Cracking and layer growth in Nb3Sn Bronze route material

A sensitive AC technique has been used to investigate Tcand layer growth in Nb3Sn diffusion layer material. This method and the more frequently used resistive Tcmeasurement have been used in conjunction to examine several pertinent topics in diffusion layer growth. Firstly, it has been shown that the 37% volume expansion that occurs when Nb3Sn is formed can be accommodated without cracks forming. Secondly, by deliberately deforming the layer the effects of cracks have been investigated; the inductive and resistive methods being sensitive to cracks along and across the layer respectively. Thirdly, by deconvoluting the increase in amplitude of the inductive signal with annealing time (t) the layer thickness (δ) of Nb3Sn in a standard multifilamentary wire can be plotted; for IMI All Bronze (3000 × 5μm filaments) at 750°C\delta\sim t^{0.25}.