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

The effect of displacement damage on the corrosion behavior in a molten FLiBe salt environment was investigated. The element distribution and microstructure around the grain boundaries (GBs) after corrosion were characterized. The results show a decrease in corrosion thickness with increasing irradiation dose and the presence of intergranular corrosion. Nanoscales M₂C carbides were observed to be distributed, with a denser and thicker distribution in samples with higher irradiation doses. Their distribution depth is related to the Cr depletion region, inhibiting Cr diffusion toward the GBs and surface. Furthermore, the nucleation mechanism of M₂C carbides along the GBs and in irradiated regions was revealed, attributed to the combined effects of thermal influences, element preferential dissolution due to corrosion, and irradiation-induced segregation.

Microfluidic technology utilizing the deterministic lateral displacement (DLD) method holds significant promise for efficiently separating micro-particles and biological cells. Despite the notable high throughput advantages associated with DLD chips, their widespread application is impeded by the substantial manufacturing costs of tens of thousands of micropillars. This study aims to explore the feasibility of employing the injection molding method for the mass production of DLD microfluidic chips. A multistage DLD chip with varied critical diameters was designed to isolate white blood cells from the human whole blood. The separation effectiveness was verified with the polydimethylsiloxane chip fabricated by standard soft lithography. Subsequently, nickel mold inserts were electroformed to fabricate thermoplastic DLD chips via the injection molding. The replication quality of micropillars under different molding parameters was studied. The capability of injection-molded chips to effectively achieve particle separation was validated. Results showed that thermoplastic chips with good replication quality were obtained, providing a scale-up production strategy for fabricating polymer-based microfluidic chips for disposable separation applications.

In this study, post-heat treatments were applied to Ti–6Al–4V (TC4) alloy fabricated by selective laser melting (SLM) to investigate the effects of annealing temperature (750–950 °C in 50 °C intervals) on the alloy's microstructure, residual stress and mechanical properties. The initial microstructure of as-SLMed TC4 alloy was dominated by needle-like α′ martensite with a high density of dislocations and minor β phase, resulting in high strength (1190 MPa) but limited ductility (2.2% elongation). Annealing led to the transformation of α′ martensite into α phase, with the β phase content remaining relatively stable. Increasing the annealing temperature caused the acicular martensite to evolve into bundles of coarse α laths, forming a basket-weave microstructure. Annealing at 750 °C for 2 h reduced the yield strength to 1040 MPa and improved elongation to 8.3%. Interestingly, both the strength and ductility decreased with further increases in annealing temperature. This unusual phenomenon was rarely mentioned in current literature and was considered to be associated with the abnormal variations in the Schmid factor of (0001) [11-20] slip system and the reduction of mobile dislocations within the coarsened α martensite. Additionally, annealing combined with air cooling effectively alleviated residual tensile stresses in the SLM-formed TC4 alloy.

We here investigated the effect of vanadium microalloying on the microstructure, mechanical properties, especially corrosion performances of low carbon bainitic steels. The corrosion behaviors of the steels with different vanadium contents in 3.5 wt% NaCl solution were evaluated by electrochemical tests (including polarization curves and electrochemical impedance spectroscopic measurements) and alternating immersion test (including weight loss and rust layer observation). Results show that the mechanical properties and corrosion resistance of low carbon bainitic steels can be synergistically improved with vanadium microalloying. With help of the electron backscatter diffraction characterization and scanning Kelvin probe force microscopy, we first discovered that although the number of micro-galvanic couples increases because of grain refinement, the Volta potential gradient between the matrix and grain boundaries are decreased with vanadium microalloying, which can promote the formation of compact protective rust layers and improve the corrosion resistance of vanadium micro-alloyed low carbon bainitic steels.

The microstructure and properties of Cu_66.6(FeCo)_33.4 and Cu₆₀(FeCo)₄₀ alloys were investigated. Microstructural observations show that CuFeCo alloys have formed dual-phase heterostructures comprising face-centered cubic (FCC) and body-centered cubic (BCC) phases. The average grain size of the CuFeCo alloys after cold rolling and aging is less than 10 μm. Cu_66.6(FeCo)_33.4 has better elongation and electrical conductivity, while Cu₆₀(FeCo)₄₀ has better tensile strength, hardness, saturation magnetization, and electromagnetic interference shielding effectiveness. An increased FeCo content in a finer second phase with a larger volume fraction, leading to more phase boundaries. This enhances the strength of the CuFeCo alloys while simultaneously reducing their elongation. The obtained results can be used for further development of alloys with FCC/BCC dual-phase heterostructures.

This paper systematically studies the changes in the microstructure and magnetic properties of CoFeSiBNb series metallic fibers before and after AC annealing. The influence of current intensity on the magneto-impedance (MI) effect of the fibers is analyzed and the mechanism of current annealing to improve the MI characteristics is further revealed. The results show that the surface of the CoFeSiBNb metallic fibers before and after AC annealing is smooth and continuous, the tensile strength of CoFeSiBNb3 fiber is 5.15 GPa and it is the most stable and fracture-reliable. After AC annealing, metallic fibers' general magnetic properties and MI ratio increase at first with current intensity and then decrease at higher intensities. Specifically, the 140 mA AC annealed metallic fiber shows excellent magnetic properties with M_s, μ_m, H_c, and M_r values reaching 94.38 emu/g, 0.4326, 34.36 Oe, and 13.94 emu/g, respectively. With an excitation frequency of f = 1 MHz, the fiber's [ΔZ/Z_max]_max, ξ_max, H_k, and H_p reached 216.81%, 31.04 %/Oe, 1 Oe, and 2 Oe, respectively. During the current annealing process, Joule heat eliminates residual stresses in the fibers while forming atomically ordered micro-domains, which improves the degree of its organizational order. Meanwhile, a stable toroidal magnetic field is generated, which promotes the distribution of the magnetic domain structure of the fibers, thereby improving the MI effect.

Refractory high-entropy alloys (RHEAs) have emerged as frontier materials for high-temperature structural applications due to their exceptional mechanical properties and thermal stability. This review aims to provide a comprehensive and in-depth summary of the latest research progress in the field of RHEAs. By systematically analyzing 253 publications since 2022, this review presents a panoramic overview of the current research status in the field of RHEAs, covering aspects from alloy design, microstructure, processing techniques, mechanical behavior, to physicochemical properties. Key strengthening and toughening mechanisms, such as solid solution strengthening, precipitation strengthening, and grain boundary strengthening, are extensively analyzed. The high-temperature mechanical performance, oxidation resistance, and adaptability of RHEAs in extreme environments including corrosion and irradiation, are critically reviewed, and the potential application value of these research findings in aerospace, nuclear energy, biomedical, and other fields is discussed. Simultaneously, the multidisciplinary characteristics of RHEAs research has revealed the trend of the field evolving from fundamental research to practical applications. Furthermore, with the aid of advanced characterization techniques and computational methods, the review elucidates the controlling effects of chemical short-range order, defect structures, and other factors on the performance evolution of RHEAs, highlighting the importance of multi-principal element synergistic effects. Based on summarizing the key scientific issues and technological bottlenecks faced by RHEAs, the article provides a forward-looking perspective on future research directions, emphasizing development strategies that integrate computation and experiments, and accelerate the transformation of fundamental research into engineering applications, thus providing insights and guidance for developing a new generation of high-performance RHEAs.

In this study, cubic Hastelloy-X was manufactured by laser powder bed fusion process. A systematic investigation focused on the microstructure and anisotropic electrochemical corrosion behavior along the building direction was conducted. Distinctive columnar dendritic features across melt pool boundaries were consistently observed in the top (HX-T), middle (HX-M), and bottom (HX-B) regions along the building direction. A significant reduction in Mo content from the HX-T to the HX-B was observed, attributed to preferential segregation of Mo during the solidification process. Typical fish-scale molten pool was observed in the HX-B and HX-M, while HX-T consisted of strip molten pool in addition to fish scale molten pool. All samples showed the typical characteristics of Goss texture <110>//BD. HX-M sample showed the largest grain size, highest intensity ∼6.35 mrd and lowest kernel average misorientation value as compared to HX-T and HX-B associated with the remelting of the former solidified layer due to the newly deposited layer. Electrochemical analysis including electrochemical impedance spectroscopy and potentiodynamic polarization scans were conducted in 10 wt% NaCl electrolytes at constant temperature of 25 ± 1 °C. HX-T showed the lowest corrosion rate as compared to HX-M, HX-B (0.55, 23.16 and 16.01 mpy for HX-T, HX-M and HX-B, respectively). The surface morphology of corroded samples revealed that the formation of a compact passive film due to the presence of high atomic % of Mo in HX-T restricted the chloride ions from the electrolyte to penetrate and react with the metal samples subsequently enhancing the corrosion resistance.

Strain‒induced precipitation is a characteristic physical‒metallurgical phenomenon during hot‒rolling in microalloyed steel production that strongly affects the overallthermomechanical control process. In this study, the strain‒induced precipitation behavior in titanium‒molybdenum microalloyed steel was comprehensively investigated, and its complex effects on the austenite/ferrite transformation during continuous cooling were analyzed for the first time, based on stress relaxation and multi‒aspect characterization methods. The stress relaxation results revealed that the fastest strain‒induced precipitation occurred at 900 °C. The precipitates were identified as FCC structured (Ti, Mo)C particles with a coherent or semi‒coherent cubic‒cubic orientation relationship to the austenite matrix. The strain‒induced precipitation proved to increase the ferrite transformation temperature and proportion, significantly refine and homogenize the transformed grains. The intermittent quenching at 0.5 C/s further revealed that the (Ti, Mo)C particles with cubic‒cubic orientation relationship to austenite matrix exerted a dual pinning effect: by pinning dislocations, these particles facilitated diffusion‒controlled ferrite nucleation and growth both at austenite grain boundaries and within grains; by pinning migrating phase interfaces, the particles inhibited the coarsening of ferrite grains. Coupled with compressive testing and strengthening contribution analysis, the strain‒induced precipitation was shown to weaken precipitation strengthening but enhance grain refinement strengthening, thereby providing a novel approach to achieving an optimal balance between microstructural homogeneity and mechanical properties.

To understand the tribocorrosion mechanism of TiB₂–Ni coating doped with La₂O₃ in the deep ocean, the wear and corrosion test of La₂O₃–TiB₂–Ni under various hydrostatic pressures was conducted and discussed in 3.5 wt % NaCl solution. The results indicate that the tribocorrosion mechanism of the La₂O₃–TiB₂–Ni coating transitions from abrasive wear with corrosion under 0.1 MPa to abrasive wear with corrosion and adhesive wear under high hydrostatic pressure. The La₂O₃–TiB₂–Ni coating shows significant enhancements in wear resistance and anti-friction properties compared to the TiB₂–Ni coating. As the hydrostatic pressure increases from 0.1 MPa to 30 MPa, the self-corrosion current density experiences an approximate increase of 43.6 μA/cm².