• MATERIAL-SCIENCE ASPECTS OF FORMATION AND EVOLUTION OF DAMAGES WHICH DEFINE THE RESOURCE EXPLOITATION OF ALUMINUM STRUCTURES OF AIRPLANES

    Machines. Technologies. Materials., Vol. 12 (2018), Issue 12, pg(s) 501-502

    The work is devoted to the study of evolution of flaws in aluminium alloys of Al-Zn-Mg-Cu, Al-Cu-Mg-Мn alloying systems and to the determination of their connection with structural factors of the material such as the size and composition of intermetallic phases conditioned by heat treatment tempers, and also to the study of the effect of big number of physical factors on the long-term behaviour of structural elements of aluminium alloys, and to the determination of the rate of formation of corrosion damages in structural elements of the aircraft wing

  • MATERIALS

    STRUCTURE, MECHANICAL PROPERTIES AND CORROSION RESISTANCE OF MAGNESIUM ALLOY WE43 AFTER EQUAL-CHANNEL ANGULAR PRESSING

    Machines. Technologies. Materials., Vol. 11 (2017), Issue 8, pg(s) 413-416

    ECAP was conducted using route Bc with an angle of 120° between the die channels and a stepwise decrease of temperature from the initial 425 °C to 300 °C at the final, 12th pass. The cumulative equivalent strain the ECAP billets underwent was about 7.8. The structure examination showed that ultrafine-grained structure with the grain size of 0.69 – 1 μm was formed during ECAP process. In addition, particles of the phase Mg12Nd with an average size of 0.45 μm were formed. The refinement of the microstructure resulted in an improvement of the mechanical properties of the alloy. After ECAP, the strength characteristics of the alloy increased to the levels of ultimate tensile strength of 300 and yield strength of 260 MPa to be compared to those for the initial state (220 MPa and150 MPa, respectively). At the same time, the ductility increased to 13.2 %, which compares favourably with the initial value of 10.5 %. The ECAP process does not affect the resistance to electrochemical corrosion. The rate of chemical corrosion was found to be reduced owing to the ECAP processing.

  • MATERIALS

    INNOVATIVE SOLUTIONS USING NITROGEN-CONTAINING STEELS

    Machines. Technologies. Materials., Vol. 11 (2017), Issue 5, pg(s) 250-253

    The report provides examples of two innovative solutions using nitrogen-containing steels. The use of nitrogen-containing steels allows to increase the durability and reliability of products; to reduce the thickness of work sections; to reduce the cost of maintenance and repair downtime. The proposed solutions: 1. Austenitic corrosion resistant cast steel with 0,5%N. After homogenizing heat treatment the steel surpasses traditional cast austenitic steels at yield strength at ~1.5-2 times, impact toughness ~ 4.5 times, hardness – by about 25%. It is recommended for the manufacture of cast valves. 2. The martensitic steel grade with 0,11-0,17% N. This steel is well proved as a material for the manufacture by cold heading of very high strength corrosion resistant fasteners.

  • INFLUENCE OF NITROGEN ADDITION ON PHYSICAL-CHEMICAL PROPERTIES AND CORROSION RESISTANCE OF STAINLESS STEELS

    Machines. Technologies. Materials., Vol. 9 (2015), Issue 1, pg(s) 3-6

    Researched were the physico-chemical properties, hardening and corrosion resistance of Cr18Ni10N type austenitic chromium- nickel stainless steels of different purity by the impurities and with different nitrogen content: from impurity level to 0.220%. It is demonstrated that nitrogen alloying is beneficial both for hardening and improvement of corrosion resistance of steel under conditions when nitrogen has the form of solid solution. Addition of 0.186-0.220% of nitrogen doesn’t reduce intercrystalline corrosion in standard environment of 0.5M H2SO4 + 0.01M KSCN and improves resistance to general and pitting corrosion in chloride-containing environments.

    Pure nitric steel shows higher resistance to intercrystalline, general and pitting corrosion in chloride solutions than normal purity steel.

  • THERMOMECHANICAL STRENGTHENING AND STABILITY OF AUSTENITIC Cr18Ni10N STEEL

    Machines. Technologies. Materials., Vol. 8 (2014), Issue 12, pg(s) 20-22

    The hardening and austenite stability as a result of nitrogen alloying steel type of Cr18Ni10 in the temperature range, which is usual for the application of such steels as corrosion-resistant structural heat-resistant and/or cryogenic ones was studied. It is shown that the nitrogen alloying is perspective for strengthening and increasing of stability of austenitic stainless steels. Additional strengthening due to the preliminary cold or warm deformation hardening increases a tendency to the martensite formation under load, which limits the operating temperature of these steels. High-strength non-magnetic nitrogen-alloyed steels on the base of Cr18Ni10 steels containing up to 0.22 % of nitrogen are suitable for cryogenic application of non-deformed articles only. Otherwise, a strain-induced martensite will always form in them at temperatures below -70 °С. High strength, ductility and toughness of these steels can be achieved simultaneously only as a result of the TRIP-effect or fine-grained structure formation.

  • IMPROVED ADHESION STRENGTH, CORROSION AND WEAR PERFORMANCE OF PLASMA-SPRAYED COATINGS DERIVED FROM PVD FILM-COATED POWDERS — CONCEPT AND PRACTICE

    Machines. Technologies. Materials., Vol. 8 (2014), Issue 3, pg(s) 28-31

    Technique and equipment for plasma spraying of wear-resistant and corrosion-resistant coatings with enhanced adhesive strength was developed. Ceramic powders coated metal thin films were used for plasma spraying. Optimal conditions for deposition of the metal films on the particles of alumina powder (40…63µm fraction) by PVD process were obtained. Deposition of two- layer films on the powder particles was carried out. The first layer was titanium and the second layer was aluminum or copper. The titanium as adhesively-active element capable of wet alumina is necessary for increase the adhesion strength vacuum films as well as plasma sprayed coatings.

    A special plasma-spray gun with external arc working in a mode of laminar plasma argon jet generation was designed. Such regime provides melting of the refractory ceramic core, saving metal films as well as localization of thermal effects during spraying process.
    The results of testing coated specimens confirmed that the developed technique improves the physical and mechanical properties of the plasma sprayed composite coatings. The sprayed composite coatings were compared with coatings sprayed using pure alumina powders in terms of adhesion, wear and corrosion properties. The shear adhesion strength increases up to about 1.9 times, the wear resistance increases about 5 to 7 times, the corrosion resistance increases about 2.5 to 5 times.

    The shear adhesion strength was measured at tension of coated specimen at room temperature by developed adhesion testing technique. The substrate was flat and dog-bone-shaped. The substrate with rectangular cross-section was partially coated with plasma- sprayed coating. The specimens were tested in uniaxial tension under displacement control. The tensile specimens were loaded to adhesion delamination of the coating. Sprayed coating was detached as a result of shear interface stresses.

  • STRUCTURE, MECHANICAL PROPERTIES AND CORROSION RESISTANCE OF MAGNESIUM ALLOY WE43 AFTER EQUAL-CHANNEL ANGULAR PRESSING

    Materials Science. Non-Equilibrium Phase Transformations., Vol. 3 (2017), Issue 5, pg(s) 176-179

    ECAP was conducted using route Bc with an angle of 120° between the die channels and a stepwise decrease of temperature from the initial 425 °C to 300 °C at the final, 12th pass. The cumulative equivalent strain the ECAP billets underwent was about 7.8. The structure examination showed that ultrafine-grained structure with the grain size of 0.69 – 1 μm was formed during ECAP process. In addition, particles of the phase Mg12Nd with an average size of 0.45 μm were formed. The refinement of the microstructure resulted in an improvement of the mechanical properties of the alloy. After ECAP, the strength characteristics of the alloy increased to the levels of ultimate tensile strength of 300 and yield strength of 260 MPa to be compared to those for the initial state (220 MPa and150 MPa, respectively). At the same time, the ductility increased to 13.2 %, which compares favourably with the initial value of 10.5 %. The ECAP process does not affect the resistance to electrochemical corrosion. The rate of chemical corrosion was found to be reduced owing to the ECAP processing.