Acta Metallurgica Sinica-English Letters最新文献

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.

Although extensive research has been conducted on the strengthening mechanism of rare-earth magnesium alloys, achieving a balance between strength and toughness has proven challenging. This paper introduces a method for regulating the overlapping structure of the lamellar long-period stacking ordered (LPSO) phase and (beta^{prime }) phase to achieve a balance between strength and toughness in the alloy. By focusing on the extruded VW93A alloy cabin component, the study delves into the mechanism of the alloy's strength and toughness through a comparative analysis of the microstructure characteristics and room-temperature mechanical properties of the alloys in various states. Additionally, the molecular dynamics simulation is employed to clarify the mechanism of the alloy's strength and toughness balance induced by the overlapping structure. The findings reveal that when the (beta^{prime }) phase precipitates in the alloy alone, a significant increase in strength is achieved by pinning dislocations, albeit at the expense of reduced plasticity. Conversely, the presence of the lamellar LPSO phase disperses dislocations between the LPSO phase lamellae, thereby enhancing plasticity by avoiding stress concentration resulting from dislocation stacking. When both phases coexist in the alloy and form an overlapping structure, the dispersion of dislocations due to the lamellar LPSO phase weakens the pinning effect of the (beta^{prime }) phase, further reducing dislocation stacking and resulting in a balance of strength and toughness in the alloy. Ultimately, the alloy with the overlapping structure exhibits an ultimate tensile strength and elongation of 421 MPa and 20.1%, respectively.

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.

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.