Diffusion bonding of pre-friction treated structural steel with reversion of deformation induced grains

In order to produce an acceptable diffusion bond in terms of quality and reliability, surface preparation becomes an indelible step in diffusion bonding process. Due to polishing requirement, surface preparation is a slow task which makes the whole process less productive. Therefore, in the present study 'pre-friction treatment' method is introduced with the main objective of reducing the surface preparation time so that the process can be more productive. Efforts have been made to investigate the feasibility of pre-friction treatment of structural steel samples for developing the diffusion bonds using impulse pressure assisted diffusion bonding. The fundamental principle of this approach is to remove the oxides and produce a deformed layer at the faying surfaces. The diffusion bonds were developed at bonding temperature 875 °C, 15 MPa maximum pulse pressure and 20-30 min bonding time. Bonds were characterized in respect of microstructural study by scanning electron microscopy, hardness distribution and tensile properties. The effect of bonding time on tensile strength and quality of the diffusion bonds were also articulated. It was observed that the ultimate tensile strength of the joint increases from 403.5 to 482.5 MPa with increase in bonding time from 20 to 30 min. Analysis of the fractured surface was also done using scanning electron microscope. The effect of post bond heat treatment on microstructure and mechanical properties of the diffusion bonds was also investigated. The post bond heat treatment of the diffusion bonds resulted in fully recrystallized grains at the interface.