EFFECT OF SUBSTITUTIONAL ALLOYING ELEMENTS (AL, SI, V, CR, MN, CO, NI, MO) ON THE DIFFUSION-COEFFICIENT OF HYDROGEN IN ALPHA-IRON

Diffusion coefficients of hydrogen in fully annealed specimens of pure iron, Fe-(0.46-5.17 at%) Al, Fe-(0.53 approximately 5.06 at%)Si,Fe-(0.47 approximately 7.67 at%)V, Fe-(0.40 approximately 5.10 at %)Cr, Fe-0.35 at%Mn, Fe-(0.41 approximately 4.79 at%)Co, Fe-(0.98 approximately 5.16 at%) Ni, and Fe-(0.51 approximately 3.35 at%) Mo alloys have been measured by the electrochemical permeation method between 283 and 313 K. The temperature and alloy composition dependence of the diffusion coefficients has been discussed by using simple trapping models. In addition, the strain fields around the substitutional alloying atoms have been examined by measuring the variation of the lattice constant with alloying. The diffusivity of hydrogen is lowered by alloying. This is caused by the hydrogen interstitial sites around the substitutional atoms acting as trapping sites. The diffusion behavior of hydrogen in the alloys is strongly influenced by the elastic interaction between hydrogen and the alloying atoms.