An improved wax-based binder was developed for the powder injection molding (PIM) of WC-TiC-Co cemented carbides.The critical powder loading and the rheologic behavior of the feedstock were determined. It was found that the critical powder loading could achieve up to 62.5% (volume fraction) and the feedstock exhibited a pseudo-plastic flow behavior. The injection molding,debinding and sintering processes were studied. The dimension deviation of the sintered samples could be controlled in the range of ±0.2% with the optimized processing parameters and the mechanical properties were better than or equivalent to those of the same alloy made by conventional press-sintering process.
A novel Sn-2.5Ag-2.0Ni alloy was used for soldering SiCp/Al composites substrate deposited with electroless Ni(5%P) (mass fraction)and Ni(10%P)(mass fraction)layers.It is observed that variation of P contents in the electroless Ni(P)layer results in different types of microstructures of SnAgNi/Ni(P)solder joint.The morphology of Ni3Sn4 intermetallic compounds(IMCs)formed between the solder and Ni(10%P)layer is observed to be needle-like and this shape provides high speed diffusion channels for Ni to diffuse into solder that culminates in high growth rate of Ni3Sn4.The diffusion of Ni into solder furthermore results in the formation of Kirkendall voids at the interface of Ni(P)layer and SiCp/Al composites substrate.It is observed that solder reliability is degraded by the formation of Ni2SnP,P rich Ni layer and Kirkendall voids.The compact Ni3Sn4 IMC layer in Ni(5%P)solder joint prevents Ni element from diffusing into solder,resulting in a low growth rate of Ni3Sn4 layer.Meanwhile,the formation of Ni2SnP that significantly affects the reliability of solder joints is suppressed by the low P content Ni(5%P)layer.Thus,shear strength of Ni(5%P) solder joint is concluded to be higher than that of Ni(10%P)solder joint.Growth of Ni3Sn4 IMC layer and formation of crack are accounted to be the major sources of the failure of Ni(5%P)solder joint.
AlSiCp (65 vol.% SiC) electronic packaging materials were manufactured by powder injection molding (PIM) and pressure infiltration process in order to obtain near net-shaped parts. SiCp preformed compacts obtained by pre-sintering process at 1150 K have high strength and good appearance, and the ratio of open porosity to total porosity is nearly 98%. The relative density of composites is bigger than 99%. The thermal conductivity of AlSiCp composites fabricated by this method is 198 Wm1K1, and the coefficient of thermal expansion (CTE) is 8.0 × 106/K (298 K).
A novel type of ZnO-Al2O3-B2O3-SiO2 glass-ceramics sealing to Kovar in electronic packaging was developed,whose thermal expansion coefficient and electrical resistance are 5.2×10-6/oC and over 1×1013 Ω·cm,respectively.The major crystalline phases in the glass-ceramic seals were ZnAl2O4,ZnB2O4,and NaSiAl2O4.The dielectric resistance of the glass-ceramic could be remarkably enhanced through the control of alkali metal ions into crystal lattices.It was found that crystallization happened first on the surface of the sample,leaving the amorphous phase in the inner,which made the glass suitable for sealing.The glass-ceramic showed better wetting on the Kovar surface,and sealing atmosphere and temperature had great effect on the wetting angle.Strong interfacial bonding was obtained,which was mainly attributed to the interfacial reaction between SiO2 and FeO or Fe3O4.
Two powder mixing processes, mechanical mixing (MM) and mechanical alloying (MA), were used to prepare mixed Al/diamond powders, which were subsequently consolidated using spark plasma sintering (SPS) to produce bulk Al/diamond composites. The effects of the powder mixing process on the morphologies of the mixed powders, the microstructure and the thermal conductivity of the composites were investigated. The results show that the powder mixing process can significantly affect the microstructure and the thermal conductivity of the composites. Agglomerations of the particles occurred in mixed powders using MM for 30 min, which led to high pore content and weak interfacial bonding in the composites and resulted in low relative density and low thermal conductivity for the composites. Mixed powders of homogeneous distribution of diamond particles could be obtained using MA for 10 min and MM for 2 h. The composite prepared through MA indicated a high relative density but low thermal conductivity due to its defects, such as damaged particles, Fe impurity, and local interfacial debonding, which were mainly introduced in the MA process. In contrast, the composite made by MM for 2 h demonstrated high relative density and an excellent thermal conductivity of 325 W·m-1·K-1, owing to its having few defects and strong interfacial bonding.
CHU Ke, JIA Chengchang, LIANG Xuebing, and CHEN Hui School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China
