An investigation of the substructural changes accompanying high-temperature creep of mono- and polycrystalline nickel samples

Abstract

Results are presented here of an investigation of the kinetics of high-temperature creep of mono- and polycrystalline nickel samples and of the associated substructural changes. It is shown that at low stresses, not exceeding the so-called linear creep limitpo creep takes place according to the Nabarro-Herring mechanism. The characteristic particle size allowed for in the Nabarro-Herring theory is similar to the size of the blocks (subgrains), measured by X-ray diffraction. In the first stage of creep at stressesp <p0 the average block size increases and the dislocation density decreases. In the second and third stages the creep does not cause any noticeable changes in the substructural characteristics (block size, dislocation density). Creep of the material is accompanied by the onset of porosity, the formation and development of which is due, apparently, to the coalescence of vacancies.