Development and processing maps of high entropy alloys for high-temperature applications

Abstract

Multicomponent high entropy alloys (HEAs) have been attracting attention worldwide and constitute an active, frontier area of research in the exploration of novel materials development. The current study focuses on design and development of a single-phase Fe25Co25Ni25Cr20V5 FCC HEA, higher-order seven component Fe35-XCo10Ni25Cr15Mn5V10Nbx (x =2.5, 5, 7.5, and 10 at. %) eutectic high entropy alloys (EHEAs), eight component Fe32.5-xCo10Ni25Cr15Mn5V10Al2.5Nbx (x= 5, 7.5, 10, and 12.5 at. %) EHEAs, Co-Fe-Mn-Ni-Ti quasi-peritectic HEAs (QHEAs), and Co-Cr-Fe-Ni-Zr QHEA by an integrated approach of combining thermodynamic simulation and experimental solidification techniques. Experimentally, it is found that the microstructure of studied EHEAs consists of FCC solid solution phase and Nb-rich (Co, Fe)2Nb-type C14 Laves phase. Further, Co25Fe25Mn5Ni25Ti20 QHEA consists of primary BCC(β) and eutectic mixture of FCC solid solution and Ti2(Ni, Co) Laves phase and (CoCrFeNi)90Zr10 QHEA shows bimodal eutectic microstructure having globular eutectic (FCC+ Ni2Zr) and lamellar eutectic (FCC + Ni7Zr2). Based on structural and microstructural characterization, a new pseudo-quasi-peritectic four-phase reaction, i.e., L + BCC (𝛽) ⟶ FCC (α) + Ti2(Ni, Co) is established for Co25Fe25Mn5Ni25Ti20 QHEA, and L + Ni2Zr → FCC (α) + Ni7Zr2 is proposed for (CoCrFeNi)90Zr10 QHEA. Further, the mechanical properties and hot deformation behavior (at different temperatures and strain rates) of developed HEAs are carried out. Also, the processing maps using multiple models are generated to identify the hot workability regimes, as well as the plausible deformation mechanism of HEAs, is understood. The optimum thermomechanical processing conditions of single-phase Fe25Co25Ni25Cr20V5 FCC HEA lie in the temperature range 1165-1235K and strain rate range 10-3 s -1 -10-1.65 s -1 as well as temperature range 1235-1373K and strain rate range 10-3 s - 1 -10-0.73 s -1 . The optimum hot workability conditions of Co25Fe25Mn5Ni25Ti20 QHEA lie in temperature range 1073-1273 K and strain rate range 10-3 s -1 -10-1.6 s -1 as well as temperature 1130-1225K and strain rate 10-0.5 -1 s-1 , while for (CoCrFeNi)90Zr10 QHEA stable region lie in temperature range 1073-1323 K and strain rate range 10-3 -10-1.3s -1 as well as 1073-1125 K and 10-3 -10-0.75 s -1 . Furthermore, the neural network-based computational approach has been established for predicting the mechanical properties and flow behavior of studied alloys. The flow curve prediction has been done by conventional models and artificial neural network (ANN) model at different hot working conditions. The performance of these models is evaluated by different parameters such as average absolute relative error (AARE), mean square error (MSE), and coefficient of correlation. Furthermore, FEM simulation predicts the effective plastic strain distribution and material flow behavior during thermomechanical processing of studied HEAs. Finally, it is observed that QHEA having peritectic and eutectic microstructure or two eutectics microstructure shows improved mechanical properties at elevated temperature.