Study On The Microstructure And Properties Of CrN And(VAlTiCrMo)N High Entropy Alloy Coatings

With the rapid development of global economy,all countries in the world have an urgent need for energy.At present,the utilization of nuclear energy and exploitation of marine resources have gradually become the most powerful growth force and driving point of world economic development.For the use of advanced engineering equipment in nuclear energy and marine resources exploitation,they are the most important basis for the efficient completion of engineering work.However,due to the particularity of nuclear fast reactor and marine environment,the damage degree of the key components in its engineering equipment is much higher than that in the land environment,and its service life is greatly reduced.As a wear-resistant coating,CrN has the characteristics of high hardness,low friction coefficient,little difference with the physical and mechanical properties of cemented carbide,good adhesion and wear resistance.Its excellent performances are expected to be used in the protection of nuclear fast reactor.In the first part of this paper,the super thick CrN coating was prepared by multi arc ion plating method,and soaked in high temperature solution sodium at 500℃for a long time.The soaking time was 1000 h,3000 h and 6000 h.The samples with different soaking time were tested and characterized.Detailed characterization images and experimental data are given for the region of phase transition and the reason of phase transition.It vividly describes the dynamic process that the diffusion of N element leads to the transformation of CrN phase to Cr₂N phase.In terms of marine corrosion protection,compared with traditional alloy materials and single nitride materials,the new concept of high entropy alloy（HEAS）composed of five or more metal and non-metal elements with equal or close to equal molar ratio is expected to improve or replace the traditional alloy materials.In the second part of this paper,the coatings of VAlTiCrMo and（VAlTiCrMo）N_X were prepared by V-Al-Ti-Cr-Mo splicing target.Its microstructure and chemical composition were analyzed by means of XRD,SEM,EDS and TEM.With the introduction of nitrogen into the high entropy alloy coating,the growth mode and crystal structure of the coating changed.The high entropy alloy coating and the corresponding nitride coating have BCC and FCC crystal structures respectively.After nitriding the high entropy alloy of VAlTiCrMo,the mechanical properties of the coating can be significantly improved,which is mainly due to the large lattice distortion.At the same time,with the increase of nitriding degree of the high entropy alloy coating,the corrosion resistance of the multi nitride coating in 3.5 wt % NaCl solution is also improved.In the process of preparation,when the nitrogen flow rate is 800 sccm,（VAlTiCrMo）N_X coating has the best mechanical properties and high corrosion resistance.