Grain-Subgrain Structure and Vacancy-Type Defects in Submicrocrystalline Nickel at Low Temperature Annealing

P.V. Kuznetsova,b, A.M. Lider a, Yu.S. Bordulev a, R.S. Laptev a, T.V. Rakhmatulina b and A.V. Korznikov c aNational Research Tomsk Polytechnic University, Tomsk, Russia bInstitute of Strength Physics and Materials Science, Siberian Branch of RAS, Tomsk, Russia cInstitute for Metals Superplasticity Problems of Russian Academy of Sciences, Ufa, Russia

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Scanning tunneling microscopy, positron annihilation and X-ray diffraction were applied for the study of annealing of submicrocrystalline nickel prepared by equal channel angular pressing. Several processes were revealed in the structure of submicrocrystalline nickel on different scale levels during annealing in the range Δ T=(20÷360)°C. A decrease of grain nonequiaxiality and further structure refinement were observed with a temperature increase in the range Δ T=(20÷180)°C. Subgrain growth with maximum =60 nm at 120°C occurred on the lower scale level within the same temperature range. Grain growth and microstress decrease in submicrocrystalline nickel observed at T>180°C indicate the beginning of recrystallization. The main positron trap centers were identified in submicrocrystalline nickel within different temperature ranges. In as-prepared samples positrons are trapped at dislocation-type defects and vacancy clusters that can include up to 5 vacancies. At the annealing temperature Δ T=(20÷180)°C positrons are trapped at low-angle boundaries enriched by impurities. Within the range Δ T=(180÷360)°C the dominant trap is dislocations.

DOI: 10.12693/APhysPolA.128.714 PACS numbers: 68.37.Ef, 61.72.J-, 61.72.Lk, 61.72.-y, 81.40.Ef, 78.70.Bj