Preparation And Microstructure Of FeCoNiCr Multi-principal Element Alloys Via Combustion Synthesis Plus Casting

Multi-principal element alloy is a brand-new alloy design concept.The main component of the alloy is no longer a single element,but the proportion of each principal element is almost equal.It leads to the formation of simple solid-solution structure,which brings many peculiar thermodynamic and kinetic effects Therefore,the multi-principal alloy exhibits excellent mechanical properties,in which makes it has important research value and application prospects.In this paper,multi-principal alloys were prepared by combustion synthesis casting method.The thermodynamics analysis shows that the combustion reaction of Fe2O3-CoO-NiO-Cr2O3-Al system can be self-sustained,and the products melts under the extremely high combustion temperature.With the investigation of the process parameters of diluent and compact density,a pure alloy melt can be obtained.The rational modification of the casting mold realizes the separation of the impurities and the multi-principal alloy melt under the action of gravity.The as-cast alloy in the graphite mold has a single FCC phase solid solution in which the elements are uniformly distributed,and the solidified structure shows a fine cell structure.The effects of Al alloying on the microstructure and mechanical properties of FeCoNiCr0.5 multi-principal alloy were investingated.The increase of Al addition induces the structure transition from FCC to BCC.As the volume fraction of BCC phase increases,the hardness and strength of the alloy increase significantly.The tensile results indicate that the work hardening behaviors of Al0,Al0.4 and Al0.6 alloys show three distinct stages,while the Al0.2 alloy exhibits a completely different tensile deformation mechanism,and ductility of Al0.2 alloy increases with the rising of strain rate.The as-cast microstructures of FeCoNiCr0.5Al0.8 is composed of the ordered/non-ordered BCC nano-composite dendrite,the network-like interdendritic FCC/BCC eutectics and the plate-like FCC/BCC eutectics.The high compressing properties can be attributed to the eutectics formed at both interdendrite and grain boundary which considerably reduces the brittlement of the interfaces.In addition,the as-cast microstructures and the corresponding corrosion behaviors of the FeCoNiCrx(x=0,0.5,1.0)multi-principal element alloys in both 0.5M sulfuric acid and 3.5%NaCl solution were systematically investigated.With the increase content of Cr,the as-cast microstructure of multi-principal element alloy shows a cellular-dendrite transformation due to the Cr-induced segregation.FeCoNiCr0.5 multi-principal element alloy exhibits an outstanding anticorrosion performance in both 0.5M H2SO4 and 3.5%NaCl solutions,while the excess Cr addition leads to the noticeable localized corrosion in FeCoNiCr multi-principal element alloys The results indicate that the distribution of Cr element plays a non-ignorable role in the anticorrosion performance.