The alloy AlCrFe₂Ni₂, known as medium entropy alloy (MEA, ∆S/R ~ 1.33) was processed using Laser Direct Energy Deposition (L-DED). The alloy is designed to develop a Widmanstätten type duplex microstructure following a solid state phase transformation which is controlled by the cooling rate. During L-DED this transformation is hardly accomplished, commonly calling for a post-build heat treatment. For the first time, an intrinsic laser-based heat treatment was applied to promote this phase transformation in the Additively Manufactured HEA in a layer by layer approach. Process parameters for the intrinsic heat treatment were varied and investigated in terms of temperature–time cycles, cooling rates and penetration depth. The microstructure of as-built and differently heat-treated samples was investigated. In the as-built condition, the duplex structure consist mainly of ordered and disordered bcc phase and a small fraction of thin fcc-plates (40%). It was found that the fcc phase fraction can be significantly increased up to 58% by applying an intrinsic heat treatment. The heat treatment involves nucleation of new fcc plates as well as thickening of the existing plates. The process-related inhomogeneity of the microstructure resulting from heat affected zones at melt pool boundaries is not eliminated due to the short interaction times. In contrast to the conventional post-process heat treatment at 900 °C for 6 h, the microhardness is not significantly reduced during intrinsic heat treatment and remains in the range of 400 HV0.3. Intrinsic heat treatment is however beneficial, since it can be applied selectively. Thus, it offers novel possibilities for surface cladding applications. Graphical Abstract

Copper is a key material for cooling of thermally stressed components in modern aerospace propulsion systems, due to its high thermal conductivity. The use of copper materials for such applications requires both high material strength and high stability at high temperatures, which can be achieved by the concept of oxide dispersion strengthening. In the present work, we demonstrate the oxide reinforcement of two highly conductive precipitation-strengthened Cu-Cr-Nb alloys using laser additive manufacturing. Gas-atomized Cu-3.3Cr-0.5Nb and Cu-3.3Cr-1.5Nb (wt.%) powder materials are decorated with Y₂O₃ nanoparticles by mechanical alloying in a planetary mill and followed by consolidation by the laser additive manufacturing process of laser powder bed fusion (L-PBF). While dense specimens (>99.5%) of reinforced and nonreinforced alloys can be manufactured, oxide dispersion-strengthened alloys additionally exhibit homogeneously distributed oxide nanoparticles enriched in yttrium and chromium next to Cr₂Nb precipitates present in all alloys examined. Higher niobium contents result in moderate increase of the Vickers hardness of approx. 10 HV0.3, while the homogeneously dispersed nanometer-sized oxide particles lead to a pronounced increase of approx. 30 HV0.3 in material strength compared to their nonreinforced counterparts.

The mechanical properties in laser-based powder bed fusion (PBF-LB/M) manufactured parts are anisotropic in nature due to the layer-wise build-up but also change due to different solidification conditions in dependence on the process strategy and the geometry. In this work, the latter effect is examined by means of simulating the thermal history on a part scale (macro temperature) and correlating the critical temperature and holding time with the local hardness and microstructure. A macro temperature model is introduced and validated with vector-based thermal simulations and thermo couple measurements from the build-up process. Two cone-shaped geometries are investigated, namely, an upright and an inverted cone. The examinations are performed and validated with Inconel 718. An outlook to further investigations and more complex, real-life applicable geometries is given.

Laser-based additive manufacturing (LAM) in all its variations is now being established as a technique for manufacturing components from various material types and alloys

Multi material additive manufacturing (MM-AM) is an attractive approach to combine the geometric flexibility in particular of powder bed based AM processes with functional integration. A major limitation of multi-material laser powder bed fusion (MM-LPBF) approaches is the risk of powder contamination. In the present study, the implementation of a concept for manufacturing of multi material parts is demonstrated. A new type of device is contructed, and the new process is tested fundamentally and gradually by experimental means. Aspects investigated include machine and process feasibility, bonding issues, and dilution. Microstructural analysis reveals the successful build of multimaterial basic geometries out of steel powder (316L stainless steel) and both nickel-based alloy and copper foil. This provides a new process whose further research offers high potential for numerous multi-material applications.