Microstructure And Strength-toughness Of CoCrFeNiMo High-entropy Alloy By Selective Laser Melting

High entropy alloys have excellent properties such as high strength and hardness,wear resistance and corrosion resistance,and have great application prospects in aerospace,communications and electronics.Compared with traditional forming technologies such as vacuum arc melting and powder metallurgy,selective laser melting(SLM)has the unique advantages of high forming accuracy and the ability to form complex structures,and has become an innovative technology for forming and preparing complex structures of high entropy alloys,but the current defects such as cracks and holes in the process of forming high entropy alloys by SLM have greatly affected the performance and application of the formed components.This paper takes CoCrFeNiMo high-entropy alloy as the research object and conducts SLM process and property research to explore the influence of process parameters,Mo element content on the solidification morphology and tissue evolution of the SLM melt pool,and reveals the inner mechanism between the process parameters,Mo element content and mechanical properties of the high-entropy alloy through the testing and analysis of relative densities,microhardness,tensile properties and impact toughness.The main studies are as follows.(1)To investigate the variation pattern between laser process parameters and microstructure.The laser power and scanning speed were used as factors,and the relative densities and surface quality of the formed parts were used as measures to obtain the process parameters for SLM forming of CoCrFeNiMo high-entropy alloy with relatively dense and excellent forming quality.The microstructure,phase composition,and element distribution were analyzed to further summarise the influence of the process parameters on the microevolution of the melt pool.(2)To explore the influence of the variation of laser process parameters on the mechanical properties of high entropy alloys.Microhardness,tensile properties,and impact toughness testing experiments were carried out and microscopic observation of the fractures was carried out.Combined with the microscopic analysis,the effect of the change of process parameters on the toughness properties of the formed parts was explored,and a process guideline based on the adjustment of laser power and scanning speed to achieve the synergistic regulation of strength and toughness of the high entropy alloy was established.(3)To analyze the effect of Mo element content on the microstructure and mechanical properties of formed parts of high entropy alloys.Microscopic inspection and mechanical properties of SLM formed CoCrFeNiMo_x(x=0.5,1,1.5)high entropy alloys were carried out to investigate the effect of Mo element content on the microstructure and mechanical properties,and to elucidate the mechanism of the effect of Mo element on the strength and toughness of formed parts of high entropy alloys.The experimental analysis of this paper shows that at a laser power of 170 W and a scanning speed of 1200 mm/s,the relative densities reach 99.94%,the surface forming quality is good,and the strength and toughness of the formed parts can be better matched,with a tensile strength of 1201.25 MPa and an elongation of 38.40%.The molar ratio of CoCrFeNiMo was found to have relatively balanced strength and toughness of the formed parts,with a tensile strength of 1222.15 MPa and an elongation of 25.75%under the same process parameters,which provides technological support for the application of CoCrFeNiMo high-entropy alloy in aerospace and other fields.