Acta Metallurgica Sinica-English Letters最新文献

Hot isostatic pressing (HIP) temperature has a significant impact on the service performance of powder metallurgy titanium alloys. In this study, a high-temperature titanium alloy, Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, was prepared under different HIP temperatures (880–1000 °C), and the microstructural evolution and mechanical properties were systematically investigated. The results demonstrated that the HIPed alloys were predominantly composed of more than 80 vol.% α phase and a small amount of β phase, and their phase compositions were basically unaffected by the HIP temperatures. Under the typical single-temperature-maintained HIP (STM-HIP) regime, the microstructure of alloy significantly coarsened as the HIP temperature increased, and the alloy strength exhibited an obvious linear negative correlation with the HIP temperature. On the basis of Hall–Petch relation, the prediction model of grain size was established, and the mathematical equation between HIP temperature and grain size (left( {d = Mleft( {T_{{{text{HIP}}}} - N} right)^{ - 2} } right)) was deduced. Furthermore, a possible evolution mechanism of microstructure was proposed, which could be divided into the decomposition of initial α′ martensite for as-received powder, formation of the globular α grains in prior particle boundaries (PPBs) region, and precipitation of the platelet α grains in non-PPBs region. For these alloys prepared by the dual-temperature-maintained HIP (DTM-HIP) regime, although their tensile properties were comparable to that of alloy prepared by STM-HIP regime with same high-temperature holding stage, higher proportion of globular α grains occurred due to more recrystallization nucleation during the low-temperature holding stage, which probably provided a solution for improving the dynamic service performance of HIPed alloys.

Diffusion-bonded Ti₂AlNb-based alloys commonly present a low strength compared with the deformed or aged ones. In this study, the post heat treatment including solution and aging treatments is proposed to optimize the microstructure, contributing to strength improvement and appropriate ductility sacrifice. An available method by the introduction of fine size (both 20–100 nm) and a high fraction (59.7% and 13.7%) of O and α₂ phases using both solution at 1000 °C for 1 h and aging at 750 °C for 5 h can result in excellent tensile strength (992 MPa and 858 MPa) at room temperature and 650 °C, respectively, which increases 5.3% and 44.5% than that of as-received sample. The aging treatment can contribute to lamellar O and α₂ grains precipitated from the B2 parent, which results in limited dislocation slip systems and slip spaces to resist plastic deformation. Moreover, the crack propagation and fracture surfaces are also comparatively analyzed to reveal the fracture behaviors in the samples with high and low strength. This study can provide a new method for the mechanical property optimization of the welded Ti₂AlNb alloys.

Twinning-induced plasticity (TWIP) steel shows great potential in engineering due to its excellent strength and ductility synergy, and strengthening research on its corrosion resistance and high-temperature oxidation resistance is critical for broader applications. Herein, the effect of annealing temperature on the high-temperature oxidation and corrosion behavior of Fe–Mn–Cr–Al–Cu–C TWIP steel is investigated. The results show that increasing the annealing temperature from 700 °C to 1100 °C reduced the mass gain of the TWIP steel oxidized at 800 °C for 8 h from 1.93 to 0.58 mg·cm⁻². Additionally, the self-corrosion current density decreases from 6.52 × 10⁻⁶ to 1.32 × 10⁻⁶ A·cm⁻², while charge transfer resistance increases from 1461 to 3339 Ω·cm⁻². The reduction in grain boundaries and dislocation density in the TWIP steel attributed to the increase in annealing temperature inhibits short-circuit diffusion, local galvanic corrosion and pitting, ultimately improving both oxidation and corrosion resistance. Moreover, high-temperature annealing prevents the formation of carbon-rich compounds and ensures uniform element distribution. The accumulation of Cu and Cu-rich products formed at the interface further protects against Cl⁻ erosion, inhibiting pitting and local corrosion, thus enhancing the corrosion resistance of the TWIP steel.

Wear is a prevalent issue across various industries. Spherical fused tungsten carbide (sFTC) reinforced nickel-aluminum bronze (NAB) matrix composite surface deposits have shown remarkable potential in mitigating wear by approximately 80%. However, the performance of these sFTC/NAB composite surface deposits is determined by their residual stress state, and the precise macroscopic and microscopic residual stresses within these composites have yet to be clearly established. To address this gap, we employed neutron diffraction to measure the residual stresses in the sFTC/NAB composite surface deposits and re-melted NAB samples produced via laser melt injection. Significant residual stresses were determined. The maximum tensile macro residual stress appears approximately 1–1.5 mm below the composite layer. Residual stresses accumulate with an increasing number of laser process tracks. The maximum tensile macro residual stress in the three-track samples reaches about 350 MPa. Preheating the base plate significantly reduces the levels of macroscopic residual stress. The WC phase displayed significant compressive thermal misfit residual stress magnitude, while the Cu matrix exhibited tensile thermal misfit residual stress. Preheating the base plate does not reduce microscopic thermal misfit residual stress levels. In addition, a finite element model was built to investigate temperature and residual stresses in the re-melted NAB samples. The predicted temperature history and residual stress agree with the experimental results.

Thermodynamically stable and ultra-thin “phase” at the interface, known as complexions, can significantly improve the mechanical properties of nanolayered composites. However, the effect of complexions features (e.g., crystalline orientation, crystalline structure and amorphous composition) on the plastic deformation remains inadequately investigated, and the correlation with the plastic transmission and mechanical response has not been fully established. Here, using atomistic simulations, we elucidate the different complexions-dominated plastic transmission and mechanical response. Complexions can alter the preferred slip system of dislocation nucleation, depending on the Schmid factor and interface structure. After nucleation, the dislocation density exhibits an inverse correlation with the stress magnitude, because the number of dislocations influences the initiation of plastic deformation and determines the stress release. For crystalline complexions with different structures and orientations, the ability of dislocation transmission is mainly dependent on the continuity of the slip system. The plastic transmission can easily proceed and exhibits relatively low flow stress when the slip system is well-aligned. In the case of amorphous complexions with different compositions, compositional variations impact the atomic percentage of shear transformation zones after loading, resulting in different magnitudes of plastic deformation. When smaller plastic deformation is produced, less stress can be released contributing to higher flow stress. These findings reveal the role of the complexions on plasticity behavior and provide valuable insights for the design of nanolayered composites.

In this work, nanocrystalline SmCo₅–Cu nanocomposite powders were fabricated from the ball-milled amorphous matrix by crystallization annealing which is lower than the traditional sintering temperature ~ 1000 °C for bulk SmCo₅ bulk magnets. Annealed Cu-doped SmCo₅ powders have a higher coercivity compared to that of Cu-free SmCo₅ one due to the combined effects of refinement effect of grain size and the pinning effect induced by Cu doping. The peak of coercivity (H_c) is located at 600 °C for annealed Cu-doped SmCo₅, which is ascribed to the improved pinning field. The pinning effect became reduced when the annealing was done at even higher temperatures. More importantly, the best comprehensive magnetic properties, including a maximum magnetic energy product (BH)_max of 12.2 MGOe together with a coercivity of 31.8 kOe and a remanence of 64.3 emu/g, could be achieved for SmCo₅-3 wt% Cu by low temperature annealing. These results demonstrate that isotropic Cu-doped SmCo₅ nanocrystalline powders are promising precursors for the fabrication of high-performance bulk magnets.

To increase the strength of the laser powder-bed fusion (LPBF) Al–Si-based aluminum alloy, TiB₂ ceramic particles were selected to be mixed with high-Mg content Al–Si–Mg–Zr powder, and then a novel TiB₂/Al–Si–Mg–Zr composite was fabricated using LPBF. The results indicated that a dense sample with a maximum relative density of 99.85% could be obtained by adjusting the LPBF process parameters. Incorporating TiB₂ nanoparticles enhanced the powder's laser absorption rate, thereby raising the alloy's intrinsic heat treatment temperature and consequently facilitating the precipitation of Si and βʺ nanoparticles in the α-Al cells. Moreover, the rapid cooling process during LPBF resulted in numerous alloying elements with low-stacking fault energy dissolving in the α-Al matrix, thus promoting the formation of the 9R phase. After a 48 h direct aging treatment at 150 °C, the strength of the alloy slightly increased due to the increase of nanoprecipitates. Both yield strength and ultimate tensile strength of the LPBF TiB₂/Al–Si–Mg–Zr alloy were significantly higher than that of other LPBF TiB₂-modified aluminum alloys with external addition.

This work investigated the anisotropy tensile properties of Inconel 625 alloy fabricated by laser powder bed fusion (LPBF) under various tests temperature, focusing the anisotropy evolution during the high temperature. The microstructure contained columnar grains with (111) texture in the vertical plane (90° sample), while a large equiaxed grain with (100) texture was produced in the horizontal plane (0° sample). As for 45° sample, a large number of equiaxed grains and a few columnar grains with (111) texture can be observed. The sample produced at a 0° orientation demonstrates the highest tensile strength, whereas the 90° sample exhibits the greatest elongation. Conversely, the 45° sample displays the least favorable overall performance. As the tests temperature increased from room temperature to 600 °C, the anisotropy rate of ultimate tensile strength, yield strength and ductility between 0° and 45° samples, decreased from 8.98 to 6.96%, 2.36 to 1.28%, 19.93 to 12.23%, as well as between 0° and 90° samples decreased from 4.87 to 4.03%, 11.88 to 7.21% and 14.11 to 6.89%, respectively, because of the recovery of oriented columnar grains.

The corrosion behavior of Ni-Co-CeO₂ composite coating was investigated under a simulated high-temperature marine atmosphere alongside Ni-Co coating. The corrosion kinetics, phase composition and microstructure evolution of the coatings were analyzed. A multi-layered oxide scale formed due to the synergistic corrosion by H₂O and NaCl. The growth mechanism of the Co₃O₄, Fe₃O₄, Fe₂O₃, CoFe₂O₄, NiFe₂O₄ and NiO in the scale was proposed according to the distribution of the CeO₂ particles. Compared to Ni-Co cating, the Ni-Co-CeO₂ coating exhibited superior corrosion resistance in the H₂O/NaCl steam, which is beacause the CeO₂ exerted a blocking effect on retarding the diffusion of Fe atoms and corrosive medium, contributing to a reduced corrosion rate and an improved oxide adhesion compared to Ni-Co coating.

The effects of strain rate on tensile properties and fracture behavior of HfNbTaTiZr refractory high-entropy alloy (RHEA) were investigated. With the increase of strain rate in the range from 0.0001 to 0.1 s⁻¹, the yield strength increases from 740 to 825 MPa, demonstrating a strain rate sensitivity coefficient of 0.0173. Notably, while the uniform elongation diminished with rising strain rates, the fracture elongation of the RHEA remained constant at ~ 43%, suggesting an enhanced non-uniform elongation and an improved resistance to tensile fracture. Single-edge notch tension test further proves that the notch toughness increases at elevated loading rates. The complete work-hardening rate curves were plotted, and the work-hardening ability of the RHEA was found not decreasing significantly after necking, especially at high strain rate. The fracture of tensile samples across all the strain rates was dominated by void growth and coalesce, with dimples on the fracture surface being smaller at higher strain rates. This work reveals an unconventional increase in fracture resistance at higher strain rates, further indicating that ductile RHEAs may possess superior potential for use in structural applications subjected to high strain rate loading.