Acta Metallurgica Sinica-English Letters最新文献

The oxidation behavior of 316L austenitic steel after thermal aging process at 600 °C for 6 h was investigated in the supercritical water (600 °C/25 MPa) with 1000 h. Results showed that the grain size and the proportion of high angle grain boundaries (HAGB) increased in the steel after thermal aging process, with the observation of micro-textures. The weight gain rate of the steel after aging process increased, presenting the decreased Cr₂O₃ contain in the oxide layer, which resulted in the increasing diffusion rate of Fe and O ions in oxide layer. The molecular dynamics simulation results confirmed the high oxidation rate in HAGB and micro-textures for the 316L steel after aging process.

Chloride-induced corrosion of steel reinforcement is the key factor leading to the degradation of reinforced concrete building durability. Improving the corrosion resistance of oxide scale of rebar has always been a research hotspot in the field of civil engineering materials. A ZIF-8 modified Ce–Sol–gel (ZCS) film was prepared on oxide scale of plain steel rebars by sol–gel method. It is observed that the |Z|_0.01 Hz value of the ZCS film reached 320 kΩ cm², which is about 29 times higher than that of blank rebar in simulated concrete pore (SCP) solution with 0.1 M NaCl. Then, they were inserted into mortar block and curing them in a curing box at T = 20 ± 2 °C and RH = 95 ± 2% for 28 days. Subsequently, these samples were subject to electrochemical impedance spectroscopy in 3.5 wt% NaCl. The |Z|_0.01 Hz value of the rebar with the ZCS film was six times higher than that of the blank rebar after immersing for 20 days, resulting in an overall increase in corrosion resistance for rebar. The results indicated that the modification by ZIF-8 could reduce the porosity of Ce–sol–gel (CS) film and improved the “labyrinth effect” of the film. Additionally, the negative charge on the surface of ZIF-8 in alkaline condition increased the repulsion effect with Cl⁻, significantly reducing the sensitivity of rebar to Cl⁻.

A Ti–5.4Al–6.4Zr–6.2Sn–0.4Mo–1.6W–0.4Nb–3.2Ta–0.5Si alloy is designed following cluster formula approach that achieves a strength level of 1 GPa at 600 ℃ in the as-cast state, superior to any existing high-temperature Ti alloys. Its composition is formulated by 17 basic units, α-{[Al-Ti₁₂](AlTi₂)}₁₂ + β-{[Al-Ti₁₂Zr₂](Mo_0.125Nb_0.125Ta_0.5W_0.25Sn_1.5Si_0.5)}₅, each unit covering a nearest-neighbor cluster plus a few next-neighbor glue atoms. This design is on the basis of the composition formula of Ti65 alloy, with an enhanced β stability via more Zr, Mo, Nb, Ta, W, Sn, and Si co-alloying. Upon copper-mold pour casting, this alloy shows a good microstructure stability. In tensile testing below at 650 ℃, its α plates thickness is nearly at the same level of 0.2 μm, which is much smaller than 0.7–0.8 μm of Ti65 at the same condition. The changes in volume fraction of β phase are increased by 86%, much less than by 105% in Ti65. Its room-temperature strength reaches the ultra-high-strength level, with an ultimate tensile strength of 1328 MPa and a yield strength of 1117 MPa, with a moderate elongation of 3.8%. At 600 ℃, its ultimate tensile strength of 1017 MPa and yield strength of 936 MPa are superior to those of any existing high-temperature Ti alloys, with an elongation of 7.2%. At 650 ℃, its ultimate tensile strength of 848 MPa still maintains a high level.

This work systematically investigates the densification, microstructure evolution and the attainment of high strength-ductility in Ti-13Nb-13Zr-2Ta alloy processed by laser powder bed fusion (LPBF). A narrow and viable process window (P_{laser power} = 175 W, v_{scanning speed} = 1000 mm/s, h_{scanning distance} = 0.1 mm and d_{layer thickness} = 0.03 mm) was accordingly determined and the relative density of Ti-13Nb-13Zr-2Ta alloy reaches 99.76%. The depth of molten pool increases gradually with the increase of energy density, and the relationship between the depth of molten pool and energy density has been quantitatively described. Three types of α′ martensites with average grain width less than 3 μm can be observed in the LPBF-fabricated Ti-13Nb-13Zr-2Ta alloys, attributed to the significantly high cooling rate and remelting process. The fine grain size, high density dislocations, nanotwins, ordered oxygen complexes and α + α″ heterostructure all contributed to the high strength (1037.75 ± 25.18 MPa) and ductility (20.32% ± 1.39%) of LPBF-fabricated Ti-13Nb-13Zr-2Ta alloy in this work.

In this study, the effects of ultrasonic coaxial assisted TIG welding (U-TIG) on the formation, microstructure, and mechanical properties of TC4 titanium alloy welded joints were investigated. The results indicated that at optimal ultrasonic power and welding current settings, remarkable improvements of welded joint were observed. Specifically, the weld depth-to-width ratio increased by 267% compared to conventional TIG welding, reaching 0.22. Furthermore, the microhardness of the welded seam increased by 53%, reaching 550.1 HV, while the tensile strength of the welded joint rose to 1197.7 MPa, representing a 12.2% enhancement. The compressing effect of ultrasound concentrates the energy of the arc, thereby improving the penetration depth of the welded seam. In addition, ultrasonic cavitation plays a crucial role in refining the grain structure of the weld seam, consequently enhancing its strength.

It is extremely difficult to strengthen bulk aluminum (Al) by twins, due to its high stacking fault energy under standard loading conditions. In this study, a simple yet effective solution was proposed for introducing twins to strengthen bulk Al. The method involves the addition of nanoparticles with high volume fraction combined with the tailoring of sintering temperature toward the melting point of Al during hot pressing. Sintering temperature plays an important role in forming twins in bulk Al containing high content nanoparticles. The twin content increases with increasing sintering temperature in the range of 590–640 °C. At sintering temperature of 640 °C, the twin content reaches 17%, enabling the significant improvement in the yield strength of the bulk Al from 251 to 400 MPa, compared with the sample with few or no twins. The twin strengthening may serve as a major strengthening mechanism for bulk Al, and its strengthening contribution is comparable to the dominant Orowan strengthening resulting from the added nanoparticles.

AlCoCrFeNi_2.1-xNi₃Al (x = 0, 5.0, 7.5, and 10 wt%, denoted as Ni₃Al0, Ni₃Al5.0, Ni₃Al7.5, and Ni₃Al10) eutectic high-entropy alloy (EHEA) matrix composites were fabricated by mechanical alloying and spark plasma sintering methods. The effects of Ni₃Al content on the microstructures, mechanical and wear properties of AlCoCrFeNi_2.1 EHEA were investigated. The results indicate that the AlCoCrFeNi_2.1-xNi₃Al composites present cellular grid morphologies composing of FCC/Ll₂ and B2 phases, and a small amount of Al₂O₃ and Cr₇C₃ phases. The addition of Ni₃Al significantly enhanced the compressive yield strength, compressive fracture strength, compressive strain and wear properties of the AlCoCrFeNi_2.1 composites. In particular, the Ni₃Al10 composite exhibits excellent comprehensive mechanical properties. The compressive yield strength, compressive fracture strength and compressive strain of the Ni₃Al10 composite, are 1845 MPa, 2301 MPa and 10.1%, respectively. The friction coefficient, wear width and depth, and mass loss of the Ni₃Al10 composite were 0.40, 0.9 mm, 20.5 mm, 0.016 g, respectively. Moreover, the wear mechanism of the Ni₃Al10 composite is major abrasive wear with a small amount of adhesive wear.

The refined explicit finite element scheme considering various strengthening mechanisms and damage modes is proposed for simulation of deformation processes and mechanical properties of carbon nanotube (CNT)-reinforced bimodal-grained aluminum matrix nanocomposites. Firstly, the detailed microstructure model is established by constructing the geometry models of CNTs and grain boundaries, which automatically incorporates grain refinement strengthening and load transfer effect. Secondly, a finite element formulation based on the conventional theory of mechanical-based strain gradient plasticity is developed. Furthermore, the deformation and fracture modes for the nanocomposites with various contents and distributions of coarse grains (CGs) are explored based on the scheme. The results indicate that ductility of the composites first increases and then decreases as the content of CGs rises. Moreover, the dispersed distribution exhibits better ductility than concentrated one. Additionally, grain boundaries proved to be the weakest component within the micromodel. A series of interesting phenomena have been observed and discussed upon the refined simulation scheme. This work contributes to the design and further development of CNT/Al nanocomposites, and the proposed scheme can be extended to various bimodal metal composites.

In the present study, Ti–Zr–Cu–Ni amorphous filler metal was used to braze MgAl₂O₄ ceramic and Ti–6Al–4V (TC4) at 875, 900, 925, 950, 975 and 1000 °C for 10 min. The effects of brazing temperature on interfacial microstructure and mechanical properties of the joints were analyzed. The results showed that typical microstructure of the TC4/MgAl₂O₄ joint was solid solution (SS) α-Ti, acicular α-Ti + (Ti, Zr)₂(Ni, Cu) layer, metallic glasses and TiO. With the increase in brazing temperature, (Ti, Zr)₂(Ni, Cu) layer gradually dispersed at bonding interface, a continuous layer of TiO appears near MgAl₂O₄ ceramic. With the increase in brazing temperature, the hard and brittle (Ti, Zr)₂(Ni, Cu) layer gradually dispersed, resulting in the maximum shear strength of 39.5 MPa. The high-resolution TEM revealed the presence of amorphous structure, which is composed of Ti, Zr, Cu, Ni and Al. The values of δ and ΔH_mix are calculated to be about 8% and −39.82 kJ/mol for the amorphous phase.

This study unpicks the influence of the glass tube suction casting (GTSC) with different inner diameters (8, 10, 12 and 14 mm) on the solidification process of the hypereutectic Al–Si alloy (A390) and dissects the underlying mechanisms of the Al–Si divorced eutectic and refinement degree of the primary silicon particles (PSPs). The results show that a smaller inner diameter of the glass tube is more favorable for achieving Al–Si divorced eutectic in GTSC A390 alloy. Conversely, a larger inner diameter is more conducive to the formation of the lamellar eutectic Si. The GTSC A390 alloy with an inner diameter of 10 mm achieves the smallest average equivalent diameter (approximately 7.4 μm) of the PSPs. Being the prior diffusion channels for solute atoms, the grain boundaries and twin growth grooves of PSPs attract solute atoms (Cu, Mg, etc.) to enrich. The enriched solute atoms occupy the diffusion destinations of some Si atoms, which limits the overall growth of PSPs. These findings provide new insights into developing a simple and effective manufacturing process to refine the primary and eutectic Si phases in hypereutectic Al–Si alloys.