Study On Preparation And Microstructure Evolution Of FeNiMoCoCrTi High Entropy Alloy Coating

High entropy alloy is a major breakthrough in the field of alloying.Compared with traditional alloy,high entropy alloy has unique multi-principal effect.The high entropy effect can greatly enhance the compatibility between elements.It also can form a solid solution with simple structure as the face-centered cubic or the body-centered cubic structure after rapid solidification.At present,the research on high entropy alloys is mainly aimed at molten cast bulk materials.however,the characteristics of melting and casting process limit the preparation size and solidification cooling rate of high entropy alloy bulk materials,and the high entropy alloy composition design often contains expensive elements such as nickel,cobalt and titanium,these factors will have a great influence on the manufacturing cost of high entropy alloy,so we should select a more cost-effective preparation process in practical application.In this paper,laser cladding is used,because laser cladding is a new surface modification process,which has the following advantages: rapid melting and rapid solidification,little heat effect on the substrate,fine and uniform grain distribution in the cladding area,excellent metallurgical bonding,and controllable width and height of the cladding.FeNiMoCoCrTi high entropy alloy coating was obtained on the surface of 45#steel by laser cladding.The orthogonal test was used to optimize the laser power,scanning speed and defocus of the process parameters.Based on the analysis of mathematical range and variance,the data of the measured parameters are sorted and summarized,and the optimum technological parameters are obtained.At the same time,the influence of each process parameter on the coating performance is studied,and the relative contrast test is done well.At the same time,the microstructure evolution of FeNiMoCoCrTi high entropy alloy was studied mechanically,and the optimal process parameter combination was detected by metal phase transformation theory.The microstructure,phase structure andhardness of high entropy alloy coating were studied by X-ray diffractometer(XRD),scanning electron microscope(SEM),microhardness test.The results show that the main factors affecting the hardness and properties of FeNiMoCoCrTi high entropy alloy coatings are laser power and scanning speed,the off-focus amount has little effect on the coating properties in a small range(30mm?50mm),it plays an auxiliary role.The experimental results show that the optimum process parameters are laser power 3000 W,scanning speed 0.015m/s,off-focus amount50 mm,and there is no obvious slag inclusion and pore in the cladding layer,and metallurgical bonding is formed between the cladding layer and the matrix.The hardness of the cladding layer is distributed between 871.2HV and 1159.4HV,which effectively improves the hardness of 45# steel.The microstructure of the cladding layer is mainly dendrite,the grain size is small and the segregation range is small,which accords with the process of rapid solidification.So that the coating exhibits good mechanical properties(austenite to martensite),its main phase group is FCC+BCC+Simple cubic1+Simple cubic2+Simple cubic3+Laves phase,in which different conditions,the composition of the phase will also change.