Alloying Elements Research Articles

Novel as-cast HfNbTaTiAl refractory multi-principal element alloys with superior strength-ductility combination at room temperature

Refractory multi-principal element alloys (RMPEAs) have attracted much attention due to their excellent high temperature mechanical properties. However, extremely low room temperature tensile ductility hinders further engineering applications. In this work, we designed novel HfNbTaTiAl RMPEAs and studied the structure-properties relation and deformation mechanism at room temperature. Results show that the yield strength of the as-cast alloy is up to 1029 MPa and the tensile ductility at room temperature is between 17.8 % and 22.8 %. The high yield strength is mainly attributed to the solid solution strengthening effect. Cross-slip provides ultimate tensile strength while maintaining the tensile ductility. Kink bands have been observed in Al9.0Hf30.3Nb15.0Ta15.3Ti30.3 alloy, which is the main reason for its excellent tensile ductility at room temperature. Overall, this study elucidated the deformation mechanism of Al9.0Hf30.3NbxTa30.3-xTi30.3 (x = 0, 10, 15) as-cast RMPEAs at room temperature, and provides meaningful insights for developing RMPEAs with excellent strength-ductility combinations.

Sample Preparation and Determination of Trace Elements in High-Entropy Alloys by Total Reflection X-Ray Fluorescence (TXRF)

High-entropy alloys (HEAs) have attracted significant attention in recent years owing to their exceptional material properties; however, trace impurities in these alloys can significantly affect their strength, toughness, and radiation resistance. This study employs total reflection X-ray fluorescence (TXRF) to determine the trace impurities in three common HEA powders prepared via suspension techniques. High-Z (Ca and Mn) and low-Z (Mg and Al) elements were quantified using the internal standard and calibration curve methods, respectively. The levels of high-Z elements are consistent with those determined using inductively coupled plasma – optical emission spectrometry (ICP-OES). Although the physical mechanisms exerted various effects on low-Z elements, qualitative and semi-quantitative analyses remained feasible, demonstrating the effectiveness of TXRF for impurities in HEAs. Additionally, the combination of suspension sample preparation and TXRF affords a nondestructive, rapid, and cost-effective methodology that requires minimal sample quantities. Consequently, TXRF is well suited for the rapid determination of impurities in HEAs.

Optimization of density and cost in the prediction of solid solution formation of multicomponent metal alloys

Multicomponent alloys or high-entropy alloys (HEAs) are the most recent breakthroughs in the metal alloying area. Their unique possibilities in mechanical properties and their vast universe of combinations turn them into a highly active research area. The properties of HEAs depend on the solid solution formation, which can be predicted by calculation. Therefore, we present a method to simulate discrete compositions of the alloy elements in the software MD 2.0, created to calculate four parameters and provide their associated statuses to predict the solid solution formation in multicomponent alloys. The HEA CoCrCuFeNi was subjected to calculation in MD 2.0, and, if all the imposed restrictions and criteria are concomitantly attended: (a) the minimum density (8.426 g/cm3) solid solution formation refers to 33.122% Co, 6.491% Cr, 9.984% Cu, 34.909% Fe, and 15.494% Ni composition; (b) the minimum specific cost (US$/kg 7.560) under solid solution formation addresses 5.059% Co, 5.174% Cr, 31.553% Cu, 33.975% Fe, and 24.239% Ni composition. Given this result, it is possible to select the optimized composition of the alloy according to the design objective.

Data‐Driven Approach Using a Hybrid Model for Predicting Oxygen Consumption in Argon Oxygen Decarburization Converter

Accurately controlling oxygen supply in argon oxygen decarburization (AOD) process is invariably desired for efficient decarburization and reducing alloying elements consumption. Herein, a data‐driven approach using a hybrid model integrating oxygen balance mechanism model and a two‐layer Stacking ensemble learning model is successfully established for predicting oxygen consumption in AOD converter. In this hybrid model, the oxygen balance mechanism model is used to calculate the oxygen consumption based on industrial data. Then the model calculation error is compensated using an optimized two‐layer Stacking model that is identified as (random forest (RF) + XGBoost + ridge regression)‐RF model by evaluating different hybrid model frameworks and Bayesian optimization. The results show that, in comparison to conventional prediction model based on oxygen balance mechanism, the present hybrid model greatly improves the control accuracy of oxygen consumption in AOD industrial production. The hit rate and mean absolute error of the present hybrid model for predicting oxygen consumption are 84.8% and 330 Nm3, respectively, within absolute oxygen consumption prediction error ±600 Nm3 (relative error of 3.8%). This data‐driven approach using the present hybrid model provides one pathway to efficient oxygen consumption control in AOD process.

A review of the preparation and prospects of amorphous alloys by mechanical alloying

The preparation of amorphous alloys typically involves rapid solidification from a molten state. Since 1980, when Yermo and Koch first achieved the amorphization of alloys by mechanical alloying (MA), researchers worldwide have developed a strong interest in this technique, which allows for the amorphization of alloy components in a non-equilibrium state at room temperature without the need for a liquid phase. MA has been widely applied in the fabrication of both equilibrium and non-equilibrium materials over the past few decades, and it remains a crucial technique for the production of amorphous alloys. This review selectively summarizes research on MA-produced amorphous alloys reported over the past two decades. It explores key issues of MA amorphization from the perspectives of both the mechanism of amorphization and the design of amorphous compositions through MA. The first section primarily elucidates commonly used methods for designing amorphous compositions at present, while the second section expounds on the transformation mechanism of MA amorphization. The third section summarizes the influence of alloy element additions on its properties, and the fourth section mainly illustrates the contribution of computational advancements to the exploration of amorphous mechanisms and the design of amorphous compositions. Finally, prospects for the development trend of preparing amorphous alloys through MA are discussed.

Microstructures and properties of a novel cemented carbide prepared using a Co–Ni–Cu multiprincipal element alloy as the binder

A Co–Ni–Cu multiprincipal element alloy (MPEA) powder was successfully synthesized through coprecipitation. Results of energy dispersive spectroscopy (EDS) and X-ray fluorescence spectroscopy (XRF) revealed nearly equal atomic ratios for Co, Ni, and Cu in the Co–Ni–Cu MPEA powder. Moreover, X-ray diffraction (XRD) confirmed a single-phase face-centered cubic (fcc) structure in the Co–Ni–Cu MPEA powder. To explore the differences in microstructure and mechanical properties, we compared a novel WC–2Co–2Ni–2Cu cemented carbide, utilizing the Co–Ni–Cu MPEA as a binder, with conventional WC–6Co and WC–3Co–3Ni cemented carbides prepared via liquid phase sintering. This comparison was conducted using scanning electron microscopy, XRD, and mechanical properties testing. Observations revealed that the surfaces of WC grains in WC–2Co–2Ni–2Cu and WC–6Co appeared smooth and flat, while those in WC–3Co–3Ni exhibited roughness with numerous terraces. In addition, the average grain size was 0.96, 1.14, and 1.22 μm in WC–2Co–2Ni–2Cu, WC–6Co, and WC–3Co–3Ni, respectively. Notably, the Co–Ni–Cu MPEA inhibited WC grain growth. WC–2Co–2Ni–2Cu (1388 HV30) exhibited hardness similar to that of WC–6Co (1406 HV30) but the highest fracture toughness (9.04 MPa∙m1/2), while WC–3Co–3Ni (1332 HV30) presented the lowest hardness. Bending strength values were recorded at 2406 MPa for WC–2Co–2Ni–2Cu, 2816 MPa for WC–6Co, and 2645 MPa for WC–3Co–3Ni, with WC–6Co exhibiting the highest bending strength. Considering their microstructures, physical properties, and mechanical properties comprehensively, the novel cemented carbides exhibited only slightly reduced bending strength compared to conventional counterparts. Thus, the Co–Ni–Cu MPEA binder demonstrates promising potential as a replacement for the conventional Co metal binder.

Role of grain refinement and phase metastability on deformation behavior of additively manufactured FeMnCoCr multiprincipal element alloys

This study investigates the deformation mechanisms of three additively manufactured FeMnCoCr multiprincipal element alloys (MPEAs), each with distinct grain sizes achieved through metastability engineering and unique deformation mechanisms. The Fe35Mn45Co10Cr10 composition serves as a baseline for comparison, exhibiting intermediate mechanical properties and deformation primarily through slip. In contrast, the Fe40Mn40Co10Cr10 composition relies on twinning mechanisms to accommodate strain and enhance work hardening. However, the Fe30Mn50Co10Cr10 composition demonstrates that grain refinement, facilitated by a body-centered cubic to face-centered cubic transformation during solidification, is more effective in improving the yield strength of the material. This comparative analysis underscores the effectiveness of grain refinement and twinning in optimizing the mechanical properties of additively manufactured MPEAs.

Thermal conductivity of binary Al alloys with different alloying elements

This work investigates the physical properties of several binary Al-Si/Ni/Fe/Cu/Mg alloys with varying alloying element contents and microstructures. The findings indicate that as the content of alloying elements increases, the number of secondary phases in binary Al alloys rises, and these phases become coarser. In hypereutectic compositions, primary phases in Al-Ni and Al-Fe alloys take on a needle-like morphology with high aspect ratios, forming a dendritic network. Regarding properties, in the hypoeutectic region, both thermal conductivity and electrical conductivity of binary alloys initially decrease sharply, followed by a more gradual decline with the addition of alloying elements. This trend occurs because thermal conductivity is mainly influenced by supersaturated solid solutions. In hypereutectic Al-Ni and Al-Fe alloys, the presence of large, needle-like primary phases significantly hinder the heat transfer, resulting in a more apparent reduction in both thermal conductivity and electrical conductivity. Among the five binary alloys, Al-Ni and Al-Fe alloys, which have lower solute concentrations of alloying elements in the Al matrix, exhibit the highest thermal and electrical conductivity. Furthermore, with increasing alloying element contents, the phonon thermal conductivity of Al-Si alloy increases more markedly compared to other alloys. The study will offer a fundamental understanding for the development of advanced alloy.

Effect of alloying elements on coexisting phases and microstructure of M174 heat-resistant aluminum alloy

Abstract This article mainly focuses on high-power density diesel engine piston alloys, with the main component system being M174 heat-resistant aluminum alloy. On this basis, the main heat-resistant alloying elements Cu, Ni, and Fe were optimized and designed. This article is based on Thermo-Calc thermodynamic software, and comprehensively calculates and analyzes the multi-component alloy equilibrium phase diagram and Scheil non-equilibrium solidification of Al-(4-6)Cu-(1.5-3)Ni-(0.7-1.1Fe)-12.5Si-0.85Mg (mt.%) heat-resistant aluminum alloy system. Through the orthogonal experimental method of alloy composition, the phase distribution and microstructure composition of different alloy compositions are obtained. Research has found that Fe-rich phases such as Al5FeSi and Al9FeNi, as well as Ni-rich phases such as A13CuNi, A17Cu4Ni, and Al3Ni, are the main heat-resistant phases of the alloy in the temperature range of 350°C-420°C, providing important support for the high-temperature mechanical properties and creep damage resistance of piston aluminum alloy. At the same time, this article further studies the solidification history and microstructure precipitation of alloys. Fe-rich heat-resistant phases such as Al5FeSi and Al9FeNi have a higher solidification sequence. As primary and secondary phases, it is easy to generate coarse solidified structures. The organizational content is sensitive to the alloy composition. A13CuNi and A17Cu4Ni mainly precipitate in a multi-component eutectic structure, with layered and petal-shaped morphologies. The research results of this article have important theoretical significance and application value for the optimization design of high-power density piston aluminum alloy composition and the coordinated control of multi-phase structure.

Refinement of microstructure and improvement of mechanical properties of directed energy deposited titanium alloys by adding Fe

Elemental alloying is a validated strategy for enhancing the mechanical properties of directed energy deposited titanium alloys. However, it is still a challenge to obtain titanium alloys with both high strength and high ductility. In this work, to balance strength and ductility, the alloying element Fe was in-situ added to the TC4 melt pool during the directed energy deposited process and the effects of its content on the microstructure and mechanical performance of the TC4 alloy deposits were investigated. The results showed that the Fe additive ranging from 0.5 to 2.0wt.% were completely solid-solved in the retained β phase of TC4 alloys. Moreover, the primary β columnar grains were transformed into fully equiaxed grains. Meanwhile, the presence of Fe refined the α-laths, increased the proportion of the retained β phase, and the continuous grain boundary α (GB-α) became discontinuous. The tensile strength of the deposited alloys was continually improved with increasing Fe content, while the elongation had a peak value. When the Fe content was 1.0wt.%, the deposited alloy exhibited the best comprehensive performance, with an ultimate tensile strength of 1071MPa and an elongation of 9.3%. The enhancement of tensile strength was attributed to the solid solution strengthening and the refinement of α-laths and primary β grains. The increased proportion of retained β phase and the formation of discontinuous GB-α were beneficial for the alloy ductility. However, increased α/β interfaces inhibited dislocation movements, resulting in a decrease in ductility. The development of this alloy is important for aerospace and other fields that require high strength, high ductility and lightweight.

Influence of doping elements X (X= Hf, Zr, Y, Re, Pd, Ir) on the structural stability and tension property of α-Al2O3/PtAl2-S interfaces

Pt-Al coatings are promising materials for protective materials for turbine blades in new-generation aero-engines. Therefore, it is worth noting that the interface stability and tension property between Pt-Al and the oxide layer, prolonging coating service time. However, systematic studies of doping elements effects on interface adhesion of α-Al2O3/PtAl2 with and without impurity S are still lacking. In this paper, the site preference of the six elements (Hf, Zr, Y, Re, Pd, and Ir) in the PtAl2 alloy, effects of doping elements on the interface adhesion and tension properties of the α-Al2O3/PtAl2-S interface are further explored, performing the first-principles calculation method. Considering comprehensively, Y doping has an excellent enhancement effect on the static interface adhesion and dynamic tensile strength, regardless of whether impurity element S exists in the α-Al2O3/PtAl2 interface. This study will provide necessary theoretical guidance for the composition design of Pt-Al coating and the research of new metal protective coating materials.

Dependence of defect susceptibility on microporosity variation in Mg-xLi-3Al-1Zn casting alloys

This study quantitatively describes relative contribution of microstructural characteristics and microporosity variation to the tensile properties of Mg-xLi-3Al-1Zn alloys from the perspective of defect susceptibility. The alloys were prepared by melting pure lithium, AZ31 alloy, and additional elements in two crucibles under an Ar atmosphere, and then mixing them to add Li in the range of 2–12 wt%. As the Li content increases, the Li-rich β phase forms along the grain boundaries of the Mg-rich α phase. At approximately 12 wt% Li, the entire matrix transitions to the Li-rich β phase, and the volume density decreases from 1.762 g/cm³ (AZ31 alloy) to a minimum of 1.435 g/cm³. Additionally, the yield strength continuously increased from 67 MPa (AZ31 alloy) to approximately 120 MPa with increasing Li content, while the tensile strength increased from 127 MPa (AZ31 alloy) to a maximum of 144 MPa at 6 wt% Li, and the elongation increased to 19 % at 10 wt% Li before decreasing at higher additions. The fracture mode during tensile deformation clearly depends on the fraction of α phase and β phase, varying with Li addition. However, all tensile properties, including yield strength, are fundamentally influenced by the fractographic porosity based on the fracture surface. The defect susceptibility coefficients on microporosity variation for tensile strength and elongation, and the maximum values achievable under defect-free conditions, are highest at 6 wt% Li and 10 wt% Li, respectively. Furthermore, the relative contributions of microporosity and microstructural components to the defect susceptibility of tensile properties can be described: tensile strength increases in the order of the mixed α+β phase, β phase, and microporosity, while the contribution of the β phase to elongation is relatively lower compared to the mixed α+β phase and microporosity.

The tensile behaviour of non-equi-atomic configurations of multiple elemental alloys: molecular dynamics based study

This article aims to study the effect of lattice distortion on the mechanical behavior of equi-atomic and non-equi-atomic configurations of high entropy alloys. Molecular dynamics-based simulations were performed with an embedded atomic method force field. Random alloy configuration of multiple elemental alloys (MEAs) was developed along with average atom (A-atom) configurations by modifying the embedded atom potential. The non-equi-atomic configuration of MEAs was generated by varying the contribution of Cr, Co, Fe, Cu, Ni, and Cr in pairs and all together. It was predicted from the simulations that the deformation governing mechanism, as well as the tensile strength of high entropy alloys, can be tailored by switching from equi-atomic to non-equi-atomic configurations of high entropy alloys. Increasing the composition of Cr, Fe, and Ni helps enhance the tensile strength and Young's modulus of the high entropy alloy, which is even higher than equi-atomic configurations. Partial Shockley dislocations, in conjunction with the phase change from fcc to hcp, primarily govern the deformation in the non-equi-atomic composition of MEAs. The tensile behaviour of MEAs was directly associated with the distortion present in the lattice, which was quantified with the help of the radial distribution function. It was revealed from the simulations that lattice distortion present in the random alloy configuration helps in improving the ductility of material by early onset of dislocation emission. A higher value of lattice distortion also increases the gap between the peak stress values in A-atom and random alloy configurations. The article will help develop high-entropy alloys for broader space, nuclear, defense, and energy generation applications.

Enhancing cryogenic mechanical properties of a cost-effective FeCrNi dual-phase multi-principal element alloy by fully constrained heterostructure and deformation twinning

This paper reports a cost-effective Fe40Cr40Ni20 (at%) dual-phase multi-principal element alloy with excellent cryogenic mechanical properties. The high strength primarily originated from an ideal fully constrained heterostructure, which enhanced back stress strengthening and dislocation strengthening. Twinning enhanced the deformability and the strength of the alloy simultaneously.

Characteristic deformation microstructure evolution and deformation mechanisms in face-centered cubic high/medium entropy alloys

Face-centered cubic (FCC) high/medium entropy alloys (HEAs/MEAs), novel multi-principal element alloys, are known to exhibit exceptional mechanical properties at room temperature; however, the origin is still elusive. Here, we report the deformation microstructure evolutions in a tensile-deformed Co20Cr40Ni40 representative MEA and Co60Ni40 alloy, a conventional binary alloy for comparison. These FCC alloys have high/low friction stresses, fundamental resistance to dislocation glide in solid solutions, respectively, and share similar other material properties, including stacking fault energy. The Co20Cr40Ni40 MEA exhibited higher yield strength and work-hardening ability than in the Co60Ni40 alloy. Deformation microstructures in the Co60Ni40 alloy were marked by the presence of coarse dislocation cells (DCs) regardless of grain orientation and a few deformation twins (DTs) in grains with the tensile axis (TA) near <1 1 1>. In contrast, the MEA developed three distinct deformation microstructures depending on grain orientations: fine DCs in grains with the TA near <1 0 0>, planar dislocation structure (PDS) in grains with other orientations, and a high density of DTs along with PDS in grains oriented <1 1 1>. Three-dimensional electron tomography revealed that PDS in the MEA confined dislocations within specific {1 1 1} planes, indicating suppression of cross-slip of screw dislocations and dynamic recovery. In-situ X-ray diffraction during tensile deformation showed a higher dislocation density in the MEA than in the Co60Ni40 alloy. These findings demonstrate that FCC HEAs/MEAs with high friction stresses naturally develop unique deformation microstructures which is beneficial for realizing superior mechanical properties compared to conventional materials.

Enhancing mechanical and anti-corrosion properties in a L12 nanoprecipitates reinforced Fe35.4Ni24Cr21Co9Mo2Cu1.6Al3Ti4 multi-principal element alloy via tailoring grain size

A Fe35.4Ni24Cr21Co9Mo2Cu1.6Al3Ti4 multi-principal element alloy (MPEA) reinforced by L12 nanoprecipitates was fabricated with four different grain sizes (~19, ~50, ~127 and ~361 μm) to optimize mechanical and corrosion properties. All samples exhibit a similar microstructure, showing spherical L12 nanoprecipitates embedded in the FCC matrix at grain interiors, accompanied by a small fraction of plate-like L12 and B2-ordered phases at grain boundaries. As grain size decreases, both yield strength and ultimate tensile strength progressively increase, while ductility decreases. The sample with a grain size of ~50 μm demonstrates the most excellent combination of strength and ductility, displaying a yield strength of ~700MPa, an ultimate tensile strength of ~1130MPa, and a total elongation of ~29.4%. Concurrently, corrosion resistance in 3.5wt.% NaCl improves as grain size decreases from ~361 μm to ~50 μm, but notably deteriorates at ~19 μm. These results suggest that the L12 nanoprecipitates reinforced Fe35.4Ni24Cr21Co9Mo2Cu1.6Al3Ti4 MPEA with grain size of ~50 μm has achieved outstanding combination of mechanical and anti-corrosion properties. Precipitation strengthening and grain boundary strengthening are responsible for the enhanced mechanical properties in the studied samples. Electrochemical impedance spectroscopy (EIS) and X-ray photoelectron spectroscopy (XPS) revealed that the passive film on the ~50 μm grain size sample is the thickest (3.09nm), composed primarily of Cr2O3 and Fe2O3, which acts as an effective barrier against Cl- penetration. In a word, tailoring grain size proves to be an effective means to achieve enhanced mechanical and anti-corrosion properties.

Exploring the effect of Cr and Mn on the intrinsic strength of the tensile properties of FeCoNi, FeCoNiMn, FeCoNiCr, and FeCoNiCrMn multi-principal element alloys using in-situ EBSD

As the composition elements in multi-principal element alloys increase, it can bring excellent mechanical properties. However, the strengthening mechanism of the additional element is still unclear. In this work, we establish a method based on the in-situ EBSD technology to explore the possible effect of additional elements on the intrinsic strength of tensile properties. We prepared four different multi-principal element alloys, including FeCoNi, FeCoNiMn, FeCoNiCr, and FeCoNiCrMn with similar initial status. We systematically investigated the evolution of the microstructure, dislocation density, twin boundary, grain size, and element distribution during the tensile process by in-situ EBSD and EDS. By carefully analyzing the results of four different multi-principal element alloys, the strength effects of the solid-solution hardening, grain-boundary hardening, twin boundary hardening, precipitate hardening, and dislocation hardening were peeled. The effect of the Cr and Mn element addition on the intrinsic strength can be explored. It is found that the element addition indeed increases the intrinsic strength from quaternary to quinary but not very clear from ternary to quaternary no matter Cr or Mn, which indicated that the intrinsic strength was more related to the number of elements in the alloy than to which element was present. This can be explained using the mixing entropy theory, which states that the intrinsic strength is enhanced when the mixing entropy is over a threshold between the MEA and HEA. This paper presents a method to study the individual factors affecting the tensile properties, which can help other researchers to better investigate HEA.

Recrystallization kinetics and mechanical properties of cold-rolled and annealed CoCrFeNi multi-principal element alloy

The microstructure and mechanical properties have been investigated in a CoCrFeNi alloy cold-rolled to 80 % thickness reduction and subsequently annealed at 600 °C. It is observed that the as-rolled microstructure comprises extended regions of different dominant crystallographic orientations along with layers of mixed orientations. Shear bands are also present in this microstructure, with the susceptibility to shear banding varying significantly from region to region. Shear bands are most pronounced in extended regions containing narrow deformation twins, and are a crucial source of recrystallization nuclei. Analysis of the recrystallization kinetics indicates that the Avrami exponent is 1.6 for the first 30 min at 600 °C and that it decreases during further annealing. Tensile test data provide evidence that the sample annealed for 8 min, with a recrystallized fraction (fRX) of 13 % and an average recrystallized grain size of 0.8 μm, does not show any significant improvement in ductility compared to that in the as-rolled condition. However, the ductility is considerably improved in the sample annealed for 15 min, where fRX is 43 % and the average recrystallized grain size is 1.1 μm. This sample demonstrates a yield strength of 850 MPa and a total elongation to failure of 25 %. The data obtained in this work and in previous publications on partially recrystallized CoCrFeNi indicate that for samples annealed after 80–85 % deformation optimized combinations of strength and ductility are obtained when the recrystallized fraction is in the range 30 % < fRX ≤ 50 %.

Вплив хімічного складу та температури гартування на розмір зерна аустеніту та твердість інструментальної сталі

Alloying elements and impurities influence ambiguously on the factors that determine the process of the austenite structure formation. This does not make it possible to qualitatively predict the direction of their influence on the change of austenite grain dispersion during austenitizing heating and the hardness of tool steel. To date, there is no information on mathematical models that reliably describe the influence of chemical composition and quenching temperature on the specified characteristics of tool steels. The influence of the chemical composition and quenching temperature on the austenite grain size and the hardness of tool steels was studied, with the development of mathematical models of such influence with the determination of the effectiveness of these factors. It was established that the size of the austenite grain and the hardness of the quenched tool steel are mainly determined by the nature and quantity of alloying elements, the degree of distortion of the crystal lattice and the quenching temperature. The main influence on the austenite grain size of tool steels is the quenching temperature and the quantity of carbon, molybdenum and tungsten in the steel. An increase in the heating temperature leads to growth, and the quantity of elements - to the dispersion of the austenite grain. According to the increase in the specific efficiency of the influence of 1% alloying element on the decreasing of the austenite grain size, they can be arranged in the following sequence: W, Mo, C, and the efficiency of their relative influence is, respectively, 1 : 1.4 : 6.7. The hardness of tool steel is mainly determined by the content of carbon, silicon, tungsten and molybdenum in the steel and the degree of distortion of the crystal lattice by them, as well as the quenching temperature. The evaluation of the effectiveness of the factors showed that the influence of carbon is 26%, tungsten – 22%, molybdenum – 20%, tempering temperature – 17% and silicon – 15%. The obtained regression equations can be used by scientists for further research and by practitioners in the selection of materials for making tools. Keywords: steel, chemical composition, temperature, quenching, grain, austenite, hardness

He irradiation resistance performance in CrNiCo, CrFeNiCo, and CrFeMnNiCo multi-principal element alloys

In this study, the He irradiation resistance of CrFeMnNiCo high-entropy alloy (HEA) and CrNiCo and CrFeNiCo medium-entropy alloys (MEAs), which have better mechanical properties than HEAs, was investigated. Thin-film samples of CrFeMnNiCo, CrNiCo, and CrFeNiCo were irradiated with up to 2 × 1020 He/m2 of 5 keV ions at 673, 773, and 873 K, respectively. In all samples, He bubble formation was observed when irradiated at 1–3 × 1019 He/m2, which depended on the irradiation temperature. At low temperatures of 673 and 773 K, even when as the irradiation dose increased to 2 × 1020 He/m2, the differences in cavity swelling due to He bubble formation among the three alloys were not large. The relative resistance (degree) to cavity swelling for the three investigated alloys was as follows: CrNiCo MEA, CrFeMnNiCo HEA, and CrFeNiCo MEA. First-principles calculation results revealed that the formation of He-di-vacancy clusters was not possible in the CrFeNiCo MEA. This is believed to be the cause of the cavity swelling decrease in the CrFeNiCo MEA. In contrast, after 2 × 1020 He/m2 at 873 K, the cavity swelling of the CrNiCo and CrFeNiCo MEAs, especially CrNiCo, was approximately four times higher than that of the CrFeMnNiCo HEA. It is believed that the He irradiation resistance of the MEAs deteriorated because of element segregation owing to high–temperature irradiation.