The Emergence of Inhomogeneity in the Chemical Composition of Powder Applicable for Manufacturing Products by Additive Technologies

Abstract

This work addresses direct metal laser-sintering (DMLS) of powders of complex chemical composition in order to manufacture products with minimal inhomogeneities in the chemical composition and structure. The raw material used was an ingot of steel 12CrH3MoCu, from which a powder of different fractional composition was processed by atomizing the melt at 1650 °C in an argon atmosphere. It has been established that the atomized melt condenses into spherical objects, according to the vapor-to-liquid scenario in which, when cooled, some of the doping chemical elements form clusters with subsequent crystallization into phases of variable composition and crystalline structure. For subsequent mechanical tests, cylindrical samples Ø 6 × 10 mm were manufactured by DMLS with EOSINT M270. The samples strength, determined under compression at a room temperature, indicated an increase of 1.5 times in comparison with the initial solid metal. On the σ (ε) diagrams in the parabolic hardening zone, randomly located local hardening extremes were recorded, followed by abrupt load drops. The obtained data testified to the heterogeneous structure of the samples. Using light and electron scanning microscopy, it was established that the revealed features in the σ(ε) dependences are due to segregation metal heterogeneity in form of cellular structures with a cell size of ~200μm. Structures of variable composition and morphology are ensembles of oxides, whose influence on the strength of the samples could be leveled by thermal treatment.