Defects in Some Hydrogenated Metallic Materials Studied by Positrons

The measurements of angular correlation of annihilation radiation and positron lifetime were performed to study defects in commercial stainless steel and nickel subjected to deformation and electron irradiation. It follows from variation of S-parameter derived from angular correlation of annihilation radiation spectra that hydrogen charging of Fe-Cr-Ni-Mn austenite steel results in appearance of modest amount of vacancies which agglomerate into small clusters during annealing at low temperatures. Electron irradiation produces much more defects, so that subsequent hydrogenation does not add much to their concentration. The major part of defects anneals out gradually to 700 K. The residual part is preserved up to 950 K. This fact testifies to bonding state of vacancies. Nickel of 3N purity was prepared in three initial states, i.e. cold-rolled and hydrogenated before and after deformation. In an initial state all samples contain, along with simple defects, vacancy clusters. Their size and concentration are much larger in hydrogenated samples, as compared with merely cold-rolled one. Annealing above 400 K causes growth of cluster size and decrease in their concentration. At 500 K clusters are observed to disappear in cold-rolled sample, while in the sample hydrogenated after deformation they survive to 600 K.