Microstructures And Mechanical Properties Of Al_0.5CrFeCoNi High-entropy Alloys Fabricated By Laser Melting Deposition

High-entropy alloys are a new type of multi-component alloys.The design of their compositions breaks the design ideas of traditional alloys and shows many excellent properties.The Al_0.5FeCoCrNi high-entropy alloy has an FCC+BCC dual-phase structure,and it is very valuable to study its strength and ductility according to the phase ratio.Traditional preparation methods are prone to metallurgical defects such as microcracks and segregation,while additive manufacturing technology provides a new method for preparing high-entropy alloys with complex shapes and excellent properties.In this paper,the Al_0.5Fe Co Cr Ni high-entropy alloy wall was successfully fabricated by laser melting deposition technology.The effect of process parameters on the surface morphology of the alloy was studied.The microstructure regulation and mechanical properties of Al_0.5Fe Co Cr Ni high-entropy alloys were studied by changing the laser power and heat dissipation rate.The reinforcement mechanism was analyzed.The main work is as follows:Al_0.5FeCoCrNi high-entropy alloy walls were fabricated with different laser powers,and the effect of heat input on its microstructure and mechanical properties was investigated.The Al_0.5FeCoCrNi high-entropy alloy walls have an FCC+BCC dual-phase structure,in which the FCC phase is dominant.Since the BCC phase is not as stable as the FCC phase at high temperature,the content of the BCC phase gradually decreases with increasing laser power.Affected by heat accumulation,inside the wall,the content of BCC phase at the bottom is the highest and gradually decreases with the increase of the deposition height.Affected by the temperature gradient and crystallization rate during solidification,the wall is mainly composed of columnar crystals.The columnar crystals inside the specimen continued to grow and became longer as the laser power and the height of the single wall increased.The increase of laser power and wall height results in grain growth and reduction of dislocation.As a result,the strength and hardness of the specimen gradually decrease,and the ductility increases.Through quantitative analysis of various strengthening mechanisms,it is found that dislocation strengthening and grain refinement strengthening are the main strengthening mechanisms.The effects of different heat dissipation rates on the microstructure and mechanical properties of Al_0.5FeCoCrNi high-entropy alloy walls were investigated.The increase in the height of the T-beam causes the wall to dissipate heat more slowly.As the heat dissipation rate gradually slows down,the heat accumulation leads to a gradual reduction of the BCC phase.The wall is composed of columnar crystals,and the slow heat dissipation rate causes the columnar crystals to grow.Heat accumulation hinders nucleation during solidification,resulting in a tendency to grow across the deposited layer.What’s more,the heat dissipation rate changes the grain number and BCC phase of the walls.As a result,the strength and hardness of the sample are gradually reduced,and the ductility is improved.