Grain refinement mechanisms of alloying molybdenum with carbon manufactured by laser powder bed fusion

Pure molybdenum produced by additive laser powder bed fusion (LPBF) processes has a coarse, epitaxially-grown columnar grain structure with cracks located at high-angle boundaries, which are embrittled through oxygen segregation. The tensile strength of these pure specimens is only 50 MPa, or 11% the metallurgically sintered, deformed, and recrystallized molybdenum. Alloying carbon can reduce cracks, increase density to 99.5%, thus 650 MPa. addition prevents boundaries high residual porosity outgassing oxygen, trapping any in oxygen-soluble Mo2C carbide, increasing boundary surface on distributed. In this study, we investigated size, strength, hardness five different molybdenum-carbon alloys via LPBF constant process parameters. Our ranged from 2.2 wt% carbon, corresponds near-eutectic composition. absence extrinsic nucleant particles melt, relationship between size solute concentration—and growth restriction factor—follows an inverse exponential Arrhenius-type equation. We attributed refinement higher contents thermal constitutional supercooling. supercooling allows grains nucleate grow underlying solidified layer, where fastest direction 〈1 0 0〉 better aligned gradient than that epitaxially growing grains.