论文部分内容阅读
Nbss/Nb5Si3 in situ composites have been the materials of intense research as a substitute of Ni-base superalloys in resent years.Due to their many favorable properties,such as high melting point,low density,good formability and abundant availability,they have been considered as the most potential materials to withstand above 1200℃.Although Nbss/Nb5Si3 in situ composites are promising for high-temperature applications,they tend to suffer from severe degradation by high-temperature oxidation.In order to improve the oxidation resistance of Nbss/Nb5Si3 in situ composite,multilayer Mo(Al,Si)2fNbSi2 coating were developed.The developed coating consists of an inner NbSi2 layer surrounded by Mo(Si,Al)2 layer,which was mainly consisted of Mo(Al,Si)2,and small amount of Mo5(Al.Si)3 and pure aluminum.After oxidation at 1250℃ for 100h,the multilayer coating exhibited an excellent protection against oxidation and good adherence to substrate.The oxidation curve followed parabolic law and even after oxidation at high temperature for 100h,the weight gain per unit area of Mo(Si,Al)2 coating is 5mg/cm2.The results showed that a continuous and compact layer of Al2O3 was formed on the coating surface to prevent oxidation below coating and substrate.The structure of the multilayer coating had obviously changes during the oxidation process.The outer Mo(Si,Al)2 layer changed to two-phase structure,which consisted of Mo(Si,Al)2 and Mo5Si3,while two interdiffusion layers,Ti-rich and Cr-rich layer,were observed between the multilayer coating and the substrate.