Study On Microstructure And Properties Of CrMnFeCoNi High Entropy Alloy Prepared By Laser Additive Manufacturing And Ultrasonic Rolling

The design concept of high-entropy alloy breaks the constraints of traditional alloy design framework and creates a new alloy system.Compared with traditional alloys,high-entropy alloys only form a simple solid solution phase,which not only has high strength and hardness,but also has good wear resistance,corrosion resistance and oxidation resistance.These make high-entropy alloys have great application and research value.At present,the preparation method of bulk high-entropy alloy mainly adopts the traditional melting and casting methods,which is a serious challenge for the preparation of some high-entropy alloys with complex shapes and ultra-fine grains.And the use of laser additive manufacturing technology could solve the above problems well as an effective way.Up to now,there have been preliminary studies on the structure and properties of high-entropy alloys manufactured by laser additive manufacturing.Since laser additive manufacturing is a process of rapid cooling,rapid heating and non-equilibrium solidification,thermal stress is inevitably generated during the preparation process,which will cause defects such as micro cracks and pores,reduces the performance of high-entropy alloys.In view of the above problems,this paper puts forward the idea of using ultrasonic rolling enhanced laser additive manufacturing to prepare high-entropy alloys.Single-layer and double-layer CrMnFeCoNi high-entropy alloys were prepared on 45 steel substrate.And combined with ultrasonic surface rolling treatment technology,the double-layer high-entropy alloy was surface strengthened,and the CrMnFeCoNi high-entropy alloy before and after ultrasonic rolling comparative Study was conducted.The single-layer CrMnFeCoNi high-entropy alloy manufactured by laser additive is composed of a typical planar crystal at the bottom,a columnar crystal in the middle,and an equiaxed crystal at the top.The double-layer high-entropy alloy has obvious interfaces.EDS results show that in the single-layer CrMnFeCoNi,the Fe content on the side of the entropy alloy near the substrate is significantly higher than that of other elements.As the distance from the substrate increases,the Fe content gradually decreases;the chemical distribution of the second layer is more uniform,approximately equimolar than first layer.After ultrasonic rolling,a gradient deformation structure appeared on the surface of the sample.The EBSD test results showed that the thickness of the grain refinement layer was about 5.5?m,and the grain size was below 1?m.XRD results show that the single-layer and double-layer CrMnFeCoNi high-entropy alloys made by laser additive show a single FCC phase,and the peak strength and peak width change significantly after ultrasonic rolling.After ultrasonic rolling,the surface roughness of the sample decreased from 1.410?m to 0.238?m,exhibiting as a near-polished surface.The microhardness measurements of CrMnFeCoNi high-entropy alloy before and after ultrasonic rolling were carried out.The average hardness of the single layer and the double layer were not much different,respectively 230.38 HV and 231.52 HV.The highest hardness appeared in the surface layer.It has a gradient distribution from top to bottom,and the surface hardness is up to 352.28HV,which is about 1.5 times higher than that of the non-ultrasonic rolling.After ultrasonic rolling,the surface hardness was 2.931 GPa,3.243 GPa,and 5.202 GPa,respectively.After ultrasonic rolling,the surface hardness increased by about 1.6times,and the surface elastic modulus did not change significantly.Friction and wear tests show that single-layer and double-layer CrMnFeCoNi high-entropy alloys have similar average friction coefficients,respectively 0.705 and 0.710,and the same wearing amount of 1.6 mg;after ultrasonic rolling,the average friction coefficient drops to 0.620.When the amount drops to 1.2 mg,the wear resistance of CrMnFeCoNi high-entropy alloy is enhanced.The main wear modes of single-layer,double-layer and ultrasonic rolling are adhesion wear,abrasive wear and layered wear,respectively.Electrochemical corrosion tests in 3.5 wt.%Na Cl solution showed that the corrosion potential of single-layer,double-layer and after ultrasonic rolling CrMnFeCoNi high-entropy alloy were-0.462V,-0.357V and-0.249 V,respectively.And the corrosion currents were 9.78 E-06 A/cm~2,6.47 E-06 A/cm~2and 4.00E-06 A/cm~2,respectively.of which the samples treated with USRP show the highest corrosion potential and the lowest corrosion current,indicating that the corrosion resistance is the best,the corrosion forms of all three samples are pitting corrosion.