Microstructure formation mechanisms of spinodal Fe-Cu alloys fabricated using electron-beam powder bed fusion

We studied the microstructure formation mechanisms of spinodal Fe-10%Cu alloys (mass %) fabricated using electron-beam powder bed fusion with various scanning speeds. Crosscorrelation electron backscattered diffraction analysis was utilized to investigate the crack initiation and propagation mechanisms related to dislocation density and residual stress in the as-built Fe-10%Cu alloys. The as-built alloys with low scanning speeds have equiaxed microstructures with coarse grains, including Cu particles. As the scanning speed increased, the grain size and Cu particle size decreased, and micro-cracks initiated at the edge of lack-of-fusion defects and then grew along the grain boundary parallel to the built direction (BD). In addition, coarse Fe3O4 particles formed on the boundary caused a decrease in thermal conductivity and tensile strength. A strong compressive residual stress parallel to the BD acts as a driving force for micro-crack propagation. The rapid cooling rate enhances local dislocation density, and lattice rotation also causes micro-crack growth, thereby deteriorating mechanical and thermal properties. Therefore, the scanning speeds should be controlled below 2000 mm/s for good strength and superior conductivity of the spinodal Fe-Cu alloy.(c) 2023 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).