UBC Theses and Dissertations
A study of interlayer assisted friction welding of incompatible materials Neelam, Jayanth R.
Friction welding has become an accepted method of joining many dissimilar materials and is now being extensively used in industry. Even though it is the single most versatile method of joining similar and dissimilar materials, there are still many more material combinations that cannot be welded by this process or which result in an unsatisfactory brittle weld. There are several applications for these materials in industry. The objective of this work was to overcome these 'no-weld' or 'brittle-weld' limitations. The proposed process involves introduction of a third element into the conventional two-element friction welding process. The third element used is a material which forms a good friction weld with both of the other two elements when welded separately. If the two parent materials are not compatible when they come into direct contact due to the formation of intermetallics and lack of conditions inducive to good bonding, the third element, which forms good welds with both of the parent parts, acts as a buffer between the other two. While keeping them apart, it forms a joint between the two incompatible parent materials. Among several probable candidates for intermediate materials, only a few meet the requirement that they create proper conditions for bonding. After a friction welding machine had been designed and built, it was successfully tested to weld both similar and dissimilar materials by both the conventional and the proposed three-element processes. Welds between compatible materials of high efficiency were obtained by the conventional process. For material combinations normally incompatible, joints were made possible with the aid of the intermediate elements. Various degrees of joint-strength depending upon the material combinations used were observed. The strength of the joints obtained between bronze and steel, for example, was increased by as much as 40% by using a copper interlayer. The welds were subjected to tensile tests. Microstructural examinations were conducted on the separated surfaces to determine the mode of failure. Electron micro-probe analyses were also conducted to determine if there were any diffusion of elements and/or formation of intermetallics. Quantitative analyses were also made on the diffused elements. Some hypotheses were put forward as to the conditions that dictate the joint strength obtained by the three-element process and also the requirements of materials which may perform adequately as intermediate materials.