Parametric optimization of multi-pass electron beam melting for molybdenum alloy containing 47.5 wt% rhenium

In this study, the effects of multi-pass electron beam melting (EBM) processes under vacuum condition on microstructure and mechanical behavior of a molybdenum alloy containing 47.5 wt% rhenium were systemat-ically investigated. Nine experimental designs were performed to improve the surface quality and minimize the defects. Results showed that beam power, scan speed, processing step and penetration depth played a critical role in the specific energy density function, which would further influence the porosity and microhardness. Mean-while, specific energy density was significantly influenced by beam power at higher scan speed (e.g. 15 mm/s) whereas it was mainly related to scan speed under lower beam power (e.g. 2 kW). With a processing step of 0.5 mm (half of the beam diameter), a continuous melt morphology and less porosity were obtained, indicating that a significant overlap between the scan tracks was beneficial for the optimization of microstructure. Micro-hardness results showed that mechanical performance can be improved with the reduction of porosity together with the increased specific energy density. Thus, a combination of 10 kW beam power, 2 mm/s scan rate and 0.5 mm processing step can realize surface optimization in melted plates through multi-pass EBM technique.