, Zr-1Mo components HIP-treated at 1023 K possessed elongation of 19.9%, and UTS of 628 MPa should be optimized in this study. More importantly, porosity regrowth behavior was investigated to evaluate subsequent heat treatment feasibility for further improvement of mechanical performance. Due to intact raw material power as well as vacuum/low pressure inside the original defect caused by evaporation of metals, porosity regrowth can not be confirmed in HIP-treated Zr-1Mo components after subsequent heat treatment(holding temperature higher than the β transus of Zr-1Mo alloy). Therefore, further improvement of mechanical performance by subsequent heat treatment for HIP-treated Zr-1Mo components is very promising and should conduct further research in the future