Super-Hard (MoSiTiVZr)N_x High Entropy Nitride Coatings With Wear And Corrosion Resistance

Because of its unique mechanical properties,functionality and economy,traditional nitride coatings have been widely used in material surface protection,such as Ti Al N,Ti N,Cr N,etc.Although these coatings have a high degree of hardness,they are not yet super-hard.Moreover,the increasingly extreme service environment also puts forward higher requirements on the performance of corrosion resistance,wear resistance,damage tolerance and binding force of surface protective coatings.As for coating design in the past,the limited element types and structures made the development of traditional nitride coatings gradually slow and no longer meet the higher requirements of tools for protective coatings.Therefore,it is urgent to change the design concept to develop better performance of surface protective coatings.Recent research on super-hard High entropy nitride（HEN）coatings has provided new ideas for the design of high-performance protective coatings.High entropy nitride coatings are developed on the basis of the research of bulk high entropy alloys（HEA）.Because of its four core effects,HEN exhibit excellent mechanical properties,oxidation resistance,thermal stability and wear resistance,and is expected to become a new material to replace the traditional protective coatings.Magnetron sputtering has unique advantages in nitride coating preparation,such as excellent controllability,repeatability and coating quality.The nitrogen content of HEN coating can be accurately controlled by adjusting N₂ flow rate during sputtering.The performance of HEN coating can be further improved by optimizing the preparation process.The specific research content of this paper is as follows:The effects of configurational entropy（CE）on microstructure and properties of the coating were investigated.Three elements（Ti,V,Zr）and five elements（Mo,Si,Ti,V,Zr）were selected as the basic components of the coating,and different configurational entropy（CE）coatings,namely,middle entropy alloy and high entropy alloy,were prepared.The high CE is the main reason for the stable phase structure of the coatings.Therefore,both coatings have the composite structure of amorphous and nanocrystalline.The size of nanocrystalline particles decreases and the disorder of the coatings increases with the increase of CE.Due to the size difference between Mo,Si atoms and other atoms,serious lattice distortion and size mismatch of adjacent atoms exist in the coating,which makes the hardness of MoSiTiVZr high entropy alloy coating much higher than Ti VZr medium entropy alloy,reaching 9.27 GPa.The（MoSiTiVZr）N_x HEN coatings with different N contents were deposited at different nitrogen flows via reactive DC magnetron sputtering.The chemical composition,microstructure,hardness,corrosion resistance,damage tolerance,and friction behavior of the coating were investigated.With the increase of N content,the phase structure of the coating changes from amorphous structure to single-phase face centered cubic（FCC）structure,and all alloy-elements form metal-nitrogen bonds.The coatings with nitrogen content of 53.7 at%have the highest hardness of 45.6 GPa,the best damage tolerance,and wear resistance.All coatings show better corrosion resistance than 304 stainless steel.However,the corrosion resistance decreases slightly as the nitrogen content increases.The structure,mechanical properties and corrosion resistance mechanism of（MoSiTiVZr）N_x coating are discussed in detail.The power of substrate bias during deposition of（MoSiTiVZr）N_0.54 HEN coating was changed.The effect of substrate bias on the properties and structure of the coating was investigated.The bombardment effect of substrate bias makes the coating change from columnar structure to smooth and dense inner structure.With the densification of the coating structure,its mechanical properties such as hardness and wear resistance are obviously increased.The coating reaches a maximum hardness of 48.4 GPa at 100 W bias power and a minimum wear rate of 9.6×10^-7 mm³/（N·m）at 50 W bias power.However,the plasticity and the binding force of the coating decreases after the bias is applied.In addition,the densification of the coating structure caused by substrate bias also reduces the corrosion rate compared with that of the coating prepared without substrate bias.In conclusion,we have successfully prepared a super-hard,wear-resistant and corrosion-resistant HEA coating.Although its toughness and binding force need to be improved,it still has great potential as a candidate material for new protective coatings in the future.