Enhancing AM high-entropy alloys with cryogenic and laser shock treatment
Researchers from Jiangsu University, Zhenjiang, China, have published a paper in the International Journal of Extreme Manufacturing focused on work to balance strength and ductility in additively manufactured high-entropy alloys (HEAs). The team achieved their stated goals using a deep cryogenic treatment (DCT) followed by laser shock peening (LSP).
Laser Beam Powder Bed Fusion (PBF-LB) Additive Manufacturing is seen as a viable technology for the manufacture of HEA high-performance engineering components. However, inherent thermal residual stress and non-equilibrium microstructures often result in unsatisfactory mechanical properties. The Jiangsu University researchers developed a post-processing method to tailor these microstructures and enhance the performance of metastable HEAs produced via PBF-LB AM.
To validate their results, the researchers evaluated the final components in terms of microstructural modifications, residual stress, microhardness redistribution, and tensile properties.
The published results indicated that the developed post-processing technique results in the formation of a gradient heterogeneous structure on the as-built sample surface, featuring gradient variations in grain size, martensitic phase content, and dislocation density, due to the grain refinement and martensitic phase transformation under DCT + LSP. The initial tensile residual stress on the surface is noted as being ‘fully transformed’ into compressive stress, achieving a peak of −289 MPa. The surface microhardness attains a maximum of 380.8 HV.
The good strength-ductility ratio was attributed to the various strengthening mechanisms of gradient heterogeneous structures, as well as the multiple effects of heterodeformation-induced (HDI) hardening, transformation-induced plasticity (TRIP), and twinning-induced plasticity (TWIP).
The researchers stated that this work provides a practical pathway and valuable scientific insights for enhancing the mechanical behaviours of additively manufactured metastable HEAs via microstructural engineering.
‘Achieving strength-ductility synergy of an additively manufactured metastable high-entropy alloy via deep cryogenic treatment followed by laser shock peening’ is available here.
