Abstract: The Au-Sn soldering alloys are commonly used in microsoldering process for microelectronic industry due to fluxless process and relatively low melting temperature with good eutectic microstructures. This study investigated the microstructures of Au-Sn soldering between AlTiC and Si substrates with Ti/Pt/Au under bump metallization (UBM). The microstructures of the solder samples under three conditions: before bonding, after bonding and after thermal-cycle aging, were investigated. The shear strength values of pre-aging and post-aging soldering were compared. The thermal-cycling temperatures were ranged from -40 to 125 °C for 300 cycles. The intermetallic compounds (IMCs) of the AuSn solders consist of AuSn, AuSn2, and AuSn4. After thermal-cycle aging, the bonding strength was increased due to the improved IMC bonding between solders and UBM; the shear surfaces were rougher due to the growth of AuSn and AuSn2.
Abstract: The effect of cooling rate on the microstructural and mechanical properties of Sn-0.3Ag-0.7Cu-0.05Ni lead-free solder alloy was studied. The microstructure of specimens was characterized by using an optical microscope (OM) and an energy dispersive X-ray spectroscopy (EDX). The mechanical properties were performed by using a universal testing machine (UTM). The results showed that the cooling rate of water-cooled specimens was about 2.37 °C/s and the cooling rate of mold-cooled specimens was about 0.05 °C/s. To compare the different cooling rates, it was found that the grain size of water-cooled specimens was finer than that of the mold-cooled specimens, this resulted in an increment of mechanical properties of solder alloy. A higher tensile strength (33.10 MPa) and a higher elongation (34%) were observed when water-cooled and mold-cooled systems were used, respectively. The microstructure of Sn-0.3Ag-0.7Cu-0.05Ni lead-free solder alloy solidified by both cooling systems exhibited three phases: β-Sn, Ag3Sn and (Cu,Ni)6Sn5 IMCs.
Abstract: In the present work, the strengthen mechanism of Ti-Si-N ternary alloys prepared by Spark Plasma Sintering (SPS) was investigated. Ti, Si and TiN substrate powders were prepared in order to obtain nominal composition of Ti-0.35Si-1TiN and Ti-0.7Si-1TiN (wt %). Homogenization was performed before extrusion. Microstructure and phase identification were analyzed by Optical Microscope (OM) and X-ray diffraction (XRD). In order to evaluate the mechanical properties of extruded specimens, micro hardness test and tensile test were carried out. The XRD results show that no Si and TiN particles are remained after SPS and no any reaction caused of intermetallic compound during heat treatment and extrusion processes. It is found that the abnormal phase with high N-content was observed in matrix phase. It is also obvious that increasing Si from 0.35Si to 0.7Si (wt %) can increase yield stress and ultimate tensile stress from 1006±15 to 1092±5 MPa and 1089±10 to 1170±10 MPa, respectively. Hence, the strengthening mechanism by addition Si content into Ti-1TiN (wt %) is only solid solution mechanism.
Abstract: This study examined the effect of natural anhydrite (CaSO4) powder additions on the microstructure and frictional properties of a 95 Bronze - 5 Graphite composite prepared by a powder metallurgy process. Natural anhydrite powder, ranging in content from 2 to 8 weight percent, was added to a premixed bronze powder composed of copper and tin and mixed, before the graphite was added. The powder mixture was compacted into disc shaped samples under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minute in a reducing atmosphere. The green and sintered densities of the samples were measured. A microstructural analysis of the sintered samples was also performed. It was found that the green density of the samples decreased with increased anhydrite content. The sintered densities were lower than the green densities due to sample expansion. A finer microstructure was observed in the samples containing anhydrite. The anhydrite additions resulted in the reduction of both the friction coefficient and wear of the bronze-graphite samples. The amount of anhydrite from 2 to 8 weight percent clearly altered the microstructure of the bronze-graphite samples, however, the level of reduction of the friction coefficient and wear were quite similar among the anhydrite containing samples.
Abstract: This study examined the effect of calcium sulfate additions on the microstructure and frictional properties of a 95bronze-5graphite material, commonly used for frictional applications. The samples were prepared using a powder metallurgy process. The calcium sulfate powder was obtained from recycled plaster molds previously used for ceramic slip casting. The plaster molds were cleaned, crushed and ball milled to obtain powder, which was calcined at 400 °C for 4 hours and screened. 2 to 8 weight percent calcium sulfate powder was added to a premixed powder composed of copper and tin and mixed before the graphite was added. The powder mixture was compacted into a disc shape under a pressure of 500 MPa. The compacted samples were sintered at 750 °C for 30 minutes in a reducing atmosphere. It was found that the green density of the samples decreased with increased amounts of calcium sulfate. After sintering, the densities were found to have decreased due to sample expansion. A finer microstructure was observed in the samples containing calcium sulfate powder, possibly due to a grain boundary pinning effect. The addition of calcium sulfate resulted in the reduction of both the measured friction coefficient and wear of the bronze-graphite samples. However, the addition of calcium sulfate powder above 6 weight percent appeared to show decreasing effects.
Abstract: The aim of this research was to study the effect of bottom ash additions to a bronze-graphite composite on the sintering behavior, as well as on the resultant physical, mechanical and tribological properties. The composites were produced by a powder metallurgy technique from prealloyed Cu-10Sn bronze powder, graphite powder and milled bottom ash powder. The compositions studied were Cu-10Sn bronze with constant 5 wt.% graphite, and 0-20 wt.% bottom ash. Samples were die compacted under 795 MPa and sintered at 850 oC for 30 minutes in an open atmosphere furnace. It was found that the sintered density of the composites decreased with increasing amounts of bottom ash. The hardness of the samples increased with bottom ash additions and reached a maximum at 5 wt.% and decreased with further additions. The frictional properties were studied using a ball-on-disc test at ambient temperature. It was found that both the friction coefficient and the wear rate were increased with increasing amounts of bottom ash.
Abstract: Bronze-based composite materials are well known for use as friction materials. They are produced by powder metallurgy techniques from bronze powder, which acts as a matrix, and various friction modifying additives. The objective of this work was to study the effect of compaction pressure and sintering time on the properties of the unmodified bronze matrix. The bronze powder used was prealloyed with a composition of Cu-10Sn. The specimens were pressed by uniaxial die compaction with pressures of 282 to 339 MPa. The sintering experiments were conducted in an alumina tube furnace at 800 °C with sintering times of 30, 45, and 60 min under a vacuum pressure of 2.25x10-2 Torr. From the results, it was found that the density of the samples increased with increasing compaction pressure. A microstructural examination of the samples for the different sintering times showed them to look very similar. Finally, the highest sintered density of 7.30 g/cm3 was obtained at 800 °C for 60 min.
Abstract: Nickel is one of the alloying elements promoting the formation of acicular ferrite at the expense of proeutectoid ferrite. The Ni addition reduces the steady-state nucleation rates of grain boundary ferrite allotriomorph in Fe-C-Ni alloys. Due to such reasons, Ni was added to modify the microstructure of the sintered steel, investigated in this study, with the aim of improved mechanical properties. The sintered steel, produced from pre-alloyed Fe-Cr-Mo powder mixed with 0.3 wt.% C, was modified by Ni addition and cooling rate. The alloy compositional change was performed additions of varied Ni contents of 1.0, 1.5, 2.0, 2.5 and 3.0 wt.%. The material processing variables were investigated by using two different cooling rates of 0.1 and 5.4 °Cs-1. Under the cooling rate of 0.1 °Cs-1, the sintered Fe-Cr-Mo-3C steel without Ni addition showed dual-phase microstructure consisting of ferrite (soft phase) and bainite (hard structure). With Ni additions, the dual-phase microstructure was replaced by bainitic structure. Microstructural heterogeneity was observed due to the presence of Ni-rich areas, which increased with increasing added Ni contents. Under the cooling rate of 5.4 °Cs-1, the sintered Fe-Cr-Mo-3C steels with and without Ni additions showed bainitic structure. Microstructural heterogeneity was similar to that of slowly cooled steel. Ni additions not only modified the sintered steel microstructure but increased tensile strength and elongation. In general, Ni pushes the C-curve of pearlite transformation to the right hand side and lowers the martensite start temperature. The absence of ferrite from the sintered steel with only 1 wt.% Ni addition and slowly cooled at 0.1 °Cs-1 suggests that Ni strongly suppresses the austenite → ferrite transformation. In another word, Ni promotes bainite formation in the sintered Fe-Cr-Mo-Ni-C steels.
Abstract: Sintered Fe-Mo-Si-C steels were prepared from pre-alloyed Fe-0.85Mo powder added with fixed 4wt.% silicon carbide powder and varied graphite powder contents. It was found that the graphite powder addition caused morphological change from black nodular to black vermicular particles and resulted in decrease of black nodular/vermicular particle fraction, increase of pearlite fraction and slight change of ferrite fraction. The black nodular particles were either graphite or Fe-Mo-Si-C/graphite core-shell particles whereas vermicular particles were totally composed of carbon. The microstructural features showed influence on mechanical property of the sintered Fe-Mo-Si-C alloys. Wear properties of the sintered steels were strongly affected by their microstructural components. The sintered Fe-0.85Mo+4wt.%SiC steels showed highest friction coefficient and volume loss. Addition of graphite to the sintered Fe-0.85Mo+4wt.%SiC steels, not only changed morphology and chemistry of black particles but also reduced friction coefficient and volume loss. The reduction of both determined wear properties were attributed to the presence of vermicular graphite particles.