Journal of Materials Engineering and Performance最新文献

Magnesium phosphate cement (MPC) shows strong potential for protecting steel reinforcement in marine structures, yet its coupled strength evolution and corrosion-protection mechanism under natural seawater remain unclear. This study presents a 161-day medium-term immersion investigation in natural seawater, combining compressive strength tests, electrochemical measurements, XRD, SEM/EDS, PLM, and MIP to distinguish the matrix effect from the pore-solution chemistry effect. Compared with ordinary Portland cement (P.O.), MPC forms a dense struvite-based matrix that inhibits the ingress of chloride ions, water, and oxygen. Its compressive strength exhibits a distinctive dual-peak behavior, reaching 65.7 MPa with smaller fluctuation than P.O., indicating superior environmental stability. Electrochemically, the steel rebars embedded in MPC maintain a stable corrosion potential of approximately -0.7 V, with the corrosion current density 2-3 orders of magnitude lower than that in P.O. Protection occurs through three synergistic stages: pore blocking by dense hydrates, chemical passivation by an α-FeOOH/Fe₃O₄ barrier, and self-repair through continued hydration and microcrack sealing. NH₃/NH⁴⁺ mainly derives from residual ammonium phosphate and ammonium-bearing struvite in alkaline microdomains, contributing to localized oxygen-poor/reducing conditions near steel. This mechanism overcomes pH-dependent limitations of P.O. and supports marine anticorrosive repair design.

Accurate prediction of the critical transformation temperatures (Ac_{1}) and (Ac_{3}) is one of the essential factors in the heat treatment of CA6NM cast martensitic stainless steel. In this study, the influence of alloy composition, heating rate, and prior austenite grain size on the critical temperatures was quantified using dilatometric measurements and statistical modeling. Six heat treatment conditions produced prior austenite grain sizes ranging from ~75 to 247 µm. Experimental results showed that grain size variations produced only minor changes in (Ac_{1}) and (Ac_{3}), indicating a weak dependence of transformation temperatures on prior austenite grain size within the investigated range. In contrast, chemical composition and heating rate had strong effects, with (Ac_{1}) and (Ac_{3}) increasing by approximately 100 °C and 115 °C, respectively, as the heating rate increased from 0.1 to 10 °C s⁻¹. Regression-based predictive model incorporating alloy composition and heating rate was developed and validated. The (Ac_{1}) model demonstrated strong agreement with experimental measurements (R² = 0.972 and RMSE = 4.78 °C) and significantly improved prediction accuracy compared with thermodynamic calculations using Thermo-Calc and previously published empirical models. The results provide an improved framework for predicting transformation temperatures in CA6NM, under continuous heating conditions.

Recent advancements in additive manufacturing have enabled fabrication of hybrid structures through combination of dissimilar materials with controlled spatial distribution. In this study, an innovative structure consisting of alternating layers of polylactic acid (PLA) and carbon fiber-reinforced PLA (Carbon-PLA) was fabricated using fused deposition modeling and evaluated under open-hole tensile (OHT) loading. The objective was to investigate the stress concentration behavior and mechanical response of the layered configuration in comparison with its constituent materials. Experimental results indicate that multi-material structure exhibited an ultimate tensile strength of 26.66 MPa, elongation of 2.78%, demonstrating intermediate behavior between PLA (25 MPa) and Carbon-PLA (36.63 MPa). Finite element simulations were employed to analyze stress distribution around open-hole region and to provide a comparative assessment of mechanical response. The results confirm that stress concentration is predominantly governed by specimen geometry, while material stiffness influences stress magnitude and failure behavior. The study provides insight into mechanical performance of layered dual-material FDM structures under stress concentration conditions. Findings highlight potential of such configurations for lightweight, low-load applications where tailored stiffness and manufacturability are of interest.

Natural fiber-reinforced biocomposites are becoming more popular due to their growing demand. This research reports the development of a biodegradable hybrid composite using a unique combination of natural plant-based fibers such as Bamboo (BO), Areca nut sheath (A), and Ramie (R) fiber, collectively termed as BOAR fiber, reinforced within a Polylactic Acid (PLA), Chitosan, Graphene Oxide (GO) matrix. To strengthen interfacial adhesion between fiber and matrix, advanced surface treatments, including alkali, plasma, enzymatic, and silane modifications, are applied. Five composite formulations (S1–S5) are fabricated by constant reinforcement of fiber (10%) and varying the composition of the matrix (80 to 60% of PLA, 5 to 15% of Chitosan and GO) through compression molding and are evaluated for their physicochemical properties. Among the samples, S3 (10%–BOAR fiber, 70%–PLA, 10%–Chitosan and 10%–GO) manifested outstanding performance, accomplishing a tensile strength of 52 MPa, flexural strength of 54 MPa, and impact strength of 0.125 kJ/m². The significance of the composite with Sample S3, with highest mechanical property improvement is substantiated by statistical validation. Overall, fiber hybridization with chitosan and GO produced a resilient biocomposite, alternative to synthetic composites for structural applications.

Aiming to enhance hardness and wear resistance, this study employed hydride–dehydride titanium powder and graphite powder to fabricate in-situ TiC particle-reinforced titanium matrix composites. It is found that the in-situ TiC particles significantly refine the α-Ti grains, from 52.0 μm in pure Ti to 6.0 μm in the Ti-4.0C composite. Overall, the Ti-1.0C material exhibits the best performance, with tensile strength of 853 MPa, yield strength of 746 MPa, and elongation of 18.0%. Compared with pure Ti, the tensile strength and yield strength respectively increase by 32.2 and 48.4%, without notable elongation decrease. The strength improvement is attributed to grain refinement, solid solution strengthening, and load transfer reinforcement from TiC. Besides, the addition of graphite has a positive effect on the improvement of the hardness and wear resistance. The Ti-4.0C sample exhibits the best wear resistance, with a friction coefficient that is reduced by 30.91% compared to pure Ti sample, while the hardness increases from 18.3 to 33.9 HRC. This study provides a new approach for enhancing the comprehensive properties of titanium matrix composites.

High-entropy carbide ceramics are promising for extreme environments due to their exceptional hardness and thermal stability, yet their relatively high brittleness hinders further application. This study balanced the hardness and toughness of the high-entropy ceramics by doping with the second phase SiC particles. The (TiZrNbV)C-SiC high-entropy composite ceramics were synthesized via fast hot-press sintering, while (TiZrNbV)C high-entropy ceramics served as a comparative control. The results indicate that within an extremely short timeframe, the (TiZrNbV)C-SiC high-entropy composite ceramic achieved an excellent relative density of 98.71%, resulting from the incorporation of the second phase. The mechanical property test results indicate that the incorporation of the second phase significantly enhances hardness, toughness, and wear resistance. The hardness and fracture toughness of the high-entropy composite ceramic are 33.00 ± 0.52 GPa and 4.57 ± 0.62 MPa m^1/2, respectively. While the H³/E² increased by 27.6% to reach 0.2162 GPa. Doping of the SiC phase inhibits crack propagation and reduces the brittleness of the ceramic. Under a 9 N load, the (TiZrNbV)C-SiC exhibits an exceptionally low specific wear rate of 1.72 × 10^-6 mm³ N^-1 m^-1, compare to the (TiZrNbV)C. This work provides a viable design strategy for simultaneously enhancing the toughness and wear resistance of high-entropy ceramics.

The Ti-45Al-8Nb-0.2Si-0.3B alloy was fabricated by hot isostatic pressing (HIP) of pre-alloyed powders produced via electrode induction melting gas atomization (EIGA). The microstructures of the pre-alloyed powders and the effects of HIP temperature and post-HIP heat treatment on the microstructures and mechanical properties of the alloy were investigated. The results indicate that the pre-alloyed powders exhibit a particle-size range primarily between 65-260 μm with a median size (D₅₀) of 131.75 μm. Large particles show cellular–dendritic surface morphology, whereas decreasing particle size leads progressively to a disordered surface morphology. The large-sized pre-alloyed powders primarily consist of the γ phase, with coarsened α₂ grains regions observed in the microstructures of some large particles. In contrast, the fine pre-alloyed powders are mainly composed of the α₂ phase. The microstructures of as-HIPed Ti-45Al-8Nb-0.2Si-0.3B alloy is composed of equiaxed near γ microstructure and dispersed Nb₅Si₃ precipitates. The microstructures also contain the α₂-phase prior particle boundaries (PPBs) and local enrichment of the α₂ phase, which is derived from the abnormally coarsened α₂ grains in the large powders. Increasing HIP temperature together with post-HIPed heat treatment effectively eliminates PPBs, however, due to the local enrichment of the α₂ phase, the fully lamellar colonies obtained after heat treatment exhibit a typical bimodal distribution. Tensile test results indicate that the strength and ductility of the as-HIPed TiAl alloy are superior to those of the fully lamellar heat-treated TiAl alloy.The factors influencing the evolution of microstructures and tensile properties are discussed as well.

Cobalt-based composite coatings with varying TiC content (0 ~ 30 wt.%) were fabricated on M2 high-speed steel (HSS) substrates via laser cladding. Microstructural evolution, phase composition, microhardness, and tribological behavior were systematically characterized. Results indicate that TiC addition alters the phase constitution of the coating. With increasing TiC content, the relative contribution of the γ-Co phase decreases, while β-Co-related phases and Ti-containing carbides become increasingly prominent. Concurrently, Ti-related complex carbides formed through metallurgical reactions between TiC and alloying elements from the substrate. The microstructure evolved from relatively coarse dendritic regions to a more refined and heterogeneous morphology with increasing TiC content. Grain refinement was significantly enhanced after TiC addition, and the average grain size decreased from 21.19 to 12.10 μm at 20 wt.% TiC. The coating microhardness increases linearly with TiC content, peaking at 695.69 HV_0.3 (36.6% higher than TiC-free coating) at 30 wt.% TiC addition, attributed to dispersion strengthening by unmelted TiC particles and in situ precipitated secondary carbides. Optimal wear resistance is achieved at 20 wt.% TiC addition, exhibiting a 57.1% reduction in volume wear rate due to enhanced microstructural homogeneity. However, higher-TiC content (30 wt.%) induces brittle spalling and increases friction coefficients from ceramic phase inhomogeneity. This study confirms that 20 wt.% TiC optimally balances hardness, wear resistance, and structural integrity for HSS tool applications.

In this study, the low-cost Mg-Ca binary alloy and also the Mg-Zn-Ca ternary alloy were developed, and the high strength of > 250 MPa and high ductility of > 10% are obtained via the conventional extrusion processing. For the typical Mg-0.4 Ca binary alloy (wt.%, named as X4 sample), the as-extruded sample exhibits yield strength (YS) of 293 MPa, ultimate tensile strength (UTS) of 298 MPa and elongation (EL) of 15.9%. For the typical Mg-1.0Zn-0.4Ca ternary alloy (wt.%, named as ZX10 sample), the as-extruded sample exhibits an optimal combination of mechanical properties: with YS of 260 MPa, UTS of 286 MPa, and EL of 24.1%. Microstructural analysis indicates that all the as-extruded alloys exhibit a typical bimodal microstructure. Compared with the un-dynamic-recrystallized (un-DRXed) regions, the dynamic-recrystallized (DRXed) regions show a weaker texture and higher basal-slip Schmid factors. All the as-extruded alloys contain abundant micron- and nano-sized Mg₂Ca phases. In addition, the Ca₂Mg₆Zn₂ phase was identified in the as-extruded ZX10 sample, and its recrystallization fraction increased to ~ 60.9%. The superior strength-ductility synergy in the as-extruded ZX10 sample is attributed to the enhancement in recrystallization fraction, together with grain refinement, precipitation strengthening, and texture modification. This study provides valuable insights into microstructural control strategies for achieving high strength-ductility synergy in low-cost biomedical magnesium alloys.

The prediction of crack propagation rates in 2024-T351 aluminum alloy is a critical concern for the aerospace and automotive industries. In this research study, experimental results and machine learning approaches are combined to investigate the effect of grain boundaries on the crack propagation behavior. Mechanical tests on notched specimens and microstructural investigations show that grain boundaries act as physical barriers, effectively slowing crack propagation. Based upon these observations, two prediction protocols are developed using multiple machine learning algorithms. A cubic spline interpolation technique was also applied to generate an expanded dataset from the original experimental data, composed of only 23 experimental data points. Cracks often initiate at notches, while grain boundaries significantly affect crack growth by retarding the propagation rate. The models achieve R² values up to 0.7143 for the CNN and 0.9958 for the MLP. The integrated experimental-machine learning framework provides an effective approach for modeling the fatigue crack propagation of 2024-T351 aluminum alloy.