To introduce the use of powder mixtures as a tool for cost effective alloy development for powder-based additive manufacturing techniques, the processing of a hot-work tool steel powder mixture using laser-based powder bed fusion of metals (PBF-LB/M) is investigated. The used feed stock material was produced by admixing low-cost mechanical crushed ferroalloy and elemental particles with inert-gas atomized iron powder. As a challenging test to this alloying strategy, the used powder mixture contains high-melting Mo- and W-rich ferroalloys to create secondary hardenable hot-work tool steels. Furthermore, a prealloyed starting powder of the same nominal chemical composition was produced by inert-gas atomization as reference. Besides, another reference state is produced by casting to compare the microstructures and mechanical properties resulting from the different processing routes.

First, the impact of the partly aspherical and chemical inhomogeneous starting powder mixture on the powder application and the densification behavior during PBF-LB/M was investigated. Suitable process parameters were evaluated. The microstructure formation was comprehensively examined using electron microscopy and the methods adapted to it.

To eliminate volumetric defects as well as chemical inhomogeneities promoted by the use of the partly aspherical and chemical inhomogeneous starting powder mixture, thermal post-treatments, in both, the fully solid state (hot isostatic pressing) as well as in a partly liquid state (supersolidus liquid phase heat-treatment) were performed. Suitable heat-treatment parameters are evaluated. Finally, the obtained microstructures and the associated achievable hardness of the post-processed PBF-LB/M samples were compared with those in the reference states.

On the one hand, thermal post-processing in the fully solid state does not dissolve remnants of high-melting feed stock constituents ferromolybdenum and ferrotungsten due to preferred carbide formation at the interfaces.

On the other hand, it was possible to achieve chemical homogenization and full redensification of the PBF-LB/M-processed powder mixture by a supersolidus liquid phase heat-treatment simultaneously. Thereby, the secondary hardness of the heat-treated samples exceeds that of the cast reference. It could be shown that, in comparison to gas atomized powder, the use of powder mixtures is a cost effective and flexible tool for alloy development in PBF-LB/M even if high-melting alloying elements are required. Comparable relative densities, chemical homogeneity, and mechanical properties can be ensured by a short supersolidus heat-treatment.