Study On SLM Forming Strategy Of High Entropy Alloy CoCrFeMnNi

Rapid evolution of high‐entropy alloys has become an important research spot in the material field.The composition of the plurality of elements has a comprehensive characteristic excellent in hardness,strength,corrosion resistance and oxidation resistance.Selective laser melting（SLM）is one of the high entropy alloy formation methods.In the forming process,the temperature is nonlinear by the intense reaction between the laser and the powder,and the resulting thermal stress makes the parts have defects such as cracking deformation and deformation.Therefore,optimizing the high entropy alloy forming strategy during SLM and analysis the effects of forming strategy on the temperature and stress of materials,are essential to explore forming mechanism of high entropy alloy fabricated by SLM,which further provide important guidelines for high entropy alloy fabricated by SLM.The thermophysical properties of materials show nonlinear characteristic changes with temperature during SLM.It is difficult to measure the law of temperature and stress evolution during SLM by experimental method.Simulation software provides a very potential way to solve these problems.In this work,the finite element model is established using ANSYS simulation software,and the Gaussian cone body heat source is used as a laser heat source,and the high entropy Co Cr Fe Mn Ni alloy forming strategy during SLM is further simulated by"life and death element"and parametric APDL language.Firstly,the simulation model of process parameters is established.The simulation study of laser power and scanning speed of high entropy alloy fabricated by SLM is carried out.When the laser power increases,the heating and cooling rate,the size of molten pool and the overlapping ratio of the scanning channel middle node（node 3）gradually increase.When the scanning speed increases,the heating rate of the central node of the scanning channel（node 3）gradually increase,and the molten pool size,cooling rate and the overlapping ratio gradually decrease.Through simulation research,the optimized forming process parameters during SLM are laser power of 90W and scanning speed of1000mm/s.Secondly,three scanning path models of“one”shape,zigzag and outer helix line are established to simulate high entropy alloy formation during SLM.The common characteristic of three scanning paths is that the surface equivalent stress of the first layer is larger than that of the second layer.Compared with the outer helix line path,the“one”shape scanning path has higher cooling rate,shorter forming time and more uniform stress distribution.The zigzag path has the shortest forming time and the greatest cooling speed,which means that it is easier to form fine grains uniform stress distribution,and the excellent properties.The scanning trace of the outer helix line path becomes shorter gradually,and the central area is not completely melted or not melted,and the phenomenon of stress concentration is serious.Through the simulation study,the optimized scanning path is the zigzag scanning pattern.Finally,the simulation models of interlayer rotation angles of 0°,45°,67°and 90°are established to explore the effects of the rotation angles on the high entropy alloy formation during SLM.Compared with interlayer rotation angles45°and 67°,the molten pool size and overlapping ratio of molten pool of interlayer rotation angle 90°have little change,which may be the same scanning channels number between 90°rotation and no rotation.However,the change of scanning channel number and length may cause a large change in molten pool size.Under the conditions of 67°rotation between layers and 45°rotation between layers,the stress in the center of the two-layer and four layer forming surface（nodes P₂ and P₄）is large,but the stress becomes smaller and uniform after cooling for a period of time,which means that a certain angle of rotation between layers is conducive to reduce the stress and stress concentration.The stress value of 67°rotation between layers is the lowest and the stress distribution is the most uniform after cooling in three and four layers.Through the simulation study,the optimized interlayer rotation angle is 67°.