Marine machinery and engine components face humid and corrosive environments. Steels or Ni-based materials with high strength and outstanding corrosion resistance are often employed in marine services for their good strength and corrosion resistance properties. High alloy strength and good corrosion resistance are difficult to achieve simultaneously. Selective laser melted (SLM) austenitic steels present a new pathway to improve strength, work hardening, and ductility. Due to SLM products’ superior strength compared to most other metal 3D printed parts, this technology is highly sought after in high-end applications. SLM can produce extremely complex geometries and reduce part counts by printing entire assemblies. SLM lowers waste and material utilisation, especially when compared to conventional manufacturing techniques. The resulting microstructure in SLM-processed alloys, is mostly composed of submicron dislocation walls. This type of microstructure may have the potential to improve corrosion resistance. SLM processing can produce a single-phased high entropy alloy samples, with not only exceptional strength-ductility combinations, but also excellent corrosion resistance in acidic environments. Rui Zhou et al. from department of Materials Science and Engineering, Hong Kong Institute for Advanced Study, City University of Hong Kong, have shown that SLM is capable of doubling the corrosion resistance of an N-doped CoCrFeNi HEA in diluted sulfuric acid, while still maintaining high mechanical performance. The sample that underwent SLM processing has an uneven microstructure with 3D dislocation cells inside each grain. The SLM-induced 3D dislocation cell structure can offer efficient diffusion pathways, allowing migration of Cr to the metal surface. This results in the formation of a thick protective Cr oxide layer that offers good corrosion resistance. Additionally, Cr segregation at cell borders creates a large number of sites for oxide nucleation and stabilises the cell structure for strong mechanical characteristics.
More information regarding SLM 3D printing of HEA can be obtained from following article:
Zhou, R., Chen, W., Li, W. et al. 3D printed N-doped CoCrFeNi high entropy alloy with more than doubled corrosion resistance in dilute sulphuric acid. npj Mater Degrad 7, 8 (2023). https://doi.org/10.1038/s41529-023-00320-1
