Interfacial Microstructure Characteristics and Mechanical Properties of a Press Bonded Ti–5Al–2Sn–2Zr–4Mo–4Cr Alloy

The microstructure evolution characteristics and the shear strength of bond and base alloys were investigated during the press bonding of the Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy. The quantitative detection of the interfacial void shows that the interfacial voids shrunk gradually with time and a bond free of voids could be obtained at the time above 10 min. The microstructure of the base alloy shows that the primary α phase tends to be equiaxed because of the increase in plastic deformation and the variation in the volume fraction and grain size of the primary α phase that are complicated with time. The grain boundary misorientation characteristics in bond and base alloys are not consistent. However, they tend to be comparable over time. The shear strength of bond and base alloys at different times was explained and compared. The compared results indicate that the enhanced strength of the bond is mainly due to the increase in the bonded area. However, the strength of the bond decreases slightly because of the slight coarsening of the grain size and the decrease in the volume fraction of the primary α phase at the time more than 20 min. The shear strength of the bond and base alloys tends to be highest and close at 10 min.

Investigation on the physical properties and diffusion layer phase transformation at the interface of Sialon-Duplex Stainless-Steel bonding

Joining SiALON to duplex stainless steel utilizes the properties of two materials which may provide an opportunity for distinctive applications. Ceramic is hard and operates at a high temperature but it is brittle whereas metal is tough but it can work at a low temperature. The benefits of the best properties of both materials can be utilized by joining them. The objectives of the research work are to investigate the physical properties and the phase transformation at the interface and at the inter-diffusion layer in between the SiAlON and duplex stainless steel. The experiment incorporated nitriding, then diffusion bonding the duplex stainless steel using the hot press. Bonding was carried out at 1200°C for the holding times of 30 minutes and 1 hour. Metallography and micro analyses were conducted to achieve the above objectives. The study has demonstrated that 30 minutes joining time is sufficient to develop the thickness of the interface. However, 1 hour joining duration achieved cohesive and sound diffusion bonding of the SiAlON to duplex stainless steel. This is possible due to the formation of diffusion interlayer which accommodates the residual stress presence during cooling down process.

Experimental investigation of spring-back phenomenon through an L-die bending process for multilayered sheets produced by the accumulative press bonding technique

For the first time in this study, the accumulative press bonding method was used to fabricate layer composites, including ceramic powder and metallic layers, and the spring-back as a functional plasticity test experimentally investigated. Al/Cu and Al/Cu/Al2O3 composites were successfully manufactured in five accumulative press bonding cycles, and in addition to spring-back evaluation, mechanical properties and plastic instability were investigated. The results showed that by the end of the third cycle, both composites were fully layered structure. However, in the fifth cycle in the Al/Cu/Al2O3 composite, plastic instability intensified and necking and fracture at all Cu layers observed due to the presence of particles in the interface and further differences in mechanical properties. As the number of accumulative press bonding cycles increases, the number of Al/Cu interfaces, which are the places where the reinforcement particles are dispersed, increases, thereby significantly improving the particle distribution and mechanical properties. The mechanical properties were improved by increasing the applied strain to the two composites, mainly due to the mechanisms underlying the severe plastic deformation processes, including cold working and microstructure improvement. The mechanical properties of the composite containing reinforcing particles improved the tensile strength and microhardness of both layers in all accumulative press bonding cycles, although the amount of elongation decreased slightly. The maximum tensile strength values of the two composites were obtained at the end of the fifth cycle, which improved the tensile strength for Al/Cu and Al/Cu/Al2O3 by about 2.65 and 2.42 times higher than unprocessed Al matrix, respectively. Experimental results of the spring-back evaluation showed that the composite with reinforcement powder due to the higher Young’s modulus had lower spring-back value. The amount of spring-back in both composites decreased with almost the same rate as the applied strain increased.

Development of Damage-Tolerant and Fracture-Resistant Materials by Utilizing the Material Inhomogeneity Effect

The improvement of fracture strength by insertion of thin, soft interlayers is a strategy observed in biological materials such as deep-see sponges. The basic mechanism is a reduction of the crack driving force due to the spatial variation of yield strength and/or Young's modulus. The application of this “material inhomogeneity effect” is demonstrated in this paper. The effectiveness of various interlayer configurations is investigated by numerical simulations under application of the configurational force concept. Laminated composites, made of high-strength tool steels as matrix materials and low-strength deep-drawing steel as interlayer material, were manufactured by hot press bonding. The number of interlayers and the interlayer thickness were varied. Fracture mechanics experiments show crack arrest in the first interlayer and significant improvements in fracture toughness, even without the occurrence of other toughening mechanisms, such as interface delamination. The application of the material inhomogeneity effect for different types of matrix materials is discussed.

Fabrication of Al/Ni Multilayer Composite by Electrodeposition and Hot Press Bonding and Investigation of its Bending Property

The Al/Ni multilayer composite with highly exothermic reactions and good plasticity was fabricated by electrodeposition and hot press bonding process. The Al/Ni multilayer composite consisted of the microscale Al and Ni layers. The Ni layers were electroplated on Al foils for a certain time and DC current, and then a mounts of deposited foils were stacked and combined as a whole bulk Al/Ni multilayer composite. In this study, the microstructure evolution, phase transformation, exothermic heat and bending property of the Al/Ni multilayer composite during various hot press bonding were studied by SEM, XRD, DSC and bending test. Under the hot press bonding condition of 400°C and 1h, the exothermic heat, the bending strength and the bending displacement reached 916J/g, 614.5MPa and 4mm, respectively. The results showed that by the increasing time of hot press bonding, the bending displacement of the Al/Ni multilayer composite improved firstly and then declined sharply. It was also found that when the time of hot press bonding increased, the bending strength and the exothermic heat decreased simultaneously, owing to the nucleation and growth of the Al3Ni phases in the interfaces between Al and Ni layers.