Role of Ti on growth, morphology and microtexture evolution of A15-based V3Ga superconductor by bronze technique

We report a rare experimental evidence of an exceptional increase in grain-boundary diffusion-controlled growth kinetics of product phase by grain-refinement due to minor alloying. Ti-addition during growth of V3Ga superconductor by coupling V and Cu(Ga)-solid solution by bronze process increases the critical current density (Jc) significantly. In this manuscript, the exact role of Ti-addition is studied based on systematic and quantitative diffusion-couple experiments that mimic the bronze-method. Metallurgical aspects like microstructural features and growth mechanism are assessed critically. Results are compared when Ti is added either to V or Cu(Ga) and to both for a fixed Ga content. Ti-addition to Cu(Ga) compared to V increases growth kinetics of V3Ga more significantly. Quantitative EPMA-analysis indicates that a mixture of Ti-free and Ti-containing V3Ga phase grows when Ti is added to V. Small precipitates grow along with Ti-containing V3Ga when Ti is added only to Cu(Ga). TEM-study indicates that these precipitates are rich in V and Ti. Much finer grains found in the precipitate-containing region lead to higher growth kinetics due to grain-boundary diffusion. EBSD-analysis shows equiaxed grains and relatively random in orientation because of alloying. This study indicates that Ti-addition to Cu(Ga) is most effective considering metallurgical aspects that influence Jc. Keywords: Superconductor material, Microstructure, Grain size distribution, Grain boundary diffusion, Microtexture