Arc Melting Research Articles

Improving Mechanical Properties of Co-Cr-Fe-Ni High Entropy Alloy via C and Mo Microalloying.

The as-cast [Co40Cr25(FeNi)35-yMoy]100-xCx (x = 0, 0.5, y = 3, 4, 5 at.%) HEAs (high-entropy alloys) were prepared by a vacuum arc melting furnace and were then hot rolled. The effect of C and Mo elements on the microstructure evolution and mechanical properties of HEAs was systematically analyzed. The results showed that when no C atoms were added, the HEAs consisted of FCC + HCP dual-phase structure. In addition, as the Mo content increased, the grain size of the alloy increased from 17 μm to 47 μm. However, only the FCC phase appeared after adding 0.5 at.% carbon in Mo microalloyed HEAs, and the grain size of the Mo4C0.5 HEA decreased significantly. Due to the Mo atom content exceeding the solid solution limit, the carbides of Mo combined with the C element appeared in the Mo5C0.5 HEA. The strength of C and Mo microalloyed HEAs significantly increased compared to HEAs with no C added. However, the Mo4C0.5 HEA exhibited excellent comprehensive mechanical properties, which was superior to a majority of reported HEAs and conventional metal alloys. Its yield strength, tensile strength, and elongation were 757 MPa, 1186 MPa, and 69%, respectively. The strengthening mechanism was a combination of fine grain strengthening, TWIP effect, and solid solution strengthening.

Inhibition of Ti-rich precipitates and improvement of the irradiation resistance in V-4Cr-4Ti by adding La element

Four kinds of V-4Cr-4Ti-xLa (nominal composition x = 0, 0.1, 0.5, 1.0 wt.%) alloys with different La contents were prepared by vacuum arc melting. Three of them (x = 0, 0.1, 1.0 wt.%) were selected for single He+ (2000 appm for peak concentration) irradiation and sequential He+/V2+ (10 dpa for peak damage) irradiation at 550 °C. The results showed that the addition of La element could refine the grains by forming the second phase La2O3 particles. Moreover, the addition of La element reduced the sum of impurity elements concentration in the alloy, which inhibited the formation of Ti-rich precipitates and affected the vacancy concentration, thus affecting the evolution of He bubbles under different irradiation types. In addition, the V-4Cr-4Ti-1.0La alloy had a lower irradiation hardening after sequential He+/V2+ irradiation, which might be related to the removal of impurity elements. This work provided a reference for the performance optimization of vanadium alloy for fusion reactors.

Effect of Cold Rolling on Microstructure and Mechanical Properties of a Cast TiNbZr-Based Composite Reinforced with Borides

The TiNbZr/(Ti, Nb)B metal matrix composite with 2.5 vol.% of borides was produced by vacuum arc melting. The composite was then cold-rolled to thickness strains of 10, 20, 50, or 80%. In the initial condition, the composite had a network-like microstructure consisting of the soft TiNbZr matrix (dendrites) and the rigid (Ti, Nb)B shell (interdendritic space). In comparison with the as-cast condition, cold rolling increased strength by 17–35%, depending on the thickness strain. After the maximum thickness strain of 80%, yield strength and ultimate tensile strength of the composite achieved 865 and 1080 MPa, respectively, while total elongation was found to be 5%. Microstructural analysis revealed that cold rolling to 50% resulted in the formation of crossing shear bands caused by the considerable difference in deformation behavior of the matrix and reinforcements. Cold rolling to 80% led to the formation of a lamellar-like microstructure comprising the interlayers of the (Ti, Nb)B phase between the TiNbZr laths. The maximum strain (80% cold rolling) shortened the (Ti, Nb)B fibers into nearly equiaxed particles, with a length to diameter ratio of ~2.

Enhanced mechanical properties of high pressure solidified CoCrFeNiMo0.3 high entropy alloy via nano-precipitated phase

CoCrFeNiMo0.3 high entropy alloy was prepared by vacuum arc melting. The effects of different solidification pressures on the microstructure and mechanical properties of CoCrFeNiMo0.3 high entropy alloy were investigated. All ambient pressure (0.1 MPa) Mo0.3, 4 GPa Mo0.3 and 7 GPa Mo0.3 alloys exhibit two kinds of structures. The FCC structure is the solid solution matrix, and the precipitated phase enrich in Cr and Mo (σ phase) is distributed in the grain boundary of the matrix phase. With the increase of the test pressure, the size of the precipitated phase gradually decreases and the volume fraction increases obviously, and tends to form nano-scale particles. Meanwhile, the precipitated phase gradually diffused into the matrix due to the increase of the pressure. The results of nanoindentation tests show that the hardness of the alloy increases significantly with the increase of solidification pressure, especially that of 7 GPa Mo0.3 alloy, which is about 2 times that of 0.1 MPa Mo0.3 alloy. The strengthening mechanism of CoCrFeNiMo0.3 high entropy alloy with increased pressure is mainly nano-precipitated strengthening. This present findings not only pave the way for designing the structure and property regulation of high pressure solidified HEAs but also promote the application orientation of various property combinations. It provides the theoretical basis for its application and is expected to be used as structural materials in various fields.

Key technology and application of AB2 hydrogen storage alloy in fuel cell hydrogen supply system

At present, there is limited research on the application of fuel cell power generation system technology using solid hydrogen storage materials, especially in hydrogen-assisted two-wheelers. Considering the disadvantages of low hydrogen storage capacity and poor kinetics of hydrogen storage materials, our primary focus is to achieve smooth hydrogen ab-/desorption over a wide temperature range to meet the requirements of fuel cells and their integrated power generation systems. In this paper, the Ti0.9Zr0.1Mn1.45V0.4Fe0.15 hydrogen storage alloy was successfully prepared by arc melting. The maximum hydrogen storage capacity reaches 1.89 ​wt% at 318 ​K. The alloy has the capability to absorb 90% of hydrogen storage capacity within 50 ​s at 7 ​MPa and release 90% of hydrogen within 220 ​s. Comsol Multiphysics 6.0 software was used to simulate the hydrogen ab-/desorption processes of the tank. The flow rate of cooling water during hydrogen absorption varied in a gradient of (0.02 ​+ ​x) m s−1 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12). Cooling water flow rate is positively correlated with the hydrogen absorption rate but negatively correlated with the cost. When the cooling rate is 0.06 m s−1, both simulation and experimentation have shown that the hydrogen storage tank is capable of steady hydrogen desorption for over 6 h at a flow rate of 2 L min−1. Based on the above conclusions, we have successfully developed a hydrogen-assisted two-wheeler with a range of 80 km and achieved regional demonstration operations in Changzhou and Shaoguan. This paper highlights the achievements of our team in the technological development of fuel cell power generation systems using solid hydrogen storage materials as hydrogen storage carriers and their application in two-wheelers in recent years.

In-situ synthesized multi-component particle reinforced TiAl composite with excellent mechanical properties

In order to overcome the inherent trade-off between strength and ductility of TiAl alloys, the BN nanosheets were added in Ti-48Al-2Cr-2Nb alloy. Ti-48Al-2Cr-2Nb-xBN (x = 0, 0.1, 0.5, 1, 2 wt%) alloys were prepared by vacuum arc melting (VAR), and the microstructures displayed a fully lamellar structure accompanied by simultaneous precipitation of Ti2AlN and TiB2 phases. The reaction of BN nanosheets with the Ti and Al elements resulted in formation of Ti2AlN and TiB2 phases. The lamellar colony size of TiAl composites was refined from 276.7 to 29.4 µm with BN content increasing from 0 to 2 wt%. While the lamellar spacing displayed an initial decrease followed by an increase, which was attributed to the synergistic effect of Ti2AlN and TiB2. Room temperature compression results showed that the compressive strength surged from 1653 to 2272 MPa as BN content rose from 0 to 0.5 wt%, with the highest compression strain of 34.7 % at 0.5 wt% BN. The high temperature compression results showed that the compressive strength increased from 887 to 1399 MPa as the BN content increasing from 0 to 1 wt%. Crack extension took the form of both trans-granular and inter-granular modes. The strengthening effect of TiAl composites was attributed to grain refinement strengthening and secondary phase strengthening via Ti2AlN and TiB2.

Microstructure and corrosion properties of Cr41CoFeNi eutectic high-entropy alloy in sulfuric acid solution

A new eutectic high-entropy alloy (EHEA) of Cr41CoFeNi was prepared by arc melting technique. The microstructure and corrosion resistance of the Cr41CoFeNi EHEA were systematically investigated by EBSD, TEM, EIS and XPS analyses. The results revealed that the Cr41CoFeNi EHEA showed a dual-phase structure consisting of BCC phase and FCC phase, and the morphologies displayed the lamellar eutectic and network-shaped eutectic. Compared with 316 L stainless steel, the Cr41CoFeNi EHEA exhibited a better anti-corrosion property in 0.5 M H2SO4 solution. This was mainly attributed to the formation of a dense and stable Cr-oxide layer on the surface of Cr41CoFeNi EHEA, which retarded further dissolution of the matrix. Moreover, bound water could adsorb metal ions to form a new protective film, which played an important role in improving the corrosion resistance of the Cr41CoFeNi EHEA. However, the elemental segregation and chemical potential difference between phases increased the defects in the passive film and accelerated its pitting corrosion of low potential phase. Moreover, the (Co, Fe, and Ni)-enriched FCC structured phase was preferentially eroded.

Thermoelectric Properties of N-type Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>x</sub>SbBi Materials Doped with La and Mn

Mg<sub>3</sub>Sb<sub>2</sub>-based n-type materials are consisted of earth-abundant elements and possess comparable thermoelectric properties with n-type Bi<sub>2</sub>Te<sub>3</sub> at low temperatures, which make them promising candidates for cooling and power generation applications in terms of cost and performance. Substitution of Sb atom with chalcogen elements (Te, Se S) is a conventional method for n-type doping, but doping cations such as rare-earth elements and transition metals is also widely studied for its unique advantages. In this study, La and Mn were selected for co-doping of Mg3SbBi, and the thermoelectric performances of the doped materials were investigated. Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>x</sub>SbBi (0  <i>x</i>  0.015) polycrystalline samples were made by sintering the fine powders of the mother alloy after arc melting, in which elemental Mn and LaSb compound were included for n-type dual doping. Considering the loss of Mg at elevated temperatures by vaporization, the molar ratio of Mg, Sb, and Bi in the mixture for arc melting was set to 4 : 1 : 1 with excess Mg. Analysis shows that all the samples are n-type, and the electrical conductivity of Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi increased by 62% from the Mn-free Mg<sub>3</sub>La<sub>0.005</sub>SbBi at 298 K. In addition, the lattice thermal conductivity (<i><sub>lat</sub></i>) decreased with increasing Mn content in the measured temperature range of 298-623 K. The minimum value of <i><sub>lat</sub></i> was about 0.60 W m<sup>-1</sup>K<sup>-1</sup> in Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi at 523 K, which is about 19% smaller than that of the Mn-free sample. As a result of these enhancements in thermoelectric performance, the maximum figure of merit (<i>zT<sub>max</sub></i>) of 1.12 was obtained in Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.01</sub>SbBi and Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi at 573 K, and the <i>zT</i> at 298 K increased by 73% to 0.35 in Mg<sub>3</sub>La<sub>0.005</sub>Mn<sub>0.015</sub>SbBi compared to Mn-free Mg<sub>3</sub>La<sub>0.005</sub>SbBi, which is beneficial to room-temperature applications.

Effect of high and low Nb content in multicomponent Nb–Ni–Ti–Zr–Co alloy on its structure, hardness and hydrogen permeability

In the present work, novel multicomponent Nb–Ni–Ti–Zr–Co alloys were synthesized by arc melting. Two alloys with low and high Nb contents and an equimolar high-entropy alloy (HEA) were produced and compared. The influence of the elemental composition on their microstructure, phase composition, lattice constants, hardness and hydrogen permeability was investigated. The synthesized Nb–Ni–Ti–Zr–Co alloys are characterized by near-equimolar BCC-(Nb, Ni, Ti, Zr, Co) and Nb-rich BCC-Nb(Ni, Ti, Zr, Co) phases. The equimolar Nb20Ni20Ti20Zr20Co20 alloy had the highest concentration of BCC-(Nb, Ni, Ti, Zr, Co) phase (84 vol %), while the Nb74Ni6Ti9Zr5Co6 alloy had the highest concentration of Nb-rich BCC phase (95 vol %). First-principles study of the lattice parameters for the Nb–Ni–Ti–Zr–Co alloy revealed that the lattice parameter of the BCC phase decreases with Ni and Co addition and increases with Nb, Zr addition. Titanium does not significantly affect the lattice constant of BCC phase for compositions close to equimolar (10–30 at. %). The microhardness of the alloys decreases with increasing Nb content, which is mainly due to the proportion of softer Nb-rich BCC phase and microstructural changes. The synthesized Nb15Ni20Ti15Zr30Co20 and Nb20Ni20Ti20Zr20Co20 alloys demonstrate high hydrogen permeability at 400 °C that makes them promising for hydrogen purification membranes. It is shown high-entropy Nb20Ni20Ti20Zr20Co20 alloy exhibit highest resistance to hydrogen embrittlement, while high Nb content alloys are strongly susceptible to embrittlement.

Grain size effect on the phase growth in CoNi/Sn sandwich diffusion couples

Grain size effect during interdiffusion is investigated by designing a sandwich couple of CG-CoNi/Sn/UFG-CoNi; (CG coarse grained (>200 µm), UFG: ultrafine grained (∼240 nm)). Phase growth is examined at temperatures 175 & 200 ℃ for various times. CG CoNi and UFG CoNi have been fabricated by Vacuum arc melting and spark plasma sintering of mechanically alloyed CoNi powders, respectively. At 175 ℃, (CoNi)Sn3 intermetallic phase is detected at CG CoNi/Sn interface and (CoNi)Sn2 phase at UFG CoNi/Sn interface. At 200℃, formation of (CoNi)Sn2 and (CoNi)Sn3 phases is observed at CG interface and only (CoNi)Sn2 at the UFG interface. Phase compositions have been confirmed by electron probe microanalysis while the corresponding crystal structure with micro-x-ray diffraction. Phase selection in the interdiffusion zone (IDZ) of CG CoNi/Sn is governed primarily by kinetic factors, while thermodynamic driving forces, assessed using CALPHAD approach, also contribute to phase formation in the IDZ of UFG CoNi/Sn. Time-dependent measurements at 175 & 200℃ for UFG CoNi/Sn reveal an accelerated growth of phases when compared with the CG CoNi/Sn. The enhanced kinetics and preferential formation of the (CoNi)Sn2 phase at the UFG CoNi/Sn interface can be ascribed to the higher proportion of grain boundaries (GBs), leads to an increase in overall diffusion flux. The sandwich diffusion couple approach ensured that all the comparisons between CG and UFG interfaces are conducted under similar conditions yielding dependable correlations. The formation of intermetallic phases and role of GBs are studied at a finer detail using correlative microscopy approach.

Effect of Ti content on the microstructure and mechanical properties of TixZrNbMoV lightweight refractory high-entropy alloys

In this study, we prepared TixZrNbMoV (x = 1, 1.5, and 2) refractory high-entropy alloys (RHEAs) with varying amounts of Ti by vacuum arc melting. The microstructures of RHEAs are investigated by neutron diffraction, electron backscatter diffraction and transmission electron microscope. The results showed that the TixZrNbMoV alloys mainly comprise body centered cubic phases and hexagonal close packed phases and the average grain size of alloys decreases as the Ti element content increases. Room-temperature compressive tests showed that increasing the Ti content of the alloys improved their ductility, although their strength decreased. Compared with some previously reported RHEAs, the TixZrNbMoV RHEAs prepared in this study possessed better comprehensive mechanical properties, with the specific yield strength of the TiZrNbMoV alloy being as high as 312 kPa·m3/kg. Finally, the deformation behavior of TixZrNbMoV RHEAs was studied by nanoindentation.

Crystal structures, bonding and electronic structures of α- and β-Ir2B3-x compounds.

The binary boron-rich compounds α-Ir2B3-x and β-Ir2B3-x, formerly denoted as α- and β-Ir4B5, were synthesized via both arc melting followed by annealing at 800 °C (900 °C) and high-temperature thermal treatment of mixtures of the elements. X-ray structure analysis of α-Ir2B3-x was performed on a single crystal (space group C2/m, a = 10.5515(11) Å, b = 2.8842(3) Å, c = 6.0965(7) Å, β = 91.121(9)°). The orthorhombic structure of β-Ir2B3-x was confirmed by X-ray powder diffraction (space group Pnma; a = 10.7519(3) Å, b = 2.83193(7) Å, c = 6.0293(1) Å). The α-Ir2B3-x structure exhibits ordered arrangements of iridium atoms. The structure is composed of corrugated layers of boron hexagons (interlinked via external B-B bonds) alternating with two corrugated layers of iridium along the c-direction; an additional boron atom (Oc. 0.46(7)) is located between iridium layers in Ir6 trigonal prisms. The boron partial structure in β-Ir2B3-x is composed of ribbons made up of slightly corrugated quadrilateral units running along the b-direction in the channels formed by 8 iridium atoms each. DFT calculations revealed a number of bands crossing the Fermi level, predicting metallic behaviors of the two compounds. β-Ir2B3-x is characterized by a pseudogap around the Fermi level and a smaller eDOS of 0.6405 states per eV per f.u. at the Fermi level, as compared to the α-Ir2B3-x value of 1.405 states per eV per f.u. The calculated electron localization functions revealed strong covalent bonds between boron atoms in the core part of the B6 hexagons, metallic B-B bonds within the quadrilateral boron partial structure and mixed covalent and metallic interactions between iridium and boron atoms. Structural relationships of α-Ir2B3-x and β-Ir2B3-x with ReB2-type structures as well as the common structural features with layered binary borides with CrB-type related structures have been discussed.

Cage compound Sc5Pt24B12: a Pt-stuffed variant of filled skutterudite structure. Electronic and structural properties.

The title compound was obtained from elements via arc melting and its crystal structure was determined from single-crystal X-ray diffraction data (space group Im3̄, a = 10.2042(6) Å). The refinement indicated the occupancy of icosahedral 2a and cubooctahedral 8c sites solely by Sc atoms which leads to the composition Sc5Pt24B12 in contrast to the previously reported ternary stannides of Gd3Ni8Sn16 type (RE5-xM12Sn24(+x) compounds). The compound is the first representative of borides crystallizing with a site exchange variant of this stannide structure type. The structural relationships of the boride structure and filled skutterudite LaFe4P12vs. the Remeika phase of Yb3Rh4Sn13-type are discussed. Analysis of chemical bonding classifies Sc5Pt24B12 as a cage compound exhibiting the ionic interaction of cationic scandium species in the cages of anionic framework, formed by covalently bonded B and Pt atoms. Electronic structure calculations show that the electronic states of atoms centered around the cubooctahedral 8c site, i.e. Sc2 3d-, Pt2 5d- and B 2p-states dominate the density of states (DOS) at the Fermi level EF. Strong effect of spin-orbit coupling on the band structure at the gamma point has been found from density functional theory calculations. Sc5Pt24B12 exhibits superconductivity with a transition temperature of TC = 2.45 K.

IRRADIATION RESISTANCE ESTIMATION METHOD BY CRYSTAL LATTICE DISTORTIONS FAST CALCULATION FOR NI, CoCrFeNi AND CoCrFeMnNi FCC-ALLOYS

Bulk materials, pure Ni, CoCrFeNi, and CoCrFeMnNi, were deposited by arc melting with subsequent cold-rolling till 85% thickness reduction and annealing at 1150°C. They were irradiated by 40 keV He<sup>2+</sup> and 280 keV Kr<sup>14+</sup> low-energy ions to the fluences of 2 × 10<sup>17</sup> cm<sup>-2</sup> and 5 × 10<sup>15</sup> cm<sup>-2</sup>, respectively. Estimation of the distortions in the alloys was by calculating the normalized distortion parameter, which tends to increase with the increment of alloy complexity and atomic radii mismatch. x-ray diffraction (XRD) and scanning electron microscopy (SEM) analysis showed a common superiority of CoCrFeNi over pure Ni in radiation resistance (less lattice deformation, no blistering). In both Ni and CoCrFeNi after ion irradiation, signs of tension microstress remained positive and the magnitudes showed similar responses, CoCrFeMnNi microstresses became compressive-negative; the dislocation density also showed decrease after Kr-irradiation compared with non-irradiation. Mn addition to the ternary alloy changed its behavior radically. Normalized distortion parameter calculation can be performed for quick simple comparative theoretical analysis comparison of the radiation resistance, but will not give full information about the difference between stoichiometries investigated.

Исследование физико-механических свойств горячепрессованных композиционных керамик системы Hf–Ti–Cr–Fe–V–N

The concept of synthesizing multicomponent (five or more components) systems in equiatomic or near-equiatomic percentages has opened a new class of materials, including high-entropy alloys (HEAs) and high-entropy ceramics (HEC). The composition of each element varies from 5 to 35 at.%. It is generally accepted that the exceptional performance of high-entropy materials is achieved through four “basic effects”: the highentropy effect, the lattice distortion effect, the slow diffusion effect, and the “cocktail” effect. The properties of multicomponent systems are determined not only by the constituent elements, but also by the formation of phases. Thus, depending on the composition and methods of preparation and processing of the alloy, the ordered and disordered phases of the solid solution are formed in the HEAs. Both the atoms of individual elements and the resulting phases contribute to the properties of HEAs. They possess valuable properties such as high corrosion resistance, wear resistance, hardness, and other particular mechanical properties. This class of materials is under active scientific study, and the methods for their production, such as vacuum arc melting, selective laser melting, magnetron sputtering, are being developed. One of the promising and highly efficient methods for producing HEAs and HECs is self-propagating high-temperature synthesis (SHS). The main advantages of this method are high productivity, low energy consumption, environmental safety, regulation of the structure and properties of the final products, and synthesis mode control due to the possibility of selecting various combustion temperature and pressure values. This study examines the effect of the temperature regime of the hot-pressing process on the structure and properties of ceramic samples of the Hf-Ti-Cr-Fe-V-N system. HEC materials are obtained as a result of high-temperature exothermic reactions with preliminary mechanical activation of the powder mixture in a planetary mill. The preparation of compact ceramic samples is carried out using the hot-pressing method in the temperature range of 1300–1450 °C. The X-ray diffraction analysis of the resulting samples allows one to determine the dependence of the structure, density, and hardness on the pressing temperature. The maximum hardness (1858±50 HV) is obtained at a pressing temperature of 1450 °C.

Изучение условий получения прекурсоров из жаропрочного сплава на основе NiAl, предназначенных для 3D технологий

This article is the second in a series of articles devoted to studying the possibilities of preparing high-quality powder materials from heat-resistant light alloys based on refractory monoaluminides of nickel (β-NiAl), ruthenium (β-RuAl) and the FeCrAl system (fechrals) for the production of compact samples/products of complex shapes using additive technologies with minimal final machining. Additive technologies are based on the use of spherical precursor micropowders with a regulated granulometric composition, good fluidity and an oxide-free surface. In the first article, the possibilities of obtaining precursors from RuAl-based alloys by plasma spheroidization of powders obtained by crushing mixtures from scrap samples of RuAl-based alloys with various additives were considered. This article examines the possibility of obtaining precursors from NiAl-based alloys by plasma spheroidization of powders obtained by crushing mixtures from scrap samples of NiAl-based alloys with various additives. It has been shown that grinding and subsequent grinding of scrap powders in an attritor makes it possible to obtain precursors using the “attrition + plasma spheroidization” scheme with characteristics that make them suitable for additive manufacturing (perfectly round shape, surface almost free of oxides, phase composition – solid solution grains on based on NiAl with thin layers of Ni3Al of nano-sized thickness). The non-uniform distribution of alloying elements in NiAl grains is caused by the short duration (5 hours) of grinding the initial powders of scrap ingots of various compositions obtained using foundry technology. This can be corrected by increasing the grinding duration to 15 hours, which will require the use of the “attrition + granulation + plasma spheroidization” scheme, since the proportion of dispersed powders that must be included in circulation will increase. It has been shown that preliminary reaction alloying in the liquid phase (vacuum arc melting), including the use of recycled materials (scrap alloy samples) as starting materials, allows one to vary the alloy compositions over a wide range, using small volumes of material, and does not require specialized equipment.

Study on the silicide phase control and room temperature mechanical properties of Nb-Si-Ti based alloys via B and Mg-microalloying

The Nb-16Si-20Ti-4Cr-1.5Al-4Hf-4Zr-1Ta-xB (x=0, 2, 4)-yMg (y=0, 0.2, 0.4) alloys were prepared by non-consumable arc melting. The effects of B and Mg addition on the microstructure and room temperature fracture toughness have been investigated. The results reveal that when the content of B element reached 4 at.%, the intermediate metastable phase Nb3Si was precipitated in Nb-Si based alloys. The cooperation of B and Mg synergistically enhances the room temperature fracture toughness of Nb-Si based alloy. B and Mg element causes the eutectic point of Nb-Si based alloy to shift to the right. The 2B-0.4Mg alloy shows the best fracture toughness, and its KQ value is 14.41 MPa·m 1/2, which increased by 34% compared to the matrix alloy. Crack deflection and secondary cracking increase the room-temperature fracture toughness of Nb-Si-based alloys.

Study on microstructure and corrosion resistance of CoCrFeNiTi0.2Mox high entropy alloy

Vacuum arc melting was employed by produting the high entropy alloys CoCrFeNiTi0.2Mox (x=0, 0.1, 0.3). We investigated the influence of Mo on the phase, microstructure, and corrosion resistance of CoCrFeNiTi0.2Mox (x=0, 0.1, 0.3). The introduction of Mo led the high entropy alloy to shift to a double-phase structure, with a rise in the volume percentage of σ phase. The corrosion resistance of high-entropy alloys decreases first and subsequently increases with increasing Mo content in 3.5 weight percent NaCl solution.

Effect of Al content on microstructure and mechanical properties of Alx(Nb3TaTi3Zr)100-x refractory high-entropy alloys

In this study, seven refractory high-entropy alloys of Al x (Nb3TaTi3Zr)100-x (x = 0, 5, 10, 15, 20, 25, 30) were synthesized by vacuum arc melting and characterized by various techniques, including XRD, SEM, EDS, compression tests at both 1200 °C and room temperature, as well as hardness tests. The analysis revealed that the alloys exhibit a single BCC structure when the Al content is between 0 and 15%, while the B2 phase appears at 20% and a mixed structure of BCC + B2 + σ phase at 30%. As the Al content increases, the hardness, stiffness, and room temperature yield strength of the alloy increases, while the plasticity decreases. Notably, the alloy with 25% Al content displayed the highest yield strength of 1400 MPa and Young’s modulus of 75.94 GPa at room temperature. Moreover, the hardness of the seven alloys increased from 247 HV to 490 HV with Al content from 0 to 30%. Furthermore, the alloy containing 30% Al exhibited a notable elevated-temperature yield strength of 143 MPa at 1200 °C.

К ВОПРОСУ ПОЛУЧЕНИЯ ФОРСТЕРИТСОДЕРЖАЩЕГО ЛИТЬЯ ИЗ ХВОСТОВ БОРОИЗВЛЕЧЕНИЯ И СТЕКЛОБОЯ ЭЛЕКТРОДУГОВЫМ СПОСОБОМ

The article investigates the characteristics of man-made waste in form of boron tailings (China) and cullet to establish the possibility of their joint use as a raw material composition in production stone forsteritecontaining casting by electric arc method. It studies of granulometric elemental, chemical and mineralogical composition of raw materials, using dispersion-gravimetric, Ultraviolet-Visible spectroscopic, microscopic, energy dispersion, as well as X-ray phase analyses. The study established true density, specific surface area, granulometric, elemental, chemical and mineralogical (XFA) compositions of raw materials and calculated modulus of acidity of the melt, which amounted to Mk = 2.04. It allows casting from two-component charge (tailings cullet) represented by percentage ratio of 70:30. In process of electric arc melting of the raw material composition, forsterite-containing stone casting was obtained, which is solidified melt of a given geometric shape made of forsterite (Mg2SiO4) in a glass phase. Thus, the conducted complex of studies testifies to the suitability of man-made waste represented by boron recovery tailings and cullet for obtaining a melt from them by electric arc method, with further production of forsterite-containing stone casting.