Preparation Of Molybdenum Alloy Oxidation Resistant Coating At High Temperature

Molybdenum(Mo)and its alloys are widely used in mining,chemical industry,aerospace,nuclear industry and many other fields.However,it is easy to be oxidized in high temperature and aerobic environment which limits its application.Therefore,it is of great significance to study and improve the high temperature oxidation resistance of molybdenum and its alloys.In this paper,by means of magnetron sputtering technology,various of SiC,MoSi₂ and ZrB₂ single component anti-oxidation coatings are prepared on Mo alloy by adjusting the sputtering process parameters(such as bias,substrate temperature,power and time,etc.)because of those ceramics with good anti-oxidation ability.Furthermore,based on the study of the relationship between the sputtering parameters and the structure of the coating phase,the MoSi ₂-SiC and ZrB₂-SiC composite coatings with different SiC doping amount are prepared by co-sputtering technology,which the composite ceramic anti-oxidation coating with MoSi₂-SiC are the inner layer as well as ZrB₂-SiC as the outer layer.Field emission scanning electron microscope(FESEM),atomic force microscope(AFM),X-ray diffractometer(XRD)and energy dispersive spectrometer(EDS)are used to characterize and analyze the micromorphology,phase structure and microstructure of the coating surface and cross section.The effects of different components and process parameters on the growth characteristics,surface(cro ss section)morphology,deposition rate and microstructure of the coating have been investigated.Atomic force microscope(AFM)have been used to detect the influence of deposition time on the growth characteristics of the MoSi₂ coating.In order to clarify the influence of substrate bias on the mechanical properties of the coating,the nano indentation instrument are used to detect the MoSi₂ coating prepared under different bias.The surface morphology of the single component films shows that the bonding effect and morphology of the films with different components are quite different.The bonding effect of SiC film and Mo matrix is poor which make films easily peel and fall off from the Mo substrate,and even cracks on the films.MoSi₂ and ZrB₂ films have a good bonding effect with molybdenum matrix,and the film does not fall off.There are no cracks,pits and other defects on the surface.The surface of SiC film is the smoothest,and no obvious undulating structure is observed.But for the ZrB₂ thin film,the surface is full of tiny granular structure.MoSi₂ film is relatively rough,and the tiny granular structure on the surface of the film is island-like aggregation.With the increase of sputtering time and power,the granular structure of ZrB₂ and MoSi₂ surface increase to a certain extent as well as the roughness of the film.For the surface morphology of the composite film,SiC doping can reduce the size of the deposited particle structure on the surface of MoSi₂ film and ZrB₂film,and decrease the island-like aggregation effect of the deposited particle structure on the surface of MoSi₂ film.Those effects are more obvious with the increasing of SiC doping power.When the doping power of SiC reaches 140 W,no granular structure can be observed on the surface of ZrB₂ film.The results show that the thickness of the films linearly increase with the increasing of sputtering time and power.With the increase of sputtering time and power,the deposition rate of ZrB₂ film linearly increases firstly and then slow down.The thickness of MoSi₂and ZrB₂ film increases firstly and then decreases with the increase of bias voltage.When the magnetron sputtering power is 140 W,the deposition rates of SiC,MoSi₂ and ZrB₂are about 3.9 nm/min,20.8 nm/min and 9.1 nm/min,respectively.EDS results show that the ratio of the number of atoms in the films deposited by magnetron sputtering changed in different degrees compared with the target.Among them,the ratio of the number of C atoms in SiC film slightly increased,the ratio of the number of Si atoms in MoSi₂ film decreased,and the ratio of the number of B atoms in ZrB₂ film increased.XRD results show that the crystallinity of MoSi₂ and ZrB₂ coatings are low,and the diffraction peaks have obvious amorphous characteristics.