Solute-induced grain refinement and defect suppression in boron-modified molybdenum manufactured via laser powder-bed fusion

• DOI: 10.1016/j.ijrmhm.2023.106384
• Publication Date: 2023-08-30T00:41:06Z
• Authors: L. Kaserer; D. Brennsteiner; J. Braun; V. Goettgens; I. Letofsky-Papst; P. Singer; H. Kestler; W. Schafbauer; G. Leichtfried
• Keywords: Equiaxed crystals; Honeycomb; Brittleness

Molybdenum manufactured with laser powder bed fusion (LPBF) has an undesirable coarse-grained, columnar microstructure interspersed intergranular cracks, high porosity, and poor mechanical strength. These defects result from a combination of the harsh LPBF process conditions disadvantageous properties molybdenum, such as its brittle-ductile transition temperature low tolerance for oxygen impurities. In order to suppress these defect-forming mechanisms improve suitability LPBF, alloy-side material adjustments simultaneous optimization are necessary. this work, effect adjusting Mo by adding 3.5 at.% B is investigated experimentally. Mo-3.5 specimens can be produced entirely free density 99.8%. The have fine, equiaxed grains average grain size 31 μm aspect ratio 1.3, thus achieving substantial refinement otherwise typically coarse-grained columnar, anisotropic pure in LPBF. Furthermore, possess honeycomb-like cellular subgrain structure. This structure formed through solute rejection during solidification consists initially solidified α-Mo cells cell <1 network ~100 nm thick intercellular Mo2B phase completely covering cells. addition, formation boron oxide inclusions, presumably B2O3, <50 within phase, provides effective mechanism scavenging impurities, ensuring segregation-free boundaries B. microstructural modifications substantially properties. Under appropriate conditions, substrate plate preheating playing crucial role, bending strength 1120 ± 172 MPa hardness 379 24 HV10 at room achieved. At test 600 °C, increase 2265 observed, angle simultaneously increases 2° 35° °C. findings indicate that limited brittle behavior lower temperatures, which residual likely initiate fracture.