Investigation On Preparation And Interfacial Diffusion Behavior In The SiC Fiber Reinforced Refractory Alloy Composites

With the rapid development of the aerospace field,a higher standard is required on the mechanical properties and temperature resistance grades of materials by hot-end structural components.SiC fiber reinforced metal matrix composite material（SiC_f/Me）is considered as an important candidate material for advanced engines and hypersonic vehicles.It can not only improve the specific strength,specific stiffness and fatigue resistance of the metal matrix,but also improve the service temperature of the matrix material.At present,SiC fibers are mainly used to strengthen titanium alloys or Ti-Al intermetallic compounds.The obtained SiC fiber reinforced titanium matrix composites（SiC_f/Ti）have made great progress in both basic research and engineering applications.However,SiC_f/Ti composites are often used for structural components below 800°C because of the limited service temperature of the matrix material.In order to satisfy metal matrix composites in higher temperature ranges for hot end components,it is urgent to prepare new metal matrix composites by combining SiC fibers with metals at higher service temperatures.SiC fiber-reinforced refractory alloy composites（SiC_f/RA）have emerged as potential high-temperature structural materials.SiC_f/RA composites have difficulty in closing during the forming process due to the higher yield temperature of refractory alloys.The higher forming temperature will bring about more severe interfacial reactions than SiC_f/Ti composites.Based on what was mentioned before,preparing fully densified SiC_f/RA composites which can avoid significant interfacial reactions between SiC fiber reinforcement and RA matrix is the goal to be achieved.In this paper,the blocking of NbW alloys was realized by constructing C/Ti/TiN diffusion barrier coatings on SiC fibers.The interfacial diffusion behavior dominated by single C coating and C/Ti/TiN diffusion barrier coatings will be explored.In addition,in order to reduce the difficulty of closure of refractory alloys,Nb/W and Ta/W nano-multilayer films with different modulation periods which were prepared by a multilayer strategy are regarded as the matrix material which can achieve complete closure at lower forming temperature.In this paper,the Ti/TiN diffusion barrier coating was first prepared on the SiC fiber with C coating by magnetron sputtering technology.Secondly,the precursor wires were obtained by depositing NbW alloy coating on their surface.Finally,SiC_f/C/NbW and SiC_f/C/Ti/TiN/NbW composites were made by the hot isostatic pressing process（1400℃/150 MPa/2 h）.Observation of the cross-section of the composite after hot isostatic pressing shows that individual single C coating is difficult to block the interfacial reaction to form a thick interfacial reaction layer,however,the integrity of the SiC fibers can be maintained by the C/Ti/TiN diffusion barrier coating.It shows that the interfacial reaction product sequence of the SiC_f/C/NbW composite is:（W,Nb）₅Si₃,Nb C,（W,Nb）₅Si₃,（W,Nb）₅Si₃+Nb C by the further microscopic observation of the interface region confirms the interfacial reaction products which are dominated by the single C coating and the C/Ti/TiN composite diffusion barrier coating,while the interfacial reaction product sequence of SiC_f/C/Ti/TiN/NbW is:（Ti,Nb）（C,N）,（W,Nb）₅Si₃+（Ti,Nb）（C,N）.It is confirmed that the dense（Ti,Nb）（C,N）layer formed during the molding process helps to form a layered interfacial reaction layer,which can effectively inhibit the interdiffusion between the SiC fibers and the matrix and maintains the integrity of the SiC fibers.When the NbW alloy coating was used as the substrate,it was found that there were still micropores that were not completely closed under the condition of hot isostatic pressing at 1400°C/150 MPa/2 h,causing the complete densification could not be achieved.Furthermore,Nb/W and Ta/W nano-multilayer films with different modulation periods were prepared by the multi-layer strategy as the matrix.Compared with the single NbW and Ta W alloy coated precursor wire,the nano-multilayer structure enabled the precursor wire to have higher tensile strength,while the nano-multilayer structure reduced the closing temperature.Complete closure was achieved at 1200°C/150 MPa/2 h and a fully densified composite was obtained.