Carbon nanotubes (CNTs) reinforced Sn-58Bi composites were successfully fabricated through ball-milling method and low temperature melting process.The influence of multi-walled carbon nanotubes (MWCNTs) on the mechanical strength and ductility of Sn-58Bi lead-free alloy was studied.The mechanical test results show that the bending strength of Sn-58Bi-0.03CNTs (mass fraction,%) composite is increased by 10.5% than that of the Sn-58Bi alloy,which can be attributed to the reduction of Sn-rich segregation and the grain refinement.The toughness of Sn-58Bi-0.03CNTs composite is increased by 48.9% than that of the matrix materials.It is indicated that the influence of CNTs on the strength of Sn-58Bi-xCNTs composite is insignificant.In addition,the fracture mechanism of CNTs reinforced Sn Bi composite was analyzed.The corresponding fracture surface comparison between the Sn-58Bi-0.03CNTs composite and the monolithic Sn-58Bi alloy was made to identify the influence of CNTs on the fracture behavior and the reinforcing effect of CNTs.
Ni-based alloy was transient liquid phase bonded using a BNi-2 interlayer. The effect of bonding parameters on the microstructures and mechanical properties of the joints was investigated. With the increase of bonding temperature or time, the number of Ni-rich and Cr-rich borides and the grain size of precipitation zone decrease. Higher bonding temperature or longer bonding time is beneficial to the diffusion of melting point depressant elements （B and Si） from the PZ to the base metal and atomic interdiffusion between the base metal and the joint. The chemical composition and microstructure of the joints bonded at 1170 ℃ for 24 h are comparable to the base metal. The shear test results show that both the room and elevated temperature shear-strengths of the joints increase with increasing bonding time. However, the effect of bonding time on elevated temperature tensile-shear strength is greater than on room temperature tensile-shear strength.
In the past twenty years,Si-B-C-N ceramic has attracted wide attention due to its special structure and outstanding properties.The ceramic generally has an amorphous or a nano-crystalline structure,and has excellent structural stability,oxidation resistance,creep resistance and high-temperature mechanical properties,etc.Thus,Si-B-C-N ceramic attracts many researchers and finds potential applications in transportation,aerocraft,energy,information,microelectronics and environment,etc.Much work has been carried out on its raw materials,preparation processes,structural evolution,phase equilibrium and high-temperature properties.In recent years,many researchers focus on its new preparation methods,the preparation of dense ceramic sample with large dimensions,ceramic matrix composites reinforced by carbon fiber or SiC whisker,or components with various applications.Research on Si-B-C-N ceramic will develop our insight into the relationship between structures and properties of ceramics,and will be helpful to the development of novel high-performance ceramics.This paper reviews the preparation processes,general microstructures,mechanical,chemical,electrical and optical properties,and potential applications of Si-B-C-N ceramic,as well as its matrix composites.
The composition of oxide film of ZrssCu3oNi5Al10 bulk metallic glass was identified by X-ray photoelectron spectroscopy. In addition, the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding. The joint interfaces were observed by scanning electron microscopy and atomic force microscopy. The hardness of joints near the interface was higher than that far away from the interface, which is attributed to the difference of structural relaxation. According to the result of micro-focused X-ray diffractometry and transmission electron microscopy, the joints retained the amorphous structure when the holding time is less than 20 min. The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection. Moreover, the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength. The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.
