Interfacial reactions and mechanical properties between Sn-4.0Ag-0.5Cu and Sn-4.0Ag-0.5Cu-0.05Ni-0.01Ge lead-free solders with the Au/Ni/Cu substrate

Sn-4.0Ag-0.5Cu (SAC) and Sn-4.0Ag-0.5Cu-0.05Ni-0.01Ge (SACNG) lead-free solders reacting with the Au/Ni/Cu multi-layer substrate were investigated in this study. All reaction couples were reflowed at 240 and 255 °C for a few minutes and then aged at 150 °C for 100-500 h. The (Cu, Ni, Au)₆Sn₅ phase was formed by reflowing for 3 min at the interface. If the reflowing time was increased to 10 min, both (Cu, Ni, Au)₆Sn₅ and (Ni, Cu, Au)₃Sn₄ phases formed at the interface. The AuSn₄ phase was found in the solder for all reaction couples. An addition of Ni and Ge to the solder does not significantly affect the IMC formation. After a long period of heat-treatment, the thickness of the (Cu, Ni, Au)₆Sn₅ and (Ni, Cu, Au)₃Sn₄ phases increased and the intermetallic compounds (IMCs) growth mechanism obeyed the parabolic law and the IMC growth mechanism was diffusion-controlled. The mechanical strengths for both the soldered joints decreased with increasing thermal aging time. The SACNG/Au/Ni/Cu couple had better mechanical strength than that in the SAC/Au/Ni/Cu couple.     

SnAgCu/Cu和SnPb/Cu界面热-剪切循环条件下化合物的生长行为

对热剪切循环条件下Sn-3.5Ag-0.5Cu/Cu和Sn-Pb/Cu界面上原子扩散和化合物的生长行为进行了研究。结果表明:再流焊后,在两界面上均形成一种Cu6Sn5化合物;随着热剪切循环周数的增加,两界面上化合物的形态均从扇贝状向层状生长,其厚度随循环周数的增加而增加,且生长基本遵循抛物线规律,说明Cu原子的扩散控制了Cu6Sn5化合物的生长。界面近域的钎料内,颗粒状的Ag3Sn聚集长大成块状。     

Sn-3.5Ag-0.5Cu/Cu界面的显微结构

研究了热-剪切循环条件下Sn-3．5Ag-0．5Cu钎料／Cu界面的显微结构，分析了界面金属间化合物的生长行为，并与恒温时效后的Sn-3．5Ag-0．5Cu／Cu界面进行了对比。结果表明：恒温时效至100h，Sn-3．5Ag-0．5Cu／Cu界面上已形成Cu6Sn5和Cu3Sn两层金属间化合物；而热-剪切循环至720周Sn-3．5Ag-0．5Cu／Cu界面上只存在Cu6Sn5金属间化合物层，无Cu3Sn层生成，在界面近域的钎料内，颗粒状的Ag3Sn聚集长大成块状；在热-剪切循环和恒温时效过程中，界面金属间化合物的形态初始都为扇贝状，随着时效时间的延长逐渐趋于平缓，最终以层状形式生长。     

Low temperature sintering and microwave dielectric properties of (Mg0.7Zn0.3)0.95Co0.05TiO3 ceramics with BaCu(B2O5) additions

The effects of BaCu(B₂O₅) additives on the sintering temperature and microwave dielectric properties of (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were investigated. The (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics were not able to be sintered below 1000 °C. However, when BaCu(B₂O₅) were added, they were sintered below 1000 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B₂O₅) was formed during the sintering and assisted the densification of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics at low temperature. BaCu(B₂O₅) powders were produced and used to reduce the sintering temperature of the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics. Good microwave dielectric properties of Q × f = 35,000 GHz, ?_r = 18.5.0 and τ_f = −51 ppm/°C were obtained for the (Mg_0.7Zn_0.3)_0.95Co_0.05TiO₃ ceramics containing 7 wt.% mol% BaCu(B₂O₅) sintered at 950 °C for 4 h.     

Suppressing effect of 0.5 wt.% nano-TiO2 addition into Sn-3.5Ag-0.5Cu solder alloy on the intermetallic growth with Cu substrate during isothermal aging

This study investigated the effects of adding 0.5 wt.% nano-TiO₂ particles into Sn3.5Ag0.5Cu (SAC) lead-free solder alloys on the growth of intermetallic compounds (IMC) with Cu substrates during solid-state isothermal aging at temperatures of 100, 125, 150, and 175 °C for up to 7 days. The results indicate that the morphology of the Cu₆Sn₅ phase transformed from scallop-type to layer-type in both SAC solder/Cu joints and Sn3.5Ag0.5Cu-0.5 wt.% TiO₂ (SAC) composite solder/Cu joints. In the SAC solder/Cu joints, a few coarse Ag₃Sn particles were embedded in the Cu₆Sn₅ surface and grew with prolonged aging time. However, in the SAC composite solder/Cu aging, a great number of nano-Ag₃Sn particles were absorbed in the Cu₆Sn₅ surface. The morphology of adsorption of nano-Ag₃Sn particles changed dramatically from adsorption-type to moss-type, and the size of the particles increased.The apparent activation energies for the growth of overall IMC layers were calculated as 42.48 kJ/mol for SAC solder and 60.31 kJ/mol for SAC composite solder. The reduced diffusion coefficient was confirmed for the SAC composite solder/Cu joints.     

Cathodic arc deposition of (Al,Cr)2O3: Macroparticles and cathode surface modifications

The present work investigates the microstructure and chemical composition of macroparticles incorporated in arc evaporated (Al,Cr)₂O₃ coatings. According to scanning and transmission electron microscopy analysis, two different types of macroparticles with a distinct difference in their shape and a noticeable variation in their chemical composition, i.e. the Al/Cr ratio, can be distinguished. In addition, the transformations on the surface of the corresponding Al-Cr compound cathodes during the evaporation process in O₂ atmosphere are studied by scanning electron microscopy and X-ray diffraction. Beside the virgin cathode material, a reaction layer consisting of various intermetallic Al_xCr_y phases with a fine-grained morphology and pillar-shaped Al₂O₃ islands was found. Correlations between the origin of the macroparticles and the observed modifications at the surface of the Al-Cr cathode are discussed.     

Characterisation of HVOF sprayed Cr3C2-50(Ni20Cr) coating and the influence of binder properties on solid particle erosion behaviour

The coating Cr₃C₂ with 50 wt.% Ni20Cr deposited by high velocity oxy-fuel (HVOF) spray process was characterized in detail to investigate the effect of annealing on the solid particle erosion behaviour and understand the influence of the binder properties. Systematic characterization of the coating was carried out using electron microscopy (scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron probe microanalysis (EPMA)), X-ray diffraction (XRD), microindentation and nanoindentation techniques. The solid particle erosion tests were done on the as-sprayed coating and coatings annealed at 400 °C, 600 °C and 800 °C using silica erodent particles. The coefficient of restitution of the coated samples was also measured by WC ball impact tests to simulate dynamic impacts. The as-sprayed coating consisted of primary carbides and binder that was a mixture of amorphous and nanocrystalline phases. Annealing leads to recrystallisation of binder phase and precipitation of secondary carbides. The coating hardness and binder ductility change with annealing temperature. The erosion resistance improves with annealing up to 600 °C. In the as-sprayed coating, the amorphous phase, inter-splat boundaries and the elastic rebound characteristics affect the erosion response. While in the case of the coating annealed at 600 °C, the presence of ductile crystalline binder, fine carbide precipitates and embedment of erodent particles together improve solid particle erosion resistance.     

Galvanic Corrosion in Molten Salts: A Discussion of the Corrosion Mechanism of Two-Phase Ni–20Cr–20/30Cu Alloys in Eutectic (Li,K)2CO3 at 650°C

The corrosion of a Ni–20Cr and three ternary Ni–20Cr–Cu alloys containing 10, 20 and 30 wt.% Cu, respectively, in a eutectic (Li, K)₂CO₃ melt was studied at 650°C under air. Ni–20Cr and Ni–20Cr–10Cu are solid-solution alloys, while both Ni–20Cr–20Cu and Ni–20Cr–30Cu are two-phase alloys composed of a Cu-depleted matrix together with a small amount of a Cu-rich phase. The results indicate that Ni–20Cr and Ni–20Cr–10Cu have similar corrosion rates, forming a scale of external NiO and inner Cr-rich oxides. The two-phase Ni–20Cr–20/30 Cu alloys corrode rapidly, producing a mixture of Ni–Cr–rich oxides and a Ni–Cu metallic phase, which may be ascribed to the accelerated corrosion of the Cu-depleted matrix coupled with the cathodic Cu-rich phase of the alloys. As compared to Ni–20Cr–30Cu, Ni–20Cr–20Cu suffers from more-severe corrosion, due to a smaller area fraction of the cathodic Cu-rich phase in the alloy. The galvanic corrosion mechanism is also discussed.     

采用辅助脉冲电流液相扩散连接Ti(C,N)-Al_2O_3的接头形成行为及强度

采用辅助脉冲电流液相扩散连接方法,对Ti(C,N)-Al2O3陶瓷基复合材料与40Cr钢进行了焊接试验,重点研究了在辅助脉冲电流作用下,界面及焊缝组织演变、基体材料溶解等界面行为,探讨了工艺参数对接头强度及断口形态影响规律.结果表明,通过采用辅助脉冲电流液相扩散连接Ti(C,N)-Al2O3与40Cr钢,可以在较短的焊接时间条件下获得较为稳定的接头强度,四点弯曲平均强度位于231~272 MPa之间;降低焊接件整体加热温度以缓解接头残余应力,控制界面和焊缝化学冶金反应进程以较少金属间化合物数量、提高固溶体含量,抑制活性元素Zr向陶瓷基复合材料中的扩散进程以减少陶瓷颗粒向焊缝中的溶解量,是提升焊接接头强度的关键因素.