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

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

Effect of Deformation on Positron Annihilation in Decomposing Copper Alloys

Positron lifetime spectra were measured in the quenched or slowly cooled Cu-3.93 at.% Ag alloy, subjected to subsequent cold rolling, as a function of isochronal annealing temperature. The results were compared with the formerly obtained data for quenched, but not deformed, C͟u-Ag alloy and for deformed C͟u-Ge solid solution. All lifetime spectra, after background and source corrections, are single exponential with the lifetimes which exceed those in well-annealed Cu solid solutions. This gives evidence to positron annihilation from a trapped state. One-component spectra may then testify to existence of a set of different traps with too weak distinction in the individual positron lifetime to be resolved as separate components. At low annealing temperatures the stage arisen from continuous decomposition is not revealed, being masked by the removal of deformation defects. The stages of discontinuous decomposition and of subsequent precipitates coagulation turn out to depend on the sample history. The role of deformation defects in the decomposition of supersaturated solid solutions is attempted to be accounted for in a wide range of annealing temperatures

Механічні характеристики сплаву γ -TiAl після дробеструменевої обробки

На сьогодні сплави на основі алюмініду титану представляють найбільший інтерес в авіакосмічній промисловості. Проведено дослідження на механічні властивості сплаву γ-TiAl із високим вмістом ніобію і встановлено вплив дробеструйної обробки. Зміцнення поверхні дробеструйною обробкою не порушує геометрії деталей, але гальмує розвиток процесів при втомлюваності. Завдяки дробеструйній обробці можна не тільки продовжити термін служби конструкцій, а й підвищити механічні характеристики сплаву. Можна стверджувати, що збільшення міцності зумовлено змінами в структурі поверхневого шару.Currently, the alloys based on the titanium aluminide are in the great demand in the aerospace industry. This research project studies the mechanical properties of the γ-TiAl alloy with a high content of niobium and the impact of shot peening processing is defined. Strengthening of the surface by shot peening, does not affect the geometry of the parts, but it hinders the development of fatigue processes. Shot peening method can not only provide the extension of construction elements’ operation period, but also enhances the mechanical properties of the alloy. Thus it can be stated that the higher durability is caused by the alteration in the structure of the surface layer