Effect of Ti substitution for Al on the cuboidal nanoprecipitates in Al 0.7 NiCoFeCr 2 high-entropy alloys
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Downloaded from https://www.cambridge.org/core. Tufts Univ, on 04 Aug 2018 at 05:01:57, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/jmr.2018.213
Effect of Ti substitution for Al on the cuboidal nanoprecipitates in Al0.7NiCoFeCr2 high-entropy alloys Chunling Li, Yue Ma, Jiamiao Hao, and Qing Wanga) Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
Shujie Pang Key Laboratory of Aerospace Materials and Performance (Ministry of Education), School of Materials Science and Engineering, Beihang University, Beijing 100191, China
Chuang Dong Key Laboratory of Materials Modification by Laser, Ion and Electron Beams (Ministry of Education), School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
Peter K. Liawb) Department of Materials Science and Engineering, The University of Tennessee, Knoxville, Tennessee 37996, USA (Received 16 March 2018; accepted 11 June 2018)
Coherent cuboidal B2 nanoprecipitation in body-centered cubic (BCC)-based high-entropy alloys (HEAs) is important for the improvement of mechanical strength. The present work primarily investigated the effect of Ti substitution for Al on the cuboidal B2 nanoprecipitates in BCC Al0.7NiCoFeCr2 HEAs. A series of (Al,Ti)0.7NiCoFeCr2 HEAs with different Al/Ti ratios were prepared by suction-cast processing, and their microstructures and mechanical properties were then characterized comprehensively. It was found that the substitution of Ti for Al can change the phase structures of ordered precipitation, from the B2-AlNi to a highly ordered L21-Ni2AlTi phase. Especially, a small amount addition of Ti (#4.2 at.%, Al/Ti ratio $2/1) renders the HEAs with cuboidal L21 nanoparticles coherently precipitated into the BCC matrix, which is attributed to the moderate lattice misfit (e 5 0.5–0.6%) between BCC and L21 phases. HEAs with such coherent microstructures exhibit high compressive yield strength of about 1700–1800 MPa. When the Ti content reaches up to 6.25 at.%, the matrix of the alloy will be turned into the r phase, rather than BCC, leading to a heavy brittleness. I. INTRODUCTION
Recently, high-entropy alloys (HEAs) have attracted more attention due to their unique properties caused by simple crystalline structures and multiple-component mixing.1–5 They generally possess simple crystalline structures, such as face-centered-cubic (FCC),6,7 bodycentered-cubic (BCC),8–10 and hexagonal close-packed (HCP) solid solution structures.11–13 For instance, the single-phase FCC CoCrFeNiMn (in equimolar fraction) HEA displays outstanding damage tolerance with higher tensile strength and fracture toughness than traditional engineering stainless steels at cryogenic temperatures.6 Refractory high-entropy alloys with a single-phase BCC structure exhibit good oxidation- and corrosionresistances at high temperatures (HTs) bes
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