Metal Science and Heat Treatment最新文献

Development of abnormal grain growth at different size distributions of disperse second-phase particles is studied with the help of numerical modeling. At an increased coefficient of variation of the particle size distribution, the abnormal growth starts at a smaller volume fraction of the second phase and develops more intensely. This implies that the evolution of abnormal grain growth can be controlled by varying the particle size.

The stages of tempering of martensite in steel 38G2 (38Mn2) steel are studied using transmission, scanning and orientation (EBSD) microscopy. The parameters characterizing the structure of the ferrite matrix and the morphology of the iron carbide particles are considered and selected to establish the structural-phase state typical for each stage of the tempering. Own and reported data are analyzed and used to design a generalized model reflecting the structural transformations of the lath-packet martensite developing in a medium-carbon steel during tempering at different temperatures.

The effect of rolling after preliminary severe deformation by equal channel angular pressing (ECAP) on the corrosion behavior of alloy Al6061 in a 3.5% NaCl solution is investigated. Optical microscopy, x-ray diffraction analysis, polarization and electrochemical impedance spectroscopy are used for the study. The alloy is subjected to ECAP with varied number of passes (0, 1 and 4) before being cold-rolled. After the ECAP and rolling, the grain size of the matrix decreases from 192.83 μm to 19.4 μm, the size of the crystallites decreases to 26.148 nm, while the dislocation density and the hardness grow. The potentiodynamic curves reveal a tendency to passivation and pitting corrosion. The decrease in the grain size makes pitting defects less probable. The increase in the number of ECAP passes helps to decrease the corrosion rate due to the refinement of grains and higher homogeneity of intermetallic inclusions in the structure.

The effect of reinforcing the aluminum matrix with different amounts of SiC particles (6, 12, and 18 wt.%) at a constant amount of Al₂O₃ particles (6 wt.%) on the microstructure and mechanical properties of the metal matrix composite was studied. Reinforced SiC/Al₂O₃ composites based on Al were produced using the stir casting method. The microstructure of the composites was examined using a scanning electron microscope. Impact toughness, hardness, tensile and compressive strength of the composites were determined. It was found that the reinforcing particles are uniformly distributed in the matrix, providing a strong bond at the interface between aluminum and SiC/Al₂O₃. It is shown that reinforcement with hybrid SiC/Al₂O₃ particles increases the hardness and tensile and compressive strength, but reduces the impact toughness and ductility of the composites. It has been revealed that reinforcement of aluminum with hybrid SiC/Al₂O₃ particles more effectively increases the mechanical properties of the composite compared to reinforcement with SiC particles.

The mechanical properties under static tension and the fatigue behavior under constant loading amplitude at elevated temperatures are studied experimentally for aluminum alloy 2024-T361 (the equivalent of AA2024-T4). It is shown that the increase of the temperature to 200 – 250°C leads to a significant decrease in the mechanical properties, fatigue life and strength of the alloy under cyclic loading according to the bending-torsion scheme. The relative decrease in the mechanical properties of the alloy upon increase of the temperature to 200 – 250°C agrees well with the data reported in earlier publications. However, the fatigue strength of AA2024-T361 is 0.164 times lower than the published limiting values for aluminum alloys. These findings may contribute to the development of tools for predicting the service life of different metals.

The microstructure, physical properties (density, porosity) and mechanical properties (compressive strength, microhardness) of composites with a matrix from magnesium alloy AZ31 (Mg – 3 wt.% Al – 1 wt.% Zn) reinforced with various amounts of graphene nanoparticles (GNPs) obtained by powder metallurgy is investigated. The GNPs content in the composite is 0, 0.75, 1.25, 1.75 and 2.25 wt.%. It is shown that the density before and after the sintering, the microhardness and the compressive strength of the composites increase with the increase of the content of graphene nanoparticles in the structure to 1.75 wt.%.

The methods of hydrostatic weighing, x-ray diffraction phase analysis, scanning electron microscopy, spectrum analysis, microindentation and tensile tests are used to analyze the influence of the substrate heating temperature in different modes of selective laser melting (SLM) on the change in the relative density and phase composition, structure, hardness and mechanical properties of alloy Ti – 23Al – 25Nb (O-alloy). Dependences of the relative density, of the crystal lattice parameters of the β- and O-phases, of the hardness, and of the aluminum content on the laser energy density (LED) used in SLM of the O-alloy with substrate temperatures of 600 and 700°C are obtained. The evolution of the porosity and of the structure of the O-alloy in different modes of SLM is determined. The structure in the O-alloy after the SLM with LED = 21 J/mm³ at substrate temperature 700°C and 30-min aging at 800°C is studied. The aging is shown to produce a beneficial effect on the set of mechanical properties of the O-alloy attest temperatures 600 and 700°C.

The effect of pressing pressure on the mechanical properties of AZ31 alloy obtained by powder metallurgy was experimentally confirmed. Composite samples were produced at pressing pressures of 200, 300, 400, and 500 MPa and a sintering temperature of 600°C for 45 min using a tubular furnace. The surface morphology of the alloy was analyzed using scanning electron microscopy. The density and porosity of the samples, as well as mechanical properties, including microhardness, tensile strength and compressive strength were determined. The results showed that at a pressing pressure of 500 MPa, the composite has increased density, strength, microhardness and the lowest porosity.

The phase composition of laser welded joints of heat-hardened aluminum-lithium alloys of the 3rd generation of grades B-1461 and B-1469 is studied after a heat treatment consisting of quenching and artificial aging. The phase composition of the heat-treated laser welded joints is studied using synchrotron radiation and high-resolution transmission electron microscopy. The mechanical properties of the welded joints are determined in static tests at normal, elevated and reduced temperatures.

The hypothesis of high mobility of special boundaries is used to suggest a mechanism of structural-textural heredity in electrical anisotropic steel (EAS). The evolution of the main crystallographic orientations in the stages of industrial production of EAS from hot rolling to high-temperature annealing is analyzed during deformation and recrystallization processes. It is shown that special misorientations, i.e., special boundaries, arise between the main orientations and evolve together with them.