Study of effects of process parameters on diffusion bonding of dissimilar materials (Ti6A14V & SS3161)

Abstract

Solid state welding is a joining technique in which similar or dissimilar metals are joined at a temperature which is well below the melting point of the base materials. It is achieved by applying sufficient pressure with or without heat, so that localized microscale and/or macroscale deformation of the faying surface occurs so that the two metals comes in intimate contact with each other, which is a prerequisite condition for inter diffusion of atoms between the base metals which will eventually result in joining of the base metals.Diffusion bonding is a type of solid state welding technique in which the materials to be joined are kept in a high vacuum or inert atmosphere, by placing them in end to end configuration, one above the other and heated to an elevated temperature, in presence of a uniaxial pressure so that perfect intimate contact is achieved between the faying surface due to deformation of asperities and localized breakdown of surface oxide layers. Diffusion bonding can be done with or without interlayers depending on the properties of the base materials to be joined. Diffusion of atoms takes place over time, at the respective elevated temperature and results in formation of various solid solutions or intermetallic compounds depending on the solubility limit of base metals atoms in one-another’s matrix. Generally there is only a small plastic deformation at the joint region and thus very delicate and micro-machined components can be joined by this method.The current thesis shows the experiments done for joining dissimilar metals Ti6A4V and SS316l. Firstly the joints were prepared in open atmosphere and various property changes were studied. After that, actual diffusion bonding machine was used and again the samples obtained arestudied for change in various properties. Comparative studies was done based on the results obtained in both the cases. The specimens prepared were cylindrical in shape having 12mm dia. each and 15mm as well as 30mm height each. The joining was done using Cu, Ni interlayer both individually as well as combined. The process parameters varied are temperature (850˚C to 950˚C), time (30 min to 90min) and pressure (6MPa to 8MPa). In order to get good quality joints with desired mechanical properties the diffusion bonding parameters such as temperature, time, pressure, surface roughness and interlayer thickness, needs to be optimized because there is a non linear relationship among the process parameters.The study of successfully joined samples was done after cutting them on WIRE- EDM. The characterization of the samples was done using Optical Microscope, XRD, SEM and EDS. For mechanical properties tensile tests were done on UTM machine and hardness test was carried out on Rockwell hardness testing machine. Based on the above results comparative study was done.