Rapid Alloy Development Using Calphad Simulation and Powder Blends in Direct Energy Deposition

Abstract

The ongoing commercialization of additive manufacturing (AM) has necessitated the need to tailor alloy chemistry as well as exploit AM process particularities such as freedom of design, print geometry and high cooling rates to meet functional application requirements. Alloys such as hot-work tool steels, including H11, are well suited for machining and tooling applications. In this work, the authors investigated and compared high-speed direct energy deposition with laser beam source (HS DED-LB/M) processability of a reference H11 alloy and its modified form (H11m). The modification of the alloy was intended to minimize the amount of retained austenite (RA) in as-built microstructure and reduce post-heat treatment steps. The investigative approach included Calphad simulation, rapid alloy blending (modified powder) and process parameter optimization to produce dense parts for microstructure characterization and mechanical properties testing. The results show that while H11 achieved a high relative density > 99.85%, H11m still had cracks parallel to the building direction. The amount of RA was equally reduced from 4.08% in H11 to 1.23% in the H11m. H11 had a comparatively superior average microhardness (591 HV0.5) to H11m (561.5 HV0.5), which can be attributed to the more carbide presence. The martensitic strengthening effect between H11 and H11m can be described as similar.