Solidification Of Alloys Research Articles

Isotropic optimizations of finite difference discretization

The isotropy is a fundamental requirement for solving partial differential equations by the finite difference scheme. In this work, we first introduce the concept of the virtual nodes to construct the finite difference scheme, and propose several stencils of finite difference discretization to optimize the isotropy of the gradient and Laplacian operators. The isotropic error of the optimized gradient stencil is reduced to 4.1% and 7.5% of the conventional scheme and the typical 4th-order isotropic stencil that is widely used in the multiphase lattice Boltzmann method, while the optimized Laplacian stencil displays the best performance in the Fourier analysis. Then, the optimized stencils are applied to suppress the spurious currents in the multiphase lattice Boltzmann method. The spurious current is reduced to only 7.2% of that calculated by the typical 4th-order isotropic stencil at the reduced temperature 0.6, at which the liquid/gas density ratio is near to 1000. Furthermore, they are adopted to rectify the dendrite directions in the alloy solidification simulations by the phase field method. The angle deviation of dendrite growth is reduced to 15.7% of the conventional scheme.

Determination of nano-graphene content for improved mechanical and tribological performance of Zn-based alloy matrix hybrid nanocomposites

The primary objective of this study is to explore the fabrication of a hybrid nanocomposite (HNC) composed of ZnAl40Cu2 alloy, graphene, and B4C particles, while also determining the optimal graphene reinforcement ratio for enhanced properties. Our methodology entails the production of HNC powders (HNPs) through mechanical milling, where we combine graphene nanoplatelets with B4C microparticles into ZnAl40Cu2 alloy powders. Throughout this process, we maintain a constant B4C content of 1.5 wt%, while varying the graphene content at 1.5 wt%, 3 wt%, and 4.5 wt%. Following the characterization of all produced powders, which includes an assessment of powder morphology, powder size distribution, and powder microhardness, we proceed to hot-press the HNPs to create bulk HNC samples. After consolidating the specimens, a comprehensive series of tests are carried out to determine microstructural, mechanical (hardness and tensile strength) and tribological properties. Our results reveal that the HNC specimen with graphene content of 3 wt% (referred to as A2) displays the most notable enhancements in properties. Specifically, A2 exhibits an impressive hardness of 163 HB, surpassing the hardness of the ZnAl40Cu2 matrix alloy, which measures at 133 HB. Furthermore, its ultimate tensile strength significantly outperforms the ZnAl40Cu2 matrix alloy, with a remarkable value of 223 MPa compared to 157 MPa. However, it is worth noting that the improvement in wear resistance for HNCs is most pronounced up to a certain threshold of graphene content, which is 3 wt%.

Study of Welding Metallurgy, Alloying Element Redistribution, and Alloy Solidification in Hastelloy B-2 Superalloy Under Pulsating Current Waveform Gas Tungsten Arc Welding

Study of Welding Metallurgy, Alloying Element Redistribution, and Alloy Solidification in Hastelloy B-2 Superalloy Under Pulsating Current Waveform Gas Tungsten Arc Welding

Manufacturing of die blanks from hard alloy granulated mixture and influence of chemical composition of the mixture on technological properties of hard alloy die blanks

The technology of manufacturing dies from a hard alloy granulated mixture includes the following operations: preparation of raw materials, forming of blanks, and subsequent sintering. The preparation of hard alloy mixtures consisting of carbide powders and binder metals is one of the main operations in the production of hard alloys. The properties of the resulting alloys largely depend on the conditions of performing this operation. All operations are interconnected, and any change in technological parameters can lead to a change in the formation of the final material structure and, consequently, its properties. This article discusses the technology of manufacturing and the production process of die blanks from a hard alloy granulated mixture. The results of laboratory studies of the hard alloy mixture, the manufacture, and production tests of die blanks are described.

Effects of Cu on the high-entropy alloys of CuxCoCrFeNi: Experiment and molecular dynamics simulations

The effects of Cu on the structure and properties of CuxCoCrFeNi were investigated experimentally and compared with the results of molecular dynamics simulations. Experimental results revealed that the alloy's crystal structure transitions from a single FCC to a biphasic FCC as Cu content increases. Mechanical testing indicated that increasing Cu content initially boosts, then reduces the alloy's yield and tensile strength, while elongation consistently increases, demonstrating enhanced plasticity. Additionally, nanoindentation tests further substantiated the notable impact of Cu content on alloy hardness. The nanoindentation simulation results show that the dislocation density increases and then decreases with the increase of Cu content, which explains the change of alloy properties with the increase of Cu content from a microscopic point of view. These findings offer valuable insights for designing and optimizing high-entropy alloys.

Определение скорости электрохимического растворения стали У10А в условиях ЭХРО с неподвижным катодом-инструментом

Introduction. In blank production, when replacing hard alloys with tool steels, difficulties arise in shaping surfaces to ensure the required parameters of productivity, quality and accuracy, due to the presence of incomplete information for assigning electrochemical processing modes for this class of materials. This fact requires additional research to determine rational processing modes that provide the necessary technological parameters (productivity, dimensional accuracy and surface roughness). The purpose of the work is to conduct research to establish the patterns of electrochemical shaping of tool steels and determine the modes of the shaping process. The work investigated the features of anodic dissolution of U10A tool steel in an aqueous NaCl solution of 10 % concentration. The range of potential changes was from 0 to 8 V. Technological performance parameters were determined (current output for the main reaction and the rate of electrochemical dissolution at a voltage of 8 V and an electrolyte pressure of 0.1 MPa). Research methods. For polarization studies, a potentiodynamic research method was chosen. Technological experiments were carried out using the model of piercing holes with a stationary cathode-tool made of stainless steel without insulation. A circular cross-section with outer diameters of 0.908 mm and inner diameters of 0.603 mm was chosen as a cathode tool. Results and discussions: it is revealed that the electrochemical dissolution of U10A tool steel in a 10 % aqueous solution of NaCl is active in the studied potential range from 0 to 8 V. The technological experiments carried out made it possible to establish the dimensions of the resulting holes — an average diameter of 1.433 mm and a depth of 0.574 mm. The current efficiency was 70.83 %. Based on the analysis of the experimental data obtained, it is established that in order to ensure high productivity of the process of electrochemical forming of U10A steel in a solution of 10 % NaCl, the feed of the cathode tool should be 0.2232 mm/min, which corresponds to the rate of electrochemical dissolution under the studied forming conditions.

Effect of Al and Si content on properties of Ti(1-x-y)AlxSiyN coating materials: First-principles calculation

This paper investigates the effect of Al and Si atomic doping on the Ti(1-x-y)AlxSiyN alloy using density functional theory (DFT). The results indicate that the phase structure stability of the alloy decreases with increasing Al and Si doping content. Particularly, excessive doping leads to the transformation of crystal structure from rocksalt to wurtzite structure with lower mechanical properties. The bulk modulus of the alloy decreases with the increase of doping content. Specifically, Al atom doping initially reduces and then increases the shear modulus and Young's modulus of Ti1-xAlxN, while Si atom doping causes the shear modulus and Young's modulus of Ti0.375-yAl0.625SiyN to increase first and then decrease. In terms of hardness, the hardness of Ti1-xAlxN increases with the increase of Al doping, but the toughness decreases. Si atom doping further enhances the alloy's hardness, reaching a maximum of 29.8 GPa, consistent with the trends observed in experimental results. Electronic structure analysis reveals that Al and Si doping induces orbital hybridization, enhancing the bonding ability and chemical bond strength between atoms. The results confirm that the ionic bonds, metal bonds and covalent bonds in multi-component nitride jointly determine the mechanical properties of the alloy.

Structural, Mechanical and Tribological Properties of Hydroxiapatite Reinforced Ti13Nb13Zr/HA Composite Produced by Friction Stir Process (FSP)

Many modification methods are applied to produce Ti-based biomedical materials. In this study, the structural, mechanical and tribological properties of unreinforced Ti13Nb13Zr alloy and Ti13Nb13Zr/HA composites with different contents of hydroxyapatite (HA) reinforcement were investigated by friction stir processing (FSP) to Ti13Nb13Zr alloy. SEM, FTIR and EDS analyzes were performed to determine the structural properties. Surface roughness values were determined using a 3D optical microscope. Surface wettability properties were investigated with a contact angle. Microhardness and wear test devices were used to determine the mechanical and tribological properties, respectively. Wear tests were carried out in a dry environment and phosphate buffered saline solution (PBS). The wear tracks were analyzed by SEM and 3D optical microscope. As a result of FTIR analysis, HA has PO43−, HPO42−, CO32− and OH− bonds. All samples exhibited hydrophilic surfaces suitable for cell adhesion. The FSP process increased the hardness and wear resistance of the Ti13Nb13Zr alloy in both atmospheres. In addition, Ti13Nb13Zr/HA composites significantly increased the hardness and wear resistance of Ti13Nb13Zr alloy and Ti13Nb13Zr alloy modified by FSP.

Prediction of the Cohesion Energy, Shear Modulus and Hardness of Single-Phase Metals and High-Entropy Alloys.

In order to facilitate the prediction of some physical properties, we propose several simple formulas based on two parameters only, the metallic valence and metallic atomic radii. Knowing the composition, for single-phase alloys, the average parameters can be calculated by the rule of mixture. The input parameters can be obtained from tabulated databases. Adopting from the literature the results of Coulomb crystal model for metals and single-phase high-entropy alloys, we have derived formulas for the shear modulus (G) and the cohesion energy (Ecoh). Based on these parameters separately, we set up two formulas to estimate the hardness in the case of pure metals. For single-phase (solid-solution) HEAs, by simplifying the Maresca and Curtin model, we obtained a formula for estimating the hardness, which takes into account the atomic misfit in addition to G. The maximal hardness for single-phase HEA is approximately 600 kg/mm2 and is obtained for a composition with a valence electron concentration of approximately 6 ÷ 7.

Effect of SiC and TiC content on microstructure and wear behavior of Ni-based composite coating manufactured by laser cladding on Ti–6Al–4V

The low hardness and poor wear resistance of titanium alloys limit their widespread industrial use. In this study, a composite coating made of Ni60, SiC, and TiC powders using laser cladding technology was used to improve the wear resistance of Ti–6Al–4V (TC4), with the microstructural characteristics, phase style, microhardness, wear behavior, and corrosion resistance studied to clarify the effects of SiC and TiC contents. The experimental results show that the main phases in the composite coatings are TiC, Ti5Si3, and Ti2Ni, which change little with changes in the TiC and SiC content. The prepared composite coatings significantly improved the hardness and wear resistance of the TC4 substrate with the 20% SiC coating showing the lowest wear rate. The main wear mechanisms of the composite coatings were the complex modes of adhesive, abrasive, and oxidative wear, and that of the TC4 substrate was microcutting. The corrosion potential (Ecorr) of TC4 is lower than that of the prepared composite coatings, and the corrosion current (Icorr) of TC4 is also higher. The corrosion resistance of the composite coatings—with intracrystalline corrosion as the primary corrosion mechanism—was better than that of the TC4 substrate.

ИССЛЕДОВАНИЕ ВЛИЯНИЯ СОСТАВА КОМПОЗИТОВ, СОДЕРЖАЩИХ ИМПАКТНЫЕ АЛМАЗЫ, НА ИХ ЭКСПЛУАТАЦИОННЫЕ ХАРАКТЕРИСТИКИ ПРИ ЛЕЗВИЙНОЙ ОБРАБОТКЕ ЦВЕТНЫХ МЕТАЛЛОВ

The paper presents the results of resistance tests of tool composite materials containing nanostructured impact diamonds, in comparison with composites based on synthetic superhard materials, diamond and cubic boron nitride (cBN), and ВК-8 (VK-8) (WC + 8 % Co) hard alloy, during blade processing of workpieces made of brass ЛС-59 (LS -59) (57–60 % Cu) and aluminum alloy AK-7 (Al 92–94 %, Si 6–8 %). Samples of composite materials for wear resistance studies were obtained by thermobaric sintering in a highpressure apparatus. The performance of composites was assessed by the wear of the cutter back surface, as well as by a specially developed method for studying the performance characteristics of composite superhard materials, based on determining their specific productivity. As a result of the tests, it is found that composites based on impact diamonds have the highest resistance when turning non-ferrous metal alloys. In particular, the wear resistance of a composite material containing impact diamonds with the addition of cBN exceeds the wear resistance of cutters made of composite 02 (belbor) by 1.5–3 times, and that of cutters made of hard alloy VK-8 by 8–10 times. Additions of impact diamond to hard alloy in the amount of 6.25 and 12.5 vol.% increase the relative wear resistance of the hard alloy composite compared to the original VK-8 alloy by 10–15 and 20–25 %, respectively.

Effect of Fe addition and ion irradiation on surface hardness in zirconium alloys: Experiments and modeling

Exploring the effect of Fe addition and ion irradiation on surface hardness in Zr alloys not only elucidates the strengthening mechanisms of individual alloying elements but also facilitates the assessment of mechanical properties under varying damage levels. In this work, the microstructural variations and surface hardness of Zr and Zr-Fe alloys were examined through Ne+ and Au3+ irradiation experiments. Electron backscatter diffraction (EBSD) characterization suggested the potential of Fe addition in Zr-Fe alloys for grain refinement. Transmission Electron Microscopy (TEM) observations indicated the formation of dislocation loops in irradiated materials, accompanied by a transformation of Zr3Fe particles from a crystalline to an amorphous state. Furthermore, nano-indentation tests were employed to measure the depth-dependent hardness, revealing an augmentation in hardness with increasing Fe content and highlighting noticeable irradiation hardening in Zr alloys. A mechanical model was then developed to theoretically investigate the contribution of diverse hardening mechanisms in ion-irradiated Zr alloys, particularly addressing the impact of non-uniformly distributed defects. Theoretical analysis denoted that the irradiation-induced defects hardening at varying depths follows distinct laws, whereas the precipitation hardening in Zr-Fe alloys was attributed to high-density strengthening particles induced by Fe addition. Moreover, it was determined that the surface hardness is governed by geometrically necessary dislocations (GNDs) and irradiation-induced defects at shallow depths, whereas precipitates and statistically stored dislocations (SSDs) dominate at relatively larger depths.

Al3Sc phase uniform distribution and aluminum grains refinement in Al-2Sc alloy achieved by NdFeB permanent magnet stirring

The rapid development of magnetic materials provides the possibility for the application of permanent magnet stirring (PMS). Numerical and experimental investigations were employed with respect to the solidification process of the Al-2Sc alloy controlled by a novel PMS using NdFeB permanent magnets under various rotation speeds (0, 50, 100 and 150 r/min). The simulated results reveal that the maximum electromagnetic force increases proportionally from 4.14 to 12.39 kN/m3 and the maximum tangential velocity increases from 0.13 to 0.36 m/s when the rotation speed of PMS enhances from 50 to 150 r/min in the ingot melt. Besides, the experimental results demonstrate that PMS can achieve a uniform distribution of blocky Al3Sc precipitated phase in the longitudinal direction under the impact of a forced fluid flow. Moreover, increasing rotation speed of PMS is beneficial to refining aluminum grain size significantly and decreasing the texture intensity in the alloy. In addition, the Brinell hardness of Al-2Sc alloy is increased by 33% to 27.8 HB and the tensile strength is enhanced by 34% to 128.2 MPa, due to the improved distribution of the strengthening Al3Sc phase and the grain refinement of Al matrix under the impact of PMS. This work provides an effective application of NdFeB permanent magnets in the metal cast field.

Effect of laser power on microstructure and properties of laser cladding AlCoCrNiSiTi0.5 high-entropy alloy coatings

Abstract Using varying laser powers, an AlCoCrNiSiTi0.5 high-entropy alloy (HEA) coating was applied to the surface of TC4 titanium alloy. The microstructure and phase composition of the coating were examined using several analytical techniques, including energy spectrometer (EDS), scanning electron microscopy (SEM), and X-ray diffraction (XRD), etc., and Vickers hardness tester was used to test the coating’s microhardness at various laser powers. Studies indicate that the coating is mostly made up of the following phases: BCC, FCC, α-Ti, β-Ti, (Si, Al)2Cr, (Ni, Co)Ti2; The coating’s mean hardness under different powers (1400 W, 1600 W, 1800 W) is 1047.87 HV, 1012.68 HV, and 846.72 HV, which is about 2∼3 times of the matrix hardness (347.27 HV). Powder overburning will occur at laser energies greater than 1800 W. The elements evaporate, thereby reducing the microhardness of the coating. The hardness of TC4 titanium alloy can be greatly increased by applying an AlCoCrNiSiTi0.5 HEA coating.

Improving mechanical properties of W-Ni3Al alloy through Zr element addition: Solid-solution and oxide particle strengthening

In this study, fine Ni3Al flakes facilitated the W-Ni3Al alloy liquid phase sintering, while the added 0.9 wt% Zr element enhanced its mechanical properties, finally obtaining the 1200 °C sintered W-Ni3Al-Zr alloy (WNZ-1200 alloy) with excellent comprehensive properties. Specifically, the relative density, tungsten grain size, bending strength, and macro hardness of WNZ-1200 alloy were 98.26 ± 0.31 %, 3.06 ± 0.65 µm, 1472.56 ± 61.90 MPa, and 76.10 ± 0.82 HRA, respectively. By analyzing the alloy’s phase and microstructure, its excellent mechanical properties were originated from the formed Ni3(Al, W, Zr) solid solution, unique nano-Al2O3 ‘rivet’, the semi-coherent interface of W/t-ZrO2, oxide dispersion strengthening, and the t-ZrO2 phase transformation strengthening.

Effect of solid solution and aging treatment on the microstructure, mechanical properties, corrosion behavior and antimicrobial properties of Ti-5Mn alloys

In this paper, Ti-5Mn alloy was subjected to different heat treatments to explore the possibility of preparing antimicrobial Ti-Mn alloys and to examine the effect of precipitate on the properties of the alloy. The microstructure, phase composition, hardness, biocorrosion properties and antimicrobial properties of Ti-5Mn alloys after different heat treatments was analyzed by metallurgical microscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray diffraction (XRD), microhardness tests, electrochemical tests and antimicrobial tests. The results have shown that the phase composition of the solid solution treated Ti-5Mn(T4) was mainly β-Ti phase, and the aged Ti-5Mn was composed of α-Ti phase and Ti17Mn3 phase, while Ti17Mn3 precipitate gradually increased with the extension of the aging time. Ti-5Mn(T4) showed the highest hardness and the best corrosion resistance and the aging process reduced the hardness of Ti-5Mn(T4) alloy. With the precipitation of Ti17Mn3, the corrosion resistance of the alloy became worse and the hardness was reduced, but the corrosion resistance of Ti-5Mn alloy was still better than that of cp-Ti. It was demonstrated that Ti-5Mn(T4) exhibited no antibacterial properties against Staphylococcus aureus, but the aging treatment improved the antibacterial property of Ti-5Mn(T4) alloy, and the antibacterial rate of Ti-5Mn alloy reached 69% after 50 h aging treatment.

EFFECT OF LONG-TERM THERMAL AGING AT 475 °C ON EMBRITTLEMENT OF Fe-32Cr-4Ni-4Cu MODEL ALLOY

The microstructure evolution and mechanical properties of a Fe-32Cr-4Ni-4Cu model alloy after long-term thermal aging at 475 °C was investigated in this study. The spinodal decomposition of the model alloy during thermal aging and the crystal structure evolution of Cu-rich precipitates were observed and analyzed using high-resolution transmission electron microscopy (TEM). It was revealed that after long-term thermal aging, the crystal structure of the precipitated Cu-rich phases in the Fe-32Cr-4Ni-4Cu model alloy transformed from a BCC structure to a multi-twin 9R or 2H structure, ultimately transforming into a stable FCC structure. During long-term thermal aging at 475 °C, the precipitated Cu-rich phase and the Cr-rich ’-phase produced by spinodal decomposition cause an increase in the hardness of the model alloy. The hardness of the model alloy in the early stage of thermal aging greatly depends on the Cu-rich precipitates. After continuous thermal aging for 1000 h, the hardness of the alloy depends on the Cr-rich ’-phase. The results of an oscillographic impact test indicate that the fracture mechanism of the model alloy after thermal aging at 475 °C is brittle fracture, which is mainly influenced by the precipitation of Cu-rich phases during the thermal aging process.

Erosion behavior of various high chromium cast iron alloys exposed to gas-blast stream of ferric oxide particles

Depositing hardfacing material onto a surface with the welding method is a common way of protecting surfaces against wear damage. In this study, five high chromium hardfacing alloys were used to prepare samples for the gas blasting erosion test. Erodent particles were ferric oxide specks with a hardness of 657 HV and an average size of 260 μm. Impinging stream eroded the surface of samples with the gas flow of 100 m/s at an angle of 30° while the particle feed was increased from 140 to 630 g. The results indicated that erosion resistance is dominated by bulk hardness of hardfaced alloys. In addition, the erosion rate for a sample containing Mo, Nb, V, and W was the lowest since it had the highest bulk hardness among all other samples.

Hardness and microstructural evolution of CoCrFeNi high-entropy alloys during severe plastic deformation

In this study, the evolution of hardness and microstructure in a CoCrFeNi high-entropy alloy processed by high-pressure torsion was investigated. An initial increase in hardness was attributed to the rapid increase in low-angle grain boundaries (LAGBs), accompanied by a high density of dislocations. With continuous straining, some LAGBs evolved into high-angle grain boundaries and completed the grain boundary strengthening. A remarkable increase in hardness was achieved in the final stage of hardness enhancement, primarily due to the formation of numerous twins within nanograins, which were mainly formed by the emission of Shockley partial dislocations emerging from grain boundaries. Furthermore, a twin trailing the stacking fault was found in the nanograin, and a critical stress for twin nucleation was estimated to be about 2.16 GPa. Defects with low-energy configurations are closely correlated with the thermal stability of nanocrystalline CoCrFeNi alloys. The defects within nanograins yielded an average strain of about 1.1 % and the corresponding strain energy was identified to about 17 J g−1.

Recover the tensile strength of hard aluminum alloy through laser assisted cold spray

In the present study, Al6061/Al2O3 composite coating was produced to repair the notched Al7075 substrate by cold spraying (CS) and laser assisted cold spray (LACS) technology. The preparation process and parameter selection of high-performance coating were discussed by combining simulation and experiment. Results showed that the LACS experiment guided by simulation results achieved high-quality bonding of single particle with the substrate. In addition, the tensile strength of samples repaired by LACS recovered to the level of original substrate, and the ductility was significantly higher than that of CS process. This is attributed to the introduction of laser irradiation heating, which improves the plastic deformation ability of particles and produces atomic-level metallurgical bonding between the particles. This study provides a possibility for the repair and remanufacture research of high-quality components, and has great development potential in future research.