Influence of cyclic pumped diffusion on the morphology and microstructure of A15 layers in bronze processed multifilamentary wire

The authors have used a novel reaction method called cyclic-pumped diffusion (CPD) to achieve near uniform A15 reaction layers on filaments throughout the cross-section of a multifilamentary composite. A detailed investigation of the spatial variation of the lattice parameter during reaction in filaments and in the bronze matrix has enabled them to optimize the time and temperature for successive reaction cycles. A 61×61 filament Nb-7.5% wt Ta-bronze composite reacted using CPD in the range 600-800°C shows a compound thickness variation between the inner and outer filaments of ~30%, while the same composite given a conventional isothermal heat treatment at 700°C shows a corresponding layer thickness variation of ~200%. The consequences of the CPD reaction method for the design of composites containing tin reservoirs are discussed