X-RAY TOPOGRAPHIC STUDIES OF DEFORMATION IN NIOBIUM AND DILUTE NIOBIUM-HYDROGEN ALLOYS

An experimental study of the deformation at a notch under tensile loading and by hydride precipitation has been conducted with x-ray diffraction topography. Lang topography, asymmetric crystal topography (ACT) and synchrotron white beam topography (WBT) were applied in this study. Crystals suitable for transmission x-ray topography (i.e. dislocation densities below 10('6) cm('-2)) were grown by the strain-anneal technique from ribbons of polycrystalline niobium of thickness less than 0.2 mm.;The generation of plasticity at a notch was studied in situ with ACT and WBT. Specimens of niobium were tested mainly at ambient temperatures although one specimen was tested at 158 K; only one specimen was a hydrogen alloy and it contained 1.8 atomic percent hydrogen. The crystals were deformed, and the resulting slip was found to agree with earlier studies.;A technique, also applicable to crystals in which the dislocation density is too high to allow the resolution of individual defects, is developed whereby the strain tensor about an arbitrary strain center may be determined from the relationship between the incremental rotation of the specimen and the resulting equi-inclination contour spacing. The analysis is used to estimate some of the strain tensor components about a precipitate of (beta)-NbH in a niobium crystal from measurements taken with characteristic x-radiation. Application of the analysis to synchrotron topography is also discussed.