Acta Metallurgica Sinica-English Letters最新文献

The eutectic high entropy alloys have attracted extensive attention and are considered one of the most promising new metal materials. The microstructures of large eutectic high entropy alloy ingot with excellent casting performance have been rarely reported. In this study, we have prepared a ton class eutectic high entropy alloy ingot via vacuum induction melting for the first time. The evolution of microstructure and macro-segregation from the edge region to the core of the ingot were also revealed. It was found that there was no significant macro-segregation in ton class eutectic high entropy alloy ingot, and chemical elements were distributed uniformly. The coupled growth of the primary phases and eutectic colonies were homogeneously distributed in the ingot, and there is no traditional columnar grain region from the edge region of the ingot to the core. The tensile strength of the sample in the R/2 region of the ton class ingot with elongation greater than 10% is 892.3 MPa, showing an excellent comprehensive mechanical property. This study exhibits an important guidance for the industrial application of large eutectic high entropy alloy casting ingot.

In this study, basalt scales were activated by air plasma and were subsequently deposited with cerium dioxide nanoparticles to obtain CeO₂-modified basalts (CB). Inspired by mussel biomimetics, polydopamine (PDA) and 3-glycidoxypropyltrimethoxysilane were further employed to modify the properties of CB to obtain functionalized basalt scales (CBD). This treatment greatly increased the interfacial compatibility between inorganic fillers and epoxy resin. At the same time, PDA can form chelates with iron ions in the anodic area to prevent further corrosion. Tensile, water absorption, and electrochemical impedance spectrum measurements showed that incorporating CBD into epoxy resins resulted in the composite coatings with higher mechanical properties, water penetration resistance, corrosion resistance, and lower wetting properties.

The aging embrittlement of 30Cr2Ni4MoV steel during service at high temperature has been attributed to the segregation of Si and Mn at grain boundary (GB). We report an alternative mechanism of aging embrittlement of 30Cr2Ni4MoV steel. Using atom probe tomography, it is found that the quenched and tempered (QT) 30Cr2Ni4MoV steel has already contained obvious Si and Mn segregations at GB, which means that the Si and Mn segregations at GB are not sufficient to induce aging embrittlement. It is discovered for the first time in aged 30Cr2Ni4MoV there newly precipitate many G-phases along GB, and Si and Mn segregations at GB of QT30Cr2Ni4MoV steel are the main reason for the precipitation of G-phase. The hard and brittle G-phase helps to promote crack initiation during impact deformation. Subsequently, the cracks can rapidly propagate along GB due to the distribution of G-phase and the segregation of Si and Mn along the GB, which leads to intergranular cracking and low impact energy as for aged 30Cr2Ni4MoV steel.

The formation and evolution of M₆C carbides in high-W superalloy following solution treatment was investigated at different temperatures. Initially, during solid solution treatment, MC and M₆C carbides was precipitated in the alloy. As the temperature increased, the morphology of M₆C carbides transitioned from granular to needle-like. During the solution treatment at 1255 °C, the MC carbides degraded and transformed into M₆C carbides, forming a symbiotic relationship between them. Nonetheless, no clear orientation relationship was observed between the two types of carbides. After further increasing the temperature to 1270 °C, the precipitation of needle-like M₆C carbides in the dendrite arm was confirmed. This was supported by electron probe X-ray micro-analyzer and selected area electron diffraction patterns. Subsequently, a detailed examination of the three-dimensional morphology and orientation relationship of the needle-like phase with the matrix was carried out using focused-ion-beam and transmission electron microscopy techniques. The results indicated that the flat interface of the needle phase exhibited a specific orientation relationship with the matrix. However, in the three-dimensional plane, the interfaces between the needle-like phase and the matrix were not straight. Furthermore, no clear orientation relationship between the non-straight interfaces and the matrix was observed. As the solution temperature increased, the tensile properties at room temperature progressively decreased, while the stress rupture properties peaked at 1260 °C, suggesting that the alloy demonstrated its optimal comprehensive performance at this temperature. A subsequent analysis was conducted on the longitudinal section of the fracture using electron backscattered diffraction. The results showed a noticeable concentration of stress at the interface between MC and M₆C carbides, which ultimately led to crack initiation at this interface. In addition, as the solid solution temperature increased, the quantity of symbiotic phases also increased. This phenomenon led to the initiation of cracks at multiple locations, which then propagated and interconnected. As a consequence, the tensile properties and stress rupture life of the alloy progressively deteriorated.

This study investigated the effect of thermal cycles on Cu-modified Ti64 thin-walled components deposited using the wire-arc directed energy deposition (wire-arc DED) process. For the samples before and after experiencing thermal cycles, it was found that both microstructures consisted of prior β, grain boundary α (GB α), and basketweave structures containing α+β lamellae. Thermal cycles realized the refinement of α laths, the coarsening of prior β grains and β laths, while the size and morphology of continuously distributed GB α remained unchanged. The residual β content was increased after thermal cycles. Compared with the heat-treated sample with nanoscale Ti₂Cu formed, short residence time in high temperature caused by the rapid cooling rate of thermal cycles restricted Ti₂Cu formation. No formation of brittle Ti₂Cu means that only grain refinement strengthening and solid-solution strengthening matter. The yield strength increased from 809.9 to 910.85 MPa (12.46% increase). Among them, the main contribution from solid solution strengthening (~ 51 MPa) was due to the elemental redistribution effect between α and β phases caused by thermal cycles through quantitative analysis. The ultimate tensile strength increased from 918.5 to 974.22 MPa (6.1% increase), while fracture elongation increased from 6.78 to 10.66% (57.23% increase). Grain refinement of α laths, the promoted α′ martensite decomposition, decreased aspect ratio, decreased Schmid factor, and local misorientation change of α laths are the main factors in improved ductility. Additionally, although the fracture modes of the samples in the top and middle regions are both brittle–ductile mixed fracture mode, the thermal cycles still contributed to an improvement in tensile ductility.

High performance e-motors require a continuous enhancement of physical and mechanical properties for non-oriented electrical steel (NOES). However, the optimization of mechanical and magnetic properties simultaneously during NOES processing is extremely challenging where both properties directly influenced by alloy grain size, crystallographic texture, and dislocation density. In the current investigation, recrystallization annealing cycles were employed to modify the microstructure with the aim of balance magnetic and mechanical properties of NOES concurrently. The results showed that with increasing annealing temperatures, the degree of recrystallization and grain size increased, while the dislocation density reduced considerably at the early stage of recrystallization. Meanwhile, the values of texture parameter (A_{{{text{overall}}}}^{*}) (which is a function of overall individual grain orientations and their alignments with easy magnetization directions) were increased. It was evident that the magnetic properties were significantly improved, however the alloy strength was reduced with increasing annealing temperatures. Here, the correlation between magnetic properties as well as alloy strength on grain size, texture, and dislocation density were determined. From crystallographic texture intensity and measured properties quantitative analyses it was concluded that grain size was the predominant factor in balancing the mechanical and magnetic properties of the studied steel. Furthermore, the optimal comprehensive properties (both magnetic and mechanical) were achieved by annealing at 800 °C, which yielded a magnetic induction B₅₀₀₀ of 1.616 T, a high-frequency iron loss P_1.0/400 of 22.43 W/kg, and a yield strength of 527 MPa.

The restoration mechanism of twin-induced plasticity (TWIP) steel during friction stir welding (FSW) changed with the degree of the deformation, and the microstructure evolution and dynamic recrystallization are complex and unclear. In this paper, the electron backscattered diffraction and transmission electron microscopy techniques were used to evaluate the dynamic grain structure of FSW joint of TWIP steel. The results showed that the dynamic recrystallization mechanisms in TWIP steel during FSW contained discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX). The recrystallization mechanism transitioned from DDRX at the initial deformation stage to DDRX and CDRX at the middle deformation stage, eventually becoming primarily CDRX at the end deformation stage. Numerous annealing twin boundaries (ATBs) were formed within the joint, and the straight ATBs primarily resulted from grain growth accidents, while cluster-shaped ATBs were formed through re-excitations and decomposition of specific grain boundaries.

This study investigated the effect of pressure, pre-charge time, punch velocity and oxygen content on the mechanical properties of X42 pipeline steel in gaseous hydrogen environment by using small punch test. When exposed to nitrogen, the fracture mode of X42 pipeline steel undergoes ductile fracture, but in the presence of hydrogen, it shifts to brittle fracture. Moreover, an increase in hydrogen pressure or a decrease in punch velocity is found to enhance the hydrogen embrittlement susceptibility of X42 pipeline steel, as evidenced by the decrease of maximal load, displacement at failure onset and small punch energy. But the effect of pre-charge time on the hydrogen embrittlement susceptibility of X42 pipeline steel is not very obvious. Meanwhile, the presence of oxygen has been found to effectively inhibit hydrogen embrittlement. As the oxygen content in hydrogen increases, the hydrogen embrittlement susceptibility of X42 pipeline steel decreases.

Magnesium alloys have large reserves and good strength, attracting a lot of attention. Herein, the thermodynamic, elastic constants, and electronic properties of the Mg-Y-Zn ternary compounds were calculated; among them, MgYZn₂ belongs to the cubic structure, MgYZn, Mg₃Y₂Zn₄, and Mg₁₄YZn-1 belong to the hexagonal structure, Mg₆YZn-1, Mg₆YZn-2, MgY₂Zn, and Mg₁₄YZn-2 possess the orthorhombic structure, and Mg₃Y₂Zn₃ is trigonal structure. The calculated cohesive energies of the results show that all compounds are thermodynamically stable. Moreover, the MgYZn₂ compound exhibits the highest modulus of 76.84 MPa, and the Mg₃Y₂Zn₃ has the biggest hardness of 6.6 GPa. In addition, the Mg₆YZn-2 has the strongest elastic anisotropic with A^U of 6.14 and A_G of 0.38, respectively. According to the population analysis, the Mg-Y covalent bond is due to the biggest bond population. The shortest weighted average bond length indicates that MgYZn₂ has better elastic properties. Furthermore, the calculated limiting thermal conductivity results show that Mg₁₄YZn-2 has better thermal conductivity with maximum values of 0.94 W·m⁻¹·K⁻¹ and 0.74 W·m⁻¹·K⁻¹ for Clarke’s and Cahill’s models.

This study used an anodic etching (AE) method to construct a hierarchical rough surface on the surface of the Cu-bearing antibacterial titanium alloy, Ti–xCu (x = 3, 5, 7 wt%), a three-dimensional structure with nested micro-/submicro-pores and internal cavities, which is conducive to the adhesion and growth of bone cells. After AE treatment, with increase of the Cu content in the alloy, the surface of Ti–Cu alloy became sharper, with more fine micropores and internal cavities, thus increasing the surface area. The results indicated that the AE/Ti–Cu alloy exhibited good antibacterial properties and had the effect of inhibiting bacterial biofilm formation. AE treatment could increase the Cu ions release of Ti–Cu alloy in saline, and the higher the Cu content in the alloy, the more Cu ions release, resulting in stronger antibacterial performance of the alloy. AE/Ti–Cu alloy showed excellent biocompatibility, similar to the pure Ti. Therefore, anodic etching is a safe and effective surface treatment method for Ti–Cu alloy, with good clinical application prospects.