Study On The Microstructure And Properties Of Ni-Cr-Co-base Multiple Principal Elements Alloy With Low Co Contents

High entropy alloys have broken the design concept of traditional alloys,and made many remarkable research achievements in catalysis,magnetic properties,especially mechanical properties in recent years.In general,the traditional Ni-based alloys have high stacking fault energy due to single principal element（Ni）,and the whole dislocation slip is the main component in the plastic deformation process,resulting in insufficient strain hardening ability,restricting the comprehensive improvement of "strength and plasticity".In this paper,based on the researches of CoCrNi based multi-principal-element alloys,the composition design is adopted to reduce the stacking fault energy of the alloy,increase the content of Cr element and appropriately reduce the expensive Co element.By taking NiCrFeCoAlTi and NiCrCoAlTi multi-principal component alloys as research objects,the relationship between microstructure and mechanical properties of the two alloys is explored.The results show that the NiCrFeCoAlTi high entropy alloy in solid solution has FCC structure,with a small amount of ordered（L12）phase and body-centered cubic（BCC）phase.After aging at 800℃/24h,the yield strength and elongation of solid solution reached 700MPa and 17.5%.After cold deformation and annealing at 700℃/1h,the alloy exhibits high tensile properties at room temperature with yield strength of 1.6GPa and elongation of 13.7%,which is superior to the properties of traditional Ni-based alloys.The medium-entropy-alloy NiCrCoAlTi alloy in solid solution has FCC structure and a small amount of BCC phase.After aging at 600℃/24h,the yield strength and elongation of solid solution reached 500MPa and 65%.After cold deformation and annealing at 600℃/24h,the alloy shows considerable tensile properties at room temperature with yield strength of 1.70GPa and elongation of 16%,which is obviously superior to the properties of traditional Ni-based alloy.Through microstructure analysis,it can be seen that the strength improvement of the designed alloy mainly comes from straining strengthening,solution strengthening,precipitation strengthening and phase strengthening of the multi-principal-element alloy.The reason for improving the plasticity of the alloy is that the movable dislocations mainly move in the form of planar-dislocations due to the low-level stacking fault energy during the deformation process,which makes the dislocations form defects such as layer dislocations,dislocation walls and sub-crystals.Both contribute the gain of excellent comprehensive mechanical properties.This study provides a new idea for the development of high-performance Ni based alloys.