Key Engineering Materials Vol. 864

Abstract: Adhesive sandwich structures with the honeycomb core of the metallic foil, polymeric papers and composites are widely and effectively used in the units of aerospace engineering and in the other industries owing to a number of undeniable advantages, including high specific strength and stiffness. In the process of designing and manufacturing of abovementioned structures, it is necessary to ensure high strength and reliability of the adhesive joint of the bearing skins and honeycomb core at a small area of their contact. The decisive factors influencing the bearing capacity of such joint are the technological parameters of the bonding process. Using the finite element modeling, the paper deals with the bearing capacity of the adhesive joint of bearing skins with the honeycomb core based on the aluminium foil and polymeric paper Nomex at transversal tearing for the key factors of the bonding process. The pattern of the adhesive joint failure (on the adhesive of honeycombs) has been revealed, depending on the depth of penetration of honeycombs ends in the adhesive, physical and mechanical characteristics of honeycombs, modulus of elasticity and tearing strength of the adhesive and thickness of the adhesive layer. Peculiar features of behavior of adhesive joints of the bearing skins with the honeycomb core based on the aluminium foil and polymeric paper Nomex under the load have been established, which should be taken into account in designing and manufacturing of honeycomb structures. The recommendations are given with regard to choosing of parameters of the process of honeycomb structure bonding, which allow providing with the acceptable accuracy the optimal depth of penetration of ends of the honeycomb core faces in the adhesive layer of specified depth.

Abstract: The present article is aimed at studying the austenite transformation kinetics and tensile properties of constructional 0.2 wt%C-Si2Mn2CrMoVNb TRIP-assisted steel subjected to isothermal holding in the subcritical temperature range (350-650 °C with the step of 50 °C) after intercritical annealing at 770 °C. The study was fulfilled using optical microscopy (OLYMPUS GX-71), electron scanning microscopy (JEOL JSM-), dilatometric analysis, tensile testing, Vickers hardness measurements. The critical temperatures of the steel were found to be Ac₁=750-760 °C and Ac₃=930 °C. The results showed that austenite demonstrated increased stability to pearlite and bainite transformations with an incubation period of decades of seconds at any of the mentioned temperatures. The bainitizing treatment at 400 °C with holding of 300-600 s resulted in ferrite/bainite/retained austenite structure with precipitates of nanosized carbide (V,Nb)C providing an improved combination of mechanical properties as compared to direct quenching (YS=548-555 MPa, UTS=908-1000 MPa, total elongation=16-18 %, PSE index=14.6-18.0 GPa%, YS/UTS ratio=0.55-0.60). The contributions of different strengthening components were estimated in order to reveal the benefits of a multi-phase microstructure for constructional applications.

Abstract: Processes of modeling the optimal composition of structural epoxy composites filled with dispersed metal waste are investigated in the article. The influence character of dispersed metal wastes introduction on the operational and strength properties of cold-cured structural epoxy composites is shown. A model for predicting the operational and strength properties of structural epoxy composites depending on dispersed solid phase of metal waste content and a highly active accelerator in them is designed.

Abstract: The structural features of epoxy polymer samples of different thicknesses under the influence of thermal energy are studied. The structure of fracture patterns of epoxy polymers, which are intensively structured in the thermal field, is investigated. The optimum temperature and duration of exposure are determined, which allows intensive production of products based on epoxy polymers with high physical and mechanical characteristics.

Abstract: The work presented in this paper is devoted to the formation of thick-layer wear-resistant coatings by technologies based on electrospark alloying, an example of essential components hardening for the heavy-duty processing equipment operating under hydroabrasive wear conditions. The aim of the paper is to improve the manufacturing and repairing technologies for the helical surfaces of the screws made of 65Г, 30X13 and 40X steels and corrosion-resistant stainless steel 12X18H10T. The above aim has been achieved owing to applying the new environmentally friendly technologies for the formation of the surface layers, and also due to the choice of the surface layers that are most resistant against hydroabrasive wear, which choice being provided for by conducting the comparative tests on the samples made of the above said steel grades and strengthened in various ways. The analysis results of the hydroabrasive wear resistance of the samples made of steel and provided with protective coatings is presented.

Abstract: Crystallographic characteristics of nanodispersed materials obtained by plasma-chemical synthesis were studied. Using industrial equipment for plasma-chemical synthesis the nanodispersed powders of high-melting carbide, nitride, carbonitride and silicide class compounds based on titanium, magnesium, aluminium, silicon were obtained. Technology for synthesis of powder fraction less than 100 nm was developed. The efficiency of nanodisperce compositions use in smelting of structural steels was determined. In the result of 10Г2С steel modification with Ti (CN) nanopowder strength, plastic properties and impact toughness were improved. Elemental composition of nanodispersed composition was determined: SiC, TiC, TiN, Ti (CN), AlN, Mg₂Si, Mg₃N₂. The elemental composition of synthesized compounds corresponded to stoichiometric composition. Microdiffractional patterns of the particles were analysed, it was shown that nanopowders belong to the solid crystalline bodies with metallic bond. It has been found, that titanium carbonitride Ti (CN) particles have face-centered and silicon carbide (SiC) particles have hexagonal crystal lattice. Experiments for steel 10Г2 and 10Г2С modifying with nanopowder compositions on base of Ti (CN) and SiC were carried out. The efficiency of nanodisperce compositions use in smelting of structural steels was determined. In the result of 10Г2С steel modification with Ti (CN) nanopowder strength, plastic properties and impact toughness were improved. The choice of nanodisperce titanium carbonitride Ti (CN) powders with 100 nm fraction for light alloy steels modifying was justified. The required criteria for choice of nanopowder modifiers were obtained: insolubility in smelt, correspondence of crystal lattice to steel matrix, commensurability with austenite germ critical radius in crystallizing.

Abstract: The main difficulty in obtaining adapters from stainless steel + zirconium metal combination lies in the formation of fragile intermetallic compounds at the weld border. By its properties, zirconium is very close to titanium, and therefore the manufacture of tubes from this combination, as well as pure titanium, is considerably difficult. Optimum explosion welding parameters have been developed, ensuring the highest adhesion strength compared to the existing production methods. At the weld border, a structure characteristic of compounds of dissimilar metals was revealed. The permissible heating temperatures for this combination are determined. The fundamental possibility of using the explosion energy as a factor stimulating the connection of dissimilar metals in order to obtain high-quality multilayer tubes, billets and products for various purposes is demonstrated, resulting in the introduction of environmentally friendly technology. Economic analysis of the manufacturing technology of bimetallic tubes by welding explosion was carried out. The cost-effectiveness of manufacturing technology of bimetallic stainless steel + zirconium metal compound nozzles, which is based on the use of high-pressure gradients and loading velocities to create production, was evaluated.

Abstract: The paper presents the results of the development of a special group of cast composite materials based on nodular cast irons. The alloys were based on alloying cast iron with copper in amounts that exceed its solubility in liquid Fe-C-Si systems (Cu>6 wt.%). A new component is obtained in the structure of castings in the form of a complex mixture based on the Cu-phase. Inclusions are relatively large (up to 200 μm) and globular in shape, with a uniform allocation in the volume of the castings. This favorably distinguishes the obtained alloys from the known cast irons and gives them high antifriction properties. With isothermal hardening, it is possible to obtain the lowest values of wear for structures of lower bainite. Developed cast composite materials are recommended to be used as tribotechnical materials working in conditions of poor lubrication and corrosion.