Journal of Materials Research and Technology-Jmr&t最新文献

The purging plug is essential for enhancing production efficiency in molten steel refining, yet it faces challenges related to structural integrity due to its lifespan often not aligning with the ladle's repair cycle. This study introduces a novel corundum-calcium hexaluminate purging plug with gradual holes designed to alleviate internal stress concentration. Utilizing a multi-objective optimization model and fluid-solid coupling heat transfer method, the impact of structural parameters on thermal and mechanical properties was systematically investigated. The numerical simulation results indicate that increasing the number of gradient layers positively impacts temperature distribution. Notably, the D-210 (1.0 mm diameter) aperture reduces the stress gradient $\Delta {\sigma }_{\max }$ by 648.06 MPa compared to D-212 (1.2 mm diameter) at the Y = 0.313 m section. Additionally, variation in inclination angle impacts tensile stress ${\sigma }_t$ and shear stress $\tau$, an inclination angle of 6° (α6) reduces maximum tensile stress by 211.41 MPa compared to an angle of 0° (α0).

Microstructure can play a vital role in defining mechanical properties of metallic materials. To elucidate this correlation in the case of Ti–15Mo–3Nb–3Al-0.2Si (TB8) alloy, herein, we designed various microstructures via heat treatment exploring the effects of grain size, precipitates and segregation on crack initiation behavior during tensile tests in metastable β-Ti alloy. After solution treatment at 830 °C, the TB8 alloy with equiaxed β grain displayed a good fracture elongation of 30.2 ± 0.63%. The adiabatic shearing band and β→α phase transformation were activated to increase the compatible deformation capability during tensile testing; however, the phase transformation caused the stress concentration in the boundary, resulting in crack initiation. For the samples prepared using solution and low aging at 440 °C, large grain, elements segregation at grain boundary and incomplete precipitates induced a slight reduction in ultimate tensile strength and elongation. After solution and aging at 520 °C, the short-rod or/and lamellar α phase precipitated in β grain effectively enhancing ultimate tensile strength (1398.71 ± 15.6 MPa). The increased boundaries provided the interface or precipitation strengthening effect, but high-density dislocations were also accumulated at the β/α interface, causing unstable deformation and crack initiation. These findings advance our understanding of the correlation between microstructure and crack initiation, and provide a basis for designing and customizing the mechanical properties of metastable β-Ti alloy.

Superplastic deformation typically occurs in non-ferrous metals at high temperatures, which results in severe surface oxidation and high energy consumption. In this study, we designed and manufactured a nano/ultrafine-grained stainless steel with a dual-phase microstructure that exhibits excellent low-temperature superplastic deformation capability. A maximum tensile elongation of approximately 500% was achieved when the tensile test was conducted at 700 °C with an initial strain rate of 5 × 10⁻⁴ s⁻¹. Even after a 500% tensile elongation, the austenite grains in the gauge section of the tensile specimen still maintained an equiaxed grain shape, and the texture also weakened significantly, indicating that grain boundary sliding and grain rotation dominated the deformation process during superplastic flow. The outstanding superplasticity is mainly attributed to the dual-phase microstructure composed of nano/ultrafine austenite grains and martensite.

Tantalum (Ta) has good potential for bone tissue engineering due to its excellent corrosion resistance and biocompatibility. However, the customization of Ta-based bone repair materials for irregularly shaped bone defects has been challenging due to their high melting point and hardness. In this work, porous tantalum granules (PTaG) were developed for the first time to repair irregularly shaped bone defects, inspired by the natural phenomenon of sand flow. PTaG were designed as a hierarchical porous structure to regulate the mechanical properties and provide a favorable space for inward growth of cells and tissues. Commercial porous titanium granules (PTiG) and Bio-Oss were used as positive controls to explore the potential of PTaG as bone substitute. The morphology, three-dimensional structure, composition, and mechanical properties of PTaG and PTiG were evaluated by SEM, X-Ray 3D imaging system, 3D laser confocal microscope, EDS, XRD, XPS, and nanoindentation. In vitro, cell compatibility and mineralization ability were evaluated for both materials. Furthermore, PTaG, PTiG, and Bio-Oss were filled in the rabbit femoral defect, and micro-CT and histological analysis were performed after 8 weeks. The results showed that the PTaG had the best bone healing effect due to the hierarchical porous structure, excellent three-dimensional connectivity and chemical stability, suitable mechanical properties and surface roughness, good biocompatibility and mineralization osteogenic activity. This work indicates that PTaG may have a positive potential for filling and repairing irregularly shaped bone defects.

Various layer stacking methods have been employed in material extrusion type three-dimensional (3D) printing to utilize their potential for addressing the inherent technological limitation of reduced surface quality due to layer stacking. The process involved fabricating a material extrusion type 3D printed mold using diverse layer height-changing methods and subsequently replicating the surface pattern with the polymer. This approach is called the layer height method (LHM) and comprises three distinct variations. The first method involves altering the height of the individual layers to generate diverse surface morphologies and, consequently, varying the range of water contact angles. The second method focuses on rapid layer height changes to facilitate liquid deposition within regions with low contact angles. Finally, a layer height gradient was systematically established within the mold, resulting in a wettability gradient surface capable of controlling the movement of water droplets across the surface. The performance of these functional surfaces was successfully validated using various experimental methods. This study introduces a manufacturing technique based on changing layer heights within the framework of material extrusion-type 3D printing technology. A wide range of intricate and diverse functional surfaces can be produced by extending the manufacturing method proposed in this study to 3D printing technologies beyond the scope of material extrusion type 3D printing.

This paper examines the high-temperature oxidation behavior of Ni-based single-crystal turbine blade film cooling holes with varying inclination angles. Utilizing the theory of oxidation kinetics, the concept of an angle influence factor is introduced, and a novel oxidation kinetic equation is formulated. This allows for precise prediction of the oxide/γ′-free layer thickness in film cooling holes across different inclination angles throughout the oxidation process. It offers a new benchmark for future lifespan prediction models, significantly impacting the assessment of the operational life of air-cooled single crystal blades.

Eutectic high-entropy alloys (EHEAs) represent attractive candidate materials for overcoming the strength-ductility trade-off, which can be enhanced through the directional alignment of the lamellar structure along the loading direction. Here, we put forward a new route to optimize the strength-ductility synergy without orientation dependence. Through a combination of severe plastic deformation and annealing, we convert the initially lamellar structure into a dual-phase structure comprised of ultrafine equiaxed grains. The significant grain refinement improves the yield strength from 703 MPa to 1199 MPa without sacrificing any ductility. During deformation, the localized softening resistance of the achieved dual-phase microstructure avoids necking, and the intrinsic microcrack-arresting mechanism effectively improves the fracture resistance. Grain boundaries and phase boundaries provide nucleation sites for dislocations and restrict dislocation transfer while the strain incompatibility is accommodated by geometrically necessary dislocations. This work demonstrates that dual-phase alloys comprised of ultrafine equiaxed grains provide a pathway for strengthening without loss of ductility.

Co_0.3Ni_0.7-xZn _xFe₂O₄ (where x = 0.00–0.7 with step 0.1) spinels or CNZF with constant Co concentration and varying of the Ni/Zn concentration were obtained by the ceramic method from initial oxides. Based on X-ray diffraction data it was concluded that all samples are single-phase (SG: Fd-3m). Concentration dependences of the lattice constant and unit cell volume correlate well with Vegard's rule and the average value of the Zn²⁺ and Ni²⁺ ionic radii. The microwave permeability was measured in the frequency range of 0.1–20 GHz by a coaxial technique. Two resonances on frequency dependences were observed. Analysis of the microwave properties and magnetostatic data showed that low-frequency magnetic peak was caused by a resonance of domain boundaries; high-frequency peak was due to a natural ferrimagnetic resonance. Obtained results opens broad perspectives for practical application of such kind of materials and possibility for microwave parameters control by the external magnetic field.

The influence of different heat treatment processes on the microstructure and mechanical properties of 18Ni300 stainless steel manufactured by selective laser melting has been investigated in the present study. The microstructures, nanoprecipitates, and mechanical properties of the differently heat-treated samples were analyzed using various precision instruments. Compared with a non-treated 18Ni300 stainless steel sample, the results showed that the microstructure was mainly composed of fine lath-like martensite, with a large number of nano-precipitates dispersed both within the martensite and in the boundaries. In addition, there was a preserved amount of austenite between the lath-like martensite and the spherical nanoprecipitate in the SAT sample. The interactions between the martensite matrix and the nanoprecipitates and dislocations were assumed to be the main reason for the high strength of 18Ni300 stainless steel. These precipitates included rod-shaped or needle-shaped, Ni3Ti, Ni3Mo, and Ni3(Ti, Mo) nano-precipitates, as well as spherical Ti–Al nano-oxidized precipitates and massive Ni-rich precipitates. The shear and by-pass mechanisms between the strengthened nano-precipitate and the dislocations were found to depend on the size of the nanoprecipitate. The influence of the nanoprecipitation on the indentation hardness became more evident after heat treatment, but the effect on the indentation modulus was not that obvious. The AT- and SAT-treatments significantly improve the strength, hardness, and modulus of samples but were found to reduce the toughness and plasticity. After the AT- and SAT-treatments, the protrusions became smaller, and the small isometric protrusion of a shear lip became significantly smaller than for the as-built material.

Transition metal (TM) elements play a key role in determining properties of magnetocaloric materials. However, the effect of TM elements on the thermodynamic behavior and magnetocaloric effect (MCE) of metallic glasses (MGs) remains elusive. In this work, ternary Tb₅₅TM_17.5Al_27.5 (TM = Fe, Co, and Ni) MGs without the complexities induced by high-entropy effects were designed. It is found that both the glass transition temperature (T_g) and the initial crystallization temperature (T_x) significantly increase with decreasing 3d electron number. It leads to the low values of T_rg, γ, and γ_m for Tb₅₅Fe_17.5Al_27.5, which is consistent with its poor glass forming ability (GFA) as evidenced by the obvious lattice fringes and structural order. Despite the mediocre value of magnetic entropy change (|ΔS_M^pk|) for Tb₅₅Fe_17.5Al_27.5, its broader magnetic transition temperature of 110.4 K associated with ∼26% evident structural order yields the maximum relative cooling power (RCP) of 546.04 J kg⁻¹ among three MGs. Moreover, a novel weighted method for evaluating 3d electron number by consideration of the concentration and species of TM elements was adopted to reveal an inverse correlation between the 3d electron number and T_g/T_x, as well as curie temperature (T_c), |ΔS_M^pk|, and RCP. It is found that with the decrease of the weighted 3d electron number of TM elements, the thermal stability of rare-earth-base MGs is effectively enhanced ascribed to the strong f - d orbital hybridization effect, along with the enhanced 3d - 3d exchange interaction that induces a high T_c. This work would help us more deeply understand the role of TM elements from the perspective of electronic structure, which is crucial for designing the novel MGs with a tunable MCE and GFA applied in various cryogenic refrigeration fields.