| Transition metal nitride(TMN)films have been widely used in the field of protective coatings due to their high hardness and excellent chemical inertness,such as machining,aerospace engines and so on.However,with the increasingly harsh and complex service environment,the comprehensive performance of TMN-based protective coating is required to meet the requirements of strengthening and toughening,as well as excellent friction and wear resistance together with corrosion resistance.Based on the development of high entropy alloy,with its characteristics of multiple principal elements and high mixing entropy,it can achieve richer structural regulation and synchronous improvement of mechanical properties,friction and wear and corrosion properties.This also provides a new idea for TMN thin films.The combination of high entropy nitride obtained by appropriate combination of elements and thin film technology is expected to achieve the microstructure regulation of high entropy nitride thin films,and the optimization and aggregation of wear resistance and corrosion resistance.In this paper,the(ZrNbHfTaMe)Nx(Me=W,Mo,Cr)of three different components have been prepared by magnetron sputtering.The influence of nitrogen flow rate on microstructure and toughening behavior of three kinds of high entropy nitride films was systematically studied,and the regulation of W,Mo and Cr on friction and corrosion properties of high entropy nitride films was explored,and the conclusions were drawn as follows:1.Using ZrNbHfTaW,ZrNbHfTaMo and ZrNbHfTaCr targets by magnetron sputtering,three groups of(ZrNbHfTaMe)Nx(Me= W,Mo,Cr)high entropy nitride thin films were prepared by magnetron sputtering by changing the nitrogen flow rate.The effects of nitrogen flow on the microstructure and mechanical properties of the films were investigated.The three kinds of ZrNbHfTaW,ZrNbHfTaMo and ZrNbHfTaCr high entropy alloy films prepared without nitrogen are amorphous with dense structure,whose hardness was maintained at 10±1GPa,and the deformation of shear zone was typical under the indentation,with no cracks found around the indentation.When nitrogen was added at 5sccm flow rate,(ZrNbHfTaMe)Nx(Me=W,Mo,Cr)high entropy nitride was formed.The films in all three groups are crystallized rapidly and exhibited NaCl structure,which also showed preferential columnar growth along the(111)crystal plane.In addition,the formation of high entropy nitride phase leads to a rapid increase in hardness,accompanied by a decrease in fracture toughness.The crystallinity of the three groups of films reaches its maximum at the nitrogen flow rate of 15 sccm,at which time the strong columnar growth leads to low fracture toughness.However,when the nitrogen flow rate increased to 30 and 60sccm,the amorphous phase appeared in the film,leading to the decrease of crystallinity of the high entropy nitride film,and the formation of nanocrystal/amorphous nanocomposite structure.Meanwhile,the relatively high hardness of the film was maintained,and the fracture toughness was significantly improved,especially in(ZrNbHfTaMo)Nx system,the radial cracks disappear completely,realizing the purpose of strengthening and toughening coordination.Although the microstructure of high entropy nitride films varied greatly with the change of nitrogen flow rate,but the hardness values changed little,the fracture toughness of high entropy nitride films can be significantly improved by the nanocrystalline/amorphous nanocomposite structures obtained at high nitrogen flow rate.2.Tribological wear tests were carried out on three groups of(ZrNbHfTaMe)Nx(Me=W,Mo,Cr)high entropy nitride films,studying the effects of microstructure and alloying elements on tribological properties of high entropy nitride films.The friction coefficients of three(ZrNbHfTaMe)Nx(Me=W,Mo,Cr)high entropy nitride films are about 0.9,0.75 and 0.8,respectively,among which(ZrNbHfTaCr)Nx films are easy to wear and fail,(ZrNbHfTaW)Nx and(ZrNbHfTaMo)Nx films show higher wear resistance,corresponding to the lowest wear rates of 6.4×10-6mm3/(Nm)and 2.1×10-6mm3/(Nm),respectively.And the results of XPS show that friction oxidation occurs in the film during the friction process.W2N and WO3 are generated in the wear marks of(ZrNbHfTaW)Nx film,while MoO2 and lubrication phase MoOx are formed in the wear marks of(ZrNbHfTaMo)Nx film,which resulting in lower friction coefficient and higher wear resistance.3.The corrosion properties of three groups of(ZrNbHfTaMe)Nx(Me= W,Mo,Cr)high entropy nitrite films in 3.5wt.%NaCl solution were studied.The Icorr values of(ZrNbHfTaW)Nx films prepared at nitrogen flow rate of 0 5sccm,15sccm,30sccm and 60sccm are 2.84×10-8,2.48×10-6,2.11×10～5,2.06×10-6 and 1.42×10-6A/cm2,respectively.The Icorr values of(ZrNbHfTaMo)Nx films are 4.12×10-7,3.04×10-6,6.27×10-5,1.68×10-5 and 2.57×10-6A/cm2,respectively.And the Icorr values of(ZrNbHfTaCr)Nx films are 1.82×10-8,2.51×10.7,8.03×10-7,3.84×10-7 and 1.32×10-7A/cm2,respectively.When nitrogen was not added,the film was high entropy amorphous glass film,and the corroded ions showed the highest corrosion resistance due to the lack of diffusion channels.When nitrogen was added to obtain the high entropy nitrous oxide film,the crystallization of film was the strongest at the flow rate of 15scccm,which was a typical columnar growth,and the corrosion resistance was the worst due to the existence of permeable diffusion channels.When the nitrogen flow rate is further increased,nanocrystalline/amorphous nanocomposite structure is formed,which inhibits the columnar growth and reduces the diffusion efficiency of corrosive ions,thus improving the corrosion resistance.Among the three groups of high entropy nitride films,the self-corrosion current(Icorr)of(ZrNbHfTaCr)Nx films is the lowest,indicating that(ZrNbHfTaCr)Nx films have the best corrosion resistance.Because the presence of Cr element in the corrosion process makes the film surface easy to form dense Cr2O3 oxidation membrane,which acting as a barrier to corrosive ions,exhibits optimum corrosion resistance. |
PDF Full Text Request