Heavy-duty gears used in rail transit and wind power sectors often require carburizing treatment to enhance their wear resistance during service. However, conventional carburizing processes face certain limitations in improving efficiency. Studies have shown when the rare earth (RE) elements are involved in some way, the carburizing atmosphere may be modified, thus increase the carburizing efficiency, and further enhance the wear resistance of the steels. Nevertheless, most existing research has focused on introducing exogenous RE elements into the steel surface during the carburizing process, while the effect of RE addition during steelmaking on the wear resistance of carburized gear steel remains insufficiently explored. In this study, 18CrNiMo7-6 gear steels with different Ce addition were prepared and subjected successively to heat treating at 1150 ^oC for 6 h, forging at 900 ^oC to 1150 ^oC, normalizing treatment at 880 ^oC for 2 h and followed by carburizing, quenching and tempering etc. Then the effect of RE addition on their friction and wear behavior was characterized via oil-lubricated sliding wear tester, contact profilometry, white light interferometry, scanning electron microscopy, transmission electron microscopy, transmission Kikuchi diffraction, and X-ray photoelectron spectroscopy, in terms of the surface morphology, subsurface microstructure evolution, and oxide scale composition on wear tracks. The results indicate that Ce addition can effectively mitigate the abrasive wear and improve the friction and wear behavior of the carburized gear steels during the steady-state wear stage, transforming the wear mechanism from a coexistence of abrasive wear and oxidative wear to oxidative wear-dominated mechanism, thereby significantly enhancing the wear resistance of carburized gear steel. Compared with carburized gear steel without RE, the wear volume of the carburized gear steels with 0.0078%Ce and 0.0126%Ce (mass fraction) is reduced by 55.3% and 49.2%, respectively. The improved wear resistance after Ce addition may be attributed to the increased hardness of the carburized layer and the modification of inclusion in the steels. The low surface hardness of the steel without RE may facilitate severe abrasive wear and pronounced subsurface plastic deformation, which readily leads to oxide scale fragmentation. Ce addition may be conductive to increasing the surface hardness of carburized gear steels, alleviating the subsurface plastic deformation, facilitating the formation of compact oxide scale, and consequently enhancing the oxidative wear resistance. Nevertheless, with the increasing Ce content, the continuously increased surface hardness results in further suppression of subsurface deformation, and there exists an increase in inclusion population and size. These two factors lead to the formation of thin, discontinuously distributed oxide scales, thereby compromising the wear resistance.

To address the performance inconsistency in hot isostatic pressing powder Ti₂AlNb alloys, herein, the influence of processing parameters on the performance of the HIP powder Ti₂AlNb alloys was clarified so that to achieve the process optimization. First, the clean powder pre-alloyed Ti₂AlNb was prepared by electrode induction melting gas atomization (EIGA) technique. The acquired powder exhibited excellent sphericity, low oxygen content (0.072%), and a microstructure predominantly composed of metastable B2 phase. Then the effect of hot isostatic pressing (HIP) parameters (temperature and holding time) and a secondary HIP treatment on the microstructural evolution and mechanical properties of HIP powder Ti₂AlNb alloy was investigated, aiming to precisely control over the B2/O/α₂ three-phase microstructure. The results indicate that with the increasing HIP temperature from 1030 ^oC to 1050 ^oC, the volume fraction of B2-phase increases from 26.8% to 31.2% in the consolidated alloy, which was accompanied by a rise in room-temperature tensile strength to 1168 MPa and an improvement in elongation at 650 ^oC to 11.2%. With the prolonging HIP holding time from 3 h to 5 h, the fraction of α₂-phase reduced to 12.0% and the standard deviation of room-temperature elongation decreased from ±2.7% to ±1.2%, significantly enhancing the consistency of mechanical properties. The secondary HIP effectively promoted the preferential nucleation and precipitation of O-phase at α₂/B2-phase boundaries, resulting in α₂ -phase microstructure with a broadened unimodal size distribution. TEM analysis revealed the specific crystallographic orientation relationships between the O-phase and parent phases: [\mathrm{2}\overline{\mathrm{1}}\overline{\mathrm{1}}\mathrm{0}]{}_{{\alpha }_{\mathrm{2}}}//[\overline{\mathrm{1}}\overline{\mathrm{1}}\mathrm{0}]_O and [\mathrm{111}]_B2//[\overline{\mathrm{1}}\overline{\mathrm{1}}\mathrm{0}]_O, confirming that the O-phase can form via two distinct precipitation pathways. This study elucidates the mechanisms by which HIP process parameters influence the microstructure evolution of the Ti₂AlNb alloy, providing meaningful reference for the fabrication of high-performance Ti₂AlNb alloy components.

Two test alloys, based on a low Nb-containing solid solution-strengthened Ni-Cr-based alloy with addition of 0.2Al+0.2Ti or 0.5Al+0.5Ti, were made by vacuum melt-casting, and then subjected to solution treatment at 1200 ^oC for 1 h and water cooling, followed by long-term aging for 10,000 h at 650 ^oC and 700 ^oC respectively. Then the effect of the Al+Ti contents on the microstructure and mechanical properties of the test alloys was investigated through thermodynamic calculations, microstructural characterization, and mechanical testing. Results show that an increase in Al+Ti content reduces the solid-liquid phase transition temperature, narrows the solidification range, and promotes the segregation of Nb and Al elements. After long-term aging treatment, the main second phase is M₂₃C₆ carbides for the 0.2Al+0.2Ti alloy, whereas for the 0.5Al+0.5Ti alloy is mainly γ′-precipitates. With the increasing exposure time, the γ′-phase undergoes significant coarsening, and its morphology transforms from cubic to rounded square. The effect of Al+Ti content on solid solution strengthening is limited, and the strength difference between the two alloys remains insignificant even after aging treatment for 10000 h, although their strengthening mechanisms differ. In the 0.2Al+0.2Ti alloy, the fine and discretely distributed M₂₃C₆ carbides effectively enhance the alloy strength during thermal exposure. In contrast, in the 0.5Al+0.5Ti alloy, the larger γ′-phase turns to split after aging for 10000 h, leading to smaller in particle size while higher in quantity and density, thereby contributing to an increase in strength.

The resistance spot welding of 1.3 mm-thick GH3536 nickel-based superalloy sheets was performed via DZ-X100 three-phase secondary rectifier spot welding machine with spherical electrodes made of BeCoCu-alloy, aiming to simulate the actual operating conditions in a production line, and to examine the applicability of the electrodes and their failure process after long term service. The results show that the useable number of times of the BeCoCu-alloy electrodes is approximately 220 times for spot welding. When the electrode fails, it can be observed that on the electrode end surface, metals-accumulation and -adhesion occur, the grains size increases, and pits appear due to erosion. These may be ascribed to that during welding, elements such as Fe, Ni, Cr etc. in the superalloy may diffuse inwards the electrode to form (Fe, Ni) substitution solid solution, as well as brittle intermetallic compounds such as Fe_0.7Cr_0.19Ni_1.1, Cr_0.19Fe_0.7Ni_0.11 and Cu_0.81Ni_0.19. Such alloying process may cause microcracks on the electrode surface, which is conductive to the occurrence of failure and spallation. The failure process involves the transformation of the alloy texture from stronger cubic {100}<001> and {110}<100> textures to weaker cubic<111>||ND texture, resulting in reduction of its relative strength from 4.12 and 5.62 to 3.05. Additionally, during the service process of BeCoCu electrode, the amount of high-angle grain boundary increases, which promotes alloying process of the electrode. These factors together lead to electrode failure.

To enhance the corrosion resistance of stainless steel, this study developed a composite nanofiller, ZIF-8/GO/Phen, composed of a zeolite imidazolate framework (ZIF-8), graphene oxide (GO), and the corrosion inhibitor 1,10-phenanthroline (Phen). This filler was incorporated into an epoxy acrylate resin (EA) matrix to fabricate a ZIF-8/GO/Phen-EA anti-corrosion coating. Furthermore, polyaniline (PANI) was subsequently electrodeposited to construct a dual-layer coating system (PANI/ZIF-8/GO/Phen-EA) with synergistic protective functions, including physical barrier, anodic protection, and inhibitor release capabilities. The composition, structure, and morphology of the synthesized materials were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The acidic corrosive environment was simulated using 0.1 mol/L hydrochloric acid solution, and the anticorrosion performance and service stability of the coating were systematically assessed using electrochemical techniques. The results indicated that the incorporation of ZIF-8/GO/Phen markedly improved the compactness of the coating, imparted active protection functionality, and strengthened its barrier effect against corrosive media. At a filler content of 1.5%, the ZIF-8/GO/Phen-EA inner-layer coating exhibited optimal corrosion resistance. After the introduction of the PANI outer layer, the self-corrosion current density of the composite coating further decreased, accompanied by a significant increase in impedance modulus. This resulting PANI/ZIF-8/GO/Phen-EA composite coating demonstrated good self-healing capability, effectively inhibiting the corrosion process of stainless steel in acidic environments.

The flue gas generated from combustion of high-chlorine containing coals may induce severe corrosion on boiler heat exchanger tubes due to chlorine-containing species, significantly compromising the operational safety. Herein the high-temperature corrosion behavior of boiler steel 12Cr1MoVG was investigated in flue gas containing different chlorine species. For this purpose, a high-temperature corrosion test rig was established to simulate the flue gas environment (Cl₂/HCl + CO₂ + H₂O + N₂, 550 ^oC/650 ^oC) in boilers firing high-chlorine coal while containing different forms of chlorine. The corrosion behavior of the steel was characterized by means of mass loss measurement, SEM-EDS, XRD, and thermodynamic calculations. The results revealed that temperature significantly influences material corrosion. When temperature increased from 550 ^oC to 650 ^oC, oxide scale thickness increased by 232.4 µm with a corresponding mass loss increase of 21.26 mg/cm². Microcracks developed in the surface oxide scale due to thermal stress. Under identical conditions, Cl₂ induced more severe corrosion than HCl. When the corrosion of steel in artificial flue gas containing HCl may generate volatile FeCl₂, whose sublimation created porous pathways allowing HCl penetration through the oxide scale to react with the steel substrate, simultaneously inducing transverse and longitudinal cracks. In contrast, when exposure to ones containing Cl₂ the steel corrosion could induce the formation of FeCl₃, which volatilizes at lower temperatures, producing dense porosity that facilitated inward chlorine diffusion and subsequent reaction with the steel substrate, ultimately causing severe oxide scale delamination and spallation. Chlorine-induced high-temperature corrosion of the steel follows an autocatalytic cycle: HCl/Cl₂ reacts with the steel to form volatile iron chlorides (FeCl₂/FeCl₃). These compounds volatilize and undergo oxidation with H₂O, regenerating HCl to sustain the corrosive cycle. This process ultimately leads to metallic oxide scale degradation through delamination and spallation. The stronger oxidizing capability of Cl₂ and higher volatility of its corrosion products result in more severe material degradation compared to HCl.

To investigate the strengthening effect of laser shock processing on Al_xCoCrFeNi (x = 0, 0.3, and 0.7) cladding layers with different Al contents, Al_xCoCrFeNi (x = 0, 0.3, and 0.7) high-entropy alloy layers were prepared on the surface of a 304 stainless steel substrate by laser cladding and subsequently subjected to laser shock processing for strengthening. The phase composition, microstructure, element distribution, microhardness, and wear resistance of the cladding layer were characterized before and after laser shock processing. The results showed that the phase composition of the Al_xCoCrFeNi cladding layer remained unchanged after laser shock processing. A plastic deformation zone (impact-affected zone) was observed in the upper part of the cladding layer. With increasing Al content, the phase of the cladding layer transitioned from single-phase FCC (Al₀ and Al_0.3) to FCC+BCC (Al_0.7), and the cladding layer was composed of columnar crystals at the bottom and equiaxed crystals in the middle and upper parts. The hardness of the cladding layers (x = 0, 0.3, and 0.7) increased by 53.9%, 42.1%, and 25.8%, respectively. Both the wear rate and friction coefficient decreased accordingly. At x = 0.7, the optimal wear resistance was achieved, with the wear rate reaching a minimum of 4.29 × 10^-5 mm³/(N·m) and the friction coefficient reaching 0.542. The main wear mechanisms of the cladding layers at x = 0 and x = 0.3 were adhesive and abrasive wear. At x = 0.7, the wear mechanism remained dominated by abrasive wear, while the cracks and spalling on the worn surface decreased.