Vol 9, No 6 (2018)

Abstract—Development of innovative composite materials capable of operating under extreme conditions requires a comprehensive engineering approach. One of the components of such materials can be represented by monocarbides and diborides of transition metals of groups IV–VI of the periodic table: titanium, zirconium, hafnium, vanadium, niobium, tantalum, as well as their binary systems. Most isomorphic pairs of monocarbides and ddiborides are characterized by unlimited mutual solubility. The HfC–TaC system is of particular interest. The melting point of TaC–4HfC exceeds 4000°C, which is the highest refractoriness among all known synthesized substances.

Abstract—The influence of thermohydrogen treatment combined with hot rolling on the structural formation in α- and near-α-titanium alloys has been studied. The prospects of obtaining submicron-grained sheet semifinished products of VT5 (Ti–5.8Al–0.1Fe, wt %) and VT20 (Ti–5.9Al–1.5V–1.2Mo–1.8Zr–0.1Fe, wt %) alloys are shown. In these materials, a submicron-grained structure allows the plastic deformation to be induced by superplasticity at temperatures reduced by 100–200°С.

Abstract—The results of development of new nickel-base superalloy having an operating temperature up to 800°C for gas turbine disks have been presented. Structures, mechanical properties, and phase transformations of six experimental compositions have been researched. Physical and chemical modeling has been used to make a right choice of an alloy; with parameters as composition equivalents (they were based on equations of nonpolarizing ionic radii). The highest level of strength, ductility, toughness, and heat resistance was exhibited at 750°C by the Ni–Co–Cr–W–Mo–Ta–Al–Ti–Nb experimental composition with the total of aluminum, titanium, and niobium equal to 10 wt % and containing 4 wt % of tantalum.

Abstract—The paper presents the results of a comprehensive study of structural and property changes in the most dangerous regions of the heat-affected zone of low-alloy cold-resistant steel with a guaranteed yield strength of 355–390 MPa before and after the post-welding tempering, including those caused by the combined impact of heating temperature under tempering and deformation, compared to base metal. The simulation was performed using a DIL 805 dilatometer and a Gleeble 3800 complex. The results of the investigation of the structure and properties of actual welded joints after welding with different rates of energy input (3.5 and 6 kJ/mm) are presented.

Abstract—Heat resistance of fiberglass plastics depends mostly on heat resistance of the polymer matrix (binder) and technological modes of production. Increasing the heat resistance and strength of electric insulation makes it possible to improve the properties of electric machines and prolong their working life. Hot pressing technology was developed and fiberglass plastic articles for electric insulation of parts of the ship propulsion complex (main and servicing diesel generators, turbo generators, electric motors) were manufactured. Exploitation modes were settled for electric insulation from different types of binders and reinforcing materials based on alkali-free, quartz, and siliceous high modulus and high strength glass fibers.

Abstract—A technique for the calculation of the steady-state temperature field in a solid part of a welded workpiece has been developed by using a moving weld pool size as input data and a boundary element method for solving the heat conduction problem. The technique allows one to calculate the effective power and thermal efficiency of a heat source. An example of a through-penetration arc welding with a tungsten electrode for the case of a 4-mm-thick aluminum alloy 1565chMU reveals the temperature gradient distributions and cooling rate at the pool boundary. A good agreement is observed between the calculated and experimental thermal cycles. The distribution of hardness in the cross section of a butt weld is presented.

Abstract—The possibility of improving the resistance of austenitic chromium-nickel steel of 09Kh18N9 and 08Kh16N11М3 grades to pitting and intercrystalline corrosion under the conditions of standby mode of a fast neutron reactor facility has been investigated. Corrosion tests lasting up to 15 000 h have demonstrated that the corrosion rate decreases significantly upon the decrease in the carbon content and the increase in the nitrogen content.

Abstract—The results of studying the mechanisms of fracture and embrittlement of the Kh18N9 and Kh18N10T austenitic steels under long-term neutron irradiation at elevated temperatures are given. The effects of the temperature and time of irradiation and the neutron radiation dose on the fracture strain and fracture mechanisms are analyzed. On the basis of the results obtained and specially performed experiments, a synergistic mechanism of embrittlement of the material under conditions of long-term high-temperature irradiation is proposed and substantiated, which is determined by the following two factors: thermal aging and helium diffusion. The thermal aging leads to the formation of various phases at grain boundaries and, hence, to a decrease in the grain boundary strength. Helium diffusion at elevated temperatures gives rise to the accumulation and growth of helium bubbles at weakened grain boundaries.

Abstract—The influence of neutron irradiation, post-irradiation annealing, and re-irradiation on the fracture toughness and mechanical properties of anticorrosive cladding material for reactor pressure vessels was investigated. Dependences for predicting the deformation diagram and fracture toughness of the weld metal, with the consideration of the effect of annealing and repeated neutron irradiation were proposed. The obtained curves may be used to calculate the stress-strain state of reactor pressure vessels, as well as to assess the brittle fracture of the material during operation of the reactor vessel after annealing.

Abstract—The paper presents the results of experimental investigations on the fracture toughness of anticorrosive cladding for the reactor pressure vessel of WWER-type reactors after irradiation in a range from 0 to 1.8 × 10²⁰ neutron/cm². On the basis of these data and results obtained earlier, the fracture toughness is derived by statistical analysis methods as a function of neutron fluence and test temperature.

Abstract—The virtual structures of titanium alloy fragments are created via EBSD using microstructural research and local crystal orientations. The uniaxial strains are calculated through a finite element method taking crystallographic characteristics, anisotropic elastic moduli, and crystallographic sliding into account. The mapping of the Schmid factor is carried out for structural fragments. The influence of measured orientations on the intensity of theoretical stress and strains in the loaded elements of polycrystalline material is studied as well.

Abstract—Having analyzed experimental data on the long-term strength of unirradiated austenitic materials and predictive dependences obtained in the context of a physical and mechanical model of intergranular fracture, the authors have determined the assurance factor for plotting the long-term strength curves for unirradiated and irradiated materials. The above model, as well as experimental results, has made it possible to calculate the normative curves for the initial and irradiated steels Kh18N9 and 08Kh16N11M3. Their validity has been verified on the basis of external and intrareactor tests.