Browsing by Author "Krasteva M."

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    INVESTIGATION OF THE INFLUENCE OF MODIFICATION WITH B, Zr AND Ti ON THE STRUCTURE AND HARDNESS OF CUAL9FE3 ALLOY BRONZE IN THE CAST STATE
    (2025-11-02) Krasteva M.; Petkov V.; Raykov P.
    In view of the changes occurring in the global production plan and the imposition by the business on the market for metal products and parts, there is a tendency to replace basic parts and castings made of cast iron and steel with those made of non-ferrous metals and alloys. Some of the most used metals are copper and aluminium, and their alloys. These alloys are alloyed or modified to produce alloys with better casting, performance and corrosion properties. Aluminium bronzes are of scientific interest because they are of industrial importance at a content of 6-12 % Al with or without the addition of other elements, crystallizing in a narrow temperature range, which determines a good thinness and a high tendency to form concentrated suctions, and alloys with a content of 9-15 % Al, where the mechanical strength and hardness increase with increasing aluminium content, but their ductility and impact toughness decrease. The development aims to increase the hardness, preserve or finesse the structure and change the grain shape of aluminium bronzes by adding a small amount of B, Zr and Ti as modifiers so that the resulting castings and parts of CuAl9Fe3B, CuAl9Fe3Zr and CuAl9Fe3Ti alloys in the cast state possess high technological, corrosion and service properties.
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    INVESTIGATION OF THE INFLUENCE OF Mо, W AND V MODIFICATION ON THE STRUCTURE AND HARDNESS OF IRON-DOPED CuAl9 BRONZE IN THE CAST STATE
    (2025-11-02) Krasteva M.; Petkov V.
    Of the group of tin-free bronzes, the most widespread in foundry production is the use of so-called “aluminium” bronze, or bronze type CuAl9. Double bronzes of this type tend to “self-anneal”, resulting in a coarse-grained cast structure. To suppress this tendency, aluminium bronzes are most alloyed with iron, manganese and nickel, but are also further modified with various modifiers. The aim of this development is to investigate the influence of Mo, W and V modification on the structure and hardness of iron alloyed CuAl9 type in the cast state.
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    METHODOLOGY AND EQUIPMENT FOR RESEARCHING CORROSION CRACKING PROCESSES IN CASTING ALLOYS
    (2024-01-01) Krasteva M.
    Corrosion cracking is the destruction of metal under static stresses and an aggressive environment. Corrosion fatigue is destruction of the metals and the alloys under the impact of cyclic mechanical pressure and aggressive environment simultaneously. Stress corrosion is the least studied and systematized in terms of literature data on the impact of various aggressive environment (type, temperature, and concentration), composition and structure of the material, mode of heat treatment, method of obtaining and cleaning the casting, methodology for determination of corrosion under stress, as well as equipment for carrying out similar studies. The purpose of this paper is to present the methodology and equipment developed for corrosion cracking testing of cast alloys.
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    Study of multiblock polyamide-6/Poly-(isoprene) copolymers by positron annihilation spectroscopy
    (2008-11-10) Bryaskova R.; Mateva R.; Djourelov N.; Krasteva M.
    Positron annihilation lifetime spectroscopy (PALS) has been used to determine the free volume in multiblock polyamide-6/poly-(isoprene) copolymers (PA-6/PI), synthesized via activated anionic bulk copolymerization. The diisocyanate functionalized telechelic PI, blocked with caprolactam (CL) has been used as a commoner and an activator at the same time. The elastic PI block incorporated into the main chain of PA-6 affects the amorphous and crystal phase of the copolymer leading to changing in degree of crystallinity. The positron annihilation lifetime spectroscopy (PAL) and Doppler broadening of annihilation line (DBAL) technique in a set of pure PA-6 and PA-6/PI copolymers with two different compositions have been applied and evaluation of the size of free-volume holes (pores), localized mainly in the disordered regions of the PA-6/PI copolymer by measuring the o-Ps lifetime (τ3) and o-Ps intensity (I3) has been performed. © Versita Warsaw and Springer-Verlag Berlin Heidelberg 2008.