Study On Microstructure And Mechanical Properties Of W-Re-Os-Ir Refractory High Entropy Alloy

In recent years,with the rapid development of aerospace and military industry,high temperature structural materials are widely required,but also higher requirements are put forward.Under the restriction of the melting point of the traditional nickel-based superalloy,the service temperature is close to the material limit,so it is of practical significance to develop a new type of ultra-high temperature and ultra-strength alloy.The concept of high entropy alloy provides a new idea for designing alloys.High mixing entropy can make the crystal structure tend to form stable solid solution phase,avoiding the generation of complex intermetallic compounds,thus obtaining excellent properties.The microstructure of refractory high-entropy alloys is usually body centered cubic（BCC）.However,alloys with BCC structure are brittle at room temperature,which limits their application to a large extent.By means of composition design,second phase particle strengthening,and adjusting the microstructure of the alloy,the room temperature properties and high temperature strength of the refractory high entropy alloy can be improved,so that the refractory high entropy alloy has good room temperature and high temperature properties.WRe Os Ir and W₆Re₆Os₂Ir₂ refractory high entropy alloys were prepared by vacuum arc furnace smelting.The alloy phase composition was predicted by solid solution criterion and binary phase diagram.The microstructure of as-cast alloy was analyzed by XRD,OM,SEM,EBSD,EDS and TEM.The mechanical properties of the alloy were tested by room temperature compression,high temperature compression,room temperature hardness and high temperature hardness tests.The results show that the two alloys both form disordered solid solutions with dense hexagonal（HCP）crystal structure and have good strength and plasticity.At room temperature,the compressive strength,yield strength and fracture strain of WRe Os Ir alloy are1151MPa,960MPa and 14.5%,respectively.At high temperature（1200℃）,the compressive strength,yield strength and fracture strain are 420MPa,380MPa and 10%,respectively.At room temperature,the compressive strength,yield strength and fracture strain of W₆Re₆Os₂Ir₂alloy are 2251MPa,1230MPa and 33.5%,respectively.At high temperature（1200℃）,the compressive strength,yield strength and fracture strain are 930MPa,620MPa and 31%respectively.WRe Os Ir alloy forms HCP single-phase solid solution,W₆Re₆Os₂Ir₂ alloy forms a disordered solid solution structure with HCP phase as matrix and Re W phase distributed dispersely.During the deformation of the two alloys,a large number of deformation twins were generated,which resulted in a large work hardening phenomenon.The Re W phase in W₆Re₆Os₂Ir₂ alloy belongs to non-deformable particles and plays a role of dispersion strengthening.The dislocation bypasses the particles to form dislocation loops,which greatly improves the strength and ductility of the alloy.The dynamic recrystallization structure of W₆Re₆Os₂Ir₂ alloy appears under the compression condition of 1200℃,and the recrystallization grains nucleate preferentially at the original grain boundary with large deformation.The high temperature compression fracture is a quasi cleavage fracture.