Microstructure and Mechanical Properties of Diffusion-Bonded CoCrNi-Based Medium-Entropy Alloy to DD5 Single-Crystal Superalloy Joint

This study focuses on the diffusion bonding of a CoCrNi-based medium-entropy alloy (MEA) to a DD5 single-crystal superalloy. The microstructure and mechanical properties of the joint diffusion-bonded at variable bonding temperatures were investigated. The formation of diffusion zone, mainly composed of the Ni3(Al, Ti)-type γ′ precipitates and Ni-rich MEA matrix, effectively guaranteed the reliable joining of MEA and DD5 substrates. As the bonding temperature increased, so did the width of the diffusion zone, and the interfacial microvoids significantly closed, representing the enhancement of interface bonding. Both tensile strength and elongation of the joint diffusion-bonded at 1110 °C were superior to those of the joints diffusion-bonded at low temperatures (1020, 1050, and 1080 °C), and the maximum tensile strength and elongation of 1045 MPa and 22.7% were obtained. However, elevated temperature produced an adverse effect that appeared as grain coarsening of the MEA substrate. The ductile fracture of the joint occurred in the MEA substrate (1110 °C), whereas the tensile strength was lower than that of the MEA before diffusion bonding (approximately 1.3 GPa).

Microstructure and Hardness of Diffusion Bonded Sialon-AISI 420 Martensitic Stainless Steel

The objective of this work was to examine the microstructure, interdiffusion of elements, and hardness of joining sialon to AISI 420 martensitic stainless steel using diffusion bonding process. These materials were diffusion bonded at 1200oC for one hour under 20 MPa in a vacuum of 2.1x10-6 Torr. The microstructural analyses showed that joining sialon to nitrided steel produced thinner reaction layers and no gap or crack were formed on the sample. Gaps were produced in joining sialon to as-received steel. From the elemental analyses, alumina and iron silicides were formed at the interface layer of sialon/as-received steel joint. Alumina and smaller amount of silicides were detected at the interface layer of sialon/nitrided steel joint. Diffusion layer and parent steel of the sialon/nitrided steel joining contained nitrides. The hardness test across the joints indicated that reaction layers possessed intermediate hardness between sialon and steel. The layers contributed to ductility of the joint that help to attain the joint.

Morphology and Chemical Composition of Ag/In/Ag Interconnections

One of the environment protection’s main aims is working out soldering materials able to replace the Sn-Pb solders commonly used so far. The joint obtained using diffusion soldering fulfills these conditions and takes up 6 times less space than in the case of conventional soldering. Moreover, it can work at the temperatures higher than 350 [°C] and it often shows mechanical and thermal stability at temperatures 2-3 times higher than the joining temperature. This paper presents the morphology and chemical composition Ag/In/Ag joint diffusion-soldered at 193 [°C] for 1.5 and 2 hours. Two intermetallic phases, namely AgIn2 and Ag2In were identified within the joint using an energy dispersive X-ray microanalysis and selected area electron diffraction techniques. Most probably the AgIn2 phase was formed during cooling of the joints from the soldering temperature because its melting point is 166 [°C]. On the other hand, the Ag2In phase is desired as its thermal stability is over 300 [°C]. This phase grows into the solder material (In) relatively fast. The exponential factor n determined from the appropriate kinetic equation was found to be 0.41, which suggests some contribution of the grain boundary diffusion process in addition to the volume diffusion (n=0.5).