Metallurgical and Materials Transactions A最新文献

A356 aluminum alloy has attracted enormous attention because of its excellent mechanical properties and good corrosion resistance. Refining the eutectic Si phase is required to improve the mechanical properties for practical applications. In this work, a new strategy is proposed by synergizing the permanent magnet stirring (PMS) with rare earth (RE) La and Ce elements simultaneously during the solidification of A356 aluminum alloy. Experimental studies reveal that the eutectic Si phase transforms from coarse needle-like and flake-like shapes to small granular morphology, and its average size reduces from 12.94 to 8.86 μm. It is noted that the additions of La and Ce can induce twins and stacking fault structures in the Si phase preventing its further growth. Meanwhile, the PMS can significantly refine the grain size of α-Al phase and generate more small size La–Ce precipitates at the front of Si phase. When PMS and rare earth are applied together, the electromagnetic force generated by PMS and the twins and stacking fault structures induced by rare earth elements La and Ce, collectively act on the A356 alloy to refine both the Si phase and α-Al phases. The refined alloy exhibits an outstanding combination of mechanical properties and wear resistance.

The recycling of scrap could cause continuous enrichment of Sn in steels. To reveal the influences of Sn on the mechanical properties and microstructure evolution of high-strength low-alloy (HSLA) steels, HSLA steels with varying Sn contents were designed and a series of continuous cooling tests were conducted. The results show that the effect of Sn on microhardness is mainly affected by the cooling rate. Under cooling rates lower than 10 °C/s, the addition of Sn increases the microhardness due to the solid solution strengthening effect of Sn. The ferrite grain size decreases with the increase of Sn content at a cooling rate of 0.1 °C/s because of the possible solute drag effect of Sn, while no refining effect was found for cooling rates between 0.5 °C/s and 10 °C/s. Under cooling rates higher than 10 °C/s, Sn reduces the ferrite and bainite transformation start temperatures and increases the bainite and martensite phase fractions. The higher hard phase fraction with increasing Sn content results in a significant increase in microhardness, and the contribution of solid solution strengthening plays a supplementary role under this condition. As one of the major residual elements in scrap, the strengthening and hardenability increasing effects of Sn should not be overlooked and may even be properly utilized in alloy design.

In this study, Cu–Zn alloys were deposited in citrate-based electrolytes on aluminum substrate by electrodeposition method. The effect of bath pH variation on the properties of the obtained Cu–Zn alloy coatings was investigated. The electrochemical behavior of the citrate-based baths and the crystalline structure, surface morphology and elemental content, electrical resistivity and thermal behavior of the alloy coatings were analyzed. According to the results of cyclic voltammetry (CV) analysis, increasing bath pH caused a negative shift in the cathodic deposition potential. In addition, the anodic dissolution peaks first shifted to the positive side with increasing pH and then shifted back to the negative direction. According to the results of XRD analysis, the phase structure of Cu–Zn alloys generally consists of α and β′ phases, but according to differential scanning calorimeter (DSC) analysis, it is possible that there is a γ phase in the structure in addition to these phases. In addition, pH increase (4.5 to 6.5) caused a relative increase in crystal grain size (~14 to ~ 25 nm). The Zn content of Cu–Zn coatings first increased (~pct 15 to ~ pct 55) with pH increase, then followed a horizontal trend (~pct 55 to ~ pct 59) with further pH increase and then exhibited a slight decreasing trend (~pct 59 to ~ pct 52). The pH increase significantly affected the surface morphology of the coatings and denser coatings were obtained with increasing pH. While the electrical resistivity of Cu–Zn coatings first increased (0.0408 to 0.0696 µΩcm for 297 K) with increasing pH, it tended to decrease (0.0696 to 0.0479 µΩcm for 297 K) again at higher pH values. In addition, the electrical resistivity of the coatings increased with increasing measurement temperature. According to DSC analysis of the coatings, endothermic peaks were obtained, possibly representing the transformation from γ to β′ phase.

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The magnetic behavior of two high-entropy alloys, CrMnFeCoNi and CrMnFeCoNi-CN, was investigated under varying degrees of deformation through uniaxial tensile tests. Microstructural, morphological, and crystalline structural analyses using XRD and SEM revealed a uniform and stable austenitic structure in all samples, with no presence of α’-martensite or ε-martensite phases. The main deformation mechanisms identified were twinning and slip dislocation for the CrMnFeCoNi-CN alloy, and slip dislocation for the CrMnFeCoNi alloy at room temperature. The alloys exhibited low magnetic moments attributed to magnetically frustrated configurations. At temperatures below 70 K, distinct magnetic states were observed ranging from paramagnetic to ferrimagnetic and spin-glass-like behavior. Antiferromagnetic interactions were confirmed by a negative paramagnetic Curie temperature for both alloys. The magnetization of the CrMnFeCoNi alloy increased with deformation, reflected in effective magnetic moments varying from 1.81 (0 pct) to 2.60 (20 pct) μB, while for the CrMnFeCoNi-CN alloy remained stable around 2.39 to 2.48 μB. The magnetization of the CrMnFeCoNi-CN alloy was found to be higher than that of the CrMnFeCoNi alloy, suggesting that the presence of C and N as alloying elements can enhance magnetization to some extent.

As one of the joints with the greatest load-bearing capacity, the hip joint requires high mechanical strength and plasticity. In this study, Ni-coated Al₂O₃ (Ni@Al₂O₃) particles of different size were employed to enhance the mechanical properties of selective laser melting (SLM)-processed CoCrMo alloys. CoCrMo–Ni@30μmAl₂O₃ composites possessed the best comprehensive mechanical properties and underwent the γ–ε martensite transition with the largest proportion of ε/γ, which contributed to the inhibition of dislocation slip and the improvement of plasticity.

Graphical Abstract

This work investigates the effects of short-time direct aging heat treatments on the mechanical properties and microstructure of additively manufactured Nitinol (NiTi) alloy. Cylindrical samples were produced through laser powder bed fusion (L-PBF), directly aged at different temperatures and compared to the solution annealed and aged conditions. Compression tests were carried out at room temperature both in cyclic mode at constant strain and incremental cyclic mode, to provide a comprehensive analysis on the superelastic features of NiTi after direct aging heat treatments. Furthermore, cyclic compression tests were performed at 37 °C to evaluate the superelastic effect at the body temperature and, therefore, the possibility to use these treatments for biomedical components. The effects of direct aging on the microstructure were characterized using transmission electron microscopy (TEM). High cyclic stability and superelastic recovery up to 10 pct of deformation emerged for the direct aged alloys. The comparable results obtained with and without the solution treatment points out that this step was not necessary in reaching superelasticity, proving the effectiveness of direct aging.

Mo(Si,Al)₂–Al₂O₃ composites were tested in four-point bending at 1300 °C. The addition of Al₂O₃ led to a decrease in grain size, and a subsequent decrease in strength for materials containing up to 15 wt pct Al₂O₃. At higher Al₂O₃ fractions, the decrease in grain size saturates and the strength is recovered as the Al₂O₃ particles prevent grain boundary sliding.

Transient thermoreflectance (TTR) signal generated from pulse laser-induced oscillation of delaminated metal films of Al, W, and In is determined and the acoustic contribution due to strain is evaluated. The decay in the amplitude of the acoustic oscillations is modeled in terms of Granato–Lṻcke theory of vibrating dislocations with mobility restricted under drag exerted by electron scattering. The values of the relative energy loss factor from the experimental observations and from dislocation modeling are shown to correlate well using the expected dislocation density in annealed metal foils.

Prominent δ-ferrite to γ-austenite transition in the coarse-grained heat-affected zone of P92 steel has been documented in situ by confocal scanning laser microscope under different thermal cycles, with emphasis on the quantifying of migration of the γ/δ interface. With reducing cooling rate, the fraction of retained δ-ferrite decreases appreciably from 12.0 to 1.6 pct. It is further quantified that the average migration distance of γ/δ interface is enhanced from 10.74 to 17.81 μm.

This work studied the effect of welding thermal cycling on the microstructures and cryogenic impact toughness of medium-Mn low-temperature steel by single-pass welding thermal simulation test. The microstructures of the heat-affected zone (HAZ) were characterized by optical microscopy, electron backscatter diffraction, X-ray diffraction, and transmission electron microscopy. The results indicated that the microstructures of fine-grain HAZ are fine-lath martensite with film-like retained austenite in the heat input range of 10 ~ 30 kJ/cm. Meanwhile, fine-grain HAZ has excellent low-temperature impact toughness, and the impact energy tested at − 40 °C can reach about 245 J. The coarse martensitic packet and block in the coarse grain HAZ seriously deteriorated the cryogenic impact toughness, and the greater the heat input, the worse the cryogenic impact toughness. The impact energy tested at − 40 °C was 71 J when the heat input was 10 kJ/cm. The cryogenic impact toughness of HAZ gradually deteriorated with the peak temperature increase because of the decrease of retained austenite content and the increase of martensitic lath width.