Refractory Coatings Research Articles

Effects of Al variations on the microstructure and mechanical properties of laser-cladding AlxNbMo0.5Ti1.5Ta0.5Cr0.5 refractory high-entropy alloy coatings

Lightweight refractory high-entropy alloy coatings (RHEAcs) of AlXNbMo0.5Ti1.5Ta0.5Cr0.5 (where x = 0, 0.1, 0.2, and 0.3) were fabricated on 316L stainless steel surface by pre-placed powder laser cladding (LC) technology. The incorporation of Al element significantly enhanced the forming quality of coatings, resulting in nearly defect-free coatings with a thickness of 1.2-1.4mm. Microstructural analysis revealed that the coatings were primarily composed of body-centered cubic (BCC) solid solution and C15-Laves phase. Due to the influence of a single brittle BCC phase, the Al-free coating exhibited high strength and brittleness, leading to numerous defects caused by thermal stress. The introduction of Al element refined the microstructure and facilitated the formation of Laves phases at grain boundaries, thereby alleviating stress to a certain extent. Consequently, the microhardness of the RHEAcs was significantly higher than that of the substrate, with the Al-free coating achieving the highest microhardness of 1250 HV, which was 5.89 times that of the substrate. Wear resistance results indicated that, prior to annealing, RHEAcs with varying Al content outperformed 316L stainless steel. Post-annealing, the coatings exhibited significantly lower friction coefficients compared with the annealed 316L substrate. The Al-free coating showed significant accumulation of abrasive particles, leading to severe abrasive and oxidative wear. Conversely, post-annealing oxidation induced the formation of dense and directional oxide accumulation, resulting in a notable improvement in wear resistance. Finally, the underlying strengthening mechanisms have been proposed and analyzed.

Dual-Action Calcium Monoaluminate Enabled Room-Temperature Curing of Inorganic Phosphate-Based High-Temperature Adhesive.

High-temperature adhesives find extensive application in diverse domains, encompassing repairs, production processes, and material joining. However, achieving their curing at ambient temperatures remains a formidable challenge due to the inherent requirement of elevated temperatures, typically exceeding 500 °C, for the curing reaction. To overcome this limitation, in this study, we developed a distinctive inorganic phosphate-based composite adhesive by incorporating dual-functional calcium monoaluminate (CA) into a traditional adhesive blend comprising Al(H2PO4)3 and MgO. This distinctive approach significantly diminishes the curing temperature, enabling it to occur at room temperature. Firstly, CA's facile hydration reaction effectively scavenges surrounding water molecules, thereby accelerating the dehydration curing process of Al(H2PO4)3. Secondly, as hydration is an exothermic process, it locally generates heat around the Al(H2PO4)3, fostering optimal conditions for its curing reaction. Moreover, the adhesive's strength is substantially bolstered through the strategic inclusion of Nano-Al2O3 (enhancing the availability of reaction sites) and Nano-SiO2 (improving overall stability). As a demonstration, the adhesive formulation with added CA containing 2% Nano-Al2O3 and 2% Nano-SiO2 achieved a remarkable tensile strength of 32.48 MPa at room temperature, underscoring its potential as an efficient solution for various practical adhesive applications. The adhesive prepared in this study harnesses the hydration properties of CA to absorb moisture and release substantial heat, introducing a novel method for ambient temperature curing. This development promises to broaden its applications in refractory materials, coatings, and equipment repair.

Ti-Zr-Nb-(V) refractory alloy coatings deposited by high-power impulse magnetron sputtering: Structure, mechanical properties, oxidation resistance, and thermal stability

Ti-Zr-Nb-(V) refractory alloy coatings deposited by high-power impulse magnetron sputtering: Structure, mechanical properties, oxidation resistance, and thermal stability

Oxidation Behavior of Lightweight Al0.2CrNbTiV High Entropy Alloy Coating Deposited by High-Speed Laser Cladding

High-temperature oxidation resistance is the major influence on the high-temperature service stability of refractory high entropy alloys. The oxidation behavior of lightweight Al0.2CrNbTiV 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 Al0.2CrNbTiV 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 Al0.2CrNbTiV 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 Al0.2CrNbTiV 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.

Enhanced Classification of Refractory Coatings in Foundries: A VPCA-Based Machine Learning Approach

Enhanced Classification of Refractory Coatings in Foundries: A VPCA-Based Machine Learning Approach

Study on the microstructure and properties of Mo0.5VNbTiCr0.25 refractory high-entropy alloy coatings

Study on the microstructure and properties of Mo0.5VNbTiCr0.25 refractory high-entropy alloy coatings

In-situ preparation and ablative resistance of multicomponent refractory carbide ceramic gradient coatings

In this work, the gradient multicomponent carbide ceramic coatings were prepared in-situ on graphite matrix using the molten salt method, and their high temperature ablation resistance was investigated. Our results demonstrate the successful preparation of (HfTi)C, (HfTiZr)C, and (HfTiZr)C–TaC ceramic coatings with a gradient distribution on the graphite matrix by altering the types of raw materials. Thermodynamic calculations and analyses indicate that the smaller the Gibbs free energy gap between different carbides, the easier the solid solution multicomponent ceramic coating is formed. After 200 s of oxy-acetylene torch ablation, it was observed that the (HfTi)C, (HfTiZr)C, and (HfTiZr)C–TaC coatings effectively protected the graphite matrix with mass ablation rates of 6.47 mg s−1, 0.61 mg s−1, and 0.51 mg s−1, respectively. The low mass loss of (HfTiZr)C and (HfTiZr)C–TaC coatings can be attributed to the synergistic protective effect of different oxides formed by oxidation of different elements.

Fabrication of amorphous AlMo0.5NbTa0.5TiZr RHEA coatings and the impact of deposition temperature on microstructure and properties

In this study, protective AlMo0.5NbTa0.5TiZr refractory high-entropy alloy coatings were prepared by DC magnetron sputtering, and the influence of deposition temperature on the microstructure, deposition rate, mechanical properties, and adhesion force was investigated in detail. All coatings are in a nearly amorphous state. Their elastic recovery ratio (ηw), microhardness (H), elastic strain failure strength (H/E), plastic deformation strength (H3/E2), and adhesion force (Lc2) are positively correlated with deposition temperature mainly attributing to the synergy of increased thickness and the generation of the nanocrystal. The coating reaches its maximum ηw, H, H/E, H3/E2, and Lc2 of 43.87 ± 0.94 %, 12.74 ± 0.37 GPa, 0.073 ± 0.002, and 0.067 ± 0.005 GPa at the deposition temperature of 500 °C and exhibits superior wear resistance and resistance to plastic deformation, compared with reported refractory Cr and α-Ta coatings.

Oxidation Performance of Nano-Layered (AlTiZrHfTa)Nx/SiNx Coatings Deposited by Reactive Magnetron Sputtering.

This work uses the direct current magnetron sputtering (DCMS) of equi-atomic (AlTiZrHfTa) and Si targets in dynamic sweep mode to deposit nano-layered (AlTiZrHfTa)Nx/SiNx refractory high-entropy coatings (RHECs). Transmission electron microscopy (TEM), field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) are used to investigate the effect of Si addition on the oxidation behavior of the nano-layered coatings. The Si-free nitride coating exhibits FCC structure and columnar morphology, while the Si-doped nitride coatings present a FCC (AlTiZrHfTa)N/amorphous-SiNx nano-layered architecture. The hardness decreases from 24.3 ± 1.0 GPa to 17.5 ± 1.0 GPa because of the nano-layered architecture, whilst Young's modulus reduces from 188.0 ± 1.0 GPa to roughly 162.4 ± 1.0 GPa. By increasing the thickness of the SiNx nano-layer, kp values decrease significantly from 3.36 × 10-8 g2 cm-4 h-1 to 6.06 × 10-9 g2 cm-4 h-1. The activation energy increases from 90.8 kJ·mol-1 for (AlTiZrHfTa)Nx nitride coating to 126.52 kJ·mol-1 for the (AlTiZrHfTa)Nx/SiNx nano-layered coating. The formation of a FCC (AlTiZrHfTa)-Nx/a-SiNx nano-layered architecture results in the improvement of the resistance to oxidation at high temperature.

Microstructure evolution and performance of TiMoCrWxTay refractory high-entropy alloy coatings prepared using laser cladding

Refractory high entropy alloy (RHEA) coatings containing W and Ta elements at the same time usually have excellent performance at high temperature, which are promising candidate materials for high temperature protective coating materials. In this work, the effects of W and Ta on the microstructure and performance evolution of TiMoCrWxTay RHEA coatings have been investigated. Experimentally, TiMoCrWxTay coatings are mainly composed of BCC phase, Laves phase and Ti-rich phase, with W and Ta atoms preferably dissolved in BCC phase. The W atoms promote the formation of dendrites and the growth of rod-like and equiaxed crystals and the Ta atoms promote the formation of cellular crystals and produce the effect of fine crystal strengthening. W and Ta atoms have significant influence on the tribological properties of TiMoCrWxTay coatings. The tribological properties of TiMoCrWxTay coatings at 800 °C are better than those at room temperature. TiMoCrWxTay RHEA coatings follow near-linear oxidation kinetics during the oxidation of 50 h at 800 °C.The oxidation resistance of the coatings first increases and then decreases with the increase of Ta content. Ta2O5, TiO2 and other oxides may have a shielding effect on the oxidation of W. In particular, The W0.3Ta0.5 shows the best tribological properties and oxidation resistance, and the mass gain of W0.3Ta0.5 is only 13.4 mg/cm2 after the oxidation test for 50 h. It indicates that TiMoCrWxTay coatings can obtain good high temperature performance by optimizing the content of W and Ta in RHEA coatings. This work can provide guidance for the research and application of TiMoCrWxTay RHEA coatings.

Effect of Si3N4 content on microstructure and frictional-wear properties of MoNbTaWTi refractory high entropy alloy composite coatings

To address the shortcomings of the Ti-6Al-4 V alloy, characterized by low surface hardness and inadequate friction and wear properties, a composite coating of in-situ TiN reinforced MoNbTaWTi refractory high-entropy alloy was developed using laser cladding technology on Ti-6Al-4 V substrate. The effects of different Si3N4 contents on coating organization and wear resistance are discussed. Analysis through X-ray diffractometry (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA) revealed that the composite coating primarily consisted of the body-centered cubic (BCC) phase and an in-situ TiN enhanced phase. Notably, at a Si3N4 content of 2.0 wt%, the average microhardness at the coating's top surface reached 808.67 HV0.1, surpassing that of the substrate by 2.33 times. The friction coefficient was reduced to 0.3009, representing only 59.01 % of the Ti-6Al-4 V substrate. Furthermore, the wear weight loss measured at 0.4×10−2 mm3 was a mere 22.35 % of the Ti-6Al-4 V substrate, with the wear area accounting for only 0.27 % of the Ti-6Al-4 V substrate. Results demonstrated that utilizing the in-situ reaction between Ti element and Si3N4, the in-situ generated TiN reinforced phase significantly enhanced the hardness and wear resistance of the coating.

Investigation of elevated temperature microstructural stability and tribological behavior of MoxNbTiZr refractory high-entropy alloy coatings optimized by Mo-doping

Refractory high-entropy alloys (RHEAs) possess substantial potential for applications in high-temperature environments. In this work, the structural and high-temperature properties of MoxNbTiZr RHEA coatings are optimized by Mo-doping. The results show that Mo-doping promotes the HCP phase precipitation and proliferation of nanotwins, strengthening the microhardness but weakening the fracture toughness of the coatings. Mo-doping raises the phase transition onset temperature and end temperature by reducing the bulk diffusion rate of MoxNbTiZr RHEAs. The BCC phase of Mo1.0NbTiZr HEA coating can be stabilized to at least 1300 ℃. Mo-doping in a particular range is favourable to accelerate the sintering and curing rate of the tribo-layer. The MoxNbTiZr RHEA coatings demonstrate outstanding high-temperature tribological performance before Mo content exceeds 0.6 at%.

Effect of Al content on the microstructure, mechanical property and lead-bismuth eutectic corrosion resistance of refractory AlxTiNbZrMoV coatings produced by magnetron sputtering

In present study, refractory AlxTiNbZrMoV (x=0.2, 0.5, 0.9 and 1.2 in molar ratio) high-entropy alloy coatings were prepared by magnetron sputtering technology. The microstructure, mechanical property and lead-bismuth eutectic corrosion resistance of the AlxRHEA coatings were investigated. With the increase of Al content, the coatings maintained the amorphous structure, and no intermediate phase was generated. The hardness and elastic modulus of the AlxRHEA coatings were higher than that of Al-free coating. After the LBE corrosion, formation of surface Fe-oxide layer occurred in the four AlxRHEA coatings. The Al0.5RHEA and Al0.9RHEA coatings exhibited improved corrosion resistance. The results indicate that for HEA, the formation of protective alumina layer can be on the basis of Al enrichment on the coating surface to continue to improve the oxidation resistance.

Application of waste raw materials as a reinforcement for protective coatings based on pyrophyllite

In this study, pyrophyllite was used for the first time in the composition of protective refractory coatings together with supplementary waste resources. The proposed refractory coatings are applicable for metallic and non-metallic structures, with the option of using them to protect machinery components in the chemical industry, metallurgy, and mining. Given that pyrophyllite has a low hardness, the goal was to improve the coating's resistance to cavitation erosion by adding 20 wt.% of hard refractory materials, i.e., crushed and micronized waste bricks based on mullite and corundum, respectively. Previous studies have demonstrated that protective coatings using a pyrophyllite filler have refractory qualities but insufficient resistance to cavitation erosion. As a result, the composition of refractory coatings, the preparation techniques, and the coating manufacturing process were altered. This study presents a simple method for combining conventional coatings made of refractory fillers (primary resource: pyrophyllite) with waste materials (mullite brick and corundum brick) used as reinforcement in protective refractory coatings for metal and non-metal structural elements that are highly resistant to cavitation erosion.

Design and characterization of LaB6/NbNiTaTi refractory high-entropy alloy coatings: Effect of in-situ TaB phase on strengthening mechanism

The excellent strength and hardness obtained from the customized phase compositions provide vast spaces for surface protection application of refractory high entropy alloy (RHEA) coatings in titanium alloys. However, the introduction of high-strength brittle phase in RHEA coatings commonly increases the cracking tendency and affects their service life. In this work, we propose a design strategy to enhance the mechanical properties of RHEA coatings by introducing an extremely stable high strength boride combined with a ductile phase. Experimentally, LaB6/NbNiTaTi RHEA coatings mainly consist of BCC phase, in-situ TaB phase and NiTi/IM eutectic phase. TaB phase with high-density (110) nanotwins inside presents needle-like morphology with the long side axis parallel to the [001] direction. Excessive needle-like TaB phase is fully fused and fractured due to its preferential growth along a specific direction. The fracture surface analysis shows that BCC phase bears the main deformation, NiTi phase can relieve stress concentration at the boundary while bearing a small amount of deformation. By contrast, the low-density dislocation distribution and the low energy extended dislocation structure in TaB phase exhibit the phase stability. In addition, the amorphous islands are formed near the high-deformation regions when the defect concentration reaches the critical value.

Corrosion and passivation behavior of in-situ TiC reinforced Al0.1CrNbSi0.1TaTiV refractory high entropy alloy coatings via doping C

This work is aimed to explore ways to further improve corrosion properties of single-phase RHEA coating by introducing in-situ TiC phase. Results shown that C/Al0.1CrNbSi0.1TaTiV RHEA coatings exhibited better comprehensive resistance to pitting and general corrosion compared to most of reported HEAs and traditional alloys. The passive film was dominated by a muti-oxide crystalline structure with a thickness of ∼ 11.52 nm. The small-size and evenly distributed TiC phase with most thermodynamically stable could be obtained via doping C and retard the nearby pitting process, improving the pitting behavior and the dense of passive film in 1.0 wt% C coating.

Additive manufacturing of functionally gradient refractory coatings using substrate dilution and in-situ carbide formation

Enabling operations in extreme environments remains a top priority for the space, defense, and energy sectors, driving the demand for ultra-high-temperature materials. Traditional materials employed in these sectors have limited operating temperatures and thus novel alternatives are of interest. Refractory metals and carbides have excellent high-temperature properties, however, their high melting points and susceptibility to cracking during solidification make them challenging to process, especially through additive manufacturing (AM) technologies. In this work, Directed Energy Deposition (DED) was used to create a functionally graded refractory coating (W-WC-Nb system on a titanium substrate) by integrating titanium into the refractory matrix through substrate dilution. By developing a new W-based alloy then adding titanium from the substrate along the build direction, a crack-free microstructure was formed within layers closer to the substrate. Additionally, an in-situ carbide formation strategy was explored, creating titanium carbide and niobium carbide phases that could improve the high-temperature and corrosion properties without the need to overcome processing difficulties associated with these high-melting carbides. These strategies allow for the development of new material systems with tailored properties and improved processibility of refractory material systems.

Evolution in microstructure and tribological behavior of laser cladded MoxNbTiZr high-entropy refractory alloy coatings with varying Mo content

The effect of the Mo element on the Ni-Ti-Zr refractory high-entropy alloy (RHEA) coatings synthesized by laser cladding were explored in terms of microstructural evolution and tribological behavior assessed by material characterization techniques and drying sliding wear tests. The findings reveal that MoxNbTiZr RHEA coatings, comprising of body center cubic (BCC) matrix phase and several hexagonal close packed (HCP) phases, have a dendrite microstructure with Mo, Nb-rich dendritic region (DR) and Zr-rich interdendritic region (IR), affected by Mo-induced thermodynamic instability. The micro-segregation between DR and IR becomes serious by the synergy effect of melting point difference, diffusion rate, and mixing enthalpy. The microhardness of the RHEA coating has a linear relationship with Mo content, with the highest value of 732.67 HV at x = 1.0. Nanotwins induced by residual stress, high cooling rate, solid-solution strengthening, fine-grain strengthening, and second-phase strengthening, cause microhardness improvement. Due to the generation of the destructive oxide layer and rising coating brittleness, the wear rate rises from 1.66 × 10−4 mm3/(N·m) to 3.75 × 10−4 mm3/(N·m). The wear mechanism of the MoxNbTiZr coatings shifts from oxidation wear to abrasive wear and eventually to three-body abrasion and severe brittle micro-peeling. Among these coatings, Mo0.6NbTiZr exhibits the optimal performance with excellent comprehensive characteristics.

Strengthening mechanisms and high-temperature oxidation properties of laser-clad TaNbZrTi refractory high entropy alloy coatings

Strengthening mechanisms and high-temperature oxidation properties of laser-clad TaNbZrTi refractory high entropy alloy coatings

Експертна оцінка критеріїв вибору методів знешкодження зарядів виведених з експлуатації твердопаливних ракет

The subject of study in this article is the processes that occur during the disposal of solid fuel rockets, methods of disposal, and criteria for choosing an effective method of disposal. This study identified the most significant criteria that determine the choice of an effective method for the disposal of decommissioned solid-fuel rocket charges. The task: to consider the risks of the man-made impact of the process of disposal of solid-fuel intercontinental ballistic missiles on the environment, associated with the emission of harmful substances into the atmosphere, the scattering of fragments, the occurrence of shock air, and seismic and soliton waves; analyze the advantages and disadvantages of existing methods of destruction and use of solid propellant charges of rocket engines; expertly evaluate the criteria for the selection of disposal methods; and a priori ranking of criteria. The method of a priori ranking was chosen as the method of solving the given problem. The following results were obtained. The degree of consistency of the experts’ conclusions was assessed using the concordance coefficient. The hypothesis regarding the significance of the concordance coefficient was tested on the basis of a comparison of the calculated value of the concordance coefficient with the tabulated value at the given values of the significance level and the number of degrees of freedom. The most significant factors that should be taken into account when choosing a disposal method are identified (economic efficiency; the possibility of reusing the fuel that is removed; manufacturability; the probability of emergency situations during the implementation of the method; environmental safety; energy intensity), and factors that can be excluded from further analysis (the need for additional special systems, the degree of mastery of the method). Conclusions. The scientific novelty of the obtained results is as follows: the formalization and mathematical processing of a priori data on the subject of research was conducted, and a comparative assessment of the degree of influence of various criteria on known and promising methods of disposal of solid rocket fuel charges is given. According to the preliminary evaluation, the set of significant selection criteria is most fully met by the cryogenic washing method, the application of which allows the use of solid fuel and crushed substances extracted from solid fuel charges to improve the characteristics of modern detonation engines, to improve the characteristics of the technological processes of applying special refractory coatings, and to organize highly efficient combustion processes in the detonation mode of fuel with the production of thermal and electrical energy.