Cr Si Research Articles

Promising Approach for Rapid Growth of High-Quality SiC Crystals Using Si–Nd–C Solutions

The solution growth method is a promising technology for growing high-quality silicon carbide (SiC) crystals. However, enhancing C solubility in the growth solution is a key issue in the rapid growth of SiC crystals. In this study, Nd was added to a Si–C solution to enhance the solubility of C and rapidly grow high-quality SiC crystals at low temperatures (1823–1923 K). First, high-temperature chemical equilibrium was used to investigate the temperature dependence of the C solubility in a Si–Nd–C solution. The solubility of C in the Si–Nd–C melt was the highest, compared to those of the conventional Si–Cr–C, Si–Fe–C, and Si–Ti–C melts at the same temperature. The initial Si–Nd alloys used for the solution growth of SiC crystals were determined as Si-(25–42 mol %) Nd at 1823 and 1923 K. Thereafter, a temperature difference method was used to grow SiC crystals from Si-35 mol % Nd, Si-35 mol % Cr, Si-35 mol % Ti, and Si-35 mol % Fe solutions at 1923 K with a temperature difference of 36 K. The solutions producing the largest quantity and size of precipitated SiC crystals in the descending order were Si-35 mol % Nd solution > Si-35 mol % Cr solution > Si-35 mol % Fe solution > Si-35 mol % Ti solution (no SiC crystals). After analyzing and comparing the values for the supersaturation (ΔC) and degree of supersaturation (σ), Si–Nd–C solutions show great promise for use in the rapid growth of high-quality SiC crystals at low temperatures.

Whole martensitic transformation process in Fe–Mn–Si–Cr shape memory alloy by improved characterization of volume resistivity

Since Fe–Mn–Si–Cr shape memory alloy (Fe-SMA) has been discovered, an improvement of the shape memory effect (SME) is challenged. Numerous attempts have been made thus far to improve SME. To effectively control such performance, it becomes imperative to comprehend the real-time behavior of the stress-induced martensitic transformation (SIMT), which is strongly related to SME, during deformation. In the past, the measurement of volume resistivity has been proposed and applied to capture the forward SIMT behavior during the tensile loading process at various strain rate. However, it is quite hard to find investigations of the reverse martensitic transformation after the loading, which is more essential for understanding SME. Therefore, a comprehensive evaluation of the whole SIMT process including the loading process at various strain rate is strongly required. In this study, an improved measurement of volume resistivity is established by introducing both the four-probe and active-dummy techniques with a development of a diameter measurement at high temperature. Then, the volume resistivity of Fe-SMA is measured during the whole deformation including loading under tension at various strain rate, unloading, and heating processes. Besides, the microstructures of Fe-SMA after unloading and heating processes are observed, respectively. Finally, the real-time whole martensitic transformation in Fe-SMA is first investigated with the novel optimization method. The negative strain rate of change in volume resistivity during whole processes can be found. More amount of austenite can be obtained at lower strain rate, resulting in a larger SME.

Stability of binary precipitates in Cu-Ni-Si-Cr alloys investigated through active learning

Binary complexes that can be found in copper alloys are investigated in this work through a combination of computer simulations and machine learning. Copper alloys are made of a copper matrix and a combination of single alloying elements in n-ary forms. Due to the coexistence of different types of phases in this matrix, complex regions exist for which information on their precise atomistic structure is missing. In order to uncover such information, we apply active learning and generate moment tensor potentials. This development is based on quantum-mechanical calculations. This approach allows the on-the-fly relaxation of many thousands of potentially novel candidates and check their stability. The ground-state energy of these structures is used to build active learning-generated convex hulls, which are in turn being compared to those from the simulations and the AFLOW database. This procedure provides an insight to additional new stable copper alloy relevant binary complexes. Here, in view of Cu–Ni–Si–Cr alloys, the binary complexes Cu–Si, Ni–Si, Cr–Si, Cr–Ni, Cu–Ni, and Cu–Cr have been investigated. Their stability and the identification of novel stable candidates are discussed based on energetic arguments and the analysis of the respective phonon dispersion. The pipeline followed in this work is able to successfully predict binary phases in Cu–Ni–Si–Cr alloys, specifically for the Cu-Si, Ni–Si, Cr–Ni and Cu–Ni complexes, and to extend the already reported structures in the AFLOW library. In the end, we show the applicability of a predicted Cu–Si stable phase and the developed machine learned potentials at the larger scale of atomistic simulations for the calculation of their mechanical properties and melting behavior. This work provides a computationally efficient framework for material structure prediction and calculation of their properties at a quantum-mechanical accuracy.

Effects of elevated temperature exposure on the residual stress state and microstructure of PVD Cr coatings on SiC investigated via in situ X-ray diffraction and transmission electron microscopy

Pure Cr coatings are being considered as corrosion-resistant layers for SiC-SiCf composite fuel cladding in light water reactors. The residual stress state and interdiffusion behavior of Cr coatings deposited on SiC substrates using bipolar high-power impulse magnetron sputtering (B-HiPIMS) and direct current impulse magnetron sputtering (DCMS) were studied using in situ X-ray diffraction experiments at 300 °C, 700 °C, and 1200 °C. After elevated temperature exposure, evolution of the coating microstructure and coating/substrate interdiffusion was characterized by transmission electron microscopy. The compressive residual stress of the dense B-HiPIMS coating at room temperature was gradually relieved at 300 °C, while the stress transitioned to a tensile state at 700 °C. Grain growth of the Cr coating and a Cr–SiC interdiffusion layer consisting of newly formed Cr–C and Cr–Si phases were observed in the B-HiPIMS coating after exposure at 700 °C. The phases in the interdiffusion layer were identified to be Cr7C3, Cr3Si, and Cr5Si3Cx experimentally and by thermodynamic predictions. For the DCMS coating, however, changes in residual stress and microstructure at the elevated temperatures were limited by the inherent porosity and inhomogeneous structure of the as-deposited coating. At 1200 °C, both coating types interacted rapidly with the underlying SiC substrate in the early stages of the experiment. The results from this study suggest that the characteristics of the Cr coatings do not significantly change at the reactor operating temperature of 300 °C, while changes in microstructure and stress state are expected in off-normal conditions of 700 °C and 1200 °C. The results from this study suggest the B-HiPIMS coating is best-suited as a protective coating for SiC fuel cladding.

Encapsulation of red mud with ultra-high performance concrete (UHPC) for immobilization of alkaline and heavy metals: Experiments and simulations

To alleviate the storage of red mud (RM) and the resulting pollution, this study presented an encapsulation-based strategy for the safe management of RM, and adopted ultra-high performance concrete (UHPC) as an encapsulating material due to its superior impermeability and chemisorption properties. It is noteworthy to find that encapsulated material suffered from a selective chemisorption and density functional theory (DFT) calculations were innovatively employed to investigate the selective chemisorption mechanism. The simulation results suggested that distinct bonding forms lead to the selective chemisorption of heavy metals, with Pb being adsorbed by Si–O–Pb chemical bonds and a strong Si–O–Pb–O–Si long chain, while As and Cr only form relatively weak As–O and Cr–O bonds through their attraction to O atoms. With the thickness of the encapsulating material increases, the synergistic effect of chemical solidification and physical package is provided to achieve a stronger stabilization effect. The leaching results indicated that the encapsulated RM exhibited exceptionally low concentrations of hazardous components (i.e., Na at 1.580 mg/L, As at 0.003 mg/L, Cr at 0.027 mg/L, and undetected levels of Pb in encapsulated RM with a thickness of 1.5 mm), far below the limits set by the United States Environmental Protection Agency (EPA). This study opening a new window for the sustainable and efficient management of hazardous solid waste.

Fabrication and Soft Magnetic Properties of Fe–Si–Cr Composites with Double-Insulating Layers Suitable for High-Frequency Power Applications

Soft magnetic composites (SMCs) are composed of alloy materials with the core and insulating layers as the shell. These composites exhibit high saturation magnetic sensitivity and low hysteresis loss, making them a promising material for various applications. The investigation of double layers is considered valuable as it can effectively address the issues of low resistivity and high dynamic loss that arise from non-uniform insulating layers in SMCs. In this study, Fe-Si-Cr/SiO2 particles with a core–shell heterostructure were produced via chemical vapor deposition (CVD). The Fe-Si-Cr/SiO2 materials were coated with different weight percentages (1–6%) of sodium silicate (SS). Subsequently, Fe-Si-Cr-based SMCs were synthesized through high-pressure molding and heat treatment. The effect of the SS weight percentage on microscopic changes and magnetic characteristics was investigated. These findings indicated that a concentration of 4 wt% of SS was the most effective at enhancing magnetic characteristics. The resultant SMCs exhibited high resistivity (21.07 mΩ·cm), the lowest total loss (P10 mt/300 kHz of 44.23 W/kg), a relatively high saturation magnetization (181.8 emu/g), and permeability (35.9). Furthermore, it was observed that the permeability exhibited stabilization at lower frequencies. According to these findings, the combination of CVD and double layers could lead to the further development of SMCs in a variety of applications.

Performance of Thermally Sprayed Nickel and Tungsten-Based Coatings in Slurry Erosion Conditions: A Review

Abstract The energy needs of a country cannot be fulfilled by a single source of energy, so renewable energy sources like solar, wind, and hydro energy are widely used throughout the world. In countries where sufficient hydro energy resources are available, hydropower plants have been installed to produce electricity. But countries where the rivers originate from hilly areas (like India and Nepal) have to deal with the losses due to the wear caused by the silt particles presented in water. The silt content in water causes the erosion of material in different components of hydropower plants. To avoid these losses thermally sprayed hard surface coatings are widely used as a protective layer. This review focuses on the performance of composite coatings based on nickel and tungsten in slurry erosion conditions. A comprehensive investigation of studies conducted on thermally sprayed nickel- and tungsten-based coatings is discussed in this review paper. The review reveals that high velocity oxy-fuel is widely used by different researchers to develop composite coatings. Materials like Ni–20Cr2O3, Ni–Al2O3, Ni–Cr–Si–B, WC–10Co, WC–10Co–Cr, and Ni–Cr–B–Si–Fe–WC (Co) have been used in different studies to minimize the wear of material in slurry conditions.

Wire and arc additive manufacturing of Fe-based shape memory alloys: Microstructure, mechanical and functional behavior

Shape memory alloys (SMA) are a class of smart materials with inherent shape memory and superelastic characteristics. Unlike other SMAs, iron-based SMAs (Fe-SMA) offer cost-effectiveness, weldability, and robust mechanical strength for the construction industry. Thus, applying these promising materials to advanced manufacturing processes is of considerable industrial and academic relevance. This study aims to present a pioneer application of a Fe–Mn–Si–Cr–Ni–V-C SMA to arc-based directed energy deposition additive manufacturing, namely wire and arc additive manufacturing (WAAM), examining the microstructure evolution and mechanical/functional response. The WAAM-fabricated Fe-SMAs presented negligible porosity and high deposition efficiency. Microstructure characterization encompassing electron microscopy and high energy synchrotron X-ray diffraction revealed that the as-deposited material is primarily composed by γ FCC phase with modest amounts of VC, ε and σ phases. Tensile and cyclic testing highlighted the Fe-SMA's excellent mechanical and functional response. Tensile testing revealed a yield strength and fracture stress of 472 and 821 MPa, respectively, with a fracture strain of 26%. After uniaxial tensile loading to fracture, the γ → ε phase transformation was clearly evidenced with post-mortem synchrotron X-ray diffraction analysis. The cyclic stability during 100 load/unloading cycles was also evaluated, showcasing the potential applicability of the fabricated material for structural applications.

Microstructure and mechanical behavior of a novel Fe–Mn–C–Cr–Si high-manganese steel

Microstructure and mechanical behavior of a novel Fe–Mn–C–Cr–Si high-manganese steel

Influence of thermomechanical treatment on the shape memory effect and pseudoelasticity behavior of conventional and additive manufactured Fe–Mn–Si–Cr–Ni-(V,C) shape memory alloys

This study evaluated the influence of heat treatment and thermomechanical training on the microstructural evolution and mechanical characteristics of conventional and additive-manufactured FeMnSi-based shape memory alloys. The conventional samples were produced by casting and rolling. The additive-manufactured samples were manufactured using the laser powder bed fusion (L-PBF) technique. Both specimens were subjected to the same heat treatment and thermomechanical training. The heat treatment involved solution annealing at 1050 °C for 2 h and aging at 750 °C for 6 h, and the thermomechanical training concluded with a 4% elongation at ambient temperature followed by annealing at 250 °C for 15 min. This training cycle was repeated four times for each sample after heat treatment. The heat treatment improved the pseudoelasticity and shape memory effect of the samples. Although training further enhanced the pseudoelasticity, it also reduced the shape memory effect. Thermomechanical training led to the formation of a large number of stacking faults, which facilitated the inverse phase transformation of martensite (ε) to austenite (γ) during unloading, resulting in improved pseudoelasticity. The heat-treated additive-manufactured samples showed the highest total recovery strain owing to the pseudoelasticity and shape memory effect. This characteristic could be due to the smaller grain size and higher volume fraction of precipitates. The precipitates and grain refinement improved the conditions for partial dislocation motion by increasing the back stresses on the martensite tip.

Formation mechanism of periodic layered structure between Fe–Cr–Si–B cast steel with high B content and molten Al

The periodic layered structures (PLSs) have been confirmed to be formed as the Fe–Cr–B cast steels containing about 3.0 wt% B were dipped into Al melt. However, there was no PLSs formed, in terms of a novel Fe–Cr–Si–B cast steel with B content much higher. The interfacial reaction between borides contained in this novel Fe–Cr–Si–B cast steel with 8.5 wt% B content and Al at 750 °C was studied using hot dip aluminizing, thermal diffusion treatment, and subsequent SEM, TEM, and 3DAP of the obtained specimens. The PLSs were formed in situ after a long period of incubation because of the high chemical stability induced by the overstoichiometric (Cr, Fe)2B. The formation of PLSs proceeded through an intermediate state which involved transformation from disordered particles to ordered Cr–Al–B intermetallic compound. Owing to the formation of the localized melt of FeAl3–Al eutectics, the understoichiometric Cr–Al–B intermetallic compound gradually drifted to agglomerate and grew under the effects of the driving force of the lamellar growth of MAB phase and the thermal flux, along with the drag of the overstoichiometric Cr–Al–B intermetallic compound due to the interlaced structure.

Controlling interfacial composition and improvement in bonding strength of compound casted Al/steel bimetal via Cr interlayer

The fabrication of Al/steel bimetal with a good metallurgical interface is always a great challenge, particularly for the improvement of bonding strength due to the inevitably extensive formation of brittle Al–Fe intermetallic compounds (IMCs) at the interface. Therefore, in this work, the electroplated Cr coating with thickness of 5 μm was firstly used as the interlayer of Al/steel bimetal to suppress Al–Fe IMCs and further improve the interfacial bonding strength. Al/steel bimetal was prepared by compound casting combined with a hot-dip aluminizing process. The results showed that the interface of Al/steel bimetal with Cr interlayer contained an unmolten Cr coating and a reaction layer, in which the latter consisted mainly of Al13Cr4Si4, Al5Cr, Al-rich solid solution and CrSi2 phases. Besides, the morphology of these new Al–Cr–Si and Al–Cr phases was granular rather than the tongue-shaped of Al–Fe phase and the polygonal blocky of Al–Fe–Si phase. Both the microstructure characterization and kinetics calculation results revealed that the application of Cr interlayer could avoid the contact between Fe atoms from steel side and Al atoms from Al alloy side, thereby suppressing the formation of brittle Al–Fe phases at the interface. Moreover, the reaction layer showed a lower nano-hardness than that of without Cr interlayer. With assistance of Cr interlayer, Al/steel bimetal with maximum shear strength of 115.5 MPa was obtained and the interface failed through the Al alloy side. The morphology characteristic and lower nano-hardness of these new phases, the composite structure consisting of Al–Cr–Si and Al–Cr layer together with the Al-rich solid solution layer greatly contributed to the enhancement of the interfacial strength for the Al/steel bimetal.

Microstructural, textural, and residual stress evolution alongside the magnetic properties through isothermal static recrystallization of cold-drawn Fe–Cr–Si–S–C ferritic high-alloy stainless steel and by JMAK modelling

The evolution of microstructures, textures, and residual stresses scale of cold-drawn (CD) 18%Cr ferritic stainless steels (FSS) round bars under isothermal static recrystallization annealing are investigated. As for determination of the new grains' formation, the size, growth, and orientation, as well as the nucleation of grains, alongside revealing the recrystallization fractions are studied by a mixed experimental and theoretical work. The recrystallization kinetics are calculated according to the Johnson-Mehl-Avrami-Kolmogorov theory. Electron backscatter diffraction (EBSD) analyses are applied for the actual specimens of an industrial wire drawing process with 20 and 35% reduction rates. The heat treatment has been implemented at three different set ratio temperatures of 0.65, 0.68, and 0.71, defining as a ratio between the temperatures of annealing and melting point (TRAM). According to the results, the nucleation is occurred at faster incubation time with higher temperature and reduction rate. The grain average size (AGS) increases gradually whereas the temperature increases. This is while the 0.71TRAM-scale annealed samples illustrate finer and more equiaxed recrystallized grains. Following recovery, recrystallized grains, and the grain growth, the overall varied AGS of 27–86 μm in the core region are achieved. Moreover, the JMAK model agrees well with the obtained experimental data. All in all, this 18Cr-FSS material is taken into account for the optimal industrial annealing production as well as the targeted material selection of the market applications. It is observed that the higher recrystallization leads the higher magnetic permeability, lower coercivity, and lower residual stresses compared to the unheated specimens.

Preparation and properties of Fe–Mn–Si–Cr–Ni shape memory alloy

Preparation and properties of Fe–Mn–Si–Cr–Ni shape memory alloy

Abrasive and Erosive Wear of TI6Al4V Alloy with Electrospark Deposited Coatings of Multicomponent Hard Alloys Materials Based of WC and TiB2

In the present work, abrasive and erosive wear of wear-resistant composite coatings with a complex structure and different phase compositions deposited on titanium surfaces was studied. The coatings were obtained by electrospark deposition (ESD) using two types of hard-alloy compositions: WC–TiB2–B4C–Co–Ni–Cr–Si–B and TiB2–TiAl reinforced with dispersed nanoparticles of ZrO2 and NbC. The influence of the ESD process parameters on the roughness, thickness, composition, structure and coefficient of friction of the coated surfaces was investigated, and their role in protecting the titanium surfaces from wear was clarified. Dense coatings with the presence of newly formed wear-resistant phases and crystalline-amorphous structures were obtained, with roughness, thickness and microhardness that can be varied by the ESD modes in the range Ra = 2.5 ÷ 4.5 µm, δ = 8 ÷ 30 µm and HV 8.5 ÷ 14.0 GPa. The new coatings were found to reduce the abrasive and erosive wear of the coated surfaces by up to four times. The influence of the geometric characteristics, composition and structure of coatings on the wear intensity and wear resistance of coatings was studied.

Effect of Ca and Ti contents on characteristics of inclusions in Fe–Si–Cr–Mn–Al–Ti–Ca–O melts

Effect of Ca and Ti contents on characteristics of inclusions in Fe–Si–Cr–Mn–Al–Ti–Ca–O melts

Štruktúra hliníkových zliatin pre vysokotlakové odlievanie

The aim of the presented paper was to carry out a review of the internal structure of alloys used for high pressure die casting (HPDC) and to experimentally perform a structural analysis of AlSi9Cu3(Fe) alloy. Several castings with varying casting parameter – maximum plunger speed vmax were cast. In pre-selected critical locations, a change in porosity was observed with the change of the speed, and the casting samples with vmax = 2 and 3 m∙s-1 showed the lowest porosity. The effect of vmax was also observed on the shape and size of the structural components, where at higher vmax the eutectic Si grew in length and decreased in thickness. EDS analysis determined found intermetallic phases to be α-Al(Fe,Mn,Cr)Si in the shape of a rhombic dodecahedron with sizes as small as 2 µm and Al2Cu occurring in both modifications – oblong grains and globular ternary eutectic.

Hodnotenie vplyvu technologických parametrov na mikroštrutúru vysokotlakových odliatkov

A number of technological parameters influence the mechanical properties of a high pressure die casting. The aim of the presented paper was to perform microstructural analysis of AlSi9Cu3(Fe) alloy casting fabricated with high-pressure die casting (HPDC) technology. Several castings with varying casting parameter – maximum plunger speed vmax were cast. In pre-selected critical spots, the effect of vmax was observed on the shape and size of the structural components, where at lower vmax the eutectic Si shortened in length and thickened. EDS analysis determined found intermetallic phases to be α-Al(Fe,Mn,Cr)Si in the shape of a rhombic dodecahedron with sizes as small as 2 µm and Al2Cu being present in both modifications – oblong grains and globular ternary eutectic. There was no significant change in microhardness of α(Al) phase found, that would be caused by the varying vmax

Phase transformations and microstructure evolutions during depressurization of hydrogenated Fe–Mn–Si–Cr alloy

Hydride formation and associated phase transformations have been extensively studied in pure Fe. However, the understanding of hydrogenation in Fe-based alloy systems is still lacking. Such an investigation is particularly important in the case of austenitic (face-centered cubic) steels given that hydrogen has been reported to alter the austenite phase stability. In the current work, we investigate the phase transformations associated with depressurization of non-hydrogenated and hydrogenated Fe–Mn–Si–Cr alloy (FMS) (Fe-28.84Mn-7.04Cr-6.14Si, in mass %) using in-situ x-ray diffraction technique. Additionally, we study the change in microstructure using electron backscatter diffraction (EBSD) and electron channeling contrast imagining (ECCI).

Властивості покриттів Cr–Si–B–MgC2 в умовах підвищенних температур

Heat resistance, as well as friction and wear of composite coatings Cr–Si–B–MgC2 under conditions of elevated temperatures implemented in friction pairs, were investigated. The selection of the Cr–Si–B–MgC2 composition and its optimal composition for spraying wear-resistant coatings loaded with friction at high temperatures are substantiated. Indicated the main influence on the properties, structure, and stability of heterogeneous coatings is exerted by alloying elements at certain concentrations, as well as technological parameters of coating application. It has been established that silicon and boron contribute to the formation of complex-alloyed high-temperature formations with increased wear resistance. The microhardness of coatings correction is realized due to the silicon percentage content, while the mechanical properties of the material are increased by additional doping with boron and magnesium carbide. The parameters of sputtering of coatings are also important, on which the formation of a heat-resistant layer directly depends. It was experimentally established that the ratio of consumption of acetylene and oxygen ~20/25 l/min ensures the stability of technological parameters of sputtering, homogeneity of the chemical composition and constancy of coating properties. At a load of up to 5.0 MPa, a sliding speed of up to 1.2 m/s and a temperature of up to 700С, the coatings of the Cr–Si–B–MgC2 system show stable structural adaptability, which ensures the minimization of friction and wear parameters. Metallographic analysis and profilography of the samples indicate that there are no visible damages on the friction surfaces, and individual sticking points are localized in thin film surface layers. It was established that the dependence of the microhardness of the surface structures on the temperature is monotonic, but jumps are also observed if polymorphic transformations or transformations of metastable states into more stable and stable ones during heating and cooling occur. Microhardness indicators are uniform because particles of inclusions and impurities are dissolved in the oxide structures, which significantly affect the microhardness, and therefore, the properties of oxides of both simple and complex compositions. Keywords: protective coatings, surface layer, resistance to oxidation, wear resistance, heat resistance