Transient liquid phase (TLP) bonding of Ti–6Al–4V/AISI 304 stainless steel using Cu/CNT composite interlayer

This paper investigates the idea of using Cu/CNT composite interlayer in the transient liquid phase (TLP) bonding of Ti–6Al–4V/AISI 304 stainless steel. In this investigation, initially TLP was carried out using a pure copper interlayer at 900, 950 and 1000 °C with the holding time 60 min. The TLP joining was then carried out at 900 °C with Cu/CNT interlayer, with the CNT weight percent, ranging from 0 to 3%. CNT was deposited on Cu foils, using electrophoretic deposition technique. Microstructure and mechanical properties of the joints were investigated with optical/electron microscopes, microhardness, and shear tests. Results showed that the interface microstructure can be divided into athermal solidification zone, isothermal solidification zone, and diffusion affected zone. The phase structure and compositions in CNT-containing samples are relatively similar to TLP samples with pure Cu interlayer. Results showed that CNT addition has expanded the diffusion areas and facilitated the diffusion across the interface. CNT addition up to 3 wt. % resulted in a significant increase in hardness up 500 VHN. The increase in hardness in the joint area can be related to the presence of various intermetallic compounds at the TLP region. The correlations between mechanical properties and microstructure and the implications of CNTs for mechanical properties of the joints are discussed.