Hot Deformation Behaviour And Processing Maps In Al_0.5CoCrFeNi High Entropy Alloy

As one of the rapid-developing alloys during recent decades, high entropy alloys have made breakthroughs in conventional alloys design. Due to excessive kinds of elements alloyed in conventional alloys design, intermetallic compounds and complex phases are more likely to be generated, which reduces the performance and mechanical properties of alloys. However, in high entropy alloys, because each of the elements has an atomic weight of no higher than 35%, the interaction between elements enhances the alloys in comprehensive properties apparently, such as strength, hardness, ductility, tempering resistance, wear and oxidation resistance. Massive potential of high entropy alloys emerges in their application to engineering and industry.But, the microstructures of as-cast high entropy alloys are mainly dendrites, in which the heterogeneity and lattice distortion in microstructure can greatly affect the properties in engineering application, especially in the field of core component processing in defence construction. Thus, the research of thermal modification technology counts to keep high pace of development of high entropy alloys.In this thesis, a typical high entropy alloy Al0.5Co Cr Fe Ni is studied. Based on the combination of Gleeble-3500 thermal simulator and finite element analysis, the deformation in elevated temperatures of the alloy Al0.5Co Cr Fe Ni is investigated in different deformation rate and deformation temperatures. The influence of different deformation rate and temperatures to rheological behaviour and microstructure of the alloy Al0.5Co Cr Fe Ni in high temperature is shown; the thermal deformation of the material model of the alloy Al0.5Co Cr Fe Ni is established; the heat treatment drawings in different deformation are drawn according to dynamic material model theory; numerical simulation analysis is implemented to the deformation process of the high entropy alloy in elevated temperatures.In this study, flow stress- strain curve of the high entropy alloys in elevated temperature has the main characteristic of dynamic recovery. With the increase of deformation temperature or the decrease of deformation rate, the flow stress in steady state reduces; precipitates dissolved gradually in microstructure of the high entropy alloy; the size of grains which are perpendicular to the compression direction decreases; the shape of the grain tends to be regular; the grains parallel to the compression direction have a characteristic of flow line and the micro-hardness between dendrites tends to decrease after the thermal deformation. Besides, during the high-temperature deformation, the high entropy alloy Al0.5Co Cr Fe Ni maintains its face-centered cubic and single-phase solid solution structure, shows fairly good thermal stability with the atomic diffusion of aluminum and nickel between lattices.The thermal deformation equation based on Arrhenius model is: 11 2 25.15 5.1514 14188 ln 11.47 10 1.47 10 Z Z?? ?? ??? ? ? ??(28) ?? ?(10)?? ?(10)? ??? ? ??? ? ?? ? ??? ?, here54.33 10 Zexp RT?? ??(28)? ?? ?; the deformation temperature is between 1100℃ and 1200℃, deformation rate is between 0.1s-1 and 1s-1. The conditions of the processing that are within the ranged do benefit to improve and enhance comprehensive mechanical properties of the high entropy alloy Al0.5Co Cr Fe Ni.