Search Results (309)

Introduction: Advancements in thermo-mechanical surface treatment of endodontic nickel–titanium (NiTi) instruments introduced another aspect of variation. Particularly related to their metallurgy, which influences their behaviour in relation to temperature. This is clinically significant, considering the variation in the temperatures inside the root canal during instrumentation. This study aimed to compare the effects of different temperatures on the bending stiffness, cyclic fatigue resistance, and cutting efficiency of two reciprocating heat-treated NiTi files: R-Motion (RM) and WaveOne Gold (WOG). Methodology: Bending stiffness was examined in a temperature-controlled water bath, measuring the maximum force in Newtons during a 3 mm tip horizontal displacement. The cyclic fatigue resistance was tested in a simulated stainless-steel canal (35° curvature, 6 mm radius) in dynamic mode at 22 °C, 37 °C, and 45 °C. Time to fracture (TTF) and length of fractured fragment were recorded, and representative samples were examined using scanning electron microscopy. The cutting efficiency was assessed using bovine bone slabs measuring 1.5 mm in thickness and 15 mm in width. The files were activated in reciprocation mode for three minutes while resting on the upper surface of the slab, while submerged in a water bath maintained at 22 °C, 37 °C, or 45 °C. The maximum cutting depth was measured in millimetres under magnification. Additionally, Differential Scanning Calorimetry (DSC) analysis was performed for three specimens of each file type. Results: RM exhibited significantly higher TTF, longer fractured fragments, and smaller cutting depths than WOG across all temperatures. The RM was significantly stiffer at 37 °C and 45 °C only. For each file type, increasing the temperature was associated with a significant increase in stiffness (p < 0.01), except for WOG between 22 °C and 37 °C (p = 0.199). The TTF was significantly higher in RM at 22 °C, while the TTF in WOG increased significantly with lower temperatures. No effect was observed on the length of the fractured fragment. Lower temperatures were also associated with reduced cutting efficiency in both files. Conclusions: Temperature has a significant impact on the properties and performance of RM and WOG and should be considered during instrumentation. File design has a greater influence on their strength and cutting ability than their transformation behaviour related to heat treatment. Full article

The feasibility of using brittle δ-Nb₃Al as the reinforcement phase in powder metallurgy nickel-based superalloys depends on both the preparation of near-spherical particles and their phase stability during hot isostatic pressing (HIP). In this study, irregular δ-Nb₃Al particles were converted into near-spherical reinforcement particles by controlled ball milling. The optimized milling condition for obtaining high-sphericity δ-Nb₃Al particles was 200 r/min for 20 h. The morphological evolution during ball milling clarifies a particle-rounding mechanism governed by edge elimination, fine-fragment adhesion, surface consolidation, and re-fragmentation. During subsequent HIP consolidation to introduce the particles into a nickel-based superalloy, extensive interdiffusion occurred between δ-Nb₃Al and the surrounding matrix, resulting in the formation of multilayer interfacial reaction zones and multiple Nb-rich secondary phases, including Laves-(Ni, Cr)₂Nb, Ni₆Nb₇, Nb solid solution, and Ni₃Nb. Quantitative analysis indicates that the retained volume fraction of δ-Nb3Al after HIP is only about 9.85%, much lower than the initial addition level. Combined with thermodynamic analysis based on the effective heat of formation model, the results show that the final phase constitution is governed by the coupled effects of diffusion kinetics and thermodynamic driving force. These findings clarify the intrinsic processing–microstructure–phase transition relationship in δ-Nb₃Al-reinforced powder metallurgy nickel-based superalloys, showing that ball milling controls the powder-state evolution of δ-Nb₃Al, whereas diffusion-driven interfacial reactions during HIP govern its retention and final phase constitution. Full article

Aluminium alloys are extensively considered in aviation and automobiles owing to their lightweight properties and favourable specific strength-to-weight ratio. Generally, the poor surface properties of these alloys limit their application, particularly in sliding conditions. To enhance the surface qualities, particularly the material’s wear resilient features, a unique surface modification process using electro-discharge coating (EDC) has been employed. This work investigates the optimisation of coating variables produced by the EDC technique utilising green compact electrodes composed of 50 wt.% tungsten disulfide (WS₂) and 50 wt.% copper (Cu) powder. The substrate material utilised was AA7075 alloy. The Taguchi–TOPSIS approach was employed to determine optimal EDC process variables, with pulse-on time (T_on), current (I_p), and pulse-off time (T_off). Wear rate (WR), surface roughness (SR), and friction coefficient (CoF) were used to assess the coating features. A wear study was performed with a pin-on-disc device with an undeviating sliding speed (0.25 m/s) and a 25 N load. The results revealed that the supreme features derived from the linear plots were I_p (4 A), T_on (80 µs), and T_off (5 µs). The ANOVA found that I_p had the utmost significant impact, accounting for 44.09%; T_off, 28.01%; T_on, 20.33%; and minimum error, 8.58%. A validation trial with perfect parameters returned values of 0.000179 mm³/Nm (WR), 0.204 (CoF), and 2.818 µm (SR). These findings are significantly better than those of the other coatings. The discrepancy among the estimated and experimental relative closeness in optimal settings is 6.34%, demonstrating that the Taguchi–TOPSIS method is more appropriate for multi-criteria optimisation. Full article

With the opening of complex service routes, the importance of the service performance of brake pads under long slope braking conditions is increasing. It is necessary to analyze the slope braking adaptability of current brake pad products. This work takes the copper-based powder metallurgy brake pads of a certain in-service high-speed train as the research object and conducts friction and wear behavior tests of the brake pads based on a full-scale brake test bench. Through microscopic observation and damage analysis, the differences in friction and wear behavior of the brake pads under stop braking and slope braking conditions are compared, revealing the wear mechanism and damage evolution characteristics of the brake pads. The results show that under the impact of high speed, high braking force, and severe thermal load in the stop braking conditions, the uneven wear of brake pads is high, and the eccentric wear of friction blocks is affected by both the friction radius and friction direction. The friction surface has a large number and size of damages, and the stability of the friction interface is poor. The brake pad exhibits a composite wear mechanism dominated by abrasive wear and brittle fracture induced exfoliation. In the slope braking condition, under the action of low speed, low braking force, and long-term stable thermal load, the uneven wear of the brake pads is relatively low, the surface damage size is small, and the friction block only has eccentric wear along the friction direction. The brake pad mainly initiates cracks along the interface of the components, which propagate parallel to the friction surface, exhibiting a progressive delamination and flaking exfoliation mechanism with a low wear rate. Although the friction interface of the brake pad is relatively stable under slope braking conditions, the cumulative delamination wear of the brake pads under long-term braking action needs further attention. Full article

Cr-based composite coatings with superior wear resistance are in growing demand for high-performance applications in the automotive, aerospace, and general manufacturing sectors. In this study, an Al10Cu alloy produced via powder metallurgy was coated with a chromium/nanodiamond (Cr/ND) composite layer using an electrodeposition process to enhance its tribological performance. The coatings were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray diffraction. The resulting Cr/ND layer exhibited a uniform thickness of 73.5–76.2 μm and markedly improved surface hardness (809.4 HV), representing a 15-fold increase over the uncoated alloy (53.6 HV). Pin-on-disk tribological testing under dry sliding conditions showed complete elimination of detectable mass loss (0.00 mg vs. 0.55 mg for uncoated) within the measurement system resolution, indicating excellent resistance to both abrasive and adhesive wear. XRD analysis revealed the formation of a hexagonal close-packed Cr₂H phase with incorporated nanodiamond particles. To capture and predict the temporal evolution of the friction coefficient, a customized dual-layer long short-term memory neural network—optimized with a look-back window of 3 timesteps and ReLU-activated dense layers—was implemented. The model achieved superior predictive performance on the coated system, with validation and test R² values of 0.9973 and 0.9965, respectively, demonstrating enhanced modeling accuracy for surface-engineered materials. These findings demonstrate a significant advancement in wear protection for aluminum alloys and introduce a robust data-driven approach for real-time friction prediction in engineered surfaces. Full article

Laser processing has been widely investigated as an effective approach for improving surface properties and consolidating advanced materials, particularly complex alloys such as titanium aluminides (TiAl). In this study, laser surface remelting was applied to binary (Ti-45Al) and ternary (Ti-45Al-2Co and Ti-45Al-2Ni) alloys produced by powder metallurgy via blended elemental (BE) and pre-alloyed (PA) powder routes. Laser powers of 50 and 100 W were employed, resulting in a high-energy-density surface remelting regime applied to both green compacts and sintered samples with relatively high initial porosity, under an argon-controlled atmosphere. Microstructural and phase analyses were performed using scanning electron microscopy (SEM) and X-ray diffraction (XRD), while mechanical behavior was assessed by instrumented microindentation. Laser processing promoted the formation of a dense and homogeneous surface layer, approximately 150 μm thick, accompanied by significant microstructural refinement and enhanced hardness and elastic modulus. While rapid solidification led to crack formation in laser-treated sintered samples, the green compacts exhibited defect-free modified layers. Overall, the results demonstrate that laser surface remelting is an effective strategy for enhancing the surface integrity and mechanical performance of TiAl alloys processed by powder metallurgy. Full article

Eutectic alloys stand out for their ability to combine high strength and good ductility; a behaviour rooted in their characteristic two-phase microstructure—lamellar or globular—formed at a constant solidification temperature that minimizes segregation and suppresses brittle phases. Their low interfacial energy limits microcrack propagation, while interfacial sliding and dislocation blocking at phase boundaries enhance both strength and toughness. In this work, we investigate how controlled microstructural modifications influence the behaviour of the eutectic high-entropy alloy AlCoCrFeNi2.1, composed of B2 (Ni–Al-rich) and L12 (Co–Fe–Ni-rich) phases. Because these phases exhibit distinct mechanical responses, microconstituent morphology becomes a design parameter. Powder metallurgy is the only processing route capable of providing the level of microstructural control required in this study. It preserves the rapidly solidified eutectic architecture of gas-atomised powders while allowing its intentional transformation during consolidation. Two strategies were implemented: (i) tuning the thermal–electrical input in Spark Plasma Sintering (SPS) and Electrical Resistance Sintering (ERS), and (ii) engineering the particle size distribution, including a bimodal design that enhances surface-energy-driven morphological transitions. SPS enables a gradual lamellar-to-globular evolution, whereas ERS induces ultrafast transformations governed by current intensity. The bimodal PSD significantly accelerates globularisation at lower energy input. EBSD-KAM (Electron Backscatter Diffraction—Kernel Average Misorientation) mapping identifies the lamellar B2 phase as metastable and highly strained, while globular B2 domains show reduced dislocation density. Nanoindentation confirms that intrinsic phase properties remain unchanged, whereas microhardness scales with morphology and lamellar spacing. These results demonstrate that the macroscopic mechanical response is governed by microstructure, establishing powder metallurgy as a uniquely powerful pathway for microstructure-driven design in eutectic HEAs. Full article

A significant amount of frictional heat is generated during the braking process of mine-used monorail cranes under heavy-load and low-speed creeping (or reciprocating speed regulation) conditions, causing thermal softening and performance degradation of the brake pads. Thus, investigating the tribological evolution mechanism is necessary to ensure reliable braking in deep underground environments. In this paper, full-scale tribological testing technology is applied to the brake system, and the friction and wear characteristics of copper-based powder metallurgy (P/M) brake pads under complex hygrothermal environments are studied. A physical experimental model coupling normal load, sliding speed, and humidity is established using a custom-designed open-structure reciprocating tester, revealing the “load weakening effect” under dry conditions and the “dual regulation mechanism” of mixed lubrication and cooling flushing under high humidity. Then, a surrogate prediction model of friction coefficient and wear rate, with respect to the operating parameters, is constructed based on Central Composite Design (CCD) and Response Surface Methodology (RSM). The reliability of the model under non-linear working conditions is estimated based on Analysis of Variance (ANOVA) and blind tests. The results indicate that the model possesses high prediction accuracy (relative error < 5%), and the feasibility of utilizing the high-humidity environment to enhance wear resistance and stability is verified. Full article

Graphene (GR) demonstrates significant potential in enhancing the mechanical performance of titanium matrix composites (TMCs), particularly by improving their tensile strength, fracture toughness, and fatigue resistance, thereby optimizing the overall structural integrity and durability of the composites; however, their practical implementation confronts two fundamental challenges: achieving uniform dispersion and mitigating excessive interfacial TiC formation, which compromises mechanical properties. This review comprehensively explores progress in the fabrication, interfacial design, and mechanical optimization of TMCs reinforced with graphene-based materials. Various processing techniques, such as powder metallurgy (PM) and spark plasma sintering (SPS), are critically analyzed in terms of their advantages and limitations for producing high-performance TMCs. This article analyzes how key parameters in processes like PM and SPS affect graphene structure, dispersion, and interfacial reactions. It outlines strategies—including surface modification, 3D structural design, and multiscale interface engineering—that enhance both strength and toughness. While progress has been made in microscale performance, challenges remain in engineering stability and long-term reliability. Future work should focus on intelligent process optimization and architectured composite manufacturing. By systematically synthesizing existing research findings, this article clarifies the advantages and limitations of current technological approaches, providing a theoretical foundation and technical roadmap for the subsequent development of graphene-reinforced TMCs that exhibit high strength, high toughness, and excellent reliability. Full article

Cold forging backward extrusion is mainly employed in the manufacturing of axisymmetric cup-like components used extensively in automotive and aerospace assemblies due to the process-induced strength that has a pivotal role in such applications. Although cold forging backward extrusion yields mechanically robust components, it demands high forces, subjecting tooling to immense stress, thereby restricting process capacity. The process encounters hindrances in gaining widespread industrial acceptance due to frequent failures of die elements, necessitating proper die design and control of major influencing factors for process viability and cost-effectiveness. The punches in backward extrusion are often susceptible to failures when processing steel billets. The punch service life is significantly affected by geometrical attributes, the type of steel undergoing deformation, and tool manufacturing aspects. Hence, the present study evaluates punch performance in cold forging backward extrusion using optimized geometrical attributes, manufactured through a design of an experimental approach comprising an L9 orthogonal array. The manufacturing factors considered are punch material, hardness, and advanced surface coating. Punches were designed for two industrial components using powder metallurgy (PM) steels—S600, S290, and S590, heat treated to 60–66 HRC, and coated via physical vapor deposition with TiN, AlTiN, and TiAlCN. Punch performance was analyzed against existing industry practices, and the strategy demonstrated improved productivity. Punch performance was determined based on the number of forgings produced before wear- and fatigue-induced failures. Significant improvements in punch performance were witnessed in both high-speed steel (HSS) and PM punches with optimized geometries. Fractographic investigations were carried out on fractured punches and analyzed, focusing on the coating’s effect on the thermal aspects of the punches. The proposed study will assist the cold-forging industry in determining appropriate variables to minimize forming responses, thereby enhancing tool life. The research also benefits industries by enhancing process robustness and improving process efficiency with respect to cost and time. Full article

Copper (Cu) is widely used in electrical and thermal management systems; however, its low hardness and limited dry sliding wear resistance reduce long-term reliability in friction-loaded conductive components. In this study, Cu–Hf and Cu–Hf–rGO hybrid composites were fabricated by powder metallurgy using 1.0–5.0 wt.% Hf and 1.0–2.0 wt.% reduced graphene oxide (rGO). The microstructure and phase evolution were characterized by SEM/EDS and XRD. Electrical conductivity and hardness were measured, while tribological performance was evaluated by dry sliding wear tests based on mass loss. Post-wear surface characteristics were analyzed by AFM and LFM to assess nanoscale topography and frictional behavior. The hybrid composites exhibited composition-dependent multifunctional enhancements. Electrical conductivity increased from approximately 3.0 × 10⁶ S/m (~5.2% IACS) for pristine Cu to about 2.0 × 10⁷ S/m (~34.5% IACS) for the composite reinforced with 3.0 wt.% Hf and 2.0 wt.% rGO, indicating an optimum Hf–rGO combination that preserves continuous conductive pathways. Hardness increased from 60 ± 3 HV_0.30 to 159 ± 12 HV_0.30 for the composite containing 5.0 wt.% Hf and 2.0 wt.% rGO, demonstrating the dominant contribution of Hf to matrix strengthening and load-bearing capacity. The mass loss after 1000 m of sliding distance decreased from about 0.12 g for Cu to approximately 0.01 g for the 5.0 wt.% Hf–2.0 wt.% rGO hybrid composite, consistent with the concurrent increase in hardness and reduction in frictional shear during sliding. Nanoscale surface analyses revealed reduced surface roughness and frictional response, supporting the formation of a smoother and lower-friction sliding interface in rGO-containing composites. Overall, Hf enhanced load-bearing capacity through matrix strengthening, while rGO contributed to stabilizing conductive pathways and solid lubrication. Full article

This study evaluates the performance of a copper-based metal matrix composite (Cu-MMC) brake pad fabricated by powder metallurgy for high-speed railway braking applications. The material was produced via homogeneous powder mixing, compaction at 650 MPa, and sintering at 950 °C for 2 h to promote densification and metallurgical bonding. The fabricated Cu-MMC exhibited densities of 5.71–5.98 g/cm³, porosities of 5.85–10.1%, and hardness values of 62–73 HV, indicating effective microstructural control. Tribological performance was assessed using a brake dynamometer at an equivalent speed of 160 km/h and a contact pressure of 0.95 MPa. The composite demonstrated a low specific wear rate of 0.11–0.14 cm³/MJ, meeting the TJ/CL 307-2014 standard for high-energy braking. Surface analysis revealed stable frictional behavior dominated by oxidative–abrasive, adhesive, and delamination wear mechanisms. Thermal evaluation showed a maximum operating temperature of 225–235 °C, below the softening temperature of copper, confirming adequate thermal stability. Full article

The steel industry contributes to approximately 7%–9% of global anthropogenic CO_2(g) emissions, with traditional blast furnace–basic oxygen furnace (BF–BOF) routes emitting up to 1.8 t_CO2 per ton of steel. In contrast, Electric Arc Furnace (EAF) steelmaking, especially when integrated with hydrogen direct-reduced iron (DRI), can reduce emissions by over 40%, positioning EAFs as a key enabler of low-carbon metallurgy. However, despite its lower direct emissions, the EAF process still depends on fossil carbon sources for slag foaming and FeO reduction, which are essential for arc stability and energy efficiency. Slag foaming plays a critical role in controlling the thermal efficiency of the EAF by shielding the electric arc, reducing radiative heat losses, and stabilizing the arc’s behavior. This review examines the mechanisms of slag foaming, discussed through empirical models that consider the foaming index (Σ) and slag foaming rate as critical parameters, and highlights the influence of physical properties such as slag viscosity, surface tension, and density on gas bubble retention. Also, the work embraces the potential use of alternative carbon sources including biochar, biomass, and waste-derived materials such as plastics and rubber to replace fossil-based reductants and foaming agents in EAF operations. Finally, it discusses the use of new materials with a biological base, such as nanocellulose, to serve as reactive templates for producing nanohybrid materials, containing both oxides, which can contribute to slag basicity (MgO and/or CaO, for example), together with a reactive carbonaceous phase, derived from the organic fiber’s thermal degradation, which could contribute to slag foaming, and could replace part of the fossil fuel charge to be employed in the EAF process. In this context, the development and characterization of renewable carbonaceous materials capable of simultaneously reducing FeO and promoting slag foaming are essential to achieving net-zero steel production and enhancing the sustainability of EAF-based steelmaking. Full article

The ball mill is a critical size reduction equipment in industries such as mining and metallurgy. However, the sustainable reliability modeling of the entire system is challenging due to its complex service conditions. This paper presents a systematic framework for the reliability analysis of ball mills based on Stress–Strength Interference Theory (SSIT). Based on a reliability block diagram (RBD), this study establishes a system-level reliability model for the ball mill. Within this framework, the cylinder model is developed using the energy conservation principle between impact energy and strain energy; the gear model comprehensively considers both contact and bending fatigue failure modes; and the bolt model is constructed through mechanical analysis in conjunction with Hooke’s law. In the case study, a laboratory-scale mill (Φ5.5 × 2.6 m shell, effective grinding chamber: 5.3 m inner diameter × 2.376 m length) operating at 14 RPM under dry grinding conditions is analyzed. The reliability of individual components and the entire system is computed using Monte Carlo simulation. The results indicate that the overall system reliability increases when one of the following three conditions is met: the surface hardness of the gear is higher and the tangential force is lower; the impact velocity on the cylinder is lower and the impacted area is larger; or the tensile force on the bolt is reduced. Full article

Al₂O₃-TiC/6061Al composites were fabricated via in situ powder metallurgy using 6061 Al, TiO₂, and graphite powders as starting materials. The effects of sintering temperature and ceramic particle content on the microstructure and mechanical properties of the composites were investigated. The wear performance of composites sintered at 1200 °C with varying ceramic particle content was also examined. The results indicate that the microstructure of the composite varied with the sintering temperature. At 1000 °C and 1100 °C, the microstructure primarily consisted of Al₃Ti, Al₂O₃, and TiC phases. At 1200 °C and 1250 °C, the microstructure was predominantly composed of Al₂O₃ and TiC phases. The 6061 Al-12% (TiO₂ + C) composite sintered at 1200 °C exhibited a tensile strength of 246 MPa, an elongation of 12.7%, and a microhardness of 104.2 HV_0.1. Regarding wear performance, the wear behavior of the composites under different loads at 1200 °C was studied. Under a 30 N load, the 6061 Al-12% (TiO₂ + C) composite demonstrated the lowest friction coefficient and wear rate, measured at 0.253 and 0.396 mm³·N⁻¹·m⁻¹, respectively. Analysis of the worn surface morphology under a 30 N load indicates that the dominant wear mechanism for the 6061 aluminum alloy is delamination wear, whereas for the 6061 Al-12% (TiO₂ + C) composite, it is primarily abrasive wear. Full article