Heat treatment effects on the metastable microstructure,mechanical property and corrosion behavior of Al-added CoCrFeMnNi alloys fabricated by laser powder bed fusion

With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex structures.This work investigates Al-added CoCrFeMnNi high-entropy alloys(Al-HEAs)pre-pared by laser powder bed fusion(PBF-LB),adding 4.4 wt.%Al reducing approximately 7%density.The contribution of post-heat-treatment to microstructure,mechanical properties,and corrosion behaviors are explored.Hot cracking along with grain boundaries in the as-built PBF-LB Al-HEAs is determined,which comes from the residual liquid film as a larger solidification temperature range by adding Al.The PBF-LB Al-HEAs mainly consist of a face-centered cubic(FCC)matrix with Al/Ni/Mn decorated dislocation cells therein and a minor body-centered cubic(BCC)phase.Upon 850℃ annealing treatment,massive BCC phases(ordered NiAl and disordered Cr-rich precipitates)generate at the dislocation cell/grain bound-aries and the dislocation cells are still retained.However,the volume fraction of BCC phases and the dislocation cells vanish after 1150℃ solution treatment.As a result,Al-HEA850 shows an over 1000 MPa yield strength with nearly no ductility(<3%);the Al-HEA1150 exhibits considerable strength-ductility properties.Meanwhile,the Al-HEA850 demonstrates the worst pitting corrosion resistance due to the preferential dissolution of the NiAl precipitates in chloride-containing solutions.After comparatively de-liberating the evolution of strength-ductility and localized corrosion,we built a framework about the effects of the heat treatment on the mechanical property and degradation behavior in additively manu-factured Al-added high-strength HEAs.