Key Engineering Materials Vols. 297-300

Abstract: In the brazed joint of stainless steel with BNi-2 filler, brittle Cr-B compounds form in the vicinity of the centerline of the brazed joint. These compounds cause a decrease in joint strength. In this study, BNi-2 filler supplemented with Cr powder has been used in brazing stainless steel in orde r to disperse brittle Cr-B compounds uniformly in the brazed joint and improve joint strength. The mechanical properties and microstructures of the brazed joints were investigated. Moreover, a comp arison of the brazed joint with that using the BNi-2 filler was conducted.

Abstract: In this study, a diffusion bonding of aluminium alloy A6061 was preformed using an Ag-28Cu filler metal in order to conduct eutectic brazing. Melting mechanism was surveyed. Interface behaviors of the brazed joints were observed after brazing and T6 solution treatment. Also, tensile property of the brazed joints was examined. During diffusion bonding of Al6061 alloys with Ag-28Cu filler metal, eutectic melts were formed by eutectic reaction between Al6061 and Ag-28Cu filler metal. It was found that the reaction layer consist of two phases formed at the interface between AA6061 and Ag-28Cu filler metal. EPMA analysis revealed that two phases in the reaction layers consist of Ag-rich phase and Cu-rich phase. Tensile strength was 300 MPa after ageing treatment at 175°C.

Abstract: Two-layered Si3N4/SiC nano-composites with 50vol.% SiC have been fabricated by two-step sintering of a powder mixture of a-Si3N4 and carbon powder with a mean size of 13nm, and 5wt.% Y2O3. Nano-sized SiC particles were formed through reactions: carbon and surface SiO2 on the Si3N4 particles, and carbon and Si3N4 particles. To combine the specific advantages of nanoscale ceramics with that of metals, they are often used together within one composite component. In this study, the fabrication and mechanical properties of a nanoscale SiC layer brazed with an Inconel alloy were investigated. It was shown that, with a variation of strain rate, the joints have a bending strength of 330-380MPa, and the deflection of the interlayer increases with increasing strain rate. The fracture types are classified into three groups; cracks grow into the metal-brazing filler layer, the ceramicbrazing filler layer or inside the ceramic.

Abstract: In this paper, a new method for welding aluminum matrix composites is mainly described. It is liquid-phase-impact (LPI) diffusion welding, which has gained China National Patent. The results show that by liquid-phase-impact diffusion welding, when the certain amount of liquid phase alloy appears, with effect of certain impact speed, the interface of matrix-reinforcement and reinforcement-reinforcement are joined perfectly. Because the welding time is very short, the harmful phase is avoided in welded area and bad effect on the interface between the aluminum matrix and reinforcement hasn’t caused, and the work efficiency has improved enormously. With the technique, particle reinforcement aluminum matrix composite SiCp/ZL101 has welded successfully, and joint strength is about 75% of the strength of composite (as-casted), deformation less than 3%.

Abstract: Two types of joining specimens with and without Ni foil interlayer between 316L–SS bar have been prepared by diffusion bonding in a temperature range of 850- 1050°C, under a uniaxial pressure of 10MPa for 1hours. The relationship between the bonding parameters and the tensile strength of the joints at elevated temperature was studied. Optimized processing parameters were suggested based on the testing results. It was found that the introduction of the interlayer may reduce the room temperature strength but increase the high temperature strength. This was attributed to the transformation of Fe0.64Ni0.36 formed in bonding process into FeNi3 at high temperature.

Abstract: For a rational design of a welded joint, it is necessary to repeatedly assess the fatigue life of the joint with various dimensions and welding conditions. In this paper, an automated, repeatable/repetitive fatigue life assessment process for a welded cruciform joint was studied. The process consists of a structural analysis to obtain the stress distribution in the vicinity of the weldtoe, a thermal elasto-plastic analysis to determine the welding residual stress, and a fatigue life assessment based on the analyzed stress distribution and welding residual stress. With changes in design conditions including dimensions and/or welding heat input, the aforementioned tasks have to be performed. Using a commercial tool for system integration, automation of a repeated process for a welded cruciform joint based on 2D modeling was achieved. In this automated system, data exchanges between programs, regardless of whether they are commercial or in-house, work well, and parametric studies for optimal design can be performed.

Abstract: The mixture of Ni based alloy powder and WC particles were used as a feeding material to modify the surface properties of cast Al-Si alloy using a CO2 continuous transverse flow laser beam with maximum power of 10 kW. Microstructures and chemical components of the laser surface cladding (LSC) layers were studied using SEM, XRD, TEM and EDS. It is shown that the LSC layers were composed of γ-（ Ni, Cr, Fe, W）matrix phase and many enhancing phases, such as Ni2Al3, Ni3Al, WC, W2C, Cr2B, etc.. The microstructure of the LSC layers was greatly affected by the scanning rate b V and the powder of feeding rate p m under the same laser power. With the increasing of b V and p m , the dissolution phenomenon of WC particles was improved; the length, the diameter and the amount of the acicular constituent were markedly reduced. Microhardness and wear resistance tests were also performed: the average microhardness of the LSC layers was around 5.1 to 5.9GPa, which was five times higher than that of the Al-Si substrate. The wear resistance of the layer was about 20 times as big as that of cast Al-Si alloy when P=6kW, b V =13.3mm s-1, p m =100mg s-1, L=500N. The results showed that the mechanical properties of LSC layers on cast Al-Si alloy can be markedly enhanced with proper processing parameters. However, due to the sudden change of physical and mechanical properties between laser modified layer and substrate, some defects, especially crack, actually occur in the surface modified layer and the interface zone. And finally Ni/WC surface gradient layer was obtained on cast Al-Si alloy through thrice laser scanning technique. The microhardness of the laser gradient layer gradually changed from surface to substrate, so that it can reduce stress concentration in the whole laser surface layer, especially in the interface zone.

Abstract: High-speed ultrasonic bonding method has been developed to join resin-coated Cu wire on Sn electrodes for high-frequency chip coils. Two-step amplitude method, which decreases the ultrasonic amplitude in the bonding process, was effective to join the resin-coated Cu wire on Sn electrodes. The surface roughness treatment for a bonder head accelerated the deformation of the wire in the bonding process and improve the bondability compared to using the bonder head without that treatment. This paper also describes bonding properties of the joint and the bonding mechanism.