Metal Science and Heat Treatment最新文献

The effect of heat treatment (quenching and aging) on the structure and mechanical characteristics of maraging steel Cr12Ni9Mo2Si (EP659A) obtained using a hybrid CMT surfacing technology consisting in multilayer cold metal transfer and layer-by-layer deformation hardening is investigated. Metallographic analysis of the samples is carried out using light and scanning electron microscopes. The local elemental composition of the surfacing is determined. Tensile tests at 20°C and impact tests at 20 and –100°C are performed. The micromechanisms of crack growth and their special features are investigated. The effect of structural segregation of the material during the CMT with deformation without heat treatment is detected. It is shown that the structural segregation in the surfaced layer disappears after the heat treatment; the strength characteristics and the impact toughness increase, and the elongation decreases slightly. The micromechanism of crack growth after the surfacing followed by heat treatment changes from a mixed viscous-quasi-brittle one to a viscous one. To obtain a set of high mechanical characteristics at room and negative temperatures in the material synthesized by CMT surfacing with interlayer forging, it is recommended to carry out a heat treatment involving water quenching from 940°C for 45 min and aging at 520°C for 240 min.

A structural model of the transformation of cubic α-Mn into high-pressure hexagonal close-packed ε -Mn phase is suggested. The model is based on the transformation of a triple of tetrahedrons into an octahedron, implemented through a shift of the diagonal of a nonplanar “rhombus” formed by the faces of neighboring tetrahedrons. Asystem of such transformations transfers a fragment of a tetrahedral α -Mn spiral into a fragment of a rod composed of octahedrons in hexagonal closest packing. The model takes into account the noncrystallographic symmetry of the considered fragments of the crystalline phases.

The possibility of production of metal powder of grade “EOS Stainless Steel PH 1” by electrolyte-plasma spraying of finished products manufactured by selective laser melting is considered. The sample is sprayed by gas-discharge plasma at atmospheric pressure in an electrode configuration, where the metal cathode is the sprayed product and the electrolytic anode is a 3% NaCl solution in purified tap water. The current-voltage characteristics of the discharge, the surface temperature of the electrodes, the topography and the elemental composition of the powder are determined.

The effect of the rolling process and modes of continuous induction annealing until the state of secondary recrystallization of a brass strip on its properties and texture parameters is studied. Their close interrelation is explained. Directions for reducing the variance of the quality characteristics are considered and examples of their implementation are presented, i.e., the use of indirect texture control, advancement of systems of online management, application of statistical spectral analysis for detecting and eliminating the causes of high-frequency inhomogeneities of the quality characteristics.

Selective laser melting (SLM) of heat-resistant nickel alloy VZh159 is used to show that at constant energy density the key factor determining the texture and the internal stresses is the hatching distance. At multiple increase in the exposure rate and decrease in the hatching distance, the micropore proportion increases exponentially due to enhancement of the dissipation of the laser radiation caused by reflection in the track overlapping zone.

The chemical composition, microstructure and properties of races of a foreign aircraft engine bearing are studied. The material and the heat treatment method are determined, the microstructure of the diffusion layer is analyzed, the thickness of the diffusion and effective layers is calculated, and curves of the distribution of hardness and residual stresses over the diffusion layer depth are plotted. The data obtained can be used for import substitution of heat-resistant bearings for aerospace applications.

A structural model of metallic melts is suggested on the basis of the structures of all modifications of Mn. The model is based on spirals of tetrablocks, i.e., unions over faces of four regular tetrahedrons. The helices composed of tetrablocks have a high density and a non-translational long-range ordering, which explains the higher experimental values of the melt density as compared to the random packing model and the blurring of the diffraction pattern of the melt. When the melt crystallizes into one of the Mn modifications, such a spiral is inherited in the form of its periodic approximant. The model makes it possible to describe adequately the changes in the structure-sensitive properties of metals during heat treatment.

The probability of martensitic transformation in stable 316L austenitic steel obtained using a 3D laser printer is investigated. Compressive deformation of the studied samples was carried out at room temperature at a high rate (2 × 10^–2 sec^–1). The features of the martensitic transition and the conditions for formation of an intermediate phase of epsilon-martensite are considered.