The Influence Of Thermo-mechanical Treatment On The Microstructure And Mechanical Properties Of Dual-phase Al_0.6CoCrFeNi High Entropy Alloy

As a new class of alloys,high entropy alloys（HEAs）take marvelous advantages on many aspects,such as mechanics,physics,and chemistry,due to many compositions,multi-scale microstructures and unique properties.Consequently,four major features of HEAs are generated,namely the high entropy effect on thermodynamics,the sluggish diffusion effect on kinetics,the lattice distortion effect on structures,and the“cocktail”effect on properties.In terms of mechanical properties,HEAs exhibit promising application potential as structural materials because of high strength,high hardness,and good wear resistance.Therefore,the strengthening and toughening of HEAs is a very important topic.Although still in exploration,they have attracted widespread attention and achieved excellent mechanical properties.However,most of these methods are applied for the mechanical properties optimization of single-phase HEAs,and few studies on dual-phase/multi-phase HEAs are reported.The dual-phase Al_0.6CoCrFeNi HEAs were studied in the present work.It was discussed that the influence of the thermo-mechanical treatment on the microstructure and mechanical properties with the aid of CALPHAD phase diagram calculation.The main conclusions are as follows:（1）As-cast Al_0.6CoCrFeNi HEA was composed of FCC and BCC/B2phases.The B2 precipitates changed their morphology when annealed at high temperature（T≥900?C）and the disordered BCC phase disappeared upon annealing.The phase evolution agreed with the CALPHAD calculation.（2）The yielding strength of the cold-rolled Al_0.6CoCrFeNi HEA was gradually decreased with the increasing annealing time/annealing temperature.Simple models were used to predict the contributions to the yielding strength improvement of the FCC+B2/BCC dual-phase Al_0.6CoCrFeNi HEA,based on the solid solution,dislocation generation and interactions,grain boundaries and other phase boundaries,and precipitations and other dispersed phases.Decent agreement were obtained between the model prediction and experiments.（3）Homogenization had little effect on the mechanical properties of Al_0.6CoCrFeNi HEA.As-cast and homogenized HEAs in this study got very similar morphologies.Flow lines could be found in the heavily-deformed cold-rolled samples along the TD plane.However,the occurrence of the multilateral equiaxed crystals in the hot-rolled HEAs indicated a dynamic recovery.（4）Al_0.6CoCrFeNi HEA had tension/compression asymmetry,and the dislocation slip was the only deformation mechanism upon tension.The power law relationship was obtained between the strain hardening exponent and rolling reduction in accordance with the change tendency.The tensile strength could be predicted from the Hollomon relationship.