The Investigation On The Preparation And The Interfacial Diffusion Behavior In The SiC Fiber Reinforced Ni₃Al Matrix Composites

The development of aerospace technology has placed higher requirements on high-performance structural materials.Continuous SiC fiber reinforced metal matrix composites?SiC_f/Me?have become the promising candidates for the new generation engines and supersonic aircraft due to their high specific strength,specific stiffness and excellent fatigue resistance.Currently,SiC fiber reinforced titanium matrix composites?SiC_f/Ti?have achieved great success both in basic research and engineering applications,but the applicable temperature of the composite is restricted by the matrix titanium alloy,so SiC_f/Ni composites have become more attractive due to their higher applicable temperature.Comparing with SiC_f/Ti composites,the interfacial reactions in SiC_f/Ni composites are much more severe during high temperature forming and service,which resulting a sharp decrement in the performance of reinforced fibers.Therefore,the prevention of interfacial reaction has become the primary task in the development of SiC_f/Ni composites.The diffusion barrier coatings have been considered to be the most effective strategy to solve the interfacial reaction.In SiC_f/Ti composites,introducing single C coating can effectively block the interfacial reaction between SiC fibers and titanium alloys which has become the most commonly used diffusion barrier coating in SiC_f/Ti composites.However,single C coating as barrier layer in SiC_f/Ni composites is not as effective as that in SiC_f/Ti composites,meanwhile the blocking behavior of single C coatings in SiC_f/Ni composites has not been proven.Besides,Y₂O₃ is a very important candidate in blocking the interfacial reaction between SiC fiber and Ni alloy due to its higher chemical stability and higher negative Gibbs free energy.Meanwhile it is of great value to study the barrier behavior of Y₂O₃ for the development of SiC_f/Ni composites.Therefore,in this work,Ni₃Al was selected as the matrix alloy,and single C coating as well as C+Y₂O₃ duplex diffusion barrier coating were introduced respectively to prepare SiC_f/C/Ni₃Al and SiC_f/C/Y₂O₃/Ni₃Al composites.The analysis of interfacial reaction products in the composites will guide the design of diffusion barrier coatings in SiC_f/Ni composites.In this paper,the analysis of microstructure in two C-coated SiC fibers prepared by chemical vapor deposition was firstly carried out,and the key factors affecting the tensile strength of the fibers were confirmed.Subsequently,the Ni₃Al coating was prepared by physical vapor deposition.The influence of substrate bias on the microstructure and mechanical properties of Ni₃Al coating was studied.The Ni₃Al coating was deposited on SiC fiber by suitable bias voltage conditions to prepare the precursor wire.SiC_f/C/Ni₃Al composites were achieved by hot isostatic pressing at1100°C/120MPa/2h.Scanning electron microscopy,transmission electron microscopy and corresponding spectrometer were used to confirm the interfacial reaction products in SiC_f/C/Ni₃Al.It was found that the thickness of the interfacial reaction layer in SiC_f/C/Ni₃Al composites was closely related to the integrity of C coating.The diffusion behavior of Ni atom dominates the formation of interfacial reaction layer.The intact C coating can slow down the diffusion of Ni but can not completely block it.Finally,the interfacial diffusion behavior under the single C coating is studied.Meanwhile,the Y₂O₃ coating with a high temperature stable phase was prepared by physical vapor deposition on the C-coated SiC fiber,and the SiC_f/C/Y₂O₃/Ni₃Al composite with C+Y₂O₃ duplex coating was prepared by the same process as mentioned above.By confirming and analyzing the interfacial reaction products of SiC_f/C/Y₂O₃/Ni₃Al composites,it is found that the intact C+Y₂O₃ duplex coating can protect the integrity of SiC fibers,but C+Y₂O₃ is not completely inert to Ni-based alloys.Y₂O₃ and Ni₃Al can form a more stable reaction product Y₄Al₂O₉,and this ternary compound might be a more efficient diffusion barrier coating in SiC_f/Ni material than Y₂O₃.