Metal Science and Heat Treatment最新文献

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 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.

The microstructure and compressive properties of the 7xxx series aluminum alloy (Al – 12.44Zn – 3.22Mg – 1.13Cu – 0.19Zr – 0.12Sr) reinforced with SiC whiskers via squeeze casting are investigated after aging treatments T6-1, T6-2, T6I4-1, and T6I4-2. For this purpose, the effect of four kinds of aging heat treatments on the properties of the aluminum metal matrix composites (AMMCs) is studied systematically through Vickers hardness and room temperature compressive testing. The microstructure is analyzed by optical microscopy, scanning electron microscopy, and x-ray diffraction. The experimental results show that the hardness of the AMMCs after four kinds of aging processes has different degrees of improvement compared to no-aging. After the T6-1, T6-2, T6I4-1, and T6I4-2 aging processes, the hardness of the composites is 325, 278, 306, and 345.8 HV, respectively. The additional T6-2 aging treatment provides the highest compressive strength and compressive strain, about 747 MPa and 7%, respectively, as well as a maximum dislocation strengthening of approximately 86.89 MPa.

An overview of the most used variants of the structural-chemical Schaeffler diagram developed by various researchers is presented. A new version of the Schaeffler diagram and equations for calculating Cr- and Ni-equivalents are suggested, which makes it possible to correctly predict the content of δ-ferrite in the structure of heat-resistant ferritic–martensitic steels of the EP450 – EP823 – EK181 – ChS139 group containing ≥ 10 wt.% Cr, after hot deformation and heat treatment. Based on the factor analysis of the relationship between the physicochemical and structural characteristics of such steels and their mechanical properties, equations are obtained in which the Cr- and Ni-equivalents are allowed for as factors determining the value of the yield strength.

The mechanisms of intragrain plastic deformation occurring in local micro-volumes of metal under the influence of temperature stresses during high-speed heating due to high-energy exposure are studied. The temperature distribution over the thickness of the sample is calculated and its experimental verification is carried out. Samples of steel 12Cr18Ni10, which does not undergo phase transformations during heating and cooling, are examined after a treatment with scanning air-plasma arc. It is shown that the intragrain plastic deformation during heating of austenitic steel is caused by thermoelastic stresses arising in the heated layer and in the volumes bordering it and manifests itself in the appearance of sliding traces in the grains. The mechanisms of the appearance of temperature stresses in the metal are proposed and substantiated.

Calculation of diagrams of components of residual stress tensor arising in the surface layer of a tribomaterial under sliding friction is used to formulate ideas about the role of the medium in creating a plasticizing and strengthening triboeffect. The characteristics of the structural state of the surface layers of brasses, aluminum and tin bronzes during their friction against steel in surface-active lubricants are presented. The conditions for achieving minimum power losses to friction and wear are determined. The role of local diffusion phenomena in quasi-spinodal phase transitions observed in surface micro-volumes of copper alloys during their contact deformation is revealed. It is shown that among industrial copper alloys, brass of the L90 type, aluminum bronzes BrA5, BrA7, and tin bronzes BrOF4-0.25, BrOF6,5-0,15 have the greatest wear resistance in surface-active lubricants. Examples of implementation of the phenomenon of selective transfer in friction pairs are given. Recommendations are developed for its use in friction units of machines and devices.