Grain Refinement of Fe-X Alloys Fabricated by Laser Powder Bed Fusion

Abstract

Grain refinement tendency of pure Fe and Fe-X (X=5~10at%Al, 2~10at%Ti) alloys produced by laser powder bed fusion (LPBF) process was investigated. Pure Fe, Al, and Ti powders were dry mixed and cubic samples were built from the mixtures. The microstructure analysis revealed that (1) the microstructure of pure Fe consisted of equiaxed grains having an average diameter of 1.7 μm with fine iron oxide particles. (2) Fe-5 and 10at%Al alloys showed coarse columnar grains. (3) Fe-2at%Ti shows a mixture of fine equiaxed and columnar shape grains. (4) the microstructures of Fe-5at%Ti and 10at%Ti alloys are fully equiaxed, and grain refinement tendency was confirmed with increasing Ti content. Ti(N,O) oxi-nitrides are efficient in reducing the grain size because of the low lattice misfit with the ferrite matrix. Additionally, the effectiveness of Ti(N,O) particles as grain refiners was confirmed by building samples using TiN powder mixed with Fe-10at%Al and Fe-2at%Ti. While these alloys alone are coarse grained, a dispersion of Ti(N,O) particles achieved a fine-grained microstructure.