Oxide entrainment and uncontrolled thermal histories limit open-arc deposition of reactive magnesium–rare-earth (Mg–RE) alloys. Here, Mg–9.54Gd–1.82Y–0.44Zr wire was deposited by wire-arc additive manufacturing (WAAM) using cold metal transfer (CMT), local trailing Ar shielding, and CMT-Advance polarity modulation. Relative to unprotected deposition, porosity decreased from 0.065% to 0.040%, while the X-ray computed tomography (CT)-detectable oxide-related defect fraction decreased from 0.02300% to 0.00047%. A three-dimensional arch-bead heat-transfer model was calibrated against complete thermocouple histories. Peak-temperature errors were 0.09–1.07%, and 0–100s root-mean-square errors (RMSEs) were 3.37–10.02 °C. Model-consistent net heat inputs were 226.7, 103.9, 113.9, and 107.1Jmm⁻¹ for CMT and CMT-Advance positive-electrode/negative-electrode (EP/EN) ratios of 0, 1, and 5, respectively. CMT-Advance increased the thermal gradient (G) and cooling intensity at the stable section, while the ratio of thermal gradient to interface velocity (G/R) increased strongly towards the substrate. Electron backscatter diffraction (EBSD) showed weak textures and a representative minimum mean grain size under EP/EN = 0. X-ray diffraction (XRD) was dominated by α-Mg and contained weak reflections indexed to Mg₂₄(Gd,Y)₅. Scanning electron microscopy (SEM) of the fracture surfaces showed dimpled rupture in all conditions, with a more uniform ductile morphology after shielding. The shielded CMT-Advance condition achieved 154.8 ± 2.8MPa yield strength, 250.6 ± 0.9MPa ultimate tensile strength, and 10.0 ± 0.2% elongation. These results separate oxygen-supply control from polarity-dependent heat input and residual-film transport within a process–microstructure–property framework.
Time–temperature–transformation (TTT) diagrams are essential for describing isothermal phase transformation kinetics in carbon and low-alloy steels and for designing heat-treatment schedules. However, their experimental construction requires extensive metallographic characterization over wide temperature–time domains, limiting rapid compositional screening. In this study, ensemble boosting algorithms were systematically evaluated for predicting four critical phase boundaries: Pearlite Start (Ps), Pearlite End (Pe), Bainite Start (Bs), and Bainite End (Be). A dataset comprising 93 experimentally reported TTT diagrams was digitized and preprocessed using strict correlation filtering and normalization procedures. Independent regression models were developed with 10-fold cross-validation and evaluated using both conventional random splitting and a stricter steel-wise compositional split strategy to assess generalization across unseen steel compositions. Among the studied models, including AdaBoost, Gradient Boosting, LightGBM, XGBoost, and CatBoost, the CatBoost model exhibited the most consistent performance, achieving (R2 ≥ 0.97 for pearlitic transformations (RMSE as low as 12°C) and stable accuracy for bainitic regions (RMSE ≈ 22°C). SHAP analysis identified transformation time, carbon, and nickel as dominant predictors, consistent with established transformation theory. The model was further validated using a steel-wise compositional split, and TTT curves for 15 independent (unseen) steel compositions were predicted. Validations against experimentally reported TTT diagrams demonstrate strong agreement between reconstructed and reported TTT curves, including accurate prediction of the transformation nose. These results demonstrate that boosting-based models provide an accurate and interpretable framework for rapid estimation of TTT diagrams, thereby helping to reduce experimental effort and supporting alloy and heat-treatment design
Metal AM has become an enabling technology for smart and sustainable manufacturing because of its advantages, including high material utilisation, design freedom and waste reduction in the production of complex parts. This review critically analyses the interactions among processing parameters, feedstock properties, microstructural changes and the operating performance of metal AM systems. Special focus is given to the transition from traditional metallic materials to materials systems featuring multiple length scales and/or nanoscale features, such as nanoparticle-reinforced metals, metal matrix nanocomposites and advanced alloy designs. Feedstock engineering, defect formation and the impact of new solid-state AM technologies on component quality and reliability are discussed. Moreover, the review emphasises the contribution of nano-engineered materials to grain refinement, bonding at the interfaces, mechanical property enhancement and multifunctional performance. The integrated process–feedstock–microstructure–property approach is suggested to develop high-performance and defect-controlled AM components. Lastly, prospects in the fields of intelligent process control, sustainable feedstock design and next-generation smart manufacturing systems are presented. This review provides a comprehensive overview of the use of advanced materials to facilitate sustainable and high-value metal AM.
Due to the need to expand copper production resources, it is becoming necessary to extract copper from substandard ore. This category of ores includes chalcopyrite-magnetite ore from the Irisu deposit, containing up to 0.92% copper and 65.7% magnetite. This article presents the results of studies using thermodynamic computer modeling with the HSC-10 system, built on the minimum Gibbs free energy principle, on the extraction of copper and other non-ferrous metals by chloride sublimation in the presence of sodium chloride and boron oxide, as well as the results of electric smelting of ferrosilicon from roasting residue. Thermodynamic modeling was employed to determine the effects of pressure and temperature on the chloride sublimation of Cu, Zn, Pb, Co, and Ag, with inhibition of iron chlorination and its conversion to roasting residue. It was found that decreasing the pressure from 0.1 to 0.001bar leads to a decrease in the almost complete (98%) conversion of copper into gaseous chlorides from 1680 to 1100 °C, zinc - from 900 to 680 °C, lead - from 900 to 650 °C, cobalt - from 1200 to 1000 °C and silver - from 1700 to 1100 °C. Optimum temperature and pressure ranges (1115-1200 °C and 0.0204-0.001bar) were found, in which a complete conversion of copper, zinc, silver, cobalt, and lead into gas occurs. Undesirable chloride sublimation of iron in these ranges does not exceed 0.3%. Chloride sublimates formed at 1200 °C and 0.01bar contain 24.2% Cu, 8.9% Pb, 4.6% Zn, 2.2% Co and 0.2% Ag. The concentration of copper in the sublimates was 31.8%, zinc, lead, cobalt and silver 32.8-33.8%. Ferrosilicon Grade FeSi25, containing 28.3-30% silicon, was generated by electric smelting in an electric arc furnace of the residue from the chloride sublimation roasting of the Irisu deposit ore, containing 75% iron oxides (including 54% Fe3O4) together with coke and quartzite.
The influences of separately adding 0.5wt% Mn and Y elements, as well as hot rolling on the microstructure, texture, mechanical behavior, and strengthening of homogenized Mg–4Zn alloy were investigated. Optical and scanning electron microscopy showed that while the grain size of homogenized Mg–4Zn alloy was significantly reduced by Mn addition, it was increased by Y addition due to the coarse intermetallic particles accumulated at the grain boundaries and the lower capability of Y in grain growth restriction. Hot rolling reduced grain size in both Mn- and Y-containing alloys, where the finest grain size of 16µm was achieved in the Y-bearing alloy. New second phase particles, such as Mn-rich and Mg3Zn6Y compounds, were formed at the expense of MgZn2 particles. Texture analysis showed that by adding Mn and Y elements, the relatively weak basal texture of the Mg–4Zn alloy was changed to basal pole splitting toward the TD in the homogenized state. Besides, hot rolling produced a strong basal texture in all three alloys, and the addition of Mn and Y decreased texture intensity due to dynamic recrystallization (DRX) and finer grain structure. Mechanical properties, assessed by shear punch testing (SPT), showed improved strength with the addition of the third elements and hot rolling. Quantitative analysis revealed that grain size and solid solution strengthening mechanisms are responsible for improved shear yield stress in both Mn- and Y-containing alloys after hot rolling.
Magnesium alloys are considered promising lightweight materials for automotive, aerospace, and other structural applications due to their low density and high strength-to-weight ratio, their limited strength, hardness, and wear resistance limit their wider industrial utilization. The present investigation is to evaluate the synergistic effects of Ti3SiC2 MAX-phase particles, NiTi shape-memory alloy, and graphene oxide (GO) particles on the microstructure, mechanical and tribological performance of stir-cast ZE41 hybrid composites. Eight samples with various weight percentages (wt.%) of Ti3SiC2 and NiTi and a constant GO were fabricated using the stir casting process under an argon gas atmosphere. Investigated experimental densities ranged from 1.803 to 2.232g/cm³, while porosity increased from 2.01% to 4.19% with increasing reinforcement wt.%, as revealed by density and porosity measurements. The microstructure and interfacial bonding were significantly refined and improved by the hybrid reinforcements, as confirmed by comprehensive characterization. The best composition, Cast-5 (88wt.% ZE41 + 5wt.% Ti3SiC2 + 5wt.% NiTi + 2wt.% GO), exhibited the maximum microhardness value of 86.2 HV and compressive strength (CS) of 227.9MPa, which are 37.5% and 46.75% higher than the unreinforced ZE41. The specific wear rate was reduced from 0.000516 to 0.000223mm³/N·m, which showed an improvement in wear resistance of 56.8%. Wear surfaces were examined by SEM, and it was found that the base alloy suffers from severe abrasive-delamination wear, and the optimized composite undergoes mild abrasive wear. The results reveal the promising performance of the ZE41 hybrid composites for lightweight potential utilization in automotive systems and aerospace industries.
Aging-induced precipitation strongly affects the corrosion behavior of Al–Li alloys, yet intergranular corrosion (IGC) and stress corrosion cracking (SCC) may respond differently to changes in precipitation and grain-boundary microstructure. In this work, the precipitation behavior, grain-boundary microchemistry, electrochemical response, corrosion-induced hydrogen absorption, IGC susceptibility, and SCC behavior of 2050 Al–Li alloy subjected to T6, T8, and double aging treatments were systematically investigated. T8 aging promoted the formation of fine and densely distributed intragranular T1 precipitates through deformation-assisted nucleation, whereas double aging produced coarser intragranular T1 precipitates and more discontinuous grain-boundary precipitation. The maximum IGC depth decreased from 190.08 μm under T6 aging to 113.12 μm under double aging, indicating a marked improvement in IGC resistance. In contrast, the SCC susceptibility index increased from 10.11% under T6 aging to 19.15% under double aging, while the T8 alloy showed intermediate behavior. The results suggest that IGC propagation is mainly associated with the continuity of the electrochemically active grain-boundary path formed by grain-boundary precipitates and adjacent solute redistribution. By comparison, SCC is influenced by the combined effects of interfacial electrochemical behavior, stress-assisted localized dissolution, and hydrogen-related processes. Consequently, the IGC and SCC resistance rankings show opposite trends under the investigated aging conditions.
Microwave dielectric ceramics are essential components in high-frequency communication systems, serving as filters, resonators, antennas, and substrates. CaO-SiO2-based ceramics are attractive candidates for such applications due to their low permittivity (εr) and cost-effectiveness. Nevertheless, the high sintering temperature (∼ 1400 °C) constrains their practical application. In this work, the effects of Li2CO3, Na2CO3, Li2CO3-B2O3, and ZnO as sintering aids on the CaSiO3 matrix are systematically investigated. The effects on phase evolution, crystal structure, densification behavior, and microwave dielectric properties are examined to elucidate the structure–property relationships. Analysis reveals that the CaO-SiO2-0.02Li2CO3 ceramic develops a highly ordered crystalline structures and uniform microstructures, delivering optimal dielectric properties (εr ∼ 6.13, Q×f ∼ 38,600 GHz, TCF ∼ −36.62 ppm/℃ @1100 °C). Incorporation of B2O3 enhances the fluxing effect, strengthening the Li2CO3-B2O3-assisted sintering effect and further lowering the sintering temperature (∼1000 °C), although its Q×f decreases slightly (33,500 GHz). This study advances the theory of low-temperature sintering for CaO-SiO2-based ceramics, underpinning their application in high-frequency devices like satellite communication resonators.
This study aims to investigate the combined effects of friction time and post-weld heat treatment on the microstructural evolution and mechanical properties of rotary friction-welded AISI 1015/AISI 304 joints. The welding process was performed at friction times of 3 and 5 s, and the sample welded at 5 s was subjected to PWHT. PWHT was conducted on the joints at temperatures of 300 °C, 400 °C, and 500 °C for 1 h, followed by air cooling. The tensile and microhardness tests were employed to assess the mechanical properties of the joints. Optical microscopy, scanning electron microscopy (SEM), and X-ray diffraction (XRD) were utilized for microstructural characterization and fractography. Results depicted a residual stress reduction at elevated temperatures. The joint strength increased with increasing welding time (up to 5 s) and the PWHT temperature (up to 400 °C). The maximum joint strength was achieved at a friction time of 5 s (440.5 MPa), which was followed by PWHT at 400 °C and then yielded a maximum tensile strength of 449.9 MPa and efficiency of 107.3%. Furthermore, maximum elongation was observed in the PWHT500 sample (8.32%). The weld zone hardness of the sample welded at 5 s equals 275 HV, which decreased to 250 HV after PWHT at 500 °C. Microstructural analysis confirmed the formation of recrystallized grains and annealing twins as well as delta ferrite. At the same time, the fractography indicated increased brittleness with increasing welding time and softening at higher PWHT temperatures.
This study investigates the effect of electromagnetic vibration-assisted gas tungsten arc welding (GTAW) on the microstructure and impression creep behavior of Hastelloy X weld metal fabricated using ERNiCrMo-2 filler metal. Electromagnetic vibration at a frequency of 300Hz was applied during welding to modify microstructural evolution. Unlike previous studies that primarily focused on microstructural refinement and room-temperature mechanical properties, the present work systematically establishes the relationship between electromagnetic vibration-induced microstructural modifications and the high-temperature impression creep behavior of Hastelloy X weld metal. Microstructural characterization was performed using optical microscopy, Field Emission Scanning Electron Microscopy (FESEM), and Energy Dispersive Spectroscopy (EDS), while impression creep tests were conducted at temperatures ranging from 973 to 1073K under applied stresses of 400–500MPa. Electromagnetic vibration refined the dendritic structure, reduced Mo segregation, and promoted a more homogeneous distribution of M₆C carbides. Compared with the conventional weld metal, the vibration-assisted weld metal exhibited up to a 42% reduction (observed at 973K and 500MPa) in steady-state impression velocity. The stress exponent increased from 3.2–3.7 to 4–4.7, while the average activation energy increased from 518 to 669kJ/mol, indicating enhanced resistance to thermally activated deformation. The obtained stress exponent values suggest that creep deformation was predominantly governed by a dislocation climb-controlled mechanism in all samples. Post-creep microstructural observations revealed the smallest deformation zone and the least microstructural distortion beneath the indenter in the vibration-assisted weld metal. These findings demonstrate that electromagnetic vibration-assisted GTAW is an effective approach for enhancing the high-temperature creep resistance of Hastelloy X weld metal, thereby improving its suitability for elevated-temperature service applications.
Stress shielding and implant-associated infection are the primary causes of orthopedic implant failure. Low-modulus metastable beta-Ti alloys are promising implant candidates, yet face the key challenge of balancing mechanical, corrosion-related, and biological properties. Herein, we developed a series of Gallium (Ga)-alloyed metastable beta Ti-Zr-Nb-Sn-Ta (TZNST) alloys, and systematically investigated the effects of Ga content (0-2.5 at%, denoted as TZNST-Ga-x) on their microstructure, mechanical attributes, corrosion performance, and in vitro cytocompatibility and antibacterial efficacy. All as-cast TZNST-based alloys exhibited a single metastable beta-phase structure, with Ga addition inducing fine dendritic structures. The TZNST-based alloys achieved a maximum 22% yield strength increment (638.3-780.7 MPa), approximately 50% compressive plasticity without catastrophic fracture, and a low elastic modulus (58.1-63.7 GPa). Among the series, TZNST-Ga-2.0 delivered the optimal comprehensive performance: it exhibited a 3.7-fold higher polarization resistance than the base alloy (TZNST-Ga-0.0) in Hanks' Balanced Salt Solution (HBSS), a MC3T3-E1 cell viability of > 98%, and an inhibition rate of 88.80% against Escherichia coli (E. coli) and 85.12% against Staphylococcus aureus (S. aureus). The antibacterial efficacy of the Ga-containing TZNST alloys arises primarily from the sustained release of Ga3 + ions from the passive film. This system possesses pH-responsive Ga3+ ion release behavior. The release of Ga3+ ions is remarkably promoted under acidic microenvironments, which endows the system with microenvironment-targeted antibacterial capability. It can be concluded that this class of Ga-alloyed beta-Ti alloys can address two important clinical problems regarding orthopedic implants, representing a promising strategy for developing multifunctional biomedical titanium materials.
Corrosion is the primary barrier for reduced safe service life of any reinforced concrete (RC) structure, particularly in the chloride-rich marine environment. Quenched and auto-tempered (QAT) reinforcing steel rebars offer superior strength and cost advantages over hot-rolled and normalized (HRN) counterparts, yet their corrosion susceptibility in aggressive environments remains a critical limitation. This study systematically investigates the corrosion behaviour of QAT (75 G) and HRN (60 G) steel rebars through a comprehensive experimental program. Microstructural characterization using optical microscopy revealed distinct case-core structures in QAT steels, which is absent in HRN steels. Tensile testing confirmed compliance with BDS ISO 6935-2:2021 standards for all grades. To evaluate corrosion behaviour, reinforced concrete specimens were cast, water-cured for 28 days, and subsequently exposed to a 3 wt% NaCl solution for up to 10 weeks. Corrosion performance was evaluated through macrocell corrosion current measurements, complemented by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization (PDP). Post-exposure surface morphology analysis and Fourier Transform Infrared spectroscopy (FTIR) of corrosion products provided further mechanistic insight. X-ray diffraction (XRD) analysis revealed significantly higher compressive residual stress and microstrain in QAT steels, which showed strong linear correlations with corrosion current. Controlled additions of Cu, Cr, and Ni progressively modified rust layer and interface characteristics, consequently reducing corrosion current in QAT steels, with the best-performing alloy (75G-4: 0.15%Ni, 0.18%Cr, 0.18%Cu) achieving corrosion resistance comparable to HRN steel at only a similar to 5% cost increase. These findings demonstrate a practical cost-effective pathway toward high-strength, corrosion-resistant QAT rebars for durable RC structures in marine environments.
This research evaluates the fabrication and comprehensive analysis of hybrid aluminum metal matrix composites (AMMCs) reinforced with Aloe vera Powder (AVP) and Eggshell Powder (ESP) using stir casting process. Three different types of composites i.e., AS1 (base sample), AS2, and AS3 were fabricated varying the composition of AVP keeping the composition of ESP fixed. The samples were undergone for different types of tests to determine the properties of the fabricated composites. From the tensile test, it was observed that the reinforcement greatly improved mechanical properties, with the AS2 composition showing the highest tensile strength of 153.61 MPa, a 28% increase from the base sample. SEM micrographs highlighted optimal reinforcement distribution in AS2, with slight agglomeration and micro-void formation in AS3, consistent with slightly reduced strength. EDX analysis confirmed the presence and successful incorporation of O and C elements from ESP and AVP, respectively. FTIR and XRD spectra demonstrated the retention of functional groups and stable FCC crystal structure with sharpened peaks in the reinforced samples. DTG and DSC studies confirmed improved thermal stability and heat absorption capacity of the hybrid samples, especially AS2. Density measurements exhibited increments with the addition of ESP and efficient particle arrangement. Hardness measurements evaluated significant increases from AS1 to AS3. This work proves that the combined ESP and AVP reinforcement was needed for the production of a low-cost and high-performance eco-friendly composites for engineering applications, wherein optimal filler proportions can be improved mechanical, physical and thermal properties of aluminum composites.
This study investigates the mechanical and tribological performance of LM26 aluminum alloy and its hybrid composites reinforced with almandine garnet and MoS2. The composites were fabricated using a bottom-pouring, two-step stir casting method with almandine garnet reinforcement ranging from 5 to 20 wt% and MoS2 from 1 to 4 wt%. Sliding wear tests performed on a Linear reciprocating tribometer, analyzed through Taguchi optimization, confirmed that this composition also achieved the lowest wear rate. Microstructural examination revealed uniform reinforcement dispersion, almandine garnet and MoS2 surface coating formation, and temperatureinduced oxidation influencing wear progression. Among the developed composites, the specimen reinforced with 5 wt% almandine garnet demonstrated the most balanced combination of mechanical strength and overall performance. However, Taguchi optimization of tribological parameters identified the composite containing 20 wt% almandine garnet and 4 wt% MoS2 as the optimum configuration for minimizing wear. The optimal parameter combination was obtained at A1B1C1D1E4, corresponding to Load (A1) = 20 N, Frequency (B1) = 20 Hz, Stroke Length (C1) = 2 mm, Temperature (D1) = 50 degrees C, and Filler Content (E4) = 20 wt%, achieving an optimization accuracy of 98.76%.
Copper-based metal matrix composites reinforced with varying weight percentages (0, 2, 5, 7, and 10 wt%) of powdered titanium carbide (TiC) particles were successfully fabricated using stir casting, followed by hot rolling as a secondary processing route to enhance their mechanical performance. The microstructural evolution, phase characteristics, and mechanical behaviour of both as-cast and hot-rolled composites were systematically studied. Microstructural examination revealed a dendritic grain structure with non-uniform grain size distribution in ascast composites, whereas hot-rolled composites exhibited a refined lath-shaped grain structure with uniform TiC particle distribution, attributed to the plastic deformation induced during rolling. XRD analysis confirmed the presence of high-intensity copper matrix peaks in hot-rolled composites and relatively stronger TiC peaks in ascast composites due to the fragmentation of coarse reinforcement particles during rolling. Mechanical testing demonstrated that hot rolling significantly enhanced both hardness and tensile strength compared to the as-cast condition. The Brinell hardness of the hot-rolled Cu-10 wt% TiC composite reached 59.54 BHN, representing a 42.1% improvement over as-cast pure copper (41.9 BHN). Similarly, the ultimate tensile strength (UTS) of the hot-rolled Cu-10 wt% TiC composite achieved 182.5 MPa, corresponding to a 50.3% improvement over as-cast pure copper (121.4 MPa). However, ductility decreased progressively with increasing TiC content and hot rolling, from 71.56% in as-cast pure copper to 48.69% in hot-rolled Cu-10 wt% TiC, owing to strain hardening effects and grain boundary restriction by TiC particles. The optimal combined strength-ductility balance, assessed through the strain hardening parameter (UTS & times; % elongation), was achieved at 5 wt% TiC reinforcement in both as-cast and hot-rolled conditions. Fractographic analysis revealed a progressive transition from ductile dimple fracture to mixed-mode and predominantly brittle fracture with increasing TiC content, consistent with the observed mechanical trends.
This work aimed to determine the feasibility of dissimilar weld joints between high-manganese austenitic stainless-steel pipes of grades 201LN and 214 using the autogenous gas tungsten arc welding (GTAW) process. Three different welding speeds, designated as 1.5, 2.5, and 3.5mm/sec, were used, and the weld joints produced were subjected to analysis of weld bead shape integrity, microstructure in solidification mode and delta-ferrite content, mechanical properties, and pitting corrosion resistance. The dissimilar weld joints were confirmed to be free of defects upon completion. As welding speed increased, the weld bead size decreased, delta-ferrite content decreased, micro-hardness increased, and ultimate tensile strength increased, whereas percentage elongation decreased. The pitting corrosion resistance increased to levels higher than those of both base metals. It was concluded that increasing the welding speed enhanced productivity and could potentially resolve issues encountered in the seafood production industry.
Structural materials in nuclear reactors operate under extreme conditions, including high temperatures, intense irradiation, and corrosive environments. These conditions drive complex microstructural evolution and degradation of mechanical properties. Accurate modelling of these behaviours is essential for predicting component lifetimes and ensuring reactor safety. In recent years, machine learning (ML) has attracted growing interest as a powerful tool for accelerating material modelling and capturing complex environmental effects by exploiting large datasets generated from experiments and simulations. This review critically evaluates the application of ML techniques to the modelling of nuclear structural materials and provides readers with a comprehensive guide to their use in this field. We begin with a conceptual overview of machine learning in material modelling, and highlight key modelling dimensions and representative ML architectures that underpin current applications. The existing literature is then analysed by grouping studies according to material class, while the ML methods employed and their respective application purposes are presented in detail. Finally, ML applications are presented and discussed in relation to the extreme environmental conditions encountered in nuclear systems, followed by a critical evaluation of current challenges and future directions.
Metal-matrix composites have gained wide recognition owing to their superior tailorability, which surpasses that of traditional alloys. The development of multicomponent metal-based high-entropy alloy (HEA) systems has increased the potential for fabricating tunable composites for surface engineering applications. It has been established that the intrinsic properties of the composites are determined by the phases present in their base alloys, reinforcement types, and volumes. Herein, 5 wt% of vanadium carbide, titanium nitride, and a combination of both ceramics were added to Co22.2Cr22.2Ni22.2Cu22.2Nb11.2 HEA and fabricated via directed-energy deposition. The investigation highlights the first-time use of both ceramics and their synergistic utilisation as hybrid reinforcement in the directed-energy-deposited HEA. The candidate with the best hardness, tribological properties, and corrosion resistance was identified after various characterisations. It was found that the composite reinforced with a combination of both ceramics had the best microhardness value of 736 +/- 30.79 HV. The titanium nitride-reinforced composite exhibited the highest wear resistance with 6.69 & times; 10-6 mm3 /Nm at 20 N applied load. However, the synergy of both reinforcements offers enhanced lubricity, resulting in the lowest coefficient of friction of 0.071. A worn track analysis revealed that the samples were characterised by a transition from severe adhesive wear to cold-welded tribo-layer formation. The unreinforced HEA demonstrated the highest corrosion resistance with 567.79 ohm polarisation resistance and a corrosion rate of 0.6909 mm/year. It was concluded that the developed HEA and its composites are promising candidates for surface engineering application.
The engineering components in high-temperature applications, such as gas turbines, boilers, aerospace, and power generation systems, result in rapid degradation of the material. This paper has studied CoMoCrSi+WC12Co composite coating on MDN420 steel by the high-velocity oxy-fuel (HVOF) spraying process and investigated the high-temperature oxidation and hot corrosion performance of the coated material. The coating integrity was excellent as the as-sprayed coating has a dense and homogeneous microstructure with low porosity (2.1 +/- 0.85%), high microhardness (909.21 +/- 25HV), and a moderate roughness of the surface Ra = 4.77 +/- 0.18 & micro;m). Simulation of severe service conditions was performed by cyclic oxidation and hot corrosion tests conducted at 700 degrees C with 20 min of cooling at room temperature between each cycle. The Scanning Electron Microscopy (SEM), Energy-Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) were used to study the change in phases, redistribution of the elements, and degradation process. XRD showed that, cyclically oxidized coating at 700 degrees C in air, an adherent continuous oxide scale leads to Cr2O3, CoO, Co3O4, and CoCr2O4 spinel phases formed with SiO2 playing a role in densifying the oxide scale. Hot corrosion with molten salt (80%Na2SO4 + 20%V2O5 at 700 degrees C), the coating formed spinel oxide phases Na2CrO4, CoV2O6 and minor WO3 traces, and retained WC partially. The parabolic rate constants of oxidation and hot corrosion relative to MDN420 substrate were 1.21 & times; 10-9 g2cm- 4s- 1 and 7.6 & times; 10- 8g2cm- 4 s- 1, respectively, indicating the suitability of the coating in high temperature surface protection. Thus, the resulting HVOF-sprayed CoMoCrSi+WC12Co can be utilized as sturdy surface protection coatings of components that have to sustain in the high-temperature corrosive conditions.
Fusion Bonded Epoxy (FBE) coatings are widely used for the protection of structural steels exposed to aggressive environments. However, despite their established use in pipeline systems, there is limited literature addressing the behaviour of FBE specifically applied to ASTM A252 steel, a material extensively used in deep foundations, port structures, and tubular components subjected to combined mechanical loading and continuous moisture exposure. This study presents an integrated evaluation of the influence of dry film thickness on the mechanical, tribological, hydrothermal, and interfacial performance of the FBE/ASTM A252 system, treating thickness as a structural variable rather than merely a geometric parameter. Coatings with thicknesses between 200 and 500 & micro;m were applied by electrostatic spraying onto surfaces prepared to Sa 21/2, followed by controlled preheating and thermal curing. Characterisation included dry film thickness measurement, discontinuity inspection, pull-off adhesion testing before and after immersion in water at 80 degrees C for 48 h, abrasion resistance under 5000 wear cycles, Shore D hardness, differential scanning calorimetry, and scanning electron microscopy coupled with energy-dispersive spectroscopy. The results show that system performance cannot be explained solely by the thermally determined degree of cure. Adhesion stability after hydrothermal conditioning and wear resistance are governed by the interaction between thickness, film architecture, stress redistribution, and interfacial anchoring quality. Thinner coatings showed greater susceptibility to interfacial degradation after thermal-moist exposure, whereas thicker films provided increased tolerance to diffusive transport and subsurface stress concentration. The primary scientific contribution lies in experimentally demonstrating that the functional response of the FBE/ ASTM A252 system arises from coupled mechanisms involving cure kinetics, film microstructure, and interface integrity, establishing mechanistically grounded criteria for defining thickness ranges in structural applications exposed to severe environments.
