Acta Metallurgica Sinica-English Letters最新文献

Despite the promising prospects of body-centered cubic iron (BCC Fe) in aerospace, energy transportation, and nuclear applications, the effects of extreme environments on its mechanical behaviors and deformation mechanisms remain elusive to date. In this work, the mechanical responses and deformation behaviors of BCC Fe single crystals under extreme loading conditions are investigated by performing the three-dimensional discrete dislocation dynamics simulations. It turns out that the yield strength (σ_y) of BCC Fe can be enhanced by increasing the strain rate ((dot{{varvec{varepsilon}}})) and/or decreasing the deformation temperature (T). With the strain rate increasing from (dot{{varvec{varepsilon}}})= 10² s⁻¹ to 10⁶ s⁻¹, the yield strength at 300 K rises from σ_y = 51.14 MPa to 1114.57 MPa. When the strain rate exceeds 10³ s⁻¹, an elastic overshoot phenomenon appears because the applied stress and the low initial dislocation density at the early tensile stage cannot drive the plastic deformation immediately. With the temperature increasing from T = 100 K to 800 K, the yield strength at (dot{{varvec{varepsilon}}})= 10³ s⁻¹ decreases from σ_y = 64.97 MPa to 59.50 MPa. Such temperature and strain rate sensitivity of deformation behaviors are clarified from variations in the configurations of dislocation evolution and dislocation density fluxes. It is demonstrated that at low strain rate ((dot{{varvec{varepsilon}}})≤ 10³ s⁻¹) conditions, the deformation behaviors of BCC Fe are dominated by the dislocation multi-slip mechanism. With increasing strain rate to e.g., (dot{{varvec{varepsilon}}})> 10³ s⁻¹, the deformation behaviors are governed by the dislocation single-slip. Our investigation on the temperature and strain rate sensitivity of deformation behaviors provides insightful guidance for optimizing the mechanical performances of BCC Fe based ferritic steels.

A series of high-strength wind power steels with various microstructural morphologies was produced by hot-rolled and thermo-mechanical controlled processes. The microstructure, microhardness, and tensile behavior observed using in-situ techniques in various types of steels were investigated. The experimental results demonstrated that the 3 microstructural morphologies (band-, net-, and fiber-structures) can be clarified and categorized; each type possesses different tensile strengths, yield behaviors, and strain hardening behaviors. This can be attributed to different strain distribution caused by the structural morphology; band-structure steels exhibit a yield plateau primarily attributed to the relatively weak constraint effect of pearlite on ferrite; net-structure steels display 3 strain hardening stages due to the staged plastic deformation; fiber-structure steels achieve superior strength through their uniform stress distribution. Furthermore, the initial strain hardening rate, transition strain, and uniform elongation were influenced by the features of the constituent phases. Based on these findings, methods for estimating the yield strength and tensile strength of the steels with two phases were discussed and experimentally validated.

This study systematically explored the oxidation behavior of a Ni-10Cr alloy without and with surface spraying hexagonal closed pack (hcp)-structured α-Al₂O₃ or α-Fe₂O₃ nanoparticles. Despite the distinct equilibrium dissociation oxygen partial pressure of the two kinds of oxide nanoparticles, they both contributed to the selective oxidation of Ni-10Cr alloy, achieving the transition from internal Cr oxidation to external Cr₂O₃ scale formation. Nano-scaled characterization indicates that a coherent interface was developed between the newly grown Cr₂O₃ grains and the hcp-structured oxide nanoparticles, whereby promoting epitaxial Cr₂O₃ nucleation surrounding the nanoparticles and kinetically accelerating the formation of a continuous Cr₂O₃ scale at the transient oxidation stage. The findings provide new insights into the selective oxidation mechanism of alloys with low Cr contents.

NiTi alloy has been widely used as orthopedic implant materials due to its unique shape memory properties and superelasticity. However, implantation failure often occurs because of the poor antibacterial ability, antioxidation property and corrosion resistance of the NiTi alloy. In order to overcome the above problems, we constructed Zn/ polydopamine (PDA)/Chitosan-Catechol (CS-C) composite coating on the surface of NiTi alloy in this paper. The surface morphology and wettability of the coating were characterized by scanning electron microscopy (SEM) and optical contact angle measuring instrument, respectively. The results showed that the Zn/ CS-C coating was successfully prepared, and exhibited good hydrophilic property, especially the sample Zn/PDA/CS-C-24 h. In addition, the corrosion resistance, antioxidation property and biological properties of the coating were systematically analyzed. The results indicated that the Zn/PDA/CS-C composite coating exhibited good corrosion resistance and antibacterial property, antioxidant property and osteogenic activity, especially sample Zn/PDA/CS-C-24 h. The sample Zn/PDA/CS-C-24 h could effectively protect osteoblasts from reactive oxygen species (ROS) damage and promote cell proliferation and osteoblast differentiation. This study provides a feasible and effective strategy for the surface modification of orthopedic implant.

The influence of V contents (0.6 wt%, 0.8 wt% and 1.0 wt%) on the microstructure and creep behavior of a Nickel-based superalloy was investigated. The results revealed that the V content exerted a significant impact on the morphology of carbide. Notably, in the alloy containing 0.8 wt% V, coarse blocky M₆C carbides formed adjacent to MC carbides, while in the 1.0 wt% V alloy, fine granular M₆C carbides exhibited a nearly continuous distribution along grain boundaries (GBs). The influence of V content on creep properties exhibited significant variations depending on temperature. At 650 °C/1010 MPa, the 1.0 wt% V alloy, containing a high density of granular M₆C carbides, demonstrated enhanced intergranular bonding strength, which contributed to prolonged creep life. In contrast, at higher temperatures (750 °C/620 MPa and 800 °C/500 MPa), GB mobility was activated, making GB slip the dominant creep mechanism. The near-continuous distribution of M₆C carbides in the 1.0 wt% V alloy restricted GB deformation compatibility, promoting stress localization and an increased density of micropores along GBs. As a result, the 0.8 wt% V alloy, with its discrete M₆C carbide distribution, exhibited superior creep resistance at elevated temperatures.

The present work investigates the corrosion behaviour of an AA2024 alloy thin wall structure produced by wire arc additive manufacturing (WAAM) with interpass rolling, focussing on the influence of interpass rolling. It is found that although interpass rolling does not change the typical configuration of thin wall structure, i.e. melt pool zone (MPZ), melt pool border (MPB) and heat-affected zone (HAZ), the plastic deformation introduced by interpass rolling leads to the variation of grain-stored energy across the structure, which consequently results in the highest corrosion susceptibility of MPB due to its relatively high stored energy.

Photogenerated electrons generated by photoexcitation of semiconductor materials can be transferred to metal materials to provide corrosion protection. Conversely, the accumulation of photogenerated holes accelerates the recombination of photogenerated carriers. Consequently, the development of efficient strategies for the consumption of photogenerated holes has emerged as a critical challenge in the field of photoelectrochemical cathodic protection technology. In this paper, TiO₂/TiOBr heterojunction photoelectrode was firstly prepared by simple hydrothermal method, and NiCo-LDH (layered double hydroxide) was further deposited on TiO₂/TiOBr to obtain TiO₂/TiOBr/NiCo-LDH photoelectrode. The construction of a heterojunction between TiO₂ and TiOBr promotes the separation of photogenerated carriers, while the deposition of NiCo-LDH reduces the overpotential for hole oxidation. Hence, the photoinduced potential drop and photoinduced current density of TiO₂/TiOBr/NiCo-LDH photoelectrode coupled with 316 L stainless steel in 3.5 wt% NaCl under simulated sunlight irradiation can be up to 303 mV and 25.87 μA/cm², respectively. This study provides a new idea for the design and preparation of TiO₂-based photoelectrodes with excellent photocathodic protection under visible light.

This study investigates the microstructural evolution of a novel low-cost second-generation Ni-based single crystal superalloy during long-term thermal exposure at different temperatures (982 °C, 1038 °C, 1093 °C) and its impact on the stress rupture properties of alloy. The results reveal that the γ′ phase undergoes coarsening and rafting at high temperatures, and its growth behavior follows the Ostwald ripening mechanism. With the increase in aging temperature and extension of aging time, the coarsening rate of the γ′ phase increases significantly. Particularly at 1093 °C, the γ′ phase undergoes the most pronounced growth, leading to a remarkable deterioration of its precipitation strengthening effect. Furthermore, under conditions of higher temperature and longer time, minor amounts of topologically close-packed (TCP) phase precipitate. As the aging temperature rises and time elapses, the precipitation tendency of the TCP phase shows a slight increase. The stress rupture testing at 1100 °C/120 MPa demonstrates that the stress rupture life decreases significantly with the increase in thermal exposure temperature and time. This is mainly attributed to the diminished precipitation strengthening effect of the γ′ phase and the deteriorating effect of the TCP phase. However, under the same conditions, the stress rupture properties of this alloy are comparable to those of the DD5 alloy. This research provides theoretical support for enhancing the service stability and reliability of single crystal turbine blades, and offers a reference for the development of cost-effective and high-performance turbine blade materials.

A heterogeneous transverse direction (TD)-tilt texture in rare-earth-containing magnesium plates typically results in obvious in-plane anisotropy in their mechanical behavior. In this study, the planar anisotropy of yield strength during tension along the rolling direction (RD) and TD is quantified in a Mg-0.1Zn-0.5Gd plate with different grain sizes and texture patterns. Regardless of the grain size, the yield strength along the RD is approximately 33 MPa higher than that along the TD in the plate with the c-axis distributed in an elliptical region. In contrast, a near in-plane isotropy of the mechanical properties is observed in the plate with the c-axis aligned primarily in a circular region. Microstructural analysis and crystal plasticity simulations show that basal slip prevailed during the tension test, with varied complementary deformation modes in different loading directions. Prismatic slip is the main complementary deformation mode during tension along the RD, whereas tensile twinning is important during tension along the TD. The yield anisotropy is primarily attributed to the varied intercept ({sigma }_{0}) in the Hall–Petch relation during tension along different directions. The invariant Hall–Petch slope (k) results in grain size independence on the mechanical anisotropy. Finally, a quantitative discussion on the differences of ({sigma }_{0}) and the similarity in (k) related to the relative activity of the deformation modes is provided.

High-entropy alloys (HEAs) show excellent prospects in microwave absorbing materials due to their designable composition and variable electromagnetic properties. In this work, FeCoCrAl_0.4V_x HEAs with body-centered cubic (BCC) single-phase solid solution structure were prepared by mechanical alloying and heat treatment. By varying the content of vanadium (V), the grain size, lattice constant, crystallinity, particle size, and microscopic morphology can be effectively adjusted, thereby enabling the optimization of their electromagnetic properties and microwave absorption performance. Doping a small amount of V element can refine the BCC grains, regulate the particle size, and enhance the electrical conductivity, which significantly improves the polarization relaxation, conduction loss, and eddy current loss of HEAs. In addition, the increased crystallinity and reduced lattice defects can enhance natural resonance loss at a high frequency (GHz), which will contribute to the improvement of impedance matching and electromagnetic attenuation. The annealed FeCoCrAl_0.4V_0.2 HEAs exhibit excellent wave absorption properties, achieving a maximum reflection loss of −44.3 dB at 1.8 mm thickness and an effective absorption bandwidth of 4.0 GHz at 1.2 mm, respectively. This study provides a new strategy for developing lightweight and high-performance high-entropy alloys microwave absorbing materials.