Effect Of Heat Treatment On Microstructure And Corrosion Property Of Alcocrfeni High-Entropy Alloy Formed By Selective Laser Melting

As a new material with great potential,high entropy alloy has brought new opportunities to China’s high-end manufacturing industry and has important research and application value.At present,high entropy alloys prepared by traditional methods such as arc melting and casting have some problems,such as high cost,low quality,simple shape and limited size,which affect their industrial application.Selective laser melting（SLM）has the advantage of discrete stacking rapid prototyping,which brings dawn to the preparation of high entropy alloys with excellent properties.In this paper,AlCoCrFeNi high entropy alloy formed by selective laser melting is taken as the research object,the microstructure and forming mechanism of SLM formed high entropy alloy are analyzed,the effects of heat treatment at different temperatures on the microstructure and properties of the alloy are studied,and the electrochemical corrosion behavior of SLM formed samples and heat treated samples in acidic,neutral and alkaline environment is further analyzed.The main research contents and results are as follows:Phase formation of high entropy alloy and basic theoretical research on selective laser melting of high entropy alloy:the formation mechanism of high entropy alloy phase and the effect of heat treatment temperature on alloy precipitates were studied theoretically;The forming mechanism and influencing factors of SLM are analyzed.The results show that adjusting the radius difference of principal atoms,mixing enthalpy and mixing entropy can promote the solid solution structure of high entropy alloy,and controlling the heat treatment temperature can control the phase transformation of the alloy.Laser power is an important process factor affecting the microstructure and properties of SLM forming alloy.Forming mechanism of AlCoCrFeNi high entropy alloy and the effect of heat treatment on Microstructure and properties:the section morphology,directional growth behavior and crack formation mechanism of SLM formed AlCoCrFeNi alloy were systematically analyzed;The effects of heat treatment at different temperatures on the phase composition,microstructure,surface hardness and residual stress of the alloy were studied;The relationship between heat treatment temperature,microstructure and properties was established.The results show that SLM AlCoCrFeNi high entropy alloy is a single BCC phase solid solution structure,which is composed of columnar dendrites and equiaxed dendrites.The residual stress accumulated during SLM forming and the crack nucleation point provided by the solid-liquid interface formed by the difference of element melting point make the alloy crack.The higher the heat treatment temperature,the higher the degree of segregation,the lower the surface hardness and the smaller the residual stress.The electrochemical corrosion behavior of AlCoCrFeNi high entropy alloy formed by SLM in three corrosion environments:the electrochemical corrosion behavior of original samples and heat treated samples in acid,alkali and salt corrosion environments was systematically studied;The electrochemical corrosion mechanism in different corrosion environments was analyzed.The results show that in 0.5mol/L H₂SO₄solution,the corrosion current density of 1250℃heat-treated sample is the lowest,there are only a few pitting pits on the corrosion surface,and its corrosion resistance is the best,while the corrosion current density of the original sample is the highest,there are a large number of corrosion pits and corrosion products on the corrosion surface,and the corrosion resistance is the worst.The higher the degree of element segregation,the easier it is to form a stable passive film;In 3.5%Na Cl solution,the sample under 850℃heat treatment has the highest corrosion current density,the most serious corrosion surface damage and the worst corrosion resistance.The sample under 1250℃heat treatment has the lowest corrosion current density,the corrosion surface is relatively complete and the corrosion resistance is the best.After heat treatment,FCC phase begins to precipitate,and the two phases will form a corrosive primary battery,and the degree of element segregation will affect the formation of passive film;In 0.5mol/L Na OH solution,the corrosion current density of each sample is the same order of magnitude,and the corrosion surface is basically intact.The corrosion resistance of AlCoCrFeNi alloy before and after heat treatment is excellent.A large amount of OH^-in the solution will promote the formation of dense oxide film,so the heat treatment temperature has little effect on its corrosion resistance.