Copper–graphite composites reinforced with SiO₂ particles were fabricated by powder metallurgy technique. Electroless copper plating was introduced to improve the interfacial bonding between SiO₂ particles and copper matrix. The microstructure, density, and hardness of the composites were characterized. The tribological properties, such as friction coefficient and wear rate of the composites, were studied using a pin-on-ring tribometer. The results show that the hard SiO₂ can restrict the severe plastic deformation and adhesion contact in the process of wear. At the same time, parts of SiO₂ particles can be broken into fine particles during wear process, which is helpful for decreasing adhesion wear and abrasive wear. Therefore, the addition of SiO₂ leads to increasing friction stability and friction coefficient, and decreasing wear rate. In addition, the electroless copper plating improves the interfacial bonding between SiO₂ and copper matrix, which prevents separation of SiO₂ from copper matrix and further increase tribological properties of the composites.

The basalt-fiber-reinforced copper-matrix composites were fabricated using spark plasma sintering. The effect of basalt fiber content on the mechanical and tribological properties of copper-matrix composites was investigated. The results show that the relative density decreased, the hardness increased and the tensile strength first increased and then decreased with the increase in fiber content. The optimal tensile strength of 276 MPa was obtained when the content of basalt fiber was 1.5 wt.%. The friction coefficient of the composites decreased, and the wear volume first decreased and then increased with the increase in the fiber content. The addition of basalt fibers reduced the plastic deformation of the copper matrix during the friction test due to its strengthening effect. Moreover, the detached basalt fibers from the Cu matrix were ground into fine particles and were helpful for forming a mechanical mixing layer, which can decrease the friction coefficient of composites.

Brazing of high nitrogen austenitic stainless steels was carried out by using Ni-Cr-B-Si filler metal. The effects of brazing temperature (1020–1100°C) on the microstructure and shear strength of the joints were investigated. The results show that BN compounds with hexagonal structure are formed at the interface by the reaction of N from substrate and B from filler. The brittle Cr₅B₃ compounds with high microhardness are observed in the centre of brazing seam. The BN content increases and the Cr₅B₃ content decreases with the increase in brazing temperature. However, the content of BN compounds played a determinable role on the joint strength. The optimal shear strength of joints was 176.7 MPa when the joining temperature was 1020°C.

微晶玻璃焊料在连接过程中的晶化行为研究 朱巍巍 1 , 陈继春 2 (1. 长春工业大学 材料科学与工程学院, 长春 130012; 2. 中国科学院 金属研究所, 沈阳 110016) 摘 要: 采用一种添加 Li 2 O 和 Fe 2 O 3 的 CaO-Al 2 O 3-SiO 2 基微晶玻璃连接氧化铝陶瓷。通过采用热分析(DTA)、扫描 电镜(SEM)和 X 射线衍射分析(XRD)等方法, 研究了微晶玻璃焊料在连接过程中的晶化行为及其对接头力学性能的 影响。结果表明, 在传统的晶化处理过程中, 此玻璃中能够析出锂辉石(LiAlSi 2 O 6)、硅灰石(CaSiO 3)、钙铁镏石 (Ca 3 Fe 2 Si 3 O 12)和钙长石(CaAl 2 Si 2 O 8)四种晶体。然而, 当采用此玻璃连接氧化铝陶瓷时, 微晶玻璃的晶化过程与连 接工艺密切相关。由于缺少足够的形核驱动力, 采用焊后直接冷却的连接工艺只能获得完全玻璃态的接头中间层。