Study On The Microstructure And The High Temperature Deformation Behavior Of Alx(Co)CrFeNi Muti-principle Alloy

Since the idea of high entropy alloys was brought up, the design philosophy of high entropy alloys had caused a wide attention. High entropy alloys were based on variety of major element as the matrix elements, and through the composition optimization, the high entropy alloys had high hardness, strength and simple structure, high temperature creep resistance and other excellent performance, which made it have great potential in the theory research and application. Previous research results were on the basis of the small size of ingot, and the microstructure with a larger size of alloy was a lack of understanding, and high temperature deformation behavior also few studied. So in this paper, we selected the relatively mature alloy with simple microstructure, the Alx (Co) CrFeNi(x=0.15,0.4,0.15,0.4,1.0) muti-principal alloys were selected to study its microstructure and high temperature stability of the microstructure, and high temperature deformation behavior of the alloy.The results showed that the alloys with larger size still was simple solid solution:The microstructure of as-cast AlxCoCrFeNi was simple FCC cellular crystal with the lower Al content, then gradually transformed into the FCC+BCC dendrites and BCC+FCC equiaxed grain and when the Al content increased to x=1and removal of precious metal Co, AlCrFeNi muti-principle alloy was simple BCC microstructure. With the increase of Al content, the hardness increased.A10.15CoCrFeNi and AlCrFeNi muti-principal alloy had high microstructure stability and resistance to softening capacity after high temperature annealing and aging treatment.And as the increase of the content of aluminium element, the needle of the second phase can be seen in A10.4CoCrFeNi muti-principle alloy after high temperature annealing,900℃and700℃long time aging treatment. The microstructure of A10.6CoCrFeNi and A10.8CoCrFeNi changed from FCC+BCC at as-cast state into FCC+BCC and sigma phase after higher temperature and700℃long time aging treatment. However the a phase dippeared after1100℃high temperature annealing heat treatment.Due to the microstructure coarsening after high temperature annealing when the content of aluminium was x=0.8and1.0, the hardness decreased. The hardness were increased after different aging temperature treatment, and at700℃, the aging hardening reached the maximum. And the hardness reached the maximum at72h after different aging time treatment at700℃. The high temperature deformation behavior of AlxCoCrFeNi alloys were studied by the stress relaxation test. The results showed that the relationship between stress and creep rate of the muti-principle alloy obeyed Nortion’s power law at the temperature of580-700℃. A10.4CoCrFeNi alloy had a higher creep resistance at high temperature, and A10.6CoCrFeNi alloy was the worst even having a higher hardness. The second phase precipitation at high temperature made x=0.4alloy had larger stress exponent (larger than10). When the content of Al was x=0.15,0.4,0.6, its activations were in the range of365-376kJmol"1,421-393kJmol-1and255-280kJmol-1, respectively.When the content of Al was x=0.15and0.6respectively, the activation volume increased with the increase of temperature. However for A10.4CoCrFeNi alloy, it decreased with the increase of temperature. The grain boundary and the two phase structure had a great influence on the high temperature deformation behavior for A10.6CoCrFeNi alloy. For A10.4CoCrFeNi alloy, the special high temperature deformation behavior attributed to the larger the lattice distortion and the second phase precipitation.