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Bassett, Julian Charles (1991) The formation of brittle phases in brazed zirconium joints. Doctoral thesis, City of London Polytechnic.
The purpose of the study was to investigate the metallurgical interactions that occur during the brazing of zirconium with Ag-28Cu filler, with particular reference to their effect on mechanical properties. The ultimate aim was to provide information that would aid in the production of tougher brazed zirconium joints than are currently being obtained.
The investigation was carried out in a number of stages:
1. A general literature survey of the metallurgy of brazed joints.
2. Zirconium brazed lap joints were made using either vacuum furnace or high frequency induction brazing. Interalloying was studied by optical and electron microscopy, X-ray diffraction and electron microprobe analysis. Interface layers were produced consisting of Cu4Zr, CuZr2, AgZr2 and Cu, distributed in a mixture between two sub-layers. Induction brazing produced high quality joints with interface layers thinner than those in vacuum brazed joints; a link between heat-up rate and wetting was observed.
3. Butt joints for mechanical testing were produced to optimum conditions. Instrumented impact testing showed that the toughest joints were those brazed with a reactive copper filler, although in all joints most of the energy absorbed was due to fracture initiation energy.
4. The greater toughness of the reactive copper brazed joints was due to a lack of flaws of any kind in their microstructure, which consisted of a eutectic of CuZr and CuZr2. In contrast, interface layer Ag-28Cu brazed joints contained shrinkage cracks and interfacial voids, along which fracture occurred.
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