Laser additive manufacturing of iron aluminides strengthened by ordering, borides or coherent Heusler phase
Abstract
Laser Additive Manufacturing (LAM) is a near-net-shape processing technology well-suited for the production of parts from intermetallic alloys. Three different iron aluminide alloys have been processed by Selective Laser Melting (SLM) and Laser Metal Deposition (LMD).
The alloys selected for LAM represent three different strategies for strengthening iron aluminides at high temperatures: Increase of the ordering temperature D0(3) B2 (Fe-30Al-10Ti; all compositions in at.%), precipitation of borides (Fe-30Al-5Ti-0.7B) and generation of coherent A2 + L2(1) microstructures (Fe-22Al-5Ti). It is shown that all three alloying strategies established from as-cast alloys can also be realised through both LAM processes, generating defect free and dense (>99.5%) samples.
Yield stress and compressive creep strength also match that of the as-cast alloys above 600 degrees C, while at lower temperatures in some cases higher yield stresses are observed. In addition, the yield stress below 600 degrees C may also depend on the building direction and may change after a heat treatment.
No general improvement of ductility is observed, specifically in case of Fe-30Al-10Ti, where the grain size in the LAM processed samples is one magnitude lower than in the as-cast alloy. However, depending on building direction and subsequent heat treatment some samples become ductile at quite low temperatures, which at least in some cases may be explained by the internal stresses measured by XRD.