Due to their excellent properties and great potential for industrial application, eutectic high-entropy alloys (EHEAs) have been a hot topic of study over the past few years. The current study reports a novel AlCr1.3TiNi2 EHEA with a low density and outstanding mechanical properties at elevated temperatures. A kilogram-scale EHEA ingot with uniform and ultrafine L2(1) and BCC lamellar structures (interlamellar spacing similar to 400 nm) was firstly prepared by a direct solidification method. The as-cast AlCr1.3TiNi2 EHEA exhibits much higher room- and high-temperature hardness and specific yield strength values than most reported refractory high-entropy alloys (RHEAS), EHEAs, and conventional Ni- and Ti-based alloys. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

It is often assumed that atoms are hard spheres in the estimation of local lattice distortion (LLD) in high entropy alloys (HEAs). However, our study demonstrates that the hard sphere model misses the key effect, charge transfer among atoms with different electronegativities, in the understanding of the severely distorted local structure in the body-centered cubic (BCC) HfNbTiZr HEA. Through the characterization and simulations of the local structure of the HfNbTiZr HEA, we found that the LLD regions in HfNbTiZr have larger average size compared with face-centered cubic (FCC) HEAs, but the magnitude of LLD significantly varies from one atomic site to another because of electron transfer from larger atoms, Hf and Zr, to smaller ones, Nb and Ti. Our finding may form the basis for the design of high performance HEAs through tuning their site-to-site chemical heterogeneity. (c) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In-depth understanding of grain boundaries (GBs) in multi-principal element alloys (MPEAs) is considered significant for designing MPEAs by GB engineering. This work explores the nanoscale GB structure and migration mechanism in MPEAs using atomic simulations. The GB-roughening transformation is observed as the mixing entropy increases, and the effect of entropy is confirmed by thermodynamic analysis. The entropy-induced transition of GB migration is proved: 1) the concentrated shuffling mechanism controls the migration of ordered GBs in low-entropy systems, leading to the obviously stepwise migration; 2) the dispersed shuffling mechanism dominates the migration of disordered GBs in high-entropy systems, resulting in the continuous migration manner. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In this study, we developed an approach to additive manufacturing of three-dimensional (3D)-architected CoCrFeNiMn high-entropy alloys by direct ink writing combined with thermal sintering. The 3D-architected CoCrFeNiMn lattices exhibit the outstanding energy absorption capacity that expands the envelope of existing architected materials. Such a high-energy absorption ability originates from the bend-dominated deformation mode of the 3D-architecture as well as the fully-annealed homogeneous microstructure of equiaxed grains, which collectively lead to remarkable strain hardening upon deformation. Our study provides a new avenue for 3D-printing advanced architected materials with extreme mechanical energy absorption for a myriad of structural applications. (C) 2020 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In the present work, uniaxial fatigue tests (R = 0.1) showed that for high-strength aluminum alloys, the crack origin also presented a tendency of transition from the outside to the inside with the stress decreasing. The interior crack-initiation mode has a characteristic of a fish-eye embracing fine granular area (FGA) originated from an inclusion. Moreover, the formation mechanism of FGA was discussed. The values of the stress intensity factor (SIF) range of a surface mode and an internal mode were calculated. The results showed that Delta K-FGA keeps constant with an average value of 1.84 MPa.m(1)(/)(2), which was close to the interior crack-growth threshold (Delta K-th, (i)), 1.911 MPa.m(1)(/)(2). Paris-Hertzberg law was used to predict the life of fatigue-crack initiation and propagation during internal fracture. The crack-growth rate within FGA and fish-eye was also estimated. Furthermore, the competitive relationship between the interior and surface cracks initiation of welded joints was discussed through the SIF range.

Fully reversed stress-controlled tension-compression fatigue experiments (R = -1) were conducted to study the cyclic deformation and fatigue behavior of 7075-T651 aluminum alloys with and without a surface mechanical rolling treatment (SMRT). The strain amplitude, ratcheting effect, and asymmetric behavior of base metal (BM) and SMRT specimens were analyzed. SMRT specimens showed more remarkable ratcheting effects and tension-compression asymmetry under high stresses. Fatigue tests showed that the fatigue strengths of 7075 Al alloys were increased significantly by the SMRT. Both BM and SMRT specimens presented a failure-mode transition from the intrusions and extrusions failure modes to the Al18Ti2Mg3 constituent phase. The hysteresis loop was utilized to obtain the plastic-strain amplitude. Furthermore, according to the cyclic-deformation behavior combined with the Manson-Coffin law, strain-life evaluation of BM and SMRT specimens under the stress-control is given.