Metal Science and Heat Treatment最新文献

The structure of four-layer coatings with a total thickness of 9 mm made of high-speed molybdenum steel S2-9-2 (W₂Mo₉Al) was studied. The coatings were obtained on a substrate of 41CrMo4 (30CrMnSi) steel by plasma cladding using a powder wire in a mixture of argon and nitrogen. The structure of the coating was studied by electron microscopy and energy-dispersive x-ray spectroscopy (EDS) on sample sections. It is shown that the microhardness of the deposited layer varies in the range of 5.2 – 6.6 GPa. This is due to the formation of an inhomogeneous structure in the deposited layer consisting of grains of an iron-based solid solution, at the joints and along the boundaries of which are inclusions of eutectic enriched mainly with Mo, Cr, and W. Grain sizes vary between 5 and 20 μm. A sub-grain structure is observed in the grain volume, indicating substructural hardening of the deposited layer. The sizes of the sub-grains vary between 1.5 and 2.5 μm. The layer of the alloy S2-9-2 deposited on 41CrMo steel exhibits a framework-like structure. The main alloying elements of the clad layer are Fe, Mo, Cr, W, and Al.

The authors studied the possibility of using the wire arc additive manufacturing (WAAM) technology for creating blanks by gradually depositing layers of three grades of stainless steel using a wire. Metallographic studies, ferromagnetic analysis, tensile and fatigue tests were carried out. It has been established that the chemical composition of the utilized grades of stainless steel has a significant effect on the morphology and degree of development of dendrites formed during the deposition process. The absence of incomplete fusion and other technological defects at the weld bead interface promoted the possibility of using WAAM to create biand tri-metal deposits. The analysis of the fracture surfaces of the samples confirmed the high quality of fusion of various grades of austenitic steels with each other and the uniformity of the deposited metal. The presence of ferromagnetic phases in the samples immediately after the additive process is significantly lower than the calculated values for steel 07Cr25Ni13 and practically reaches the values that are characteristic for this steel after heat treatment.

The interrelation of the structure and tribomechanical characteristics of the metal materials that comprise the friction members is considered, specifically the interactions between copper alloy – steel and steel with Cu – Zn coatings – steel. The formation of a wear-resistant structural state in the operational layer of Cu – Zn alloys with concentrations of up to 93% of Zn is described. The tribomechanical efficiency of Cu – Zn coatings obtained by two methods is considered from the standpoint of the regularities of the formation of a wear-resistant structure, namely friction-mechanical treatment and cold gas-dynamic spraying. It is demonstrated that regardless of the technology used for the surface modification of a steel product with a copper-based alloy, a secondary self-organizing structure with parameters characteristic of the wear-resistant state is formed in the operational layer as a result of contact deformation, which ensures an increase in the durability of tribological contacts.

We study the structure and mechanical properties of rolled rods of Ti6Al4V titanium alloy with various chemical compositions and structures. The globular, lamellar, transient, mixed, and basket structures of the alloy are obtained by varying the modes of deformation and annealing. It is shown that the rods with globular structures have higher strength and plasticity properties than rods with lamellar structures. Regression models are constructed for the evaluation of the mechanical properties of rods made of Ti6Al4V alloy with different structures.

Changes in the structure, phase composition, chemical composition, Vickers microhardness, and contact modulus of elasticity of a high-strength titanium α + β-alloy of the VST2 martensitic class during quenching after heating in the 700 – 1000°Ñ range were studied using the methods of optical microscopy, XRD phase analysis, microindentation, and thermodynamic calculations in ThermoCalc. The experimental data were in good agreement with the results of thermodynamic calculations. Arelationship between changes in the microhardness and contact modulus of elasticity of VST2 alloy, quenched from 700 – 1000°C, and the structure and phase composition of the alloy during quenching was established.

The VZhM4 single-crystal Ni-based superalloy was tested for high-temperature salt-induced corrosion resistance in Na₂SO₄ + NaCl at 750°C. The equilibrium composition of phases formed during the interaction of the alloy with oxygen and sulfur across the temperature range of 600 – 1000°C were calculated. Changes in the structure and composition of the surface layer of the alloy during high-temperature salt corrosion were studied using scanning and transmission electron microscopy. The results obtained were used to compile structural diagrams for the corrosion layer formed on the alloy after 5 and 20 test cycles. The quantitative composition of the main phases in the corrosion products was determined. A qualitative assessment of Re, Ta, and Ru diffusion was performed.

The microstructure and mechanical properties of a Mg – 3.5Gd –2.4Nd – 0.8Y – 1.0Zn – 0.7Zr (wt.%) alloy subjected to overburning during quenching and further aging at temperatures of 200, 250, and 300°C with an exposure duration of 1 – 100 h were studied. Tensile tests were carried out, and the microhardness of the alloy was determined. The Mg₃(Zn, REE) phase particles were shown to distribute along the grain boundaries after overburning, resulting in a significant softening of the material and a decrease in its mechanical properties. At the same time, the alloy subjected to aging at a temperature of 300°C showed stable strength properties regardless of the exposure duration. The exception is its relative elongation, which tended to increase with an increase in the exposure duration. Following aging at 200 and 250°C, the alloy exhibited the highest strength properties; however, the relative elongation values were close to zero.

The microstructure of alloys of the Cu – Cr – Zr system after equal channel angular pressing and aging is investigated by scanning and transmission electron microscopy. Mechanical properties and electrical conductivity are determined. Recovery and additional precipitation of dispersed particles are observed in deformed alloys after annealing at temperatures of 200 – 500°C, but static recrystallization does not develop. Increasing the annealing temperature to 600°C is accompanied by development of recrystallization, and a completely recrystallized structure is observed within the alloy with a minimum content of alloying elements, while deformed areas are found in alloys with a high content of chromium and zirconium. The influence of structural evolution on mechanical properties and electrical conductivity is discussed.

Various systems of biocompatible alloys (mainly based on Ti – Nb and Ti – Ta systems), used for medical purposes, were considered. The specifics of the production of such alloys by selective laser melting have been analyzed. The potential of future use of additive technologies for the creation of high-quality, safe material using β-titanium powder alloys for medical products with enhanced performance characteristics is discussed.

We study the structure and mechanical properties of 38G2F structural steel after quenching and high-temperature isothermal tempering of different durations. By analyzing the stress-strain diagrams in conventional and true coordinates, we reveal specific features of the deformation behavior of samples on the yield plateau and in the uniform stage of deformation. We also analyze the influence of the distribution of strain component ε_yy along the working part of the sample on the variations of strength and plastic characteristics of steel in different stages/periods of tension.