Nikolai N. Shamarin

Introduction. Severe plastic deformation (SPD) is one of the most promising methods for modifying the structure of non-ferrous alloys, enabling them to be transformed into ultrafine-grained (UFG) and nanocrystalline states. At the same time, for the practical implementation of such materials in machine-building equipment components, the issues of their thermal stability and wear resistance under extreme loads during contact interaction in scratching and sliding friction remain critically important. The purpose of the work is a comprehensive study of the effect of various thermal and severe plastic deformation conditions on the structural, mechanical and tribological characteristics of Cu-9Al-2Mn bronze. The paper studies samples of Cu-9Al-2Mn bronze in different initial states: annealed at 700°C, quenched from 900°C and aged at 400°C. To form a UFG structure and enhance strength properties, the workpieces were subjected to deformation processing by multi-axial forging at room temperature followed by rolling. In order to study recrystallization processes and the thermal stability of the UFG alloy, annealing was performed at 400°C for 30 minutes and at 500°C for 10 minutes. Materials and methods. Metallography, transmission electron microscopy and X-ray diffraction analysis were used as the primary methods for characterizing the structure and phase composition. Mechanical properties were evaluated based on Vickers microhardness measurements and static tensile tests. Resistance to localized surface damage was determined by scratch testing under a linearly increasing load from 0.5 to 30 N. Wear resistance and coefficient of friction were investigated under dry sliding friction using a pin-on-disc scheme (counterbody — steel 52100) under a load of 20 N and at a constant speed of 0.1 m/s. Monitoring of the tribosystem dynamics was carried out using vibrometry and recording acoustic emission (AE) signals. The surface topography of wear tracks and balls was studied by confocal laser scanning microscopy. The change in structure beneath the friction surface was also investigated using metallography. Results and discussion. The effect of heat treatment, severe plastic deformation (SPD), and subsequent annealing on the structure, mechanical, and tribological properties of Cu-9Al-2Mn bronze is studied. It is shown that SPD (multi axial forging and rolling) produces an ultrafine grained (100–300 nm) structure with high dislocation density and deformation martensite, resulting in a yield strength of 998 MPa and a microhardness of 3.24 GPa. Low temperature annealing at 400°C further increases the yield strength to 1,095 MPa owing to polygonization and precipitation hardening. Annealing at 500°C induces recrystallization, partially restoring ductility. Tribological tests under dry sliding friction revealed that SPD significantly enhances wear resistance while maintaining an unchanged coefficient of friction. Scratch depth in scratch testing is reduced by ~40%, and the damage mechanism changes from ductile ploughing to microcutting. Acoustic emission and vibration correlate with the change in wear mechanisms.

CuAl7 aluminum bronze walls were fabricated by wire-feed electron-beam additive manufacturing. Al:Ni powder mixtures with ratios of 1:2 and 2:1 were deposited onto the walls and remelted twice to improve chemical homogeneity. The as-built surface layers of the sample remelted with the 1:2 powder mixture (12as) consisted of an α-Cu solid solution, grain-boundary β΄-Cu3Al, and AlNi particles. Addition of the 2:1 Al:Ni powder mixture (21as) resulted in the formation of martensitic β΄-Cu3Al structures with elongated α-Cu grains. Annealing at 900 °C followed by water quenching resulted in coarsening of Al-Ni particles in the 12an samples and β΄ → β΄1 transformation in the 21an sample. Tribological testing demonstrated reduced wear and friction for sample 21an, which can be explained by the pseudoelastic behavior of β΄1 martensite during sliding against steel counterparts.

Introduction. Silicon bronzes are widely used in critical friction units due to their combination of corrosion resistance, machinability, electrical conductivity, and satisfactory mechanical properties. Electron beam additive manufacturing (EBAM) is promising for the production of complex parts, but it forms a large columnar grain structure, leading to anisotropy of properties and limiting their practical application. Methods of severe plastic deformation (SPD), such as multi-axis forging and rolling, are effective for refining the structure, eliminating anisotropy, and increasing strength. However, their effect on the overall properties of silicon bronzes has not been sufficiently studied. Purpose of the work. The purpose of this study is a comparative analysis of the effect of the structural state of silicon bronze on its mechanical characteristics and tribological properties under dry sliding friction. Research methods. Samples in five structural states were obtained by electron-beam additive manufacturing (1), hot rolling (2), multi-axis forging (3), rolling at room temperature (4), and low-temperature annealing after rolling (5). The structure of the samples was investigated by optical metallography and transmission electron microscopy. Mechanical tests were carried out by tensile testing of double-sided dog-bone samples and Vickers microhardness testing. Tribological tests for dry sliding friction against 52100 steel were carried out with a constant load and speed. During friction, the friction coefficient (FC), vibrations in the normal and tangential directions, and acoustic emission (AE) were recorded. A detailed analysis of the surface and subsurface layer of friction tracks was performed using confocal laser scanning microscopy, as well as scanning electron microscopy with energy-dispersive X-ray spectroscopy (EDS). Results and discussion. The microstructure of the samples after EBAM exhibits large columnar grains, while after hot rolling it shows large equiaxed grains with twins. Multi-axial forging results in the formation of subgrains (lamellae) (<100 nm) with a high dislocation density. Rolling leads to further refinement of the original grains and the formation of elongated submicron grains. Low-temperature annealing forms more equiaxed submicron grains (100–200 nm) with a reduced dislocation density and high-angle boundaries. Samples with a coarse-grained structure have low strength and hardness. After SPD, the strength and hardness increase significantly, and the relative elongation decreases compared to the original material. Low-temperature annealing provides maximum strength with partial restoration of ductility and a decrease in hardness. The smallest and most stable friction coefficient, as well as minimum vibration amplitudes (especially in the tangential direction), were recorded for samples after SPD. The greatest wear occurred for the sample in the as-received condition (hot rolling). SPD reduces wear by 2.1–2.2 times compared to the hot-rolled and EBAM samples. Low-temperature annealing increases wear by 10% relative to the sample after rolling. The predominant wear mechanisms were determined to be: mixed (adhesive-oxidative) for bronze after EBAM; adhesive for hot rolled; and oxidative for samples after SPD. Based on metallographic studies, it was found that the depth of subsurface deformation is maximum for coarse-grained samples (145–155 μm) and decreases by 3.3–4.7 times after SPD. Conclusion. A comprehensive study has revealed a decisive influence of the structural state of 96% Cu-3% Si-1% Mn bronze on its key properties. The use of SPD methods (multi-axial forging and rolling) has proven to be highly effective in dramatically improving the mechanical and tribological properties of silicon bronze, regardless of the original production method (hot-rolled steel or electron beam additive manufacturing).

The present paper compares the microstructure and mechanical properties of Inconel 625 alloy samples produced by using wire-arc additive manufacturing (WAAM) and wire electron beam additive manufacturing (WEBAM). The obtained wall-shaped samples did not contain any macroscopic defects in the form of cracks, delaminations and geometry distortions. The WAAM-built “wall” exhibits finer dendritic structures (WAAM—10–16 μm; WEBAM—20–25 μm). Also, the WAAM-built one is characterized by the more homogeneous-sized distribution of microstructure components. In both cases, the material is represented by the γ-phase, with large precipitates of MC-type carbides in the interdendritic spaces. Additionally, the sample obtained using the WAAM contained aluminum oxide. It was found that the intrinsic periodic heat treatment is not sufficient for the formation of the γ″-phase, and it is necessary to perform a subsequent long-term aging. However, the overall mechanical properties of both samples show similar levels of yield stress and ultimate tensile strength, and demonstrate the same degree of anisotropy.

Introduction. Electron beam additive manufacturing (EBAM) is a promising method for producing new alloys with unique properties. At the same time, existing problems with obtaining a high-quality structure require a search for a technical solution that ensures grain refinement and the formation of a more homogeneous microstructure. For strain-hardened copper alloys, severe plastic deformation (SPD) methods are effective ways to control their structural state and mechanical properties. Currently, the effect of severe plastic deformation on the structure, mechanical, and tribological properties of Cu-Al-Si-Mn bronze, which is promising for industrial application, has not been studied. The aim of this work is to study the relationship between the structural state formed as a result of severe plastic deformation and the mechanical and tribological properties of Cu-Al-Si-Mn bronze samples. The paper studies samples of Cu-Al-Si-Mn bronze, made from bronze (3% Si-1% Mn) wires and commercially pure aluminum using multiwire electron beam additive manufacturing. For targeted changes in structure and properties, the resulting additively manufactured blanks were subjected to severe plastic deformation. Multi-axial forging and rolling were used as SPD methods, aimed at significant grain refinement and increased strength characteristics. The work uses such research methods as transmission electron microscopy (TEM) for a detailed analysis of the submicron structure after SPD, X-ray diffraction (XRD) to identify the phase composition of the alloy, tensile tests to determine key mechanical properties such as tensile strength, yield strength, and percentage of elongation, microhardness measurements to assess the hardening of samples using Vickers loads, confocal laser scanning microscopy (CLSM) for three-dimensional analysis of the surface topography and studying the morphology of worn surfaces, and dry sliding friction tests to assess the wear resistance of the material and the friction coefficient in the absence of lubrication under specified loads and sliding speeds. Results and discussion. Based on the data of transmission electron microscopy, it was found that the use of multi-axial forging and rolling led to significant changes in the structure of the material, as well as its phase composition. Based on the X-ray diffraction analysis, it was revealed that severe plastic deformation contributed to the deformation-induced dissolution of the γ- and β-phases. The results of tensile tests showed that the highest strength is achieved after intense plastic deformation by rolling, after multi-axial forging. SPD by multi-axial forging and subsequent rolling led to an increase in the microhardness of bronze. The results of tribological tests showed that SPD contributes to a decrease in the friction coefficient (FC) compared to the material in the printed state. Heat treatment of samples after SPD led to an increase in FC and an increase in fluctuations in its value. SPD by multi-axial forging and subsequent rolling contributes to a significant increase in the wear resistance of samples under dry sliding friction conditions. Low-temperature annealing after SPD leads to a decrease in the wear resistance of deformed samples. Thus, the use of SPD makes it possible to increase the strength and wear resistance of bronze samples of the Cu-Al-Si-Mn system.

The paper investigates the microstructure and mechanical properties of a steel matrix composite reinforced with tungsten (W) particles and a mixture of tungsten carbide and nickel (WC(Ni)) obtained by a hybrid additive manufacturing method using wire electron beam additive manufacturing with powder addition. The composite exhibits a gradient structure including three zones: a matrix of high alloy steel 401S45, a transition layer with a low concentration of W/WC(Ni) and a surface layer enriched with particles of reinforcing phases. SEM, TEM and XRD methods revealed a heterogeneous microstructure consisting of α-Fe (80 vol.%), γ-Fe (10 vol.%) and carbide phases, as well as suppression of the formation of brittle Me₃C intermetallides due to the controlled diffusion of W, C and alloying elements. The microhardness of the composite increases from 350 HV (matrix) to 650 HV (reinforced layer) due to dispersion hardening and formation of the carbide skeleton. Compression tests showed record strength of the reinforced layer (1720 ± 60 MPa) due to effective load distribution by W/WC(Ni) particles, but brittle failure is observed in tensile tests due to stress concentration at the interfaces.

The authors investigated the microstructure and mechanical characteristics of 56GM steel-based composite produced by wire electron-beam additive manufacturing with the addition of W + WC(Ni) powders during printing. The analysis demonstrates that 56GM/(W + WC(Ni)) composite alloy is characterised by a gradient structure consisting of 56GM base layer, 56GM – 56GM/(W + WC(Ni)) intermediate layer and 56GM/(W + WC(Ni)) composite layer. The base layer of 56GM steel is characterized by a multidirectional acicular structure, which corresponds to the ferrite-martensite state. In 56GM – 56GM/(W + WC(Ni)) intermediate layer the acicular structure becomes less pronounced. In 56GM/(W + WC(Ni)) composite layer an equiaxed grain structure is formed, with an average grain size of 8.59 μm, along the boundaries of which cracks are observed. WC particles are located mainly along the boundaries of small grains and in small quantities inside the grains themselves. It was found that 56GM/(W + WC(Ni)) composite is mainly composed of α-Fe (~80.6 vol. %), Ni (~6 vol. %), WC carbide phase (~10.3 vol. %) and γ-Fe (3 vol. %). The structure and properties of initial 56GM steel change both in the area of direct addition of alloying powder and in the underlying layers due to diffusion processes and infiltration of W + WC(Ni). Microhardness values increase from ~3.5 GPa to ~6.5 GPa with distance from the substrate to the composite layer. In uniaxial tensile tests, the ultimate tensile strength and yield strength values reached 1100 – 1200 MPa and 835 MPa in the intermediate layer, respectively.