Search Results (541)

The abnormal effect of hot isostatic pressing (HIP) on the fatigue properties of DD6 single crystal superalloy was investigated. The results showed that HIP combined with standard heat treatment (SHT) reduced the fatigue life under 880 °C and 800 MPa. HIP treatment eliminated inner shrinkage porosity effectively; however, the amount of micropores increased in the subsequent SHT. Moreover, HIP treatment enlarged the size of γ′ precipitates gradually and altered the morphology of carbides greatly. Small MC carbides decomposed into M₂₃C₆ carbides, and a serrated structure formed on the surface of large-size MC carbides, which led to the positive and negative effects on fatigue properties, respectively, depending on the morphology and size of carbides. Recrystallized microstructures were observed after HIP treatment, accompanied by fine, continuous precipitates along recrystallized grain boundaries. This led to a sharp decline in the elevated-temperature fatigue properties of DD6 superalloy fabricated at a drawing velocity of 150 μm/s. The abnormal decrease in fatigue life of DD6 single crystal superalloy was attributed to micropore formation, coarsening of γ′ precipitates and recrystallization. Thus, it is essential to optimize the HIP treatments in the future development of single crystal superalloy blades. Full article

6082 aluminum alloy is widely applied in marine engineering, rail transportation and other industries owing to its excellent comprehensive performance. Welding heat source characteristics exert a decisive influence on the microstructure and mechanical properties of welded joints and become a major constraint for the application of medium-thick aluminum alloy welded structures. In this work, comparative tests of TIG and MIG welding were carried out on 16 mm thick 6082 aluminum alloy plates. Combining thermal simulation, metallographic observation and mechanical property tests, the temperature field distribution, microstructure, microhardness, tensile properties and bending properties of the two kinds of joints were systematically studied. The results show that TIG welding possesses high heat input, forming a broad temperature field with steep thermal gradients. Its weld microstructure is coarse and accompanied by severe coarsening of Mg₂Si precipitates, and the joint presents a highly fluctuating M-shaped microhardness distribution. The average tensile strength of TIG welded joints is 194 MPa, and all specimens fracture in the heat-affected zone. By contrast, MIG welding with low heat input produces a uniform temperature field, as well as a fine and homogeneous weld microstructure with dispersed precipitates. Its microhardness distribution is stable, and the average tensile strength reaches 256 MPa, 32% higher than that of TIG joints. Both welding methods deliver favorable bending performance. The difference in heat input and cooling behavior changes the grain evolution and precipitate characteristics and further dominates the final mechanical performance of joints. MIG welding is more suitable for multi-layer, multi-pass welding of 16 mm thick 6082 aluminum alloy. This work clarifies the correlation between heat input, microstructure and mechanical properties, and the optimized process can effectively improve the microstructural uniformity of the weld joint and enhance its mechanical properties. Full article

High-translucency 4 mol% yttria-partially stabilized zirconia (4Y-PSZ) is widely used for esthetic restorations, but sintering conditions that balance translucency and microstructural control remain unclear. This study evaluated the independent effects of peak temperature, holding time, and heating rate on the microstructure and total luminous transmittance of monolithic 4Y-PSZ. Disks were sintered at peak temperatures of 1470–1560 °C, holding times of 30–180 min, and heating rates of 3–10 °C/min. Grain size and internal defect density (≥0.5 µm) were quantified by scanning electron microscopy, and total luminous transmittance at 0.5 mm thickness was measured using a spectrophotometer. Higher peak temperatures and longer holding times increased grain size (0.481 ± 0.020 to 0.785 ± 0.035 µm, and 0.503 ± 0.037 to 0.730 ± 0.041 µm, respectively) and reduced defect density, whereas heating rate had no significant effect on either. Transmittance remained within a narrow range (approximately 40–43% at 0.5 mm) across all schedules, with 1560 °C yielding the lowest value. These findings indicate that the microstructure of monolithic 4Y-PSZ is governed primarily by peak temperature and holding time, while transmittance is relatively insensitive to the sintering schedule. Practically, a peak temperature of 1500–1530 °C with a 1–2 h hold provides a robust processing window balancing densification, grain coarsening, and optical performance for clinical workflows. Full article

Titanium-bearing blast furnace slag is rich in high-melting-point titanium-containing minerals including perovskite, melilite and spinel, which result in the loss of titanium resources and hinder the comprehensive utilization of such slag. On this basis, combined with process mineralogy theories, this study adopted multiple characterization methods, including a polarized light microscope with transmitted and reflected light, XRD and EPMA. These simulations reveal that the bulk SiO₂ content dictates titanium distribution among the mineral phases, thereby laying a solid foundation for the subsequent experiments. Meanwhile, quantitative analyses were performed on the microstructure, mineral composition and perovskite grain size of the slag. The occurrence state and migration law of titanium in the slag were systematically investigated. The results show that the microstructure of titanium-bearing blast furnace slag presents a porphyritic structure at different SiO₂ levels. Its main mineral phases include perovskite, pyroxene, spinel and glass. Titanium is predominantly hosted in perovskite, with small amounts distributed in the pyroxene, spinel and glass phases. Reducing the SiO₂ content facilitates the formation and grain coarsening of perovskite and promotes the migration of titanium from pyroxene and glass into perovskite. When the SiO₂ content is 20%, the perovskite content reaches 44.3%. Among them, the proportion of grains larger than 40 μm is 59.94%, and the distribution ratio of titanium in perovskite is 86.78%. Under the experimental conditions of this study, 20% SiO₂ is the optimal level. These findings can provide a theoretical reference for the efficient separation and recovery of titanium from titanium-bearing blast furnace slag. Full article

This study investigates the effect of sintering temperature on the hot-corrosion behavior of Ti-6Al-4V alloy in a molten salt environment. Samples were sintered at 800 °C, 900 °C, 1000 °C and 1100 °C, then exposed to the Na₂SO₄—25%NaCl for 300 h at 650 °C. The corrosion kinetics were evaluated by measuring the mass change in the specimens, and the results were correlated with their corresponding corrosion rates. The results show that the sintering temperature drives corrosion kinetics by influencing the sample density and grain size. The sample sintered at 900 °C shows a low corrosion rate due to its refined microstructure. This refined microstructure provides a high grain boundary density, which serves as a diffusion path and enables the formation of a dense, protective Al₂O₃–TiO₂ layer, as confirmed by XPS. In contrast, the sample sintered at 800 °C exhibits high porosity, resulting in an initial weight loss due to molten-salt penetration and evaporation of volatile metal chlorides. The samples sintered at 1000 °C and 1100 °C exhibit coarsened grains, leading to a thicker, brittle oxide layer and severe delamination, which in turn result in high corrosion rates. The results show that optimizing the sintering temperature to around 900 °C would enhance hot-corrosion resistance in salt-contaminated environments. Full article

This study investigates the correlation between sintering temperature, microstructure, and mechanical properties in AlSi10Mg alloy produced by supersolidus liquid phase sintering and subsequent artificial aging. Sintering was performed at 571, 575, and 579 °C using different heating rates for a total duration of approximately 5 h, followed by a 2 h dwell at the sintering temperature. At low sintering temperature, the alloy exhibits relatively fine α-Al grains with uniformly distributed Si precipitates, whereas intermediate temperature promotes Si coarsening. At higher temperature, excessive liquid formation leads to coarse α-Al grains and the development of partially interconnected Si networks. β-Al₅FeSi progressively coarsen with increasing sintering temperature. In the as-sintered state, the modest mechanical properties result from coarse α-Al grain size and subgrain structure, as well as from the size, morphology, and distribution of the Si phase. After aging (at 160 °C for 6 h following solution treatment at 530 °C for 30 min), the hardness and UTS were almost double (going from 44 ± 1 to 103 ± 2 HV and from 121 ± 1 to 273 ± 40 MPa). Meanwhile, α-Al grain size and Si morphology remained unchanged and Fe-rich intermetallics partially transformed into the more stable γ-Al₃FeSi₂ phase. Full article

GH4141 + 0.2 wt.% Y₂O₃ superalloy was fabricated using laser powder bed fusion (LPBF) technology and subjected to solution and ageing heat treatments. The effects of laser power (1100, 1300, 1500 W) on the microstructure and mechanical properties of the ODS nickel-based superalloy were investigated. The results indicate that as the laser power increased from 1100 W to 1300 W, defects such as cracks and pores in the specimens decreased, the grains were refined, and the microstructure became more uniform; when the laser power was further increased to 1500 W, the grain size coarsened significantly, precipitation phases at the grain boundaries became coarser or locally aggregated, and crack sensitivity increased. EDS analysis revealed enrichment of C, Cr, Mo and Ti in the dark phases at the grain boundaries, which may be associated with MC-type and M₂₃C₆-type carbides; no significant agglomeration of Y₂O₃ particles was observed in the matrix. Room-temperature tensile properties exhibited a pattern of initially increasing and then decreasing with increasing laser power. The tensile strength and elongation after fracture of the specimens were relatively similar under 1100 W and 1500 W conditions, whilst the specimen tested at 1300 W achieved the optimal balance of strength and toughness, with a tensile strength of 1460 MPa and an elongation after fracture of 14.3%, representing increases of approximately 9.8% and 54% compared to the 1100 W and 1500 W conditions, respectively. At 760 °C, the 1300 W specimens still maintained excellent high-temperature strength. Full article

Scandium (Sc) is well recognized as a potent grain refiner, yet optimizing its addition amount in the Al-Cu-Mg-Ni-Fe (A242) system remains a longstanding challenge, critically important for material performance in high-temperature automotive and aerospace applications. The present work, therefore, presents a study of low-Sc modified A242 alloys, demonstrating that 0.2 wt.% Sc microalloying of the system has a pronounced effect on its solidification-driven microstructural evolution, improving the high-temperature formability of the alloy over a 20–200 °C temperature range. The study demonstrates that this addition triggers a dramatic columnar-to-equiaxed grain transition, reducing the average grain size by 90.8% (from 400 ± 100 μm to 37 ± 10 μm) and fragmenting the brittle, continuous intermetallic network into a highly uniform architecture. Uniaxial compression testing revealed that, while the as-cast solid-solution alloy slightly reduces room-temperature strength due to solute trapping, it delivers an exceptional 142% increase in strain-to-failure at 200 °C (exceeding 0.8 mm) compared to the base alloy. This significant enhancement in ductility is driven by thermally stable Al₃Sc dispersoids that exert Zener pinning pressure, halting thermal grain coarsening and activating superplastic deformation mechanisms. These findings support the development of advanced thermoforming applications, with the finite element (FE) model predicting process improvements that enhance manufacturing efficiency. This work presents a validation and simulation-ready material framework that substantiates the viability of low-Sc-modified A242 alloys for such operations. Full article

This industrial-scale study investigates cerium’s effect on inclusions, microstructure, and mechanical properties in Ti-bearing high-strength steel BT700L through comparative trials of two production batches (with/without 0.0035% Ce). Characterization via SEM/EDS, automatic inclusion analysis, and Factsage thermodynamic simulations revealed that Ce addition reduced spherical Al-Mg-Ca-O-S inclusions (from 24 to 7 per 2 mm²; size decreased from 17 μm to 10 μm) while promoting composite inclusions with AlCeO₃-Ca(Mn)S cores and Ce-containing Ti(C)N shells. Although square Ti(C)N inclusion numbers remained stable, their average size increased from 8 μm to 11 μm. Ce addition eliminated banded microstructure and refined grains through heterogeneous nucleation (Ce₂O₃ exhibits low misfit of 4.00% with α-Fe). Mechanically, yield strength increased marginally (<5%) with unchanged tensile strength and reducing elongation. However, −20 °C impact toughness decreased by 22%. This duality—beneficial grain refinement versus detrimental coarsening of angular TiN inclusions acting as stress concentrators—provides critical insights for optimizing Ce addition in industrial Ti-bearing high-strength steel BT700L. Full article

This study investigates the oxidation behavior and microstructural evolution of Sanicro 25 steel (X7NiCrWCuCoNb25-23-3-3-2) after long-term exposure to water vapor at 700 °C for 30,000 h. Particular attention was paid to the relationship between protective oxide-scale formation, chromium depletion in the near-surface region, and the possible changes in secondary-phase stability in the steel substrate. FIB-SEM tomography was applied to characterize the oxide scale and the underlying affected zone, enabling three-dimensional visualization of oxide morphology, interfacial voids, and microstructural reconstruction beneath the scale. Long-term exposure resulted in the formation of a continuous Cr-rich oxide scale with a thickness of approximately 2.6 µm and local Mn enrichment. The scale exhibited a complex multilayered morphology, consisting of outer Cr-rich oxide crystallites, fine-grained chromium oxides, and an inner heterogeneous Mn-enriched region, suggesting the possible formation of mixed spinel-type oxides. Si-enriched regions were observed near the oxide/metal interface; however, no continuous Si oxide layer was detected. Despite the presence of interfacial voids, no scale spallation was observed in the investigated regions. SEM-EDX analysis revealed a chromium-depleted subsurface zone extending to approximately 6.5 µm below the oxide scale. CALPHAD calculations suggest that local chromium depletion may reduce the thermodynamic stability of Cr-rich M₂₃C₆ carbides and the Nb–Cr–N-type Z phase. This possible reduction in phase stability may contribute to the formation of a precipitate-depleted region and local microstructural reconstruction beneath the oxide scale. In the bulk region, where oxidation effects were negligible, the microstructure consisted of an austenitic matrix containing M₂₃C₆ carbides, σ phase, Cr–Ni–Fe nitride with an A13-type structure, ε-Cu precipitates, Z phase, and W-rich Cu-containing TCP precipitates. The simulations further suggest that most secondary phases form during the early stage of annealing, whereas prolonged exposure is dominated by diffusion-controlled coarsening. Overall, Sanicro 25 shows good resistance to long-term steam oxidation at 700 °C due to the formation of a continuous Cr-rich protective scale. However, this protection is accompanied by chromium depletion and local near-surface microstructural changes, which should be considered when assessing the long-term stability and service performance of this steel under high-temperature steam conditions. Full article

High-entropy alloys exhibit a broad light-responsive spectrum, spanning the ultraviolet to visible range, and their light absorption coefficient is significantly higher than that of traditional binary oxides. Cr/AlCrNbSiTiN/AlCrNbSiTiO gradient nano-multilayer coatings with excellent solar selective absorption properties are prepared using ion source enhanced magnetron sputtering. The effects of thickness of the absorption layer of AlCrNbSiTiN (3/4/5 min, denoted as S-3/4/5) are systematically investigated. It is worth noting that nano-multilayer coatings of S-3, S-4, and S-5 exhibit nearly perfect absorption rates of 0.9847, 0.9888, and 0.9879, respectively. The TEM images shows clear interfaces between the various coating layers, exhibiting a gradient structure that combines nanocrystalline and amorphous characteristics. From the substrate to the surface, there is an increase in the content of nanocrystalline phases, coarsening of grain sizes, and a decrease in the amount of amorphous phases. The primary absorption layer of AlCrNbSiTiN displays a typical face-centered cubic nitride structure. The XPS analysis reveals that the high-valent oxides (Nb⁵⁺, Cr⁶⁺) ensure thermal stability, whereas mixed valence states of Cr³⁺/Cr⁶⁺ may enhance visible light absorption through multi-electron transitions. This study analyzes how both the thickness of absorbing layers and high-temperature annealing affect the optical properties and photothermal conversion performance of AlCrNbSiTiN-based high-entropy coatings, which provides valuable insights for developing high-performance selective absorbers. Full article

Wind turbine towers rely on welded joints for structural continuity, and the coarse-grained heat-affected zone (CGHAZ) at these joints is the principal site of fatigue damage under service loading. This study characterises the influence of welding heat input on the microstructural constitution, high-cycle fatigue response, and fracture mechanisms of Gleeble-simulated CGHAZs in a Nb-microalloyed wind power steel. Thermal cycles representative of submerged arc welding at 15, 25, 35, and 45 kJ/cm were applied, and the resulting microstructures were examined by optical microscopy, SEM, EBSD, and TEM. Raising the heat input produced systematic microstructural coarsening: the densities of low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) fell by approximately 40% and 26%, respectively, while the mean equivalent diameter (MED) and prior austenite grain (PAG) size grew by roughly 64% and 67%. Life partitioning showed that crack nucleation accounted for more than 84% of total fatigue cycles in every condition, identifying it as the life-governing damage stage. Over the 15-to-45 kJ/cm range, the CGHAZ fatigue strength at 2 × 10⁶ cycles deteriorated from 246.9 MPa to 208.5 MPa (a 15.6% reduction), while the mean fatigue striation spacing widened from 0.142 μm to 0.183 μm (an increase of 28.9%). These results demonstrate that judicious heat-input selection is a practical and effective means of preserving CGHAZ fatigue integrity in wind tower steel fabrication, and they address a previously unresolved gap concerning high-cycle fatigue fracture mechanisms in this critical microstructural zone. Full article

This study systematically investigated the effects of air-cooled pre-hardening and oil-quenched quenching-and-tempering processes on the microstructure, mechanical properties, and polishing performance of P20 plastic mold steel. Increasing the austenitizing temperature from 820 °C to 940 °C resulted in a more uniform carbide distribution, a slight improvement in hardness, and enhanced polishing performance for both processes. However, grain coarsening at 940 °C reduced the impact toughness from 157.6 J to 111.7 J. After tempering at 650 °C, both processes yielded a tempered sorbite microstructure. However, in the air-cooled samples, the carbides were aligned along the bainite lath direction, whereas in the oil-quenched samples, they exhibited an equiaxed, non-directional distribution owing to the complete recovery of the matrix. Austenitizing at 940 °C followed by air cooling and tempering at 550 °C provides the optimal balance of hardness, toughness, and polishing performance. Mitigating elemental segregation and narrowing the segregation bands represent key strategies for further enhancing polishing performance. Full article

Laser cladding has attracted considerable attention for titanium alloy surface modification owing to its high energy density, rapid cooling rate, and excellent metallurgical bonding capability. To investigate the effect of Nb content on the microstructure and properties of NiTi-based coatings, composite coatings containing 10–40 wt% Nb were fabricated on a titanium alloy substrate via laser cladding. The effects of Nb content on phase constitution, microstructure evolution, mechanical properties, tribological performance, residual stress, and surface topography were systematically characterized using XRD, SEM, EDS, microhardness testing, wear testing, digital image correlation, and atomic force microscopy. The results show that increasing Nb content significantly affected the solidification behavior and phase evolution of the coatings. With increasing Nb addition, the dominant phase gradually evolved from NiTi to a coexistence structure of NbTi₄ and NiTi, while Ti dilution and elemental segregation became increasingly pronounced. The crystallite size increased from 19.63 nm to 25.91 nm, accompanied by intensified dendritic segregation and surface roughening. Among all samples, the coating containing 10 wt% Nb exhibited the best overall performance, characterized by the finest microstructure, the lowest surface roughness, the lowest residual stress, and the best wear resistance. The superior performance of the low-Nb coating was mainly associated with its finer and more homogeneous microstructure, reduced elemental segregation, lower stress concentration, and enhanced grain-boundary strengthening effect. Excessive Nb addition intensified Ti dilution, grain coarsening, residual stress accumulation, and microstructural heterogeneity, thereby degrading the overall coating performance. More importantly, this study reveals that Nb-regulated Ti dilution behavior governs the synergistic evolution of elemental segregation, surface roughening, residual stress accumulation, and tribological degradation during laser cladding. This work provides new insight into the process–structure–property relationship of NiTi-based composite coatings and offers theoretical guidance for the composition optimization and engineering application of high-performance laser-clad coatings on titanium alloys. Full article

To address the erosion-induced failure of large-caliber gun barrels under extreme thermochemical coupling, this study systematically investigates the microstructural evolution of multi-layered gradient regions along the radial direction of 32CrNi3MoV steel under extreme thermochemical cycling. Leveraging SEM, EBSD, TKD, and double-beam aberration-corrected TEM, combined with JMatPro thermodynamic simulations, the phase transitions, crystallographic characteristics, and substructural evolution spanning from the bore surface to the matrix are elucidated. The results demonstrate that a three-layer gradient structure forms along the radial direction. The topmost layer is a chemically stabilized metastable austenite diffusion layer with a thickness of 1.5–4.0 μm. which is attributed to the suppression of martensitic transformation due to C/N interstitial diffusion lowering the MS temperature. The observed high-density dislocation tangles and stacking faults within this austenite diffusion layer result from thermal mismatch stresses during rapid thermal cycling. The subsurface region is a martensitic transformation layer with a thickness of 70–97 μm, exhibiting a substructural gradient from nanostructured high-density twinned martensite to refined lath martensite. Thermodynamic analysis indicates that rapid heating (≈10⁵ °C/s) facilitates significant austenite nucleation and growth during the reverse phase transformation, subsequently forming nanostructured martensitic grains via non-equilibrium transformation during rapid cooling. Adjacent to this is a matrix tempering layer extending approximately 160 μm. Nanoindentation hardness profiling reveals that the peak radial hardness (≈1000 HV) occurs within the fine-grained martensitic zone approximately 40 μm from the surface. In contrast, the tempered layer exhibits reduced hardness (≈400 HV) compared to the original matrix (≈500 HV). This is primarily attributed to transient high-temperature over-tempering effects, which induces carbide coarsening and the loss of solid solution strengthening, alongside the softening of prior austenite grain boundaries. This study clarifies the micro-to-nanoscale evolution of the barrel microstructure, providing critical theoretical insights for understanding erosion mechanisms and improving lifetime predictions. Full article