Search Results (198)

This work investigated the effect of yttrium addition on the pre-oxidation behavior of Fe–25Ni–20Cr–4Al–1Nb–1Mn–1.5Si-based alloys at 1000 °C in a 4% H₂ + 0.2% CH₄ + Ar + 0.25% H₂O atmosphere. The oxidation resistance and oxide scale adhesion were evaluated through cyclic oxidation tests and micro-scratch measurements. Results show that the Y-free alloy formed a discontinuous oxide layer, whereas all Y-containing alloys formed a continuous and dense Al₂O₃ scale. Incorporating 0.2 wt.% Y increased the work of adhesion by approximately 7 to 9 times relative to the Y-free sample, indicating a pronounced interfacial strengthening effect. The role of yttrium content and oxygen partial pressure in promoting alumina-scale formation was discussed based on thermodynamic considerations and microstructural evidence. Full article

The effects of Ti/Nb microalloying-induced MC-type carbide precipitation and tempered microstructure evolution on the dry-sliding wear behavior of low-carbon martensitic wear-resistant steels were systematically investigated. Three experimental steels with different microalloying strategies (0.04Ti, 0.1Ti, and 0.04Ti/Nb) were subjected to quenching and subsequent tempering. Microstructural features, carbide characteristics, and mechanical properties were characterized using optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD), transmission electron microscopy (TEM), tensile testing, and impact testing, while wear performance was evaluated by pin-on-disk tests under dry-sliding conditions. The results indicate that wear resistance is governed by the combined effects of tempered martensite stability and MC-type carbide precipitation. Low-temperature tempering effectively reduces the wear mass loss of Ti-containing steels by enhancing their resistance to abrasive shear deformation while maintaining sufficient toughness. In contrast, the Nb-containing steel exhibits a stage-dependent wear response associated with the formation and destabilization of oxide-derived third-body debris during sliding. (Nb,Ti)C precipitates act as microscale load-bearing units, contributing to strength enhancement and subsurface damage suppression, but their influence on wear behavior strongly depends on tempering temperature. The dominant wear mechanism is abrasive micro-cutting, accompanied by fatigue-induced spalling and oxidation-assisted damage at later stages. These results demonstrate that wear performance cannot be correlated with hardness alone, but instead requires the coordinated optimization of carbide precipitation and tempered microstructural stability. This work provides microstructural guidance for the design of microalloyed martensitic wear-resistant steels. Full article

A systematic investigation was conducted on the effects of Cr alloying on the tensile behavior and microstructural evolution of TiZrNb medium-entropy alloys at 673 K. For comparison, the influences of Al and Cu alloying on the mechanical properties of TiZrNb were also examined. Although Al and Cu alloying enhanced the ultimate tensile strength at room temperature, their improvements in strength and ductility at 673 K were limited. In contrast, the TiZrNb_98.5Cr_1.5 alloy retained a single body-centered cubic (BCC) phase without forming the conventionally expected Laves phase. Cr effectively suppressed the formation of Zr-rich precipitates. At a strain rate of 1.67 × 10⁻³ s⁻¹ and 673 K, TiZrNb_98.5Cr_1.5 exhibits an increase in the ultimate tensile strength of approximately 408 MPa compared with the base TiZrNb alloy, while the fracture elongation increases from 10% to 25% and the threshold stress rises from 669 MPa to 1196 MPa, achieving a markedly improved strength–ductility synergy. These results indicate that Cr alloying effectively stabilizes the microstructure and enhances the mechanical performance of TiZrNb alloys at 673 K by suppressing precipitate formation and reducing dislocation accumulation, outperforming Al and Cu alloying at the same temperature. Full article

This study investigates the 55%Al-Zn-Si coating system. Using microstructural characterization and thermodynamic simulation, we systematically analyzed its microstructure formation, solidification behavior, and the regulatory effects of Cr, Nb, and V micro-alloying elements. The results show that the typical coating consists of a primary α-Al dendritic skeleton and an interdendritic Zn-rich eutectic phase, exhibiting a characteristic spangle morphology. The addition of Si is crucial. By participating in the formation of a Fe-Al-Si ternary compound layer, it effectively suppresses the intense reaction at the Fe/Al interface, providing essential conditions for the sufficient growth of the outer Al-rich dendrites and the formation of a continuous transition layer. Thermodynamic analysis further clarifies that the coating solidification follows three distinct stages: precipitation of the primary α-Al phase, an Al-Si binary eutectic reaction, and a final Al-Zn-Si ternary eutectic transformation. Regarding micro-alloying, this study reveals the specific roles of different elements: Cr significantly refines the transition layer structure, promoting its transformation from coarse lamellae into a fine and uniform morphology; V tends to combine with Al to form high-melting-point enriched regions, inhibiting the growth of Fe-Al intermetallics and reducing the thickness of the brittle transition layer by approximately 50%; conversely, the addition of Nb disrupts the normal solidification sequence, inducing abnormal segregation of Al-rich and Si-rich phases, which compromises the homogeneity and integrity of the coating structure. Through an in-depth analysis of the fundamental solidification mechanism and micro-alloying effects, this research provides an important theoretical basis for optimizing the microstructure of hot-dip Al-Zn sheets via precise composition design and micro-alloying strategies. Full article

Titanium alloys, particularly β-type Ti-13Nb-13Zr, are promising biomedical materials due to their low elastic modulus and excellent biocompatibility. However, their bioactivity needs improvement for better bone integration. In this study, a calcium-phosphate (Ca/P) coating was prepared on a Ti-13Nb-13Zr alloy via micro-arc oxidation (MAO) in an electrolyte containing calcium acetate and dipotassium hydrogen phosphate. The effect of applied voltage (300 V, 400 V, and 500 V) on the phase composition, surface morphology, and in vitro bioactivity of the coatings was investigated. Surface characterization was performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). The results show that increasing the voltage increased the surface roughness, average pore size, and rutile TiO₂ content in the coating. The Ca/P ratio in the coating approached 1.67 at 500 V, similar to that of natural bone. After immersion in simulated body fluid (SBF) for 20 days, the coating formed at 500 V induced the highest deposition of hydroxyapatite (HA), completely covering the microporous surface. These findings indicate that MAO treatment at 500 V significantly enhances the bioactivity of the Ti-13Nb-13Zr alloy, making it a promising candidate for orthopedic implants. Full article

High-temperature carburization (HTC, 950–1050 °C) has emerged as a pivotal low-carbon, energy-efficient manufacturing technology for gear steels, accelerating carbon diffusion for reducing processing cycles by over 60% while achieving significant energy savings and emission reductions. However, the inherent contradiction between HTC efficiency and microstructural stability, specifically austenite grain coarsening, severely degrades mechanical properties (e.g., strength, toughness, fatigue resistance) and limits widespread application. This review systematically synthesizes recent advances in austenite grain size regulation during HTC of gear steels, focusing on the core scientific framework of “grain coarsening mechanism—regulation strategy—performance enhancement”. It elaborates on thermodynamic and kinetic mechanisms of austenite grain growth, ripening behavior of microalloying precipitates (Nb(C,N), Ti(C,N), AlN, etc.), and their synergistic grain-refining effects. Comprehensive coverage of regulatory strategies (microalloying design, pretreatment technologies, process optimization, and integrated regulation) and characterization techniques is provided, along with a quantitative correlation between grain size, microstructure, and surface performance (wear resistance, corrosion resistance, and fatigue life). Numerical simulation and predictive models (empirical, theoretical, multiphysics coupling, machine learning-based) are critically analyzed, and current challenges (temperature-grain stability trade-off, multifactor synergy understanding, industrial scalability) and future research directions (advanced microalloying systems, intelligent process optimization, cross-scale modeling, green technology integration) are proposed. This review aims to provide theoretical guidance and technical support for optimizing the HTC performance of gear steels, catering to the demands of high-power-density transmission systems in automotive, aerospace, and heavy machinery industries. Full article

Hydrogen embrittlement (HE) critically limits the application of ultra-high-strength press-hardened steels (PHS) in hydrogen-containing environments. This study investigated the effect of Nb microalloying on HE resistance of 1500 MPa-grade PHS. Even with higher hydrogen contents, steel 1500Nb exhibits better HE resistance than steel 1500. The results show that Nb addition plays effective role in grain refinement, mitigating stress concentration, and effectively postponing the initiation of intergranular cracks under hydrogen-charged conditions. Additional, hydrogen diffusivity in 1500Nb steel is lower than 1500 steel, attributed to both grain refinement effect and solute drag effect of Nb. Full article

In this work, the effects of Nb and Mo additions on the precipitation behavior and strengthening mechanisms of three ultra-low carbon Ti-Mo-Nb steels with a predominantly ferritic microstructure were investigated under two different thermo-mechanical processing (TMP) routes. A water-quenching step after hot rolling followed by furnace cooling was found to refine the average precipitate size and increase their volume fraction, leading to a significant strength improvement. Specifically, this process increased the yield strength by approximately 110~180 MPa, reaching levels above 750 MPa, with the 22Mo-Nb steel achieving a peak ultimate tensile strength of ~790 MPa. The precipitates exhibited dispersed, interphase, and grain boundary morphologies, none of which correlated directly with the TMP route or steel composition. While variations in Mo content showed little influence on precipitate characteristics, the addition of Nb markedly promoted precipitation. The strength of these Ti-Mo-Nb ferritic steels is primarily determined by precipitation strengthening. Through optimized TMP parameters and microalloying additions, the overall precipitation strengthening contribution was elevated to the 300~400 MPa range. Full article

Manufacturing heavy-gauge high-strength steel plates with uniform through-thickness properties is challenging due to the limited hardenability and significant cooling rate variations inherent to heavy sections. However, the mechanism governing microstructural homogenization across such large cross-sections remains not fully understood. This study investigates the through-thickness microstructure and mechanical properties of a 60 mm thick high-Nb microalloyed Q690 steel plate processed by direct quenching (AQ) and subsequent tempering at 530 °C and 580 °C. Characterization was performed at the surface (0t), quarter-thickness (1/4t), and core (1/2t) locations. Results revealed a pronounced gradient in the as-quenched state: while the surface consisted of fine lath martensite/bainite, the core formed coarse granular bainite containing blocky martensite–austenite (M-A) constituents. This microstructural heterogeneity resulted in poor core toughness (~24 J). High-temperature tempering at 580 °C promoted the complete decomposition of these metastable M-A constituents into ferrite and fine carbides, significantly improving the core impact energy to ~49 J. However, a toughness gradient persisted compared to the quarter-thickness (>120 J), attributed to the inherited coarse matrix and the formation of grain boundary carbides. Notably, high yield strength was maintained across the thickness despite matrix recovery. This is primarily attributed to a potent anti-softening effect provided by thermally stable (Nb,Ti,Mo)C nanoprecipitates, which generate strong Orowan strengthening. These findings highlight the critical role of optimizing the trade-off between M-A decomposition and carbide evolution in promoting the microstructural and property homogenization of heavy-gauge steels. Full article

The paper focuses on materials characterization and in vivo biocompatibility tests of Ti–6Al–7Nb–0.3REE wt.% alloys (REEs—Y, Ce, La) for use as a promising material to produce personalized medical implants and shed light on possible toxicity effects of REE alloy microdoping. All alloys were produced by the electric arc melting method and characterized by scanning electron microscopy (SEM), optical microscopy (OM), energy-dispersive X-ray spectroscopy analysis (EDX), X-ray diffraction (XRD), true density analysis, micro- and nanoindentation methods, and reducing/oxidation melting techniques. True density of alloys increased in the following order: Ti−6Al−7Nb−0.3Y (4.4563 ± 0.1075 g/cm³) < Ti−6Al−7Nb−0.3Ce (4.7255 ± 0.2853 g/cm³) < Ti−6Al−7Nb−0.3La (4.8019 ± 0.0111 g/cm³). XRD analysis indicated that Ti–6Al–7Nb–0.3Y alloy consisted of single α–Ti phase in comparison with Ti–6Al–7Nb–0.3La (α–Ti to β–Ti = 82 to 18) and Ti–6Al–7Nb–0.3Ce (α–Ti to β–Ti = 90.5 to 9.5). The single-phase Ti–6Al–7Nb–0.3Y alloy had the finest α–Ti phase crystallites (22.32 nm); the larger α–Ti crystallites in the dual-phase Ti–6Al–7Nb–0.3Ce and Ti–6Al–7Nb–0.3La (30.77 nm and 29.83 nm, respectively) suggested the presence of the β–Ti phase (23.34 nm and 25.61 nm, respectively). REE microdoping of alloys changed the lattice volume (∆V): α–Ti phase—0.269% for Ti–6Al–7Nb–0.3Y, 1.799% for Ti–6Al–7Nb–0.3Ce, 0.595% for Ti–6Al–7Nb–0.3La; and β–Ti phase—0.334% for Ti–6Al–7Nb–0.3Ce, 0.670% for Ti–6Al–7Nb–0.3La. Nanohardness (H) and elastic modulus (E) increased in the following order: Ti−6Al−7Nb−0.3La (4.01 GPa and 135 GPa, respectively) < Ti−6Al−7Nb−0.3Y (4.39 GPa and 137 GPa, respectively) < Ti−6Al−7Nb−0.3Ce (4.67 GPa and 146 GPa, respectively). In vivo tests were conducted using 46 sexually mature male Wistar rats by means of skin implantation of samples with d = 11 mm and h = 1 mm. Our research shows that Ti–6Al–7Nb–0.3La alloy (Group 2) and Ti–6Al–7Nb–0.3Ce alloy (Group 3) induced sustained hepatotoxic and nephrotoxic effects. Ti–6Al–7Nb–0.3Y alloy induced a slight local inflammatory response; however, serum biochemical analysis suggested this effect was compensated. Full article

This study employed a Gleeble-3800TM thermal simulator to conduct thermal cycle experiments on the coarse-grained heat-affected zone (CGHAZ) of Nb-Ti-La microalloyed steel under welding heat inputs of 50, 80, 100, and 120 kJ/cm. A systematic analysis was carried out to investigate the influence of heat input on the microstructure and impact toughness of the CGHAZ. The results indicate that the microstructure of the CGHAZ across different heat inputs consists of acicular ferrite (AF), granular bainite ferrite (GBF), polygonal ferrite (PF), as well as hard phases such as M/A constituents and degenerated pearlite (DP). With increasing heat input, the content of GBF decreases monotonically, while the content of PF increases monotonically, and the amount of hard phases rises continuously. In contrast, the content of AF initially increases and then decreases, reaching its peak at 100 kJ/cm. The microstructural changes induced by higher heat input lead to increased inhomogeneity in the local microstrain, thereby causing a monotonic reduction in crack initiation energy. Regarding crack propagation energy, the optimal performance is achieved at 100 kJ/cm due to the formation of a high proportion of AF, which heterogeneously nucleates on La-rich inclusions. This structure provides a high density of high-angle grain boundaries that effectively hinder crack propagation. Consequently, under the combined influence of crack initiation and propagation behaviors, the CGHAZ exhibits the best impact toughness at a heat input of 100 kJ/cm. Full article

A comprehensive investigation was conducted into the microstructural evolution, high-cycle fatigue properties, and corresponding fatigue fracture mechanism of the simulated coarse-grained heat-affected zone (CGHAZ) in low-carbon microalloyed steel with different Nb contents. The results demonstrated that an increase in Nb content led to a higher density of both low-angle and high-angle grain boundaries (LAGBs and HAGBs), a reduction in the mean equivalent diameter (MED), and a refinement of the prior austenite grains (PAGs) in the CGHAZs. The crack initiation lifetimes accounted for over 97% of the total fatigue life in the CGHAZs, thereby establishing it as the dominant mechanism governing fatigue failure. The fatigue strength of the simulated CGHAZs exhibited a continuous increase from 212.6 MPa to 231.9 MPa as the Nb content was increased from 0.018 wt.% to 0.055 wt.%. The augmentation of Nb content has been demonstrated to be a successful strategy for enhancing the CGHAZ fatigue strength of low-carbon microalloyed steels. Full article

In alignment with the European Union’s 2050 carbon-neutrality targets, the automotive industry is intensifying efforts to adopt lightweight materials that ensure structural integrity without compromising safety. Press-hardened steels (PHS), offering a combination of ultra-high strength and formability, are at the forefront of these developments. Standard PHS grades rely on Ti–B microalloying; however, further alloying with Nb and V has been proposed to enhance hydrogen embrittlement resistance via microstructural refinement and hydrogen trapping. This study investigates hydrogen transport and mechanical degradation in a Ti–Nb–V microalloyed PHS compared to a conventional Ti-only 22MnB5 grade. Electrochemical permeation, thermal desorption, and mechanical testing were employed to characterize hydrogen diffusivity, solubility, and trapping mechanisms. The Ti–Nb–V variant demonstrated lower hydrogen diffusivity, higher solubility, and improved resistance to delayed fracture, attributable to the presence of fine NbTiV precipitates. Full article

This study evaluated the surface functionalization of a non-equiatomic TiZrNbTaMo high-entropy alloy (HEA) by micro-arc oxidation (MAO) in Cu-rich electrolytes to tailor its performance for biomedical implants. The Cu content was varied, and the resulting coatings were investigated for their morphology, phase constitution, chemical structure, wettability, and cytocompatibility. X-ray diffraction (XRD) measurements of the substrate indicated a body-centered cubic (BCC) matrix with minor HCP features, while the MAO-treated samples depicted amorphous halo with sparse reflections assignable to CaCO₃, CaO, and CaPO₄. Chemical spectroscopic analyses identified the presence of stable oxides (TiO₂, ZrO₂, Nb₂O₅, Ta₂O₅, MoO₃) and the successful incorporation of bioactive elements (Ca, P, Mg) together with traces of Cu, mainly as Cu₂O. MAO treatment increased surface roughness and rendered a hydrophilic behavior, which are features typically favorable to osseointegration process. In vitro cytotoxic assays with MC3T3-E1 cells (24 h) showed that Cu addition did not induce harmful effects, maintaining or improving cell viability and adhesion compared to the controls. Collectively, MAO in Cu-rich electrolyte yielded porous, bioactive, and Cu-incorporated oxide coatings on TiZrNbTaMo HEA, preserving cytocompatibility and supporting their potential for biomedical applications like orthopedic implants and bone-fixation devices. Full article

Crystal grain size control in steel is critical for achieving mechanical properties. This study investigates the effectiveness of microalloying with titanium, niobium, zirconium, and yttrium to inhibit grain growth with the pinning effect. The comparison of selected microalloying elements in the exact same conditions is crucial for understanding their effect and is novel. Hot-rolled samples were annealed across a wide range of temperatures (1050 to 1200 °C) for up to eight hours. Microstructural analysis confirmed the presence of stable precipitates and non-metallic inclusions such as Nb(C,N), Ti(C,N), ZrO₂, and Y₂O₃ acting as obstacles to grain boundary migration. All microalloying elements significantly outperformed the reference steel, but their effectiveness was highly dependent on the annealing temperature. Titanium was the most effective inhibitor at lower temperatures (1050 °C), while zirconium maintained control up to 1150 °C. Critically, at the highest temperature of 1200 °C, only the yttrium-alloyed steel retained a fine-grain structure, demonstrating superior thermal stability. Niobium, conversely, only showed a minimal effect at 1050 °C, though this grade also exhibited the highest hardness (up to 165 HB) due to precipitation hardening. The kinetics of grain growth were successfully modeled using the Arrhenius-type Sellars–Whiteman equation, accurately describing the behavior for up to four hours of annealing. The findings provide critical insight for selecting optimal microalloying strategies based on maximum operating temperature. Full article