Search Results (20)

This study investigates the role of Al alloying in tailoring the oxidation resistance of AlTiCrZrNbTa refractory high-entropy alloy (RHEA) coatings on Zry-4 substrates under high-temperature steam environments. Coatings with varying Al contents (0–25 at.%) were deposited via magnetron sputtering and subjected to oxidation tests at 1000–1100 °C. The results demonstrate that Al content critically governs oxidation kinetics and coating integrity. The optimal performance was achieved at 10 at.% Al, above which a dense, continuous composite oxide layer (Al₂O₃, TiO₂, Cr₂O₃) formed, effectively suppressing oxygen penetration and maintaining strong interfacial adhesion. Indentation tests confirmed enhanced mechanical integrity in Al-10 coatings, with minimal cracking post-oxidation. Excessive Al alloying (≥17 at.%) led to accelerated coating oxidation. This work establishes a critical Al threshold for balancing oxidation and interfacial bonding, providing a design strategy for developing accident-tolerant fuel cladding coatings. Full article

WMoTaNbV refractory high-entropy alloys (RHEAs) have received widespread attention due to their excellent low-temperature toughness, hardness, and wear resistance. In recent years, the rapid development of surface modification technology represented by laser cladding has provided a new technological path for RHEA surface forming, and at the same time put forward higher requirements for raw material powder. In this study, WMoTaNbV RHEA spherical powder was prepared by radiofrequency plasma spheronization, and then WMoTaNbV RHEA coating was prepared on the surface of Ti6Al4V (TC4) alloy by laser cladding technique. The experimental results show that the prepared alloy powders have very high sphericity and are almost free of agglomeration and oxidation. Coatings with laser powers of 3.1–3.9 kW (gradient setting of 2 kW) were tested, with the 3.3, 3.5, and 3.7 kW coatings showing the best of the abrasion resistance. The microhardness of the 3.3 kW, 3.5 kW, and 3.7 kW coatings was 1.72, 1.97, and 1.76 times higher than that of the substrate, and the wear resistance was 1.83, 3.42, and 2.13 times higher than that of the TC4 substrate, respectively. This experimental result shows that the surface hardness and wear resistance of WNbMoTaV RHEA coating can be effectively improved by precisely regulating the laser power, thus improving the surface hardness and friction and wear properties of TC4 titanium alloy. Full article

High-strength bolts are prone to crack initiation from the threaded hole during fastening due to large loads, which can compromise their performance and reliability. To enhance the durability of these bolts, coatings are often employed to strengthen their surfaces. NbMoTaW refractory high-entropy alloy coatings are widely used in hard coating applications due to their exceptional mechanical properties. However, the brittleness of this alloy at room temperature limits its performance in high-stress environments. To enhance the ductility of NbMoTaW alloys, this study systematically investigates the effect of varying titanium (Ti) content on the alloy’s properties. First-principles calculations were employed to analyze the elastic properties of TixNbMoTaW alloys, including elastic constants, the elastic modulus, the bulk modulus (B)-to-shear modulus (G) ratio (Pugh’s ratio), Poisson’s ratio (ν), and Cauchy pressure (C12–C44). The results indicate that the addition of Ti significantly improves the alloy’s plasticity. Specifically, when the Ti content is x = 2, the B/G ratio increases to 3.23, and Poisson’s ratio increases to 0.39, indicating enhanced deformability. At x = 0.75, the elastic modulus (E) increases to 273.78 GPa, compared to 244.99 GPa for the original alloy. The experimental results further validate the computational findings. X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses indicate that all alloys exhibit a single body-centered cubic (BCC) phase. Room-temperature compression tests show that as the Ti content increases, the yield strength, fracture strength, and plasticity of the alloys significantly improve. Specifically, for a Ti content of x = 0.75, the yield strength reaches 1551 MPa, the fracture strength is 1856 MPa, and the plastic strain increases to 14.6%. For Ti1.5NbMoTaW, the yield strength is 1506 MPa, the fracture strength is 1893 MPa, and the plastic strain is 17.3%. Overall, TixNbMoTaW refractory high-entropy alloys demonstrate significant improvements in both plasticity and strength, showing great potential for coating applications in high-stress environments. Full article

In response to the poor wear resistance and high-temperature oxidation resistance of titanium alloys during service, a series of lightweight refractory high-entropy alloys (RHEAs) can be designed for the laser cladding coating of titanium alloy surfaces, with due consideration of the compositional and structural characteristics of titanium alloys. Firstly, the structural stability, mechanical and thermal properties of four lightweight RHEAs (MoNbTiV, AlMoNbTiW, CrMoNbTiV, and AlCrMoNbTiV) with equal atomic ratios were designed and calculated using first principles combined with quasi-harmonic approximation (QHA). The results indicate that all four RHEAs are stable BCC, exhibiting elastic anisotropy and ductility. The lightest density is 6.409 g/cm³. Adding Al/Cr can cause structural distortion and affect its mechanical properties. Their Young’s moduli are in the following order: AlCrMoNbTiV > MoNbTiV > CrMoNbTiV > AlMoNbTiV. The thermal expansion coefficients of the four RHEAs and titanium alloys are very close, with a difference in linear expansion coefficient of less than 1.16 × 10⁻⁵/K. Meanwhile, the metallurgical bonding of four types of RHEA coatings was successfully achieved on a Ti-6Al-4V(TC4) substrate through laser cladding technology, and all coatings exhibited a unique BCC solid solution phase. Full article

In this work, the influence of laser power (LP), scanning speed (SS), and powder feeding speed (PF) on the porosity, dilution, and microhardness of lightweight refractory high-entropy alloy (RHEA) coatings produced via laser cladding (LC) was investigated. Variance analysis (ANOVA) was deployed to ascertain the effect of LP, SS, and PF on performance metrics such as porosity, dilution, and microhardness. The Non-dominated Sorting Genetic Algorithm II (NSGA-II) was then applied to optimize these processing parameters to minimize porosity, achieve suitable dilution, and maximize microhardness, enhancing the mechanical properties of RHEA coatings. Finally, machine learning models—Random Forest (RF), Gradient Boosting Decision Tree (GBDT), and Genetic Algorithm-enhanced GBDT (GA-GBDT)—were developed using orthogonal experimental data, with GA-GBDT demonstrating superior predictive accuracy. The proposed approach integrates statistical analysis and advanced ML techniques, providing a better understanding into optimizing LP, SS, and PF for improved RHEA coatings performance in industrial applications, thereby advancing laser cladding technology. Full article

High-temperature oxidation resistance is the major influence on the high-temperature service stability of refractory high entropy alloys. The oxidation behavior of lightweight Al_0.2CrNbTiV refractory high entropy alloy coatings with different dilution ratios at 650 °C and 800 °C deposited by high-speed laser cladding was analyzed in this paper. The oxidation kinetic was analyzed, the oxidation resistance mechanism of the Al_0.2CrNbTiV coating was clarified with the analysis of the formation and evolution of the oxidation layer, and the effect of the dilution rate on high-temperature performances was revealed. The results showed that the oxide layer was mainly composed of rutile oxides (Ti, Cr, Nb)O₂ after isothermal oxidation at 650 °C and 800 °C for 50 h. The Al_0.2CrNbTiV coating in low dilution exhibited better oxidation performance at 650 °C, due to the dense oxide layer formed with the synergistic growth of fine AlVO₃ particles and (Ti, Cr, Nb)O₂, and higher percentage of Cr, Nb in (Ti, Cr, Nb)O₂ strengthened the lattice distortion effect to inhibit the penetration of oxygen. The oxide layer formed at 800 °C for the Al_0.2CrNbTiV coating was relatively loose, but the oxidation performance of the coating in high dilution improved due to the precipitation of Cr₂Nb-type Laves phases along grain boundaries, which inhibits the diffusion of oxygen. Full article

The low hardness and poor wear resistance of laser-cladding 316L stainless steel impose significant constraints on its practical applications. In this study, a strategy for strengthening laser-cladding 316L stainless steel with WMoTaNb refractory high-entropy alloy as a reinforcement material is proposed. The results confirm that the coating primarily comprises a body-centered cubic (BCC) Fe-based solid solution, a network-distributed hexagonal Fe₂X (X = W, Mo, Ta, and Nb) Laves phase, and a diffusely distributed face-centered cubic (FCC) (Ta, Nb)C phase. The Fe-based solid solution distributes along columnar and fine dendrites, while the Laves phase and (Ta, Nb)C phase are in the inter-dendrites. The presence of a significant number of network Laves phases exhibiting high strength and hardness is the primary factor contributing to the enhancement of coating microhardness. The hardness of the composite coating is increased by nearly twice compared to that of the 316L coating, resulting in an improved wear resistance. The present work can shed light on designing and fabricating 316L stainless steel coating with enhanced hardness and wear resistance. Full article

We compiled, assessed, and ranked refractory high-entropy alloys (RHEAs) from the existing literature to identify promising coating materials for hot-forging dies. The selection methodology was rigorously guided by decision science principles, seamlessly integrating multiple attribute decision making (MADM), principal component analysis (PCA), and hierarchical clustering (HC). By employing a combination of twelve diverse MADM methods, we successfully ranked a total of 22 RHEAs. This analytical technique unveiled the top five RHEAs: Ti₂₀-Zr₂₀-Hf₂₀-Nb₂₀-Cr_20, Al_20.4-Mo_10.5-Nb_22.4-Ta_10.1-Ti_17.8-Zr_18.8, Ti₂₀-Zr₂₀-Hf₂₀-Nb₂₀-V₂₀, Al_11.3-Nb_22.3-Ta_13.1-Ti_27.9-V_4.5-Zr_20.9, and Al_7.9-Hf_12.8-Nb₂₃-Ta_16.8-Ti_18.9-Zr_20.6 pertinent for generating data on other significant properties, including wear resistance, fatigue (both thermal and mechanical), bonding compatibility with the substrate die material, oxidation resistance, potential reactions with the workpiece, cost-effectiveness, fabricability, and more. The three highest-ranked RHEAs share key characteristics, including a body-centered cubic (BCC) crystal structure, thermal conductivity below ~70 W/mK, and impressive yield strength at ambient and elevated temperatures, surpassing 1100 MPa. Moreover, they exhibit a remarkable ~73% similarity among themselves. The decision science-driven analyses yield sound metallurgical insights and provide valuable guidelines for developing RHEA coatings tailored for hot-forging dies. The strategy for designing RHEA-based coating materials for hot-forging dies should focus on compositions featuring a substantial presence of refractory metals while maintaining a BCC crystal structure. This combination is likely to deliver the desired blend of thermal and mechanical properties, rendering these coatings exceptionally well-suited for the demanding requirements of hot-forging operations. Full article

Refractory high-entropy alloys (RHEAs) contain alloying elements with a high melting point, promising high-temperature applications due to their unique properties. In this work, laser cladding is used to prepare RHEA_S based on NbMoTaTiNi. At the same time as laser cladding, the ultrasonic field is used, and then the microstructural characteristics, grain size, residual stress, wear, and hardness of the coating are evaluated. The results show that the coating is biphasic and includes the γ (Ni) and NbMoTaTiNi phase. The NbMoTaTiNi phase had a uniform distribution throughout the coating when the ultrasonic field was applied, so that when the ultrasonic field was not used, the NbMoTaTiNi powder, in addition to spreading uniformly, had the un-melting of large particles. This caused an increase in the residual tension of the coating. The conversion of columnar grains to the equiaxed, and the reduction in structural defects, were other characteristics of using the ultrasonic field. The formation of equiaxed grains with zigzag grain boundaries reduced the friction coefficient, wear volume loss, and the wear rate of the coating applied with ultrasonic. Full article

TiMoNbX (X = Cr, Ta, Zr) RHEA coatings were fabricated on TC4 titanium alloy substrate using laser cladding technology. The microstructure and corrosion resistance of the RHEA were studied by XRD, SEM and an electrochemical workstation. The results show that the TiMoNb series RHEA coating was composed of a columnar dendrite (BCC) phase, a rod-like second phase, a needle-like structure and equiaxed dendrite, but the TiMoNbZr RHEA coating showed high-density defects, similar to those in TC4 titanium alloy, which were composed of small non-equiaxed dendrites and lamellar α’(Ti). In the 3.5% NaCl solution, compared with TC4 titanium alloy, the RHEA had a lower corrosion sensitivity and fewer corrosion sites, showing better corrosion resistance. The corrosion resistance of the RHEA ranged from strong to weak in this order: TiMoNbCr, TiMoNbZr, TiMoNbTa and TC4. The reason is that the electronegativity of different elements is different, and the speeds of the formation of the passivation film were very different. In addition, the positions of pores appearing in the laser cladding process also affected the corrosion resistance. Full article

WVTaTiCr_x (x = 0, 0.25, 0.5, 0.75, 1) refractory high-entropy alloy coatings were prepared on a 42-CrMo steel plate using laser cladding. The purpose of this work is to investigate the effect of the Cr content on the microstructure and properties of the WVTaTiCr_x coating. The morphologies and phase compositions of five coatings with different Cr contents were comparatively observed. In addition, the hardness and high-temperature oxidation resistance of the coatings were also analyzed. As a result, with the increase in Cr, the coating grains were more refined. All the coating is mainly composed of the BCC solid-solution phase, which promotes the precipitation of the Laves phase with the increase in Cr. The addition of Cr greatly improves the hardness, high-temperature oxidation resistance and corrosion resistance of the coating. The WVTaTiCr (Cr₁) exhibited superior mechanical properties, especially in terms of its exceptional hardness, high-temperature oxidation resistance and outstanding corrosion resistance. The average hardness of the WVTaTiCr alloy coating reaches 627.36 HV. After 50 h of high-temperature oxidation, the oxide weight of WVTaTiCr increases by 5.12 mg/cm², and the oxidation rate is 0.1 mg/(cm²·h). In 3.5 wt% NaCl solution, the corrosion potential of WVTaTiCr is −0.3198 V, and the corrosion rate is 0.161 mm/a. Full article

Metal corrosion leads to serious resource waste and economic losses, and in severe cases, it can result in catastrophic safety incidents. As a result, proper coatings are often employed to separate metal alloys from the ambient environment and thus prevent or at least slow down corrosion. Among various materials, high-entropy alloy coatings (HEA coating) have recently received a lot of attention due to their unique entropy-stabilized structure, superior physical and chemical properties, and often excellent corrosion resistance. To address the recent developments and remaining issues in HEA coatings, this paper reviews the primary fabrication methods and various elemental compositions in HEA coatings and highlights their effects on corrosion resistance properties. It is found that FeCoCrNi-based and refractory high-entropy alloy coatings prepared by the laser/plasma cladding method typically show better corrosion resistance. It also briefly discusses the future directions toward high-performing corrosion-resistant coatings based on HEA design. Full article

High entropy metal sub-lattice stabilized nitride coatings based on multicomponent refractory transition metals (TM = Ti, Nb, V, Ta, Zr, Hf) are promising candidates for extreme conditions due to their high thermal, mechanical, and corrosion properties. The aims of the current work included the investigations of the possibilities of the novel High Target Utilization Sputtering (HiTUS) technique applied to reactive sputtering of TiNbVTaZrHf–xN coatings from the viewpoints of hysteresis behavior during reactive sputtering as well as the structure, composition, stoichiometry, and mechanical properties of the resulting coatings. With increasing nitrogen content, coating structures varied from amorphous in metallic alloy coatings to textured nano-columnar fcc structures. Despite certain deviations of TM from equiatomic concentrations, homogeneous solid solutions corresponding to single-phase multicomponent nitride analogous to high entropy stabilized compounds were obtained. Mechanical properties were found to be proportional to nitrogen content. The highest hardness H_IT ~ 33 GPa and indentation modulus E_IT ~ 400 GPa were found in a slightly sub-stoichiometric (~42 at% nitrogen) composition. H_IT/E_IT and limited pillar split measurements suggested that these coatings exhibit low fracture toughness (around 1 MPa.m^1/2). The work confirmed that reactive HiTUS is suitable for the preparation of multicomponent nitrides with the control of their stoichiometry and mechanical properties only via nitrogen additions. Full article

In order to improve the high-temperature oxidation resistance of refractory high-entropy alloys (RHEAs), we used micro-arc oxidation (MAO) technology to prepare ceramic coatings on AlTiCrVZr alloy, and the effects of voltage on the microstructure and high-temperature oxidation resistance of the coatings were studied. In this paper, the MAO voltage was adjusted to 360 V, 390 V, 420 V, and 450 V. The microstructure, elements distribution, chemical composition, and surface roughness of the coatings were studied by scanning electron microscopy (SEM), energy dispersive (EDS), X-ray photoelectron spectroscopy (XPS), and white-light interferometry. The matrix alloy and MAO-coated samples were oxidized at 800 °C for 5 h and 20 h to study their high-temperature oxidation resistance. The results showed that as the voltage increased, the MAO coating gradually became smooth and dense, the surface roughness decreased, and the coating thickness increased. The substrate elements and solute ions in the electrolyte participated in the coating formation reaction, and the coating composition was dominated by Al₂O₃, TiO₂, Cr₂O₃, V₂O₅, ZrO₂, and SiO₂. Compared with the substrate alloy, the high-temperature oxidation resistance of the MAO-coated samples prepared at different voltages was improved after oxidation at 800 °C, and the coating prepared at 420 V showed the best high-temperature oxidation resistance after oxidation for 20 h. In short, MAO coatings can prevent the diffusion of O elements into the substrate and the volatilization of V₂O₅, which improves the high-temperature oxidation resistance of AlTiCrVZr RHEAs. Full article

Refractory high entropy alloys have broad application prospects due to their excellent comprehensive properties in high temperature environments, and they have been widely implemented in many complex working conditions. According to the latest research reports, the preparation technology of bulk and coating refractory high entropy alloys are summarized, and the advantages and disadvantages of each preparation technology are analyzed. In addition, the properties of refractory high entropy alloys, such as mechanical properties, wear resistance, corrosion resistance, oxidation resistance, and radiation resistance are reviewed. The existing scientific problems of refractory high entropy alloys, at present, are put forward, which provide reference for the development and application of refractory high entropy alloys in the future, especially for plasma-facing materials in nuclear fusion reactors. Full article