Materials Science最新文献

A brief review of known digital speckle pattern interferometry methods for retrieving the surface displacement and deformation fields under dynamic loads is presented. A new nondestructive test method of three-step phase-shifting correlation speckle pattern interferometry to study the dynamic loads of structural materials is proposed. In this method three speckle interferograms (SIs) of the specimen surface, differing only by arbitrary unknown phase shifts, are recorded before the loading and one SI is recorded under the dynamic load. The surface displacement field under dynamic loading is determined using the obtained SIs. Two algorithms for the implementation of the method are proposed. They use an integrating bucket technique to record SIs and make it possible to determine the phase maps of the surface displacement fields at any moment of applying the dynamic load. We can use this method to produce a temporal sequence of surface displacement fields during loading.

High efficiency of corrosion inhibition of aluminum alloy in a 0.1% NaCl solution with a composition of guar gum and potassium sorbate was established. The formation of an organic adsorption film was found on the surface of the metal samples. The degree of metal protection against corrosion by this inhibitory composition was more than 90%. The results of the research can be used for the development of eco-friendly “green” corrosion inhibitors of aluminum alloys from renewable plant materials.

The features of plastic relaxation and recrystallization processes of steels of various types with different crystal lattices were studied. It was established that structural signs of collective or secondary recrystallization, as well as high-speed shear or rotational plastic deformation, were observed in the laser impact zone. The conditions of the course of these processes associated with the behavior of defects in the crystal structure under pulsed loading were discussed. The conditions of laser action ensured the dynamic processes of restoring the structure of steels.

Mathematical models of the dependence of the critical pitting temperature (CPT) of AISI 304, AISI 321, 12Kh18N10T and 08Kh18N10 steels on their chemical composition, structural heterogeneity, as well as pH and chloride concentration of circulating water were developed. Models were based on quadratic regressions with first order partial derivatives and on polynomials with a reduced number of signs. By applying mathematical models, it was established that the pitting resistance of these steels increases with an increase in the average distance between oxides, the average diameter of austenite grain, specific magnetic susceptibility, the decrease in the volume of δ-ferrite and the number of the smallest oxides up to 1.98 μm in size. The positive effect of Cr and Mn on the pitting resistance of the studied steels was studied. Probably this occurred due to the increase of the solubility of N in austenite, reduction of the Fe atoms diffusion intensity to the surface of stable pittings and the increase of Cr to metastable pittings, contributing to their repassivation, which increased the pitting resistance of steels. The developed mathematical models are recommended for choosing optimal grades of austenitic steels and predicting their pitting resistance during operation of heat exchangers in circulating waters.

The effect of the nanocrystalline layer formed by mechanical pulse treatment on the velocity of surface acoustic waves in 65G steel samples was studied. Acoustic waves with frequencies equal to 3; 6 and 9 MHz were used. Different thicknesses of the nanocrystalline layer were obtained by the stepwise grinding method. The method of estimating the acoustic properties of the formed layer based on the velocity of surface acoustic waves in the case when the depth of wave penetration is greater than its thickness was described. An additional measurement of the nanocrystalline layer thickness was carried out using metallographic studies to determine its acoustic characteristics.

The thermoelastic state of a heterogeneous orthotropic circular cylindrical shell with an open profile under the condition of convective heat exchange between the surfaces of the shell and the environment is investigated. A generalized shear mathematical model of heterogeneous anisotropic shells of the first order and two-dimensional non-stationary heat conduction equations are used in this case. Using the methods of Fourier and Laplace integral transformations, an analytical solution to the non-stationary problem of thermal conductivity and the quasi-static problem of thermoelasticity for a finite hinged shell supported at the edges is found. The stress state and deflections of the shell are calculated for the case of material properties change in the radial direction according to the power law.

Operating costs at different enterprises increase because of high wear and corrosion of components. These components can be protected by the electric arc spraying of pseudoalloy protective coatings. The coating was obtained by simultaneous spraying of copper and iron wires. The microstructure was investigated with an electron microscope and the phase composition was assessed by X-ray diffractometry. The porosity and microhardness of the coating were also evaluated. The coating was dense and consisted of Cu and Fe metallic lamellas together with homogenously distributed minor Cu₂O, FeO oxide phases. The microhardness of the coating is 2.1±0.7 GPa. An electrochemical test of the coating was performed in a 3% NaCl solution. The pseudoalloy coating of copper-iron system with a thickness of 500 μm was high corrosion resistant in this solution.

A theoretical-experimental approach for predicting the kinetics of fatigue crack growth and determining the life time of the responsible elements of structures in hydrogen is proposed. Based on the created calculation model of fatigue crack growth, experimentally constructed kinetic diagrams of fatigue failure of 35KhN3MFA steel, the residual life of the rotor shaft of the turbo generator, weakened by a surface semi-elliptical crack in air, and in gaseous hydrogen environment, are determined. Hydrogen reduces the residual life of the rotor shaft by two orders of magnitude in hydrogen, compared to its residual life in air.

The austenitic stainless steel 316L is used for numerous components due to its excellent corrosion resistance. However, forming of components influences the microstructure and can thus change the corrosion resistance of the steel. In this context, the corrosion rate of the steel 316L is determined for the case of uniform corrosion of various cold-rolled conditions by ageing tests in 0.5 M H₂SO₄. The microstrain, the martensite fraction, and the residual stress state are quantified using X-ray diffraction. The surface roughness is measured by laser scanning microscopy. Three different model equations are derived by means of multiple regression to predict the corrosion rate as a function of the specimen properties. The analysis shows that a particularly simple model equation, which predicts the corrosion rate only via the plastic strain, shows insufficiently large deviations from the experimentally determined corrosion rates. However, a low divergence to the experimental results with a mean deviation of less than 4% is achieved by using a model equation that takes microstructural parameters and the surface ratio into account. Within this model equation, an increased corrosion rate is achieved with higher microstrain and residual compressive stress of the austenite phase as well as a higher surface-area ratio. A higher fraction of martensite is found to lower the corrosion rate.

A composite inhibiting pigment based on natural silicate (wollastonite) and acid salt (zinc monophosphate) was obtained by the method of mechanochemical modification. The new composite pigment wollastonite–zinc monophosphate has high protective properties on aluminum alloy in the environment of weakly acidic atmospheric precipitation, and is superior to a simple mixture of calcium silicate and zinc monophosphate in protective characteristics. An effective corrosion-resistant film consisting of calcium, zinc and aluminum phosphates is formed on the surface of the alloy in the extract of the composite pigment.