Study On Strengthening-toughening And Tribological Properties For MoSi₂-based Films

Molybdenum disilicide（MoSi₂）film has the dual characteristics of metal and ceramics,its high hardness and excellent anti-wear performance make it a valuable surface protection material,which can effectively prevent the wear and corrosion of the surface of parts.However,with the development of the manufacturing industry,higher requirements have been put forward for the hardness and wear resistance of the film material under harsh working conditions.Therefore,it is crucial to design MoSi₂-based films with high hardness,high toughness,low friction and wear resistance.In this paper,a series of Mo-Au（Ag）-Si solid solution films and MoSi₂/Au（Ag）nanocomposite films with different Au（Ag）contents were prepared by magnetron sputtering.The effect of trace Au or Ag doping on the microstructure of the films were investigated,and the hardness,toughness and tribological properties of the films were systematically studied,revealing the toughening mechanism and tribological mechanism of Mo-Au（Ag）-Si films and MoSi₂/Au（Ag）nanocomposite films.The research results are as follows:（1）X-ray diffraction analysis shows that the phase structure of all films is C40hexagonal structure,exhibiting（111）preferred orientation.After a small amount of Au atom doping（Au/Mo atomic ratio R=0.10）,Au atoms tend to replace Si atoms in MoSi₂ films to form a Mo-Au-Si solid solution films.However,when R=0.20,Au atoms aggregated and segregated to form MoSi₂/Au nanocomposite films.Nanoindentation tests show that the Mo-Au-Si solid solution film has a hardness of 15.4 GPa and a fracture toughness of 2.52MPa m^1/2,compared with pure MoSi₂,the hardness and toughness are increased by 41.3%and 68.0%,respectively.The first-principles calculation shows that the increase in hardness of Mo-Au-Si solid solution film may be related to the increase of bulk modulus and elastic constants C₃₃ and C₁₁.The increase of toughness is mainly due to the strengthening of its metallic bonds after doping with a small amount of solute Au.（2）The tribological test results show that the Mo-Au-Si solid solution films exhibit excellent tribological properties,with a friction coefficient of 0.08,which is only 38%of that of the MoSi₂ films.X-ray photoelectron spectroscopy analysis and first-principles calculation show that the introduction of trace Au atoms can induce the formation of MoSi O_x lubricating phase in Mo-Au-Si solid solution film.（3）The research on the mechanical properties and tribological properties of MoSi₂films with different Ag content found that the introduction of trace Ag atoms（～1.7 at.%）can replace the Si atoms in the MoSi₂ sublattice to form a Mo-Ag-Si solid solution.Compared with the pure MoSi₂ film,the Mo-Ag-Si solid solution film has a higher hardness（13.7 GPa）.With the increase of Ag content（～5.3 at.%）,the solid solution structure disappears and forms MoSi₂/Ag nanocomposite structure.The precipitation of soft Ag phase leads to a sharp decrease in the hardness of MoSi₂/Ag nanocomposite film.In addition,X-ray photoelectron spectroscopy and Raman spectroscopy analysis shows that the reason for the excellent tribological properties of Mo-Ag-Si solid solution coating is mainly attribute to the existence of tribo-oxidation products（Mo O₃）and bimetallic self-lubricating phases（Ag Mo_xO_y）on the wear surface.First-principles calculation further confirmed that the doping of trace solute Ag atoms can promote the spontaneous oxidation of Mo-Ag-Si solid solution films,which is an important reason for the tribo-oxidation reaction.