Fully dense and crack free molybdenum manufactured by Selective Laser Melting through alloying with carbon

Abstract

Pure molybdenum processed by Selective Laser Melting (SLM) shows a coarse–grained, columnar microstructure interspersed with cracks. The aim of this study was to process molybdenum by SLM with mechanical properties of powder metallurgically produced material by employing a novel alloying concept for molybdenum powder. Alloying of molybdenum with 0.45 wt% carbon leads to constitutional supercooling, thereby changing the solidification mode from planar to cellular. A refined microstructure with interlocking grains could be achieved. Cracking was entirely suppressed, and porosity was reduced to almost zero. A cellular microstructure with a misorientation angle between the individual cells <0.5° was found. The alpha–Mo phase is surrounded by a closed network of Mo2C. The oxygen content was lowered during SLM processing due to outgassing of CO. The typically intergranular fracture mode of pure SLM molybdenum was changed to transgranular for Mo – 0.45 wt% C. Comparing Mo – 0.45 wt% C to pure molybdenum, the relative density, hardness and bending strength were increased by 1.9%, 65% and 340%, respectively.