Formation Of Fine-grained Structure Research Articles

Optimizing 3D Laser Foil Printing Parameters for AA 6061: Numerical and Experimental Analysis

Abstract This study utilizes a technology known as 3D laser foil printing (LFP) to create precise structures by layering metal foils using laser welding. Metal foils have the advantages of rapid cooling and efficient heat conduction, allowing for the formation of fine-grained structures. However, when dealing with materials like aluminum alloys in laser processes, defects can arise as a result of their high reflectivity. To address this challenge, laser circular oscillation welding (LCOW) is applied to the LFP process. LCOW's circular motions with higher scanning frequencies widen the keyholes and reduce some defects such as spattering, bubble formation, and microcracks. Simulation predictions with an error margin of approximately 10% in comparison to experimental results demonstrate the reliability of the model. Furthermore, the study integrates circular packing design with artificial neural networks to create comprehensive processing maps tailored to different criteria for extracting optimal welding parameters. As a result, for the optimized processing parameters screened using the above systematic process, no cracks were observed on the upper surface of the 3D LFP parts produced with a laser power of 800 W and a scanning speed of 550 mm/s, and only 0.12% porosity was observed from the cross section of the sample. Future research will focus on incorporating simulation results to model microstructures more precisely and continually refining LCOW parameters as new materials and technologies emerge, ensuring the ongoing enhancement of weld quality in the 3D LFP process.

USING THE ADVANTAGES OF NANOTECHNOLOGY FOR THE PRODUCTION OF COMPOSITE MATERIALS OF THE TYPE NGO/CERAMIC MATRIX

Using the advantages of nanotechnology, composite ceramic materials of the type of graphene oxide nanocolloid/ceramic matrix were obtained in two stages. First, finely porous corundum (1500ºC) and barium titanate (1300ºC)ceramic samples containing 2 mass % graphene structures nanoplatelets were synthesized. The next stage of the study involved the preparation of graphene oxide in nanocolloid form (2 mg/ml, dispersion in H2O) which was impregnated in the solid porous ceramic samples to obtain composite materials. For the characterization of the ceramic samples, mainly infrared spectroscopy, X-ray phase analysis, scanning electron microscopy and light microscopy were used. The results obtained from the studies carried out showed that with the introduction of small amount of graphene nanoplatelets in the initial blends followed by solid state sintering, part of the added graphene is burned out which imparts significant porosity to the ceramics obtained. On the other hand, the addition of graphene initiates the formation of well-shaped fine-grain structure of the ceramic samples, and they had sufficient porosity.

A novel strategy to achieve uniform ultrafine grains in Mg-Al-Sn-Ca alloy via pre-twinning combined with differential-thermal asymmetric extrusion

Obtaining fine grains with weak textures is an efficacious way of simultaneously improving the strength and ductility of magnesium (Mg) alloys. In this paper, an Mg-Al-Sn-Ca alloy with uniformly ultrafine grains and a weak texture has been prepared via pre-twinning followed by differential-thermal asymmetric extrusion (DAE). The alloy exhibits good strength and ductility (ultimate tensile strength: ∼381 MPa; elongation: ∼22 %). The results show that {102} tensile twins significantly promote dynamic recrystallization (DRX) during DAE, which beneficial for the formation of uniform fine grain structure and weak bimodal texture. This research provides valuable insights and methods for tailoring excellent mechanical properties of Mg alloys, facilitating their practical application in various engineering scenarios.

ОТХОДЫ ОБОГАЩЕНИЯ ЖЕЛЕЗИСТЫХ КВАРЦИТОВ КАК СТРУКТУРНЫЙ КОМПОНЕНТ МЕЛКОЗЕРНИСТОГО БЕТОНА

The article describes problematic situation with waste accumulation from iron ore concentrate production (beneficiation tailings) from ferruginous quartzite at JSC Olkon (Murmansk Region). The task is to utilize beneficiation tailings as a fine-grained concrete component. The paper presents results of beneficiation tailings diagnostics and their testing as a part in the processes of fine-grained concrete structure formation in comparison with quartz sand from the Olenegorsk quarry. According to the research, the replacement of natural sand with beneficiation tailings in their original form leads to a decrease in strength due to insufficient compaction of mixture under adopted vibration compaction modes. At the same time, the use of ground beneficiation tailings in binder composition ensures increase in strength of concrete compared to concrete on "pure" cement and increase of efficiency by using clinker part of binder in formation of concrete strength by 57-58%. The study recommends the use of fine-grained concrete composition of class B40 for production of vibration-pressed urban land improvement products (paving slabs, curbstones, etc.). It reveals prospects for further research in construction and technological utilization of ferruginous quartzite enrichment tailings as a factor in the formation of biosphere-compatible living environment in the region.

A MODEL OF MICROSTRUCTURE EVOLUTIONUNDER HIGH- STRAIN RATE DEFORMATION OF COPPER

A physical model of high-strain rate deformation of metallic materials has been developed to describe the evolution of microstructure during the process. The model is based on representations of the mechanisms of grain boundary sliding, strain-induced grain growth and dynamic fragmentation of coarse grains developed in the framework of the theory of nonequilibrium grain boundaries. These representations are modified for the description of high-speed flow and supplemented by a model of dynamic recrystallization. It is shown that during high-strain rate deformation of metallic materials, grain boundary sliding dominates in the material regions with a fine-grained submicron structure and the material deforms in the superplasticity mode. In regions of material with larger grain size, grain volume deformation dominates, accompanied by fragmentation and formation of fine-grained structure with submicron grain size. The transformation of the structure from fine-grained to coarse-grained occurs due to strain-induced grain growth. Transformation of structure from coarse grain to fine grain occurs due to dynamic fragmentation. The transition from grain boundary sliding to grain volume deformation occurs at grain size corresponding to the optimum value for the course of dynamic recrystallization. The cyclic change of deformation mechanisms (from grain boundary strain-induced to grain volume deformation) is caused by alternation of the processes of deformation-stimulated grain growth and dynamic fragmentation. The alternation of the above cycles of grain boundary and intragranular deformation in different regions of the material makes it possible to maintain a high strain rate and suppress the processes of both local hardening and local softening. The high strain rate is achieved at the expense of a high strain of the regions in which grain sliding dominates. In the regions dominated by intragranular deformation, the structure is “prepared” for superplastic flow.

Применение метода Бриджмена для получения термоэлектрического кремния, легированного германием и фосфором

Heavily donor or acceptor doped metallurgical silicon is a promising candidate as a high-temperature thermoelectric energy converter due to the extremely low cost of its fabrication. The problem of silicon-based thermoelectric materials is the high value of the thermal conductivity; however, modern technologies offer several options for solving this problem at once. In the present work, silicon ingots heavily doped using Si:P compound were grown by the Bridgman directional crystallization method with a small (up to 5 at. %) germanium impurity fraction. The main thermoelectric parameters of the material were measured in a wide temperature range (50 – 800 °C). These are Seebeck coefficient, electrical conductivity and thermal conductivity. Based on the measurement results, the value of the thermoelectric figure of merit was calculated. The latter determines the value of the thermoelectric conversion efficiency. The study of electrical properties shows that phosphorus from the SiP compound is introduced into the lattice as a dopant and creates a high concentration of conduction electrons. The chemical analysis of the ingots showed the presence of additional background impurities, the concentration and composition of these impurities vary over the bulk of the sample. Despite the presence of impurities, the material demonstrates relatively high thermoelectric characteristics, and the efficiency is at the level of the best world results. A further potential for optimizing thermoelectric characteristics due to the possibility of a fine-grained polycrystalline structure formation is discussed.

Microstructural evolution of Al-Mg-Er-Zr alloy by equal channel angular extrusion at room temperature

To obtain excellent mechanical properties, Al-Mg alloy was processed through a combination of equal channel angular pressing (ECAP) and micro-alloying techniques. In this study, the microstructural evolution of Al-Mg-Er-Zr alloy during ECAP at room temperature were systematically investigated. TEM results confirm that the Al3(Er, Zr) particle exists in the initial material and saturated dislocations form dense dislocation walls. The grains were refined with an average grain size of 2.8 μm after 4 passes of ECAP. Continuous dynamic recrystallization was identified and this mechanism led to the formation of fine grain structure. The (101)-oriented coarse grains were relatively stable once they had been formed.

Grain Refiner Settling and Its Effect on the Melt Quality of Aluminum Casting Alloys.

Grain refiner particles, which are intended to induce the formation of fine equiaxed grain structure during the solidification of aluminum alloys, are prone to settling during the holding of the liquid metal, which phenomenon can affect not only the grain size but the spatial distribution of the double oxide films in the melt. In this study, the settling of Al3Ti inoculant particles, as well as its effects on melt quality and grain refinement, were studied. During the experiments, the Ti-concentration of a liquid Al-Si-Mg-Cu alloy was increased to 0.3 wt.% by the addition of Al-10%Ti master alloy at different melt temperatures. Particle settling and grain size evolution were studied by quantitative metallography, while the interactions of grain refiners and bifilms were investigated by scanning electron microscopy (SEM). The evolution of melt quality was assessed by the computed tomographic (CT) analysis of reduced pressure test (RPT) samples. It was found that effective grain refinement was only realized when the introduced blocky Al3Ti particles were dissolved and re-precipitated in the form of (Al,Si)3Ti at a lower temperature. Without dissolving at higher holding temperatures, Al3Ti particle settling has taken place within 10 min. The settling of (Al,Si)3Ti particles improved melt quality by the aided sedimentation of bifilms in the melt.

Coatings from high-entropy alloys: State and prospects

The authors made a brief review of recent publications by foreign and domestic researchers on the structure, phase composition, and properties of films and coatings of five-component high-entropy alloys (HEA) on various substrates and modification of the HEA surface by various types of processing. The main methods of applying films and coatings are considered: magnetron sputtering, thermal sputtering, laser sputtering, and electrodeposition. Particular attention is paid to the deposition of coatings on stainless steels and titanium alloys. The positive change in the tribological, strength properties, and corrosion resistance of film coatings in a wide temperature range is analyzed and possible causes of the observed effects are discussed. The role of solid solution strengthening, formation of fine-grained structure, and the formation of oxide layers enriched with one of the HEA components were taken into account. The authors identified new methods for applying coatings from HEA and subsequent processing. Using Nb and Ti doping as an example, their role in increasing microhardness, wear resistance, and reducing the friction coefficient in coatings were revealed. Electrolytic polishing, electroerosive machining, mechanical polishing and their combination are considered among the methods of HEA surface treatment. A number of works propose a method of powder borating to increase the surface strength and wear resistance of HEAs. The paper considers analysis of works on electron-beam processing as one of the promising and high efficient methods of HEA surface hardening.

Investigation of deformation zone parameter at multichannel angular extrusion

The paper presents the results of research on the modern process of multichannel angular extrusion. Analysis of the literature has shown that the use of non-equal angular extrusion leads to a smaller size of microstructure in one pass than equal-angular compression. Accordingly, non-uniform angular extrusion is well suited for the formation and changing of fine-grained metal structure, and also significantly increases its strength, ductility and toughness due to shear deformation. However, the known methods of non-uniform angular pressing are mostly used for the manufacture of intermediate products (rods, strip), which to achieve the required level of properties require additional processing. Additional thermal or deformation processing could have a negative impact on the structure and properties of the product. Thus, the urgent task is to develop and study processes in which intense plastic deformation is the final operation. One of these processes is multichannel angular extrusion. The aim of the study is to determine the characteristics of the deformation zone and plastic flow of the metal in this process. The analysis of the grid has allowed to identify certain elements of the deformation zone. A special tool has been developed to provide multi-channel angular extrusion. The peculiarity of the developed tool is the matrix integrated into the container and made collapsible. This design provides removal of the extruded profile after processing. It has been found that the central layers of metal deform more easily, and the layers, the flow of which slows down due to contact friction between the tool and the workpiece, deform with a delay. The adequacy of the mathematical model of the process developed in the QForm © program was also confirmed with the help of experimental data.

Microstructure, superplasticity, and mechanical properties of Al–Mg–Er–Zr alloys

Minor additions of rare-earth elements improve the mechanical properties of aluminum-based alloys due to precipitation strengthening, increased recrystallization resistance, and grain refinement effects. This study investigated the microstructure, room temperature mechanical properties, and superplasticity of Al–Mg–Z–Er alloys with the Mg content in a range of 2.1–4.9 wt%. The alloys' microstructure was presented by an Al-based solid solution matrix enriched with Mg, the (Al,Mg) 3 Er phase of solidification origin, and nanoscale secondary precipitates of the Al 3 (Er,Zr) L1 2 –structured phase. The Al 3 (Er,Zr) precipitates provided the Orowan strengthening mechanism, led to a strong recrystallization resistance and the Zener pinning effect during elevated temperature deformation. An increase of the Mg solute resulted in a solid solution strengthening and facilitated dynamic recrystallization at elevated temperatures. In the alloy with 4.9%Mg, a combined effect of fine L1 2 precipitates, high solute Mg, and (Al,Mg) 3 Er particles led to a fine-grained structure formation and superplasticity with the maximum strain rate sensitivity m of 0.51 and the elongation-to-failure of 550–600% at the constant strain rates of (0.8–1) × 10 −2 s −1 . The mechanical properties at room temperature were studied after the post-deformation annealing of the thermomechanically treated alloys and after the superplastic deformation. The developed Arrhenius-type mathematical model of superplastic deformation behavior showed excellent predictability for the studied alloys with different solute Mg. • Microstructure and tensile properties for thermomechanical-treated Al–Mg–Er–Zr alloys were studied. • A L1 2 -Al 3 (Er,Zr) precipitates parameters were studied after annealing of as-cast and rolled samples. • Increase in Mg solute improved solid solution strengthening and superplastic properties. • Model with excellent predictability of the superplastic deformation behavior was developed.

Структура и механические свойства алюминиевого сплава АК12Д, подвергнутого обработке трением с перемешиванием

The application of friction stir processing (FSP) to modify the structure of the Al–Si alloys, in particular the fragmentation of large silicon particles, can lead to an increase in the level of mechanical properties. This work is aimed to study features of local surface hardening of AK12D aluminum alloy (Al–Si–Cu–Ni–Mg system) during FSP and subsequent T6 hardening heat treatment. The authors investigated the influence of FSP and subsequent heat treatment parameters on the structure, microhardness, and hardness of the AK12D alloy. FSP was carried out at speeds of processing tool rotation and traverse of 2000 rpm and 8, 16 mm/min, respectively. The subsequent hardening T6 heat treatment was carried out according to the standard regime for the AK12D alloy. The paper shows that the FSP mode at a rotation speed of 2000 rpm and a traverse speed of 8 mm/min contributed to the formation of a monolithic and defect-free treatment zone. The study revealed that the formed microstructure is heterogeneous due to the influence of various thermomechanical effects. The most intense structural changes occurred in the stir zone. Friction stir processing and subsequent heat treatment led to fragmentation and partial dissolution of intermetallide particles in the α-Al solid solution followed by its decomposition and formation of secondary hardening phases. Moreover, the FSP and T6 heat treatment led to the formation of quasi-equiaxed fine-grained structure. The AK12D alloy microhardness after treatment under the study varied nonmonotonically and depended on the structure in different zones. At the same time, the Brinell hardness values after FSP and subsequent T6 heat treatment increased compared to the initial heat-treated state.

Friction stir processing of austenitic stainless steel cold spray coating deposited on 304L stainless steel substrate: feasibility study

In this work, the feasibility test of friction stir processing (FSP) of 1.5-mm-thick austenitic stainless steel cold spray coating deposited on 304L stainless steel substrate was performed using tungsten carbide tool. Applied FSP parameters (advance speed 50 mm/min, rotation speed 300 rpm, axial force 20 kN, tilt angle 1.5°) allowed to perform FSP treatment with a higher depth than the coating thickness. As a result, the material mixing at the coating-substrate interface was observed. The microstructure observation revealed that the coating microstructure in the stir zone was significantly modified. EBSD analysis confirmed that full material recrystallization during FSP allowed the formation of dense and uniform fine-grained structure with the mean grain size of 1.9 mm. Average coating microhardness was decreased from 406 to 299 HV. Further FSP parameter optimization should be carried out in order to improve the process reliability and avoid any coating failure during treatment.

Microstructural and mechanical characterisation of Al-Zn-Mg-Cu alloy processed by multi-directional cryo-forging

Aim of the present investigation is to study the microstructural and mechanical properties of Al-Zn-Mg-Cu alloy before and after multi-direction forging (MDF) at cryogenic condition up to 3 cycles. Microstructure evolution of specimen was examined using optical microscope and orientation imaging microscopy as well as X-ray diffraction. Mechanical properties were measured by tensile test and Vickers micro hardness. Microstructural investigation shows that after 3 cycle of MDF average grain size was reduced to 8 µm with low angle grain boundaries (LAGBs) and high dislocation density. Mechanical examination displays an improvement in hardness, yield strength and ultimate tensile strength is due to increases in grain boundaries and strain hardening effect. After 3 cycles of MDF process with cumulative strain ΣΔε = 3.64 led to the formation of fine grain structure, and microhardness were observed to be 168 HV.

The grain structure refinement of metals and alloys under severe plastic deformation: experimental data and analysis of mechanisms

Wide opportunities of using fine-grained materials as structural and functional materials with advanced physical and mechanical properties have proved the importance of improving the existing technology and creating new processing methods and treatment conditions for such ma-terials. At the same time, a preliminary theoretical analysis using mathematical models gives an opportunity to significantly reduce the cost of such experimental studies. Thus, it is necessary to develop multilevel models of polycrystalline metals and alloys based on crystal plasticity with the description of structure, deformation mechanisms and refinement at various scale levels. To con-struct a correct model of such a class, it is necessary to analyze information and arrange a large amount of experimental data about grain structure refinement. The article presents a review of the experimental studies describing and analyzing the grain structure refinement during severe plastic deformations of various metal alloys. The refine-ment mainly occurs at low temperatures that are a priori lower than the temperatures at which re-crystallization becomes an important factor and the solid-state phase transitions may take place. We have summarized the significant physical mechanisms of the grain refinement during cold deformation based on the arranged experimental data from the review. All the considered articles pay attention to the local accumulation of lattice dislocations inside the grains (in the form of flat clusters), which leads to the lattice curvature and separation of grains into cells. As a result of a further accumulation of dislocations in the walls, there comes an increase in misorientation of the neighboring cells. The curved lattice is unstable (it seems clear that the flat clusters become a source of such curvatures) and relaxes with the formation and movement of the partial disclina-tions, which leads to the rotation of the adjacent grain regions and creation of new grain bounda-ries. In addition, the mesoscale defects located at the junctions of the grains (including the boundary intersection disclinations), flat clusters of the dislocations of the orientational mismatch at the grain boundaries and partial dislocations in the grains have a significant effect on the frag-mentation. The articles about the severe plastic deformation at high temperatures are briefly de-scribed here. It is noted that recrystallization is the main mechanism of the fine-grained structure formation under these conditions. We suggest including the description of the discussed mechanisms in the multilevel con-stitutive material models. When new experimental data appear for a specific process of the severe plastic deformation, the considered refinement mechanisms can be added.

Comparative analysis of fine-grained structure formation in an Al-Zn-Mg-Cu alloy during multidirectional isothermal forging and uniaxial compression

A comparative study of the mechanical behavior and microstructural evolution in a cast coarse-grained 7475 Al alloy during uniaxial compression and multidirectional forging at 490°C and 10–4 s–1 was performed. It was shown that high-temperature deformation of the alloy led to grain refinement accompanied by strain softening. At similar processing conditions, the deformation path provided by multidirectional forging was found to be more favorable for grain refinement and strain softening than that of uniaxial compression.

The effect of vibratory conditioning on tensile strength and microstructure of 1018 mild steel

PurposeThe purpose of this paper is to investigate the prominence of mechanical excitations at the time of welding. In the past years, the process of welding technology has expanded its influence in manufacturing. The crucial drawback of conventional welding is prompted by internal stresses and distortions, which is the focal reason for weld defects. These weld defects can be diminished by the process called post-weld heat treatment (PWHT), which consumes more working hours and needs skilled workers. To replace these PWHT processes, mechanical vibrations are introduced during the process of welding to diminish these weld defects.Design/methodology/approachIn the current research, the mechanical vibrations are transferred to weld-pool through vibro-motor and DC motor connected to the electrode. As per standards, the tensile test specimens were prepared for welding with different voltages of vibro-motor and DC motor respectively. The weld joints were tested for tensile strength and analyzed the microstructure at the fusion zone.FindingsMelt-ability at fusion zone of 1018 mild steel was investigated by the single-stroke intense heat process of fusion welding. It is observed that the mechanical vibrations technique has a profound influence on the enhancement of the fusion zone characteristics and grain structure. The peak value of the tensile strength is observed at 100 s of vibration, 190 V of vibro-motor voltage and 18 V of electrode voltage. The tensile strength of the welded joints with vibrations is increased up to 22.64% when it is compared with conventional welding. The enhancement of the tensile strength of the weld bead was obtained because of the formation of fine grain structure. So, mechanical vibrations are identified as the most convenient method for improving the mild steel alloys weld quality.Originality/valueA novel approach called mechanical vibrations during the process of welding is implemented for fusion zone refinement.

Structure, Texture and Mechanical Properties through the Section of the Hot-Extruded Tube of Titanium Alloy PT-1M

The study considers the formation of the structure, texture, and hardness of hot extruded tube of titanium alloy PT-1M. It is shown that hot extrusion at 840 °C, which is higher than the α-phase recrystallization temperature, results to the development of dynamic and primary recrystallization processes and ensures the formation of homogeneous and fine-grained structure through-out the cross section with a two-component tangential texture (0001)TD<100>ED+(0001)TD<110>ED (TD – tangential direction, ED – extrusion direction) and hardness of 155 HV. It has been established that a higher cooling rate of the surface areas of the tube after extrusion results to a less active development of recrystallization processes, which lead to the formation of a finer granular structure near the outer surface. This weakens recrystallization component of (0001)TD<110>ED, compared to other areas of the tube.

Effects of pin diameter and number of cycles on microstructure and tensile properties of friction stir fabricated AA1050-Al2O3 nanocomposite

Nanocomposites of Al-Al2O3 are fabricated by means of friction stir processing (FSP). Effects of pin diameter and number of FSP cycles on tensile properties of the nanocomposites are investigated and the variations are correlated to the evolution of microstructure and distribution of nanoparticles in addition to agglomeration of Al2O3 nanoparticles. Investigation of agglomeration has been considered as an indirect indication for efficiency of the process for distribution of nanoparticles. The ductility of the nanocomposite is found to improve due to grain refinement during FSP. However, the ductility is likely to degrade if Al2O3 particles agglomerate and form coarse particles. The composite fabricated using the 6-mm pin indicates the maximum ductility which is attributed to formation of fine grain structure and efficient distribution of nanoparticles in the composite. Although, the grain structure in the composite fabricated using 8-mm pin is well refined, this sample shows significantly lower ductility with respect to the other samples. This was attributed to formation of coarse agglomerated particles. The second pass of FSP is found to slightly improve ductility and strength in composites fabricated using 4- and 6-mm pins but enforce significant improvements in the one with 8-mm pin. This is indeed because the second pass results in significant change in the distribution of nanoparticles or agglomerated particles in the latter case and negligible in the former ones. Grain structure and nanoparticle distribution and agglomeration can all affect the fracture surface of the tensile specimens of the fabricated nanocomposite to be ductile or brittle.

Microstructure of WC–Co–VN hard-alloy matrix for diamond-bearing details of drilling tools

The paper presents the research results on the structure and performance characteristics improvement of WC-Co hard-alloy matrix samples formed via the methods of cold and further hot moulding for the diamond-bearing details of drilling tools. It is shown that applying vanadium-nitride in 3 % in the composition of 94WC-6Co source materials provides the increase of sample hardness from 22.8 to 34.2 hPa, the compressive and bending strength from 4800 to 5340 MPa and from 2200 to 2280 MPa correspondingly, as well as the decrease of wear intensity from 1710×10-6 to 5200×10-6 g/m. The effect of formation of fine-grained structure for WC−CoNbN hard-alloy matrix with improved mechanical and performance characteristics revealed in the study points to the necessity of their usage in the development of efficient tools for drilling of oil and gas wells.