Investigation of the Effect of the Thermo‐Mechanical Processing of Additively Manufactured CoCrFeNiAl_0.4 High‐Entropy Alloy

Abstract

Thermomechanical processing (TMP) is a significant route to tune the microstructure and mechanical properties of high‐entropy alloy (HEA), which employs plastic deformation and heat treatment. Herein, bulk CoCrFeNiAl0.4 high‐entropy alloy has been fabricated by powder plasma arc additive manufacturing (PPA‐AM), which was subjected to TMP including different extents of plastic deformations and followed by annealing. The evolution of microstructure and mechanical properties of the HEAs during TMP is studied, and the contribution of strengthening mechanisms to the improvement of mechanical properties is quantified. By increasing the plastic deformation of TMP, the hardness and yield strength of the alloys increase by 94% and 105%, respectively, and are accompanied by a strain of 29.1%. Based on analysis and calculations, it is found that grain boundary strengthening significantly contributes to the improved performance of bulk CoCrFeNiAl0.4 HEA fabricated by PPA‐AM + TMP. PPA‐AM + TMP synthesis is an innovative way to prepare bulk HEAs with a refined microstructure and better mechanical properties.

Strengthening and Toughening of the Co34Cr32Ni27Al3.5Ti3.5 Alloy Through Coherent L12 Nanoprecipitates

“…[50] Thus, the annealed treatment improved the strength and fracture elongation of the sample due to the reduction of grain size and formation of the precipitated phase. According to the analysis in Figure 8c,d, the current CRA Co 34 Cr 32 Ni 27 Al 3.5 Ti 3.5 MEA demonstrates an exceptional balance of strength and ductility superior to most reported similar H/MEAs, [16,[51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] suggesting that the strengthening-toughening strategy adopted in this work is effective.…”

“…The ultimate tensile stress (UTS) of the CR sample increased from 820.5 to 1687.3 MPa, while the fracture elongation decreased to 1.9%. Compared with CRA-1173 K and [16,[51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] CRA-1373 K samples, the CRA-1273 K sample had a UTS of 1109.3 MPa, which was 35.2% higher than the as-cast sample in Figure 8a. The CRA-1273 K sample maintains superior properties (YS = ≈678.4 MPa and uniform elongation [UE] = ≈44.…”

“…Figure 8. Mechanical properties of Co 34 Cr 32 Ni 27 Al 3.5 Ti 3.5 MEA under different processing conditions: a) representative tensile engineering stress-strain curves, b) true stress-strain curves, and corresponding strain-hardening ones, c) variations of YS, UTS, and UE, d) UTS versus UE of current Co 34 Cr 32 Ni 27 Al 3.5 Ti 3.5 MEA, compared to various M/HEAs [16,[51][52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68]. …”

Effects of Cold Rolling and Annealing Treatment on Microstructure and Properties of CoFeNiMnV High‐Entropy Alloys

“…The yield strength of the directly deposited sample is 406 MPa, the ultimate tensile strength reaches 702 MPa, and the uniform elongation is 32.7% (Figure 9b). Compared with HEAs [32,[56][57][58][59] without any subsequent treatment, PPA-AM deposited CoFeNiMnV has relatively higher hardness, yield, and tensile strength. This may be because CoFeNiMnV HEAs deposited with PPA-AM have a more homogeneous microstructure and precipitate many fine σ phases in the FCC matrix (as shown in Figure 3a).…”