Role of substrate heating in controlling meltpool behavior and reaction layer formation by the multibeam laser directed energy deposition

Maintaining compositional homogeneity in equiatomic CrMnFeCoNi high-entropy alloys (HEAs) during processing of directed energy deposition (DED) is challenging due to substrate-induced dilution and elemental decomposition. This study investigates the optimal processing parameters for overfocused multibeam laser DED (MBL-DED) using a gas-atomized powder on high-speed steel substrates. Single-bead tracks were formed under varying laser powers (60–200 W), scanning speeds (10–40 mm/s), and substrate temperatures [room temperature to 200 °C]. The results showed that preheating at 100 °C improved bead continuity without inducing excessive dilution, whereas 200 °C expanded Fe-enriched reaction zones. Under optimal conditions with a laser power of 120–140 W and scanning speeds of faster than 30 mm/s, single-bead tracks without observable meltpools while preserving near-equiatomic composition were formed. Elemental decomposition was effectively mitigated under high scanning speeds. Integrated control of laser power, scanning speed, and substrate preheating is critical for achieving microstructural and compositional integrity of HEAs in the MBL-DED.