Analysis of Strengthening in HPT Processed Hydrogenated Palladium

AbstraktPure annealed samples of Pd 99.99% have been loaded with hydrogen to four different concentrations between 0.025 and 0.45 % H/Pd, and then subjected to Severe Plastic Deformation by High Pressure Torsion (HPT) at temperatures 293 and 233 K, to a von-Mises strain eps(VM) = 82. After that, their mechanical strength has been investigated by hardness tests, while the grain size/distribution was evaluated by TEM. The strength (characterized by the critical resolved shear stress tau) showed a marked increase with increasing hydrogen content followed by a saturation at the highest hydrogen concentration achieved. Although the average grain size (d) decreased with increasing hydrogen content, the strength does not follow a Hall-Petch law with d^(-1) nor d^(-1/2). DSC exhibits at least 2 lattice defect peaks indicating the annealing of vacancies and dislocations at annealing temperatures higher than those observed in HPT processed samples without hydrogenation. Although the densities of both these defects increase with increasing H content, they cannot be directly correlated with the strength increase. However, the measured dislocation densities N well fit the relation (tau) proportional to SQRT(N). Thus, these results suggest that the observed increase/saturation in strength is a consequence of hydrogen induced increase of dislocation density rather than that of vacancy concentration and/or density of vacancy agglomerates.
NameWerbach, Katharina
VeranstaltungHy-SEA 2014 (Int. Conf. on Hydrogen Storage, Embrittlement and Applications)
StadtRio de Janeiro
Art der VeranstaltungKonferenz
Keywords:103018 Materialphysik