Joining advanced materials by diffusion bonding

The selection of suitable joining techniques is vital for the successful utilization of advanced materials in engineering. Sophisticated mechanical fasteners have been developed and these may be combined with adhesive bonding, but they usually incur a weight penalty and the associated fastener holes can limit the fatigue strength of the joint. The principal alternative joining techniques are summarized in Figure 10.1. In all fusion welding techniques the base metal is melted and the fusion zone will have a cast microstructure. The high temperature required can lead to a wide heat affected zone either side of the fusion zone associated with a steep temperature gradient. With high cooling rates, residual stresses and component distortion can occur. These are reduced in the much narrower fusion and heat affected zones produced with laser and electron beam welds. Fusion welding is usually unsuitable for joining dissimilar materials or for metastable alloys produced by rapid quenching if the quenched microstructure must be preserved.