Search Results (3,851)

Aluminum–copper alloys, typified by ZL205A (AlCu5MnTiCdV, GB/T 1173), pose severe casting challenges due to their wide solidification interval, poor fluidity, and susceptibility to gas porosity and shrinkage defects. This study introduces a negative-pressure frozen sand mold casting process as a solution to these challenges and systematically quantifies its thermal and microstructural advantages over conventional resin sand and atmospheric frozen sand casting. Using inverse heat conduction analysis of multi-point thermocouple data, the interfacial heat transfer coefficient (IHTC) was quantitatively determined for 14 experimental conditions varying in mold type, pressure level, moisture content (2–6 wt.%), and initial freezing temperature (−20 to −40 °C). The results demonstrate that negative pressure combined with frozen sand molds (6 wt.% moisture, −40 °C) produces the highest active-period average IHTC of 236 W/(m²·K), representing a 2.8-fold increase over atmospheric frozen sand casting and a 1.6-fold increase over negative-pressure resin sand casting. This enhanced thermal driving force promotes grain refinement and effective gas removal, yielding superior mechanical properties: tensile strength of 200.6 MPa and elongation of 9.3% in the as-cast state, and 478.5 MPa and 7.4% after T6 heat treatment. Using the optimized process parameters, a thin-walled cabin component (Ø180 mm × 300 mm, minimum wall thickness 3 mm) was successfully fabricated without defects. These findings establish quantitative process–thermal–microstructure–property relationships for negative-pressure frozen sand casting of wide-solidification-interval aluminum alloys. Full article

FeRh alloys undergo an antiferromagnetic–ferromagnetic magnetoelastic transition accompanied by significant volume change, and thus exhibit giant magnetostriction. However, few studies have explored how Fe substitution for Rh affects the transition behavior, magnetostrictive properties, and the correlation between their respective variations in this system. Herein, we systematically explore the magnetoelastic transition behavior and magnetostrictive properties of the Fe_50+xRh_50−x (x = 0, 0.25, 0.5) alloys. Experimental results demonstrate that the magnetoelastic transition temperature decreases, whereas both magnetostriction and its associated magnetic field response sensitivity increase with increasing Fe substitution. These findings provide an effective route to optimize the overall magnetostrictive performance of FeRh based alloys. Full article

The aim of this study was to comparatively evaluate the effects of electrolytic-plasma surface hardening (EPSH) and laser surface hardening (LSH) on the microstructure, phase state, microhardness, and friction behavior of low-carbon Steel 20. EPSH was performed using a two-stage regime of 320 V for 3 s followed by 200 V for 40 s and a thermocyclic regime of 320 V for 2 s, 200 V for 2 s, and 50 V for 2 s repeated for five cycles. LSH was carried out at a scanning speed of 7 mm/s and 75% of the maximum laser power (approximately 2250 W) using single- and double-pass treatments. The modified layers were characterized by SEM, XRD, microhardness measurements, and dry sliding tribological tests. EPSH produced the strongest hardening response, reaching approximately 600 HV with a hardened-layer depth of 70–100 μm. Double-pass LSH increased the near-surface microhardness to approximately 460 HV. Phase analysis revealed Fe_1−xO after EPSH, Fe₃O₄ after single-pass LSH, and Fe_1−xO, Fe₃O₄, and Fe₂O₃ after double-pass LSH. All treatments reduced the coefficient of friction compared with untreated steel. Overall, EPSH provided deeper and stronger hardening, whereas LSH produced more localized surface modification and oxidation. Full article

The thermomechanical behavior of the Ti-6Al-4V (Ti64) alloy under hot deformation is determined by a complex interplay between strain hardening and thermally assisted restoration processes that finally lead to the formation of the resultant microstructure and mechanical properties. In this research, the effects of deformation temperature (700, 800, and 900 °C) and strain rates (low, moderate, and high) on microstructural evolution, hardness, and dislocation density of Ti64 alloy were systematically studied. Deformed samples were prepared by hot forging under specified deformation conditions, followed by characterization using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) analysis, and Vickers hardness (HV3) testing. The results demonstrated a gradual change from the stable α + β lamellar microstructure at 700 °C to fragmented lamellae and severe globularization at 900 °C, evidencing the increased significance of dynamic recovery (DRV), dynamic recrystallization (DRX), and globularization with increasing deformation temperature. The hardness distribution was strongly dependent on the deformation location, with the outer regions exhibiting higher hardness than the specimen centers; the maximum hardness of approximately 365 HV was obtained in the outer region at 900 °C under high deformation, whereas the center region remained comparatively softer. This spatial variation was attributed to the competition between deformation-induced dislocation accumulation and thermally activated softening. XRD analysis revealed that dislocation density greatly depends on a synergistic influence of deformation temperature and strain. The maximum dislocation density was achieved at moderate deformations at 700 °C and at high deformations at 800 °C, while a significant decrease took place at 900 °C under severe deformations, proving the dominance of thermally activated processes of recovery and recrystallization. Williamson–Hall analysis further indicated that lattice strain and microstrain did not always follow the same trend, confirming that macroscopic lattice distortion and local crystallographic strain represent distinct aspects of the deformation response. Thus, the comprehensive analysis of the microstructure, mechanical properties, and crystallographic features demonstrates that deformation temperature has a crucial influence on the strain hardening vs. dynamic softening balance. Among the investigated conditions, deformation at 900 °C with a relatively low strain rate provided the most favorable combination of lamellar fragmentation, globularization, dynamic restoration, and a comparatively homogeneous hardness response, indicating its potential for controlled thermomechanical processing of Ti64. Full article

Aluminum bronze alloys are widely used in marine engineering components due to their good mechanical properties, wear resistance, and corrosion resistance. However, surface degradation such as wear and corrosion remains a challenge during long-term service. In this study, nanosecond pulsed laser surface melting (LSM) was applied to an aluminum bronze alloy at different laser powers to improve its surface performance. The results show that LSM treatment leads to the formation of a remelted layer with increased content of the martensitic β’ phase and reduced α phase. The sample treated at 140 W (L2) exhibited the highest surface hardness (186.957 HV, 36.42% higher than that of the untreated sample) and the smallest wear scar width (763.5 μm, a 24.33% reduction). The L2 also achieved the best corrosion resistance, with a corrosion potential of −0.26515 V (increased by 0.03 V), corrosion current density of 5.34145 μA/cm², and polarization resistance of 3382.9 Ω·cm². The improved performance is attributed to the formation of martensite and the increase in aluminum-rich phases on the surface. Full article

The joining of solid-state sintered silicon carbide (SiC) was achieved using a novel Si-Ti-Al ternary alloy via vacuum brazing. This study investigates a predominantly non-carbide-dominated interfacial bonding mechanism and the influence of brazing temperature on joint microstructure, mechanical properties, and high temperature reliability. The high Si content promoted the incorporation of Ti into Ti–Si phases within the brazed seam, thereby limiting the amount of Ti available for reaction with SiC. No continuous TiC layer was detected within the spatial resolution of the employed characterization methods. Minor discrete Al₄C₃ precipitates were identified at the interface but did not constitute the dominant bonding phase. Brazing at 1360 °C yielded an optimal microstructure featuring highly regular coral-like eutectic clusters, resulting in a peak room temperature shear strength of 102.8 MPa. The joints also exhibited favorable high temperature reliability, maintaining a shear strength of 58.4 MPa at 1000 °C. Microstructural analysis following thermal exposure revealed partial coarsening of primary blocky phases and interfacial Al₄C₃ precipitates via Ostwald ripening, which contributed to the reduction in high temperature strength. Nevertheless, the robust retention of fine eutectic clusters ensured satisfactory structural stability under thermal loading. This work provides a viable strategy for designing Si-based brazing fillers for high-performance SiC ceramic joining. Full article

Controlling prior austenite morphology during single-pass hot rolling is essential for improving the strength–ductility balance of strip casting high-strength steels. In this study, Fe–0.24C–1.5Si–1.8Mn steels with and without 0.03 wt.% Nb were deformed by 50% at 950–1100 °C and subsequently held at 350 °C for 60 min for bainitic transformation. The effects of deformation temperature and Nb addition on austenite dynamic recrystallization, bainitic microstructure, and mechanical properties were investigated. For the Nb-free steel, recrystallization occurred at all these investigated deformation temperatures. The addition of 0.03 wt.% Nb markedly suppressed austenite recrystallization during hot deformation, resulting in the retention of elongated deformed austenite after deformation at 950 °C. Compared with the bainitic microstructure formed from fine recrystallized austenite in the 0Nb steel (without Nb addition), that formed from elongated austenite in the 03Nb steel (with 0.03 wt.% Nb) deformed at 950 °C exhibited a smaller lath width and higher HAGB and dislocation densities. In addition, the volume fraction of retained austenite increased from 4.5% to 9.8%, while its average thickness decreased from 105.6 nm to 49.1 nm. Consequently, under identical deformation conditions (50% reduction at 950 °C), Nb addition increased the yield and tensile strengths from 1064 MPa and 1261 MPa to 1088 MPa and 1323 MPa, respectively, while the total elongation remained nearly unchanged (24.8% vs 24.6%). These findings provide new insights into the optimization of thermomechanical processing for strip casting bainitic steels. Full article

Flow-passing components such as volutes and fixed guide vanes operating in high-velocity liquid flows with high sediment concentrations are subjected to long-term cavitation erosion and sand-particle abrasion, which cause substantial economic losses. To reduce the manufacturing and maintenance costs of mechanical equipment serving such environments, laser cladding was employed to fabricate Fe₄₅Cr₂₅Ni₂₀Ti₅Mo₅ multi-principal-element alloy coatings on Q235 steel substrate, and the effect of laser power on the microstructure and properties of the coatings was systematically investigated. On the basis of preliminary investigations, the present work elaborately analyzes the wear resistance and cavitation-erosion resistance of coatings fabricated under laser powers of 1000 W, 1200 W and 1400 W. The results reveal that the coating hardness gradually decreases from a maximum value of 485.67 HV_0.2 to 363.15 HV_0.2 with increasing laser power. When the laser power is 1200 W, the coating prepared under this laser power maintains a good balance between hardness and microstructural integrity. Under identical friction-and-wear test conditions, its wear rate reaches only 3.15 × 10⁻⁵ mm³/(N·m), which is reduced by 19.64%, 27.92% and 39.19% compared with the coatings produced at 1000 W, 1400 W and bare Q235 steel, respectively. After a 20h cavitation-erosion test, the mass loss of this coating is merely 2.56 mg, representing reductions of 72.88%, 81.5% and 96.91% relative to the 1000 W coating, 1400 W coating and Q235 steel substrate. The coating fabricated at 1200 W exhibits outstanding wear resistance and cavitation-erosion resistance. The results indicate that, under the experimental conditions of this study, the wear resistance and cavitation-erosion resistance of the coating can be effectively optimized by adjusting the laser power. Full article

Accurate determination and prediction of pickling time are essential for preventing under-pickling and over-pickling and for improving the surface quality of hot-rolled high-strength steel. In this study, an electrochemical endpoint detection method combined with hybrid machine-learning models was developed to predict the pickling time of hot-rolled automotive high-strength steel. The variation in open-circuit potential during hydrochloric-acid pickling was monitored using an electrochemical workstation, and a potential-derivative near-zero method was proposed to determine the completion of oxide-scale removal. Based on repeated experiments under ten representative process conditions, a potential-derivative threshold of −5 × 10⁻⁴ V/s was adopted as the operational criterion for identifying the pickling endpoint. The effects of oxide-scale thickness, HCl concentration, pickling temperature, and accelerator concentration on pickling time were subsequently investigated. To describe the nonlinear relationship between these variables and pickling time, BP, GA-BP, ELM, and PSO-ELM regression models were established. The 48-observation dataset was evaluated using leakage-free grouped nested six-fold cross-validation repeated ten times, with all observations from the same strip group kept within the same fold. Among the investigated models, PSO-ELM exhibited the best prediction performance, achieving R² = 0.85 ± 0.05, MAE = 7.27 ± 1.01 s, MAPE = 0.14 ± 0.02, and RMSE = 9.65 ± 1.48 s. These quantities are regression-performance statistics and are not interpreted as the percentage prediction accuracy. The proposed endpoint criterion and regression framework provide a laboratory-scale basis for data-driven pickling-time estimation within the investigated material and process ranges, and broader industrial application requires validation using larger multi-grade production datasets. Full article

A low-carbon Cu-bearing marine structural steel was fabricated based on the chemical composition of HSLA-100 steel. The microstructural evolution, variation in nanoscale Cu-rich precipitates, and their synergistic effects on the mechanical properties and hydrogen embrittlement (HE) behavior under different tempering durations were systematically investigated. The results showed that the original lath bainite gradually transformed into tempered bainite and equiaxed ferrite with a prolonged tempering time. The Vickers hardness exhibited a typical upward-then-downward trend and reached a peak value of 322 HV at the tempering time of 1 h. The average size of Cu-rich precipitates increased from 7.2 nm to 13.2 nm, while the number density rose rapidly and finally stabilized. The as-rolled sample exhibited the minimum plastic loss after hydrogen charging owing to the hydrogen-trapping effect of high-density tangled dislocations. Short-time tempering (0.5 h) generated fine Cu-rich precipitates with a weak hydrogen-trapping capacity and abundant mobile dislocations, resulting in severe HE deterioration. The optimal HE susceptibility was achieved after 1 h of tempering. Combined with our experimental microstructure-property results and previous published literature, this improvement is inferred to originate from the hydrogen-trapping effect of adequately grown Cu-rich precipitates, together with a substantial decrease in mobile dislocation density. Excessively long tempering (2 h) induced irreversible temper brittleness and grain boundary deterioration, which aggravated the hydrogen-induced plastic degradation. This work clarified the coupled regulation mechanism of the Cu precipitate morphology, dislocation configuration, and temper brittleness on the HE performance of low-carbon marine steel, providing a reliable theoretical basis for the process optimization and anti-hydrogen damage performance improvement of high-strength marine steels. Full article

This study presents an entropy-based framework for segmenting and characterizing the deformation behavior of AZ31B magnesium alloy sheets using acoustic emission (AE) signals obtained during tensile and V-bending tests. Shannon entropy was calculated from four AE parameters (duration, count, signal energy, and frequency centroid). The entropy values were normalized and averaged to identify transitions between deformation stages. Individual AE waveforms were transformed into normalized time–frequency images using the continuous wavelet transform (CWT), and quantitative features extracted from these images were used for Random Forest classification of the entropy-defined stages. Internal five-fold cross-validation yielded accuracies of 94.6% and 96.42% for tensile and V-bending deformation, respectively, indicating that the stages were distinguishable in the CWT-based feature space. Hierarchical density-based spatial clustering of applications with noise (HDBSCAN) separated fracture-associated AE signals during tensile deformation. The results indicate that the proposed method can characterize deformation-stage evolution and provide additional information on fracture-associated AE responses in AZ31B sheets. Full article

Compressor rotor blades in marine engineering applications are exposed to harsh, corrosive environments and complex aerodynamic loads, making them prone to premature failure. This study investigates the fracture of 12th-stage 2Cr13 martensitic stainless-steel blades following a maintenance overhaul. Despite the replacement of several cracked blades, five blades fractured shortly after restart, accompanied by abnormal vibration. A comprehensive failure analysis was conducted, including macroscopic inspection, fractographic observation, energy-dispersive spectroscopy, metallographic examination, and mechanical property testing. The results indicate that the fractures are multi-source high-cycle fatigue. Crack initiation in the new blade originated from pre-existing transverse mechanical damage, while in the old blades, it initiated from sharp pits and microcracks introduced by sandblasting, which compromised surface integrity. The material exhibited a normal tempered sorbite structure and adequate mechanical properties, with slight strengthening due to service-induced precipitation and dislocation accumulation. The failure followed a typical evolution of multi-source initiation, propagation, crack coalescence, and final overload ductile fracture. These findings highlight the critical role of surface integrity in blade reliability. Full article

This study investigates the fabricability, microstructures, and mechanical and corrosion behavior of a multi-material structure (MMS) composed of niobium alloy (NbZr1) and titanium alloy (Ti64) using a wire arc directed energy deposition process. The microstructure of NbZr1 alloy primarily consisted of equiaxed grains oriented in the rolling direction, while the deposited Ti64 microstructure exhibited ‘banding’ morphology and a basket-weave structure composed of α phase lamellae in a β matrix. The MMS interface revealed good metallurgical bonding and was free from defects such as cracks, pores and intermetallic phases. Niobium diffusion from NbZr1 into the Ti64 alloy resulted in the formation (β-Ti + Nb) of a solid solution which imparted strength to the MMS. Hardness testing showed that microhardness values follow the following trend: NbZr1 substrate > MMS interface > Ti64 deposit. The NbZr1–Ti64 multi-material structure developed in this study exhibited a balanced combination of ductility (22.73% elongation) and moderate tensile strength (254.18 MPa), outperforming most reported NbZr1-Ti64 MMS studies. All tensile specimens failed in a ductile manner on the NbZr1 side. The MMS demonstrated superior corrosion resistance, exhibiting the lowest corrosion current density and corrosion rate compared to its individual counterparts. Full article

This study investigated the deformation behavior and damage evolution of AA7075-T6, Anodized AA6061-T6-T6 (oxide layer with an average thickness of 8.71 µm), and Al-15 vol.% SiC-T4 (particle size range of 3.1–8.3 µm) under scratch, Hertzian-type indentation, and nanoindentation loading conditions. Through controlled mechanical testing, the materials’ responses to varying test conditions were characterized in terms of penetration depth and width, resistance to deformation, and cracking mechanisms on surface and sub-surface. Results revealed that Al-15 vol.% SiC T4 exhibited the highest stability and scratch resistance due to the reinforcing effect of SiC particles, while AA7075-T6 demonstrated moderate strength with noticeable plastic deformation. Anodized AA6061-T6 showed enhanced surface hardness post processing but increased susceptibility to brittle cracking and coating delamination under higher loads and reciprocating passes. Findings indicated a transition from load-controlled to structure-controlled behavior at elevated forces, influenced by strain hardening and microstructural constraints. Hertzian-type indentation further highlighted differences in subsurface damage and crack propagation patterns among the materials. Holistically, the study established a clear correlation between microstructural features and mechanical performance, guiding material selection and surface engineering for improved wear and contact damage resistance. Full article

The development of protective coatings is a key requirement to extend the operating window of structural materials in lead-cooled fast reactors, particularly at temperatures where corrosion of conventional steels becomes increasingly challenging to control. In this work, a code-oriented, systematic and technology-agnostic screening of candidate coating systems was performed to assess their chemical compatibility with liquid lead under representative and controlled conditions. Different coating technologies and material systems were investigated. Part I of the work covers atmospheric plasma spraying, high-velocity oxy-fuel spraying, and cold gas spray of Al-rich austenitic and ferritic alloys, and chrome electrodeposition. The results show that, while Al-rich metallic coatings can effectively protect the underlying substrates under the investigated conditions, Cr-based materials studied here cannot. Such an outcome provides a comparative basis for the down-selection of coating technologies for LFR components. Full article