Vacancy release upon heating of an ultrafine grain Al-Zr alloy: In-situ observations and theoretical modeling

JOURNAL OF ALLOYS AND COMPOUNDS

卷:862

Article

Lefebvre, W.¹  Skiba, N., V^2,3  Chabanais, F.¹  Gutkin, M. Yu^2,3  Rigutti, L.¹  Murashkin, M. Yu^4,5  Orlova, T. S.⁶ 

[1] Normandie Univ, Grp Phys Mat, CNRS, INSA Rouen,UNIROUEN, F-76000 Rouen, France

[2] Russian Acad Sci, Inst Problems Mech Engn, St Petersburg 199178, Russia

[3] Peter Great St Petersburg Polytech Univ, St Petersburg 195251, Russia

[4] St Petersburg State Univ, St Petersburg 198504, Russia

[5] Ufa State Aviat Tech Univ, Inst Phys Adv Mat, Ufa 450000, Russia

[6] Russian Acad Sci, Ioffe Inst, St Petersburg 194021, Russia

关键词: Cavities;    Pore;    UFG;    Vacancy;    Grain boundary;    Severe plastic deformation;    In-situ;    Annealing;    Disclination;   

DOI  :  10.1016/j.jallcom.2020.158455

来源: Elsevier

【 摘 要 】

The present study demonstrates the direct observation of pore formation by rapid release of vacancies in ultrafine grain (UFG) Al-0.4at%Zr alloy during in-situ annealing in a scanning transmission electron microscope. The ultrafine grain structure was preliminary obtained by high pressure torsion processing at a hydrostatic pressure of 6 GPa up to 10 revolutions. In-situ annealing reveals the rapid formation of pores in triple junctions (TJs) of grain boundaries (GBs) during the first few minutes followed by their subsequent slow resorption with the complete disappearance of some of them. During annealing, no noticeable displacement of GBs is observed. By considering the evolution of non-equilibrium GBs inherited by the severe plastic deformation, a theoretical description is suggested which describes: (i) the pore formation at disclinated TJs as a thermodynamically driven process of free volume dissolution through generation of vacancies, which then migrate to the TJs and coagulate at them with growth of the pores diminishing the strain energy of the TJ disclinations, and (ii) further decrease of the TJ disclination strain energy through the climb of extrinsic GB dislocations towards the disclinated TJs, accompanied with dissolution of the TJ pores by emission of vacancies which provide the dislocation climb. The rapid release of excess vacancies during the early stage of heat treatment is consequently identified as a phenomenon responsible for accelerated atomic mobility. This work hence provides a new perspective for understanding the accelerated precipitation kinetics observed in severely deformed alloys. (C) 2021 Elsevier B.V. All rights reserved.

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