Research On The Strengthening Mechanism And Properties Of CoCrNi-based Multi-principal Alloys

The emergence of multi-principal alloys has broken the traditional design thinking of alloys and has a very broad application prospect in aerospace and deep-sea fields due to its excellent performance.It is found that the three-principal CoCrNi alloy has good ductility,high work-hardening rate and corrosion resistance,and more interestingly,the strength and plasticity of CoCrNi alloy are simultaneously improved at low temperature,and its tensile strength reaches 1.3 GPa and tensile strain increases to 45%,which is a kind of lowtemperature structural material with great potential for application,however,the low strength of CoCrNi alloy at room temperature seriously limits its application in engineering materials.However,the low strength of CoCrNi alloy at room temperature seriously limits its application in engineering materials.In this paper,we aim to improve the room temperature strength of CoCrNi alloy and investigate it by three strengthening methods(fine grain strengthening,precipitation strengthening and dispersion strengthening).The influence of alloy composition and preparation process on the structure and mechanical properties of CoCrNi alloy is investigated in depth by theory and experiment.First,the effect of annealing temperature,time and other parameters on the strength of CoCrNi alloy in the rolled state was investigated by the method of fine grain strengthening.It is found that the strength of CoCrNi alloy decreases with the increase of annealing temperature(600℃)when the recrystallization temperature is between 500℃ and 600℃,and increases instead of decreasing when the temperature is 500℃,the tensile strength reaches 1833 MPa and the hardness exceeds 550 HV.The annealing time and deformation have less influence on the mechanical properties of rolled CoCrNi alloy,and the hot rolling and cold rolling reduce the dislocation density of the alloy was reduced by hot rolling and cold rolling,which slightly improved the plasticity.Secondly,the(CoCrNi)94Al3Ti3 alloy was prepared by introducing a small amount of Al and Ti elements into the CoCrNi alloy in combination with the method of precipitation strengthening,and the effects of rolling and aging processes on the mechanical properties of the alloy were investigated.It was found that the strengthening of(CoCrNi)94Al3Ti3 alloy after solid solution-rolling-aging process is a case of synergistic effect of multiple mechanisms,and its strength is mainly provided by three strengthening mechanisms,namely solid solution strengthening,fine grain strengthening and precipitation strengthening,together.Fine grain strengthening dominates at the lower aging temperature,and the precipitation strengthening mechanism dominates when the grain grows and precipitation phase precipitates after the temperature exceeds 700℃.The desired strong plasticity combination can be obtained by controlling the precipitation phase precipitation by regulating the aging temperature.Finally,the effect of TiC content on the CoCrNi alloy was investigated using the method of diffusion strengthening.It was found that the introduction of TiC changed the CoCrNi alloy from a single-phase FCC structure to a two-phase structure of FCC+TiC,and it was found that TiC produced dissolution and precipitation phenomena in the CoCrNi alloy.The hardness of the alloy increased with the increase of TiC content from 188 HV to 712 HV,while the excess TiC caused the compressive strength to decrease rather than increase.In addition,the introduction of TiC effectively improves the corrosion resistance and wear resistance of the CoCrNi alloy.