Crack defects and formation mechanism of multi-principal element alloy FeCr0.5NiCu0.5 coating fabricated by Laser cladding

Laser cladding technology presents a promising method for fabricating multi-principal element alloy (MPEA) coatings, yet cracks remain one of the most prevalent defects in HEA laser cladding. In this study, FeCr0.5NiCu0.5 multi-principal element alloy coatings were produced on heat-resistant steel (12Cr1MoV) using laser cladding with varying scanning speeds. The study systematically examined the types and mechanisms of cracks within the multi-principal element alloy coatings and also summarized the effects of scanning speed on the coating's dilution rate and cooling rate. Results indicate that an increase in scanning speed significantly elevates the coating's dilution rate and the risk of cracking. With the increase in scanning speed, the cooling rate has risen from 2.68 × 10 3 K/s to 3.7 × 10 4 K/s, achieving an order of magnitude improvement. The secondary dendrite arm spacing (SDAS) has diminished from 4.02 µm to 1.8 µm, resulting in a significant refinement of the grains. Cracks within the coating are categorized into macrocracks and microcracks. Macrocracks originate at the interface between the coating and the substrate, induced by the substantial thermal expansion coefficient mismatch between the multi-principal element alloy and heat-resistant steel. Microcracks manifest as intergranular cracks due to the distribution of low-melting-point Cu elements along the grain boundaries, which increases the brittleness of the boundaries.