EFFECT OF HYDROGEN ON THE MECHANICAL-PROPERTIES OF PD

The effect of lattice strain on hydrogen diffusion in Pd was investigated in the range of 23-68 degrees C by an electrochemical method. The solubility of hydrogen in Pd increased slightly due to deformation. The activation energy for hydrogen diffusion was determined to be 22.4 kJ mol-1, which was not affected by deformation. The diffusion coefficient was found to be represented by D=1.32*10-3 exp(-22.4 kJ/RT) cm2 s-1 in the annealed state. However, it decreased slightly with increasing deformation, suggesting that the interaction energy of hydrogen atoms with the trapping sites is very small. The effect of hydrogen on the mechanical properties was examined, and the result showed that the hydrogen content had a strong influence on the mechanical properties; the tensile elongation was increased by addition of hydrogen within the solubility limit, but a further addition of hydrogen resulted in the formation of hydride in the matrix and reduced the elongation.