Analysis of Conditions for the Nucleation of Grain Boundary Nanopores in Submicrocrystalline Materials under Intensive P
- PDF / 357,242 Bytes
- 4 Pages / 612 x 792 pts (letter) Page_size
- 11 Downloads / 186 Views
is of Conditions for the Nucleation of Grain Boundary Nanopores in Submicrocrystalline Materials under Intensive Plastic Deformation V. N. Perevezentseva,b and A. S. Pupynina* a Mechanical b
Engineering Research Institute, Russian Academy of Sciences, Nizhny Novgorod, 603024 Russia Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod, 603950 Russia *e-mail: [email protected] Received June 9, 2020; revised June 30, 2020; accepted July 1, 2020
Abstract—A model describing the nucleation of grain boundary nanopores in submicrocrystalline materials under intensive plastic deformation is proposed. The effect of internal stress fields from planar mesodefects, external hydrostatic pressure, and the degree of oversaturation with nonequilibrium strain-induced vacancies in a material on the pore nucleation rate is analyzed. Keywords: submicrocrystalline materials, grain boundaries, mesodefects, nonequilibrium vacancies, nanopores. DOI: 10.1134/S1063785020100120
Submicrocrystalline (SMC) materials formed by the methods of intensive plastic deformation (IPD) have unique physicomechanical properties [1]. However, the durability of SMC materials is often observed to decrease after intensive plastic deformation under long-term loading conditions. It has been demonstrated by Betekhtin et al. [2–4] that this effect may be associated with the presence of nanopores on grain boundaries (GBs) and triple grain junctions (TGJs) in initial SMC materials. According to [4], a certain fraction of nanopores evolves into micropores during the creep of SMC materials at an increased temperature to create fracture “nuclei,” which decrease their durability. Nanopores were observed after intensive plastic deformation in Al [5, 6], Cu [7, 8], Ti [9, 10], and some other metals and alloys. However, the question of reasons for the nucleation of nanopores under intensive plastic deformation occurring under high hydrostatic pressure preventing pore nucleation is still under discussion. The objective of this work is to analyze the possibility of nanopore nucleation on grain boundaries in SMC materials via the agglomeration of nonequilibrium strain-induced vacancies in a field of internal tensile stresses from mesodefects accumulated in grain boundaries under intensive plastic deformation [11, 12]. In the volume of polycrystal grains under intensive plastic deformation, nonequilibrium strain-induced vacancies are formed in a great amount, which is characterized by oversaturation Sv = Cv d /C0 , where Cvd is the atomic concentration of strain-induced vacancies
and C0 is the thermodynamically equilibrium atomic concentration of lattice vacancies. Experimental data show that the atomic concentration of nonequilibrium vacancies in SMC materials attains rather high values: Cvd ~ 4 × 10–4 [13]. It is noteworthy that such concentrations of vacancies in ordinary polycrystals and single crystals are typical for temperatures close to the melting point. The formation of pores under the conditions of high oversaturation with nonequilibrium vacancies ap
Data Loading...
