Zakharova N. Influence of structural factors on deformation and fracture mechanisms and mechanical properties of sintered alloys on Fe and W base

Українська версія

Thesis for the degree of Candidate of Sciences (CSc)

State registration number

0401U001027

Thesis Registration Form

0401U001027.pdf

Applicant for

Specialization

  • 01.04.13 - Фізика металів

28-03-2001

Specialized Academic Board

Д 26.207.01

Institute for Problems in Materials Science

Essay

The dissertation work is devoted to studying the influence of structural state of sintered powder tungsten and iron on the complex of mechanical properties and on the fracture mechanism. The influence of porosity on strength characteristics, strain hardening and plasticity of sintered iron is studied. A mathematical expression which describes the dependence of material plasticity on its porosity is obtained. The concepts about the influence of porosity on low-temperature brittleness are developed. In frames of Ioffe model there is obtained a mathematical expression describing the increase of the ductile-brittle transition temperature with the growth of porosity. It is shown that in surface layers of pores in sintered metals there is observed a strong segregation of impurities and alloying elements, which often exceeds the segregation in grain boundaries. By the techniques of scanning electron microscopy "in situ" and of acoustic emission with the determination of the coordinates of the active cross sec tion and simultaneous recording the stress-strain curve the peculiarities of deformation and fracture mechanisms of sintered porous iron are studied. On the example of sintered powder tungsten the influence of plastic deformation and thermal treatment on the structure and mechanical properties of sintered BCC metals is studied. A complex investigation of structure, dislocation substructure, crystallographic texture, impurity segregation and mechanical properties of tungsten semi-finished products produced from sintered powder tungsten billets is carried out. The influence of the kind of thermo-mechanical treatment (rotation forging, screw and four-rolls rolling) on the porosity, texture, structure and mechanical properties of rods is investigated. There are developed the concept about the optimum structural state for tungsten wire during thermomechanical treatment as well as the way of controlling structure in the process of producing tungsten wire.

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