鈮合金(Nb-10Hf-1Ti)之真空硬銲接合研究

Abstract

Abstract Niobium is primarily used as an alloying element in spe- cialty steels and superalloys,and also used as a carbide in cutting tools for machinery.Niobium base-alloys have been wide- ly studied over the last forty years,because of its favorable high-temperature strength and good low temperature ductility, increasing its application on using as a structural material for the aerospace industries.Its strengthening characteristics co- mbined with a low neutron-absorption cross-section,also prompt- ed its application in the nuclear industries.This research work presents either the joining of Nb-10Hf-1Ti(C-103)alloys by va- cuum brazing using Ti-15Cu-15Ni(wt%) or BNi-2 foil as a brazing joint alloy.The effects of brazing process parameters(such as brazing temperature,brazing time,surface roughness,over-lap distance and post-welded heat treatment) on the properties of brazed joints had been throughly investigated.Both interfacial microstructures and mechanical properties of the brazed joints had been investigated to evaluate the joint quality. The experi- mental results show that considerable surface roughness and over-lap distance are beneficial to the brazing of Nb-10Hf-1Ti (C-103)alloys.It can be observed that the bonding exhibit good wetting between the TiCuNi filler metal and C-103 base-alloys. The element distributions of Nb,Ti,Cu and Ni were examined by energy dispersive X-ray analysis.It was found that copper and nickel remain in the center of brazed region and form brittle eutectic phases.The microstructure of the brazed joints con- sists mainly of αTi-Nb solid solution and eutectic phase struc- ture.The volume of eutectic phase in the joint region decreased with increasing brazing temperature and time. High joint shear strength (such as 302 MPa) had been obtained when the process was carried out at approximately 1223K for 5 min. The brazing of BNi-2 filler metal and C-103 base-alloys was conducted at the temperature range of 1323-1423K for 5-20 min. The optical and scanning electron microscopic results indicate that a good wetting existed between BNi-2 and C-103 alloys.The diffusion of boron and silicon from brazing filler metal into base-alloys at the brazing temperature is the main controlling factor for the microstructural evolution of the joint interface. The element distributions of Nb,Ni,Cr,Fe,Si and B were examined by EPMA line-scanning analysis.It is found that silicon,iron and chromium remain in the center of brazed region and form brittle eutectic phases,but boron distribution is abnormally high along two sides of the joint as it has readily diffused from brazing filler metal into the base-alloys. Joint shear strengths of as high as about 337MPa are obtained when the brazing was processed at approximately 1423K for 10 min.