Soft chemistry synthesis and laser powder bed fusion processing of Fe–Ni alloy based powders: A route for the manufacturing of porous multiphase Fe–Ni alloy parts

Abstract

Fe–Ni alloy based powders of different stoichiometry and purity were synthesized by thermal decomposition of a co-precipitated oxalic precursor. By modifying the oxygen partial pressure of the gaseous flow, a nearly pure Fe64Ni36 Invar powder and a composite Fe50Ni50-Fe3O4 powder were prepared. The composite particles present an original microstructure consisting of an intimate mixture of Fe50Ni50 and Fe3O4 submicronic grains. The behavior of the composite powder was studied in laser powder bed fusion (LPBF) process. Reduction of iron oxide and specific microstructural changes were revealed. Subsequent conventional heat post-treatment allowed to remove the remaining iron oxides and to form porous multiphase Fe–Ni alloy 3D parts. Repeatable heterogeneities of microstructure and composition, at a periodicity corresponding to the thickness of the powder bed used in the LPBF process, constitute the hallmark of the laser treatment carried out on the composite powder.