Additively manufactured equiatomic CoCrFeMnNi high entropy alloy: Precipitation-induced heterogeneity by mechano-chemical coupling

• Published in: Journal of alloys and compounds 2023-03, Vol.938, p.168514, Article 168514
• Main Authors: Taheriniya, Shabnam, Choi, Nuri, Yang, Sangsun, Sonkusare, Reshma, Yu, Ji Hun, Lee, Jai-Sung, Rösner, Harald, Peterlechner, Martin, Boll, Torben, Gammer, Christoph, Hahn, Horst, Divinski, Sergiy V., Wilde, Gerhard
• Format: Article
• Language: English
• Subjects: Additive manufacturing; High-entropy alloy; Segregation; Strain mapping; Transmission electron microscopy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2022.168514

Additive manufacturing via selective laser melting of gas-atomized equiatomic powder was used to fabricate a CoCrFeMnNi high-entropy alloy. Analytical transmission electron microscopy, nanobeam diffraction, atom probe tomography and nanoindentation were employed to provide a comprehensive overview on the evolution of microstructure and nano-hardness upon annealing at a moderate temperature of 550∘C motivated by a maximum heat release at that temperature. A complex mechano-chemical coupling was observed, which leads to segregation and phase separation at grain boundaries. The as-manufactured material contained alternating regions of equiaxed and columnar grains. The corresponding microstructure is composed of high-angle grain boundaries and intrinsic dislocation networks, which displayed heterogeneous segregation of Mn and to some extent Ni. Longer annealing led to Cr enrichment at high-angle grain boundaries, and later to a phase separation with neighboring Cr-rich and MnNi-rich regions. Synergetic effects of segregation, nano-precipitation and dislocation accumulation at high-angle grain boundaries give rise to built up stresses which increase and homogenize hardness in the 3D-printed CoCrFeMnNi alloy. •Laser evaporates Mn during synthesis and leads to Mn enrichment at different boundaries as it diffuses back in the matrix.•Different solidification conditions dictate the shape of Mn-rich dislocation networks in columnar and equiaxed grains.•The GBs are curved in equiaxed grains and segmented in columnar grains with heterogeneous Ni enrichment in certain segments.•The fusion of Ni and Mn is the driving force to the enrichment of Ni at certain segments of HAGBs and dislocation networks.•The Cr-rich sigma phase nucleates and grows along the same direction as the grain after heat treatment at 550°C for 10 h.