Study On Strengthening And Toughening Mechanism Of High Performance CoCrNiAlTi Multi-principalalloy

The multi-principal alloy is composed of a plurality of elements together as a main element.The innovative alloy design concept of multi-principal alloy breaks the classification limit of traditional alloys,and the type and quantity of alloys are rapidly expanded.Multi-principal alloys have many excellent properties compared to conventional alloys.Although the multi-principal alloy has only experienced development in just over a decade,it has shown remarkable research results in many fields.Multi-principal alloys have superior strength and plasticity compared to conventional alloys,and still have excellent excellent ductility not only at room temperature but also in low temperature environments.In this paper,a CoCrNiAlTi alloy ingot with a weight of 16kg was prepared by vacuum induction melting technology,and the alloy was further processed by hot forging and cold forging.In this paper,the related deformation mechanism and strengthening and toughening mechanism of the as-cast,hot forged and cold forged states of the alloy at room temperature and low temperature were initially explored,and the following results were obtained:?1?The as-cast CoCrNiAlTi alloy is a FCC single-phase solid solution.The as-cast alloy has a room temperature yield strength of 470 MPa and a plastic elongation of 72%.After heat treatment,the alloy's room temperature yield strength can reach 570 MPa.The as-cast alloy exhibits higher strength in a low temperature environment.At 77 K,the yield strength of the alloy can reach 720 MPa.When deformed at room temperature,the initial deformation of the alloy is dominated by dislocation motion,and the mid-deformation is dominated by stacking fault movement.During the deformation process,the alloy undergoes phase transformation and HCP phase is formed.At 77 K deformation,the stacking fault in the alloy occurs earlier,and the density is higher,and HCP phase is formed.?2?The hot forged CoCrNiAlTi alloy consists of three phases of FCC phase,L1₂phase and HCP phase.The grain structure of the alloy after hot forging is significantly refined.The hot forged alloy has a room temperature yield strength of 930 MPa and a plastic elongation of52%.During the heat treatment process,the L1₂phase can be rapidly precipitated in the structure,and a significant precipitation strengthening effect is produced,so that the room temperature yield strength of the alloy can reach 1100 MPa.The alloy has a higher strength at77 K,a tensile yield strength of 1210 MPa,and the same plasticity as the room temperature environment.When deformed at room temperature,the deformation of the alloy is dominated by stacking faults,and a new HCP phase is formed during the deformation process.At 77 K deformation,the stacking fault density in the alloy is higher,and the HCP phase is more produced,exhibiting a higher strain hardening rate than the room temperature environment.?3?The grain structure of the cold forged CoCrNiAlTi alloy is more refined.After cold forging,the average grain size of the alloy can reach 5?m.The cold forged alloy has a room temperature yield strength of 1330 MPa and a plastic elongation of 24%.After heat treatment,the alloy has a yield strength of 1500 MPa and a plastic elongation of 17%.At 77 K,the strength of the alloy rises rapidly.When the tensile strength reaches 1900 MPa,the alloy still shows no obvious yielding phenomenon,indicating that the cold forged alloy has higher strength in low temperature environment,but the low temperature plasticity of the alloy is not good.Therefore,in-depth research is needed.