Acta Metallurgica Sinica-English Letters最新文献

Pitting corrosion poses a significant challenge to 9Cr18 high-carbon chromium bearing steel in chloride-rich environments, severely compromising its structural integrity. The study systematically investigates the pitting behaviour of 9Cr18 bearing steel under salt spray conditions, focusing on the progressive evolution of surface morphology and cross-sectional characteristics of pits on finished bearings. Scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction were employed to examine the surface morphology, elemental composition and phase structure of corrosion products over varying salt spray exposure durations. The results show that 9Cr18 steel exhibits localized pitting with “volcanic crater”-like pits in the early stage of salt spray corrosion. After 48 h, pitting develops into a “multi-point” pattern, marking the initial transition toward uniform corrosion. Until 240 h, corrosion products completely cover the surface, indicating the complete transformation from localized pitting to uniform corrosion. The high carbon and chromium content in 9Cr18 steel promotes carbide precipitation and uneven distribution in the matrix. Cr-depleted regions near the carbide/matrix interface serve as preferential sites for pitting initiation. The low effective utilization of chromium reduces the overall corrosion resistance of 9Cr18.

This study investigates using an antioxidation copper particle-free paste, formulated with self-reducing copper formate, for Cu-Cu bonding in electronic packaging applications. The research highlights the oxidation resistance of copper formate compared to traditional copper nanoparticles (CuNPs) and its ability to generate CuNPs through thermal decomposition. Experimental results demonstrate that the sintering process benefits from releasing reductive gases during decomposition, improving joint quality with reduced porosity and enhanced mechanical strength at elevated temperatures. Molecular dynamics simulations further elucidate the sintering behavior of CuNPs, providing significant insights into pore collapse, atomic mobility, and neck formation. The findings indicate that increased temperatures enhance surface and bulk diffusion, facilitating robust particle connections. Overall, this work establishes the potential of copper formate for achieving reliable interconnects in semiconductor devices, paving the way for advancements in material formulations for direct copper–copper bonding.

It is rather difficult for titanium alloy ultra-thick plates to achieve superior weld formation and excellent mechanical properties along the weld penetration direction due to the large fluctuations of the molten pool, largely limiting their engineering application. In this study, 106-mm-thick Ti–6Al–4V ELI alloy plates were successfully butt welded via electron beam welding (EBW). The defect-free EBW joint with full penetration was obtained. The precipitated secondary α (α_s) in heat affected zone (HAZ), α lamellae in fusion line (FL) and α′ martensite in fusion zone (FZ) increased the α_s/β, α/β and α′/β interfaces, respectively, resulting in the higher microhardness and impact energy values (57 J in the HAZ, 62 J in the FL and 51.9 J in the FZ) than those in the base material (BM). The impact energy of the joint in this study was higher than that for Ti–6Al–4V ELI alloy joints as reported, which was mainly attributed to the formation of the relatively thicker α phase and finer interlamellar spacing in this study, enhancing the resistance to crack propagation. Furthermore, the average fracture toughness (90.2 MPa m^1/2) of the FZ was higher than that of the BM (74.2 MPa m^1/2). This study provides references for the welding application of titanium alloy ultra-thick plates in the manufacture of large-sized components.

Zinc (Zn)-based materials show broad application prospects for bone repair due to their biodegradability and good biocompatibility. In particular, Zn metal foam has unique interconnected pore structure that facilitates inward growth of new bone tissue, making it ideal candidates for orthopedic implants. However, pure Zn metal foam shows poor mechanical property, high degradation rate, and unsatisfactory osteogenic activity. Herein, Zinc-manganese (Zn-Mn) alloy foams were electrodeposited in Zn and Mn-containing electrolytes to overcome the concerns. The results showed that Mn could be incorporated into the foams in the form of MnZn₁₃. Zn-Mn alloy foams showed better mechanical property and osteogenic activity as well as moderate degradation rate when compared with pure Zn metal foam. In addition, these properties could also be regulated by preparation process. The peak stress and osteogenic activity increased with deposition current (0.3‒0.5 A) and electrolyte pH (3‒5), but decreased with electrolyte temperature (20‒40 °C), while the degradation rate exhibited opposite tendency, which suggests high deposition current and electrolyte pH and low electrolyte temperature can fabricate Zn-Mn alloy foam with favorable mechanical property, moderate degradation rate, and osteogenic activity. These findings provide a valuable reference for the design and fabrication of novel Zn-based biodegradable materials.

The Mg–9Li–1Zn (LZ91) alloy was subjected to an ultrasonic surface rolling process (USRP) with varying passes for the purpose of modifying its surface state. The USRP transformed surface residual stress from initial tensile stress to compressive stress, decreasing the surface roughness and increasing the ratio of the β-Li phase. The USRPed LZ91 sample (3 passes) showed superior corrosion resistance, with the corrosion current density changing from 57.11 to 24.70 μA cm⁻², and the polarization resistance increasing from 576.3 to 1146.1 Ω cm². According to the corrosion procedure evaluations, in situ observation revealed that the LZ91 alloy initially experiences pitting, which subsequently develops into cracking. The substantial area coverage of the β-Li phase facilitates the formation of a protective film on the surface, effectively delaying localized corrosion.

Press hardening with manganese-boron steels is a prominent manufacturing technique that allows for reduced weight and expense in automotive construction, while providing enhanced crash performance. Nevertheless, the development of a loosely attached oxide layer during press hardening and following additional processing of the layer presents a significant risk to the dimensional precision of the completed product. Here, we develop a new preprocessing approach to address the scale spallation issue by introducing trace amounts of silicate and tungstate into the rinsing solution following pickling. We demonstrate that the pre-deposited membrane promotes the formation of a noticeably thinner, more continuous and stickier oxide scale at high temperatures, enabling the direct application of automobile painting onto the scale. Our research provides an economical remedy to the troublesome scale flaking issue without requiring any modifications to the existing production line, and conveys a thorough comprehension of the mechanism by which the preprocessed membrane resists high-temperature oxidation.

The reactor pressure vessel (RPV) is susceptible to brittle fracture due to the influence of ion irradiation and high temperature, which presents a significant risk to the safe operation of nuclear reactors. It has been demonstrated that pulsed electric current can effectively address the issue of embrittlement in RPV steel. However, the relationship between pulse parameters (duty ratio, frequency, current, and time) and the effectiveness of pulse current processing has not been systematically studied. The application of machine learning methods enables autonomous exploration and learning of the relationship between data. Consequently, this study proposes a machine learning method based on the random forest model to establish the relationship between the parameters of electrical pulses and the repair effect of RPV steel. A generative adversarial network is employed to enhance data diversity and scalability, while a particle swarm optimization algorithm is utilized to optimize the initialization weights and biases of the random forest model, aiming to improve the model’s fitting ability and training performance. The results indicate that the coefficient of determination R-square (R²), root mean squared error and mean absolute error values are 0.934, 0.045, and 0.036, respectively, suggesting that the model has the potential to predict the performance recovery of RPV steel after pulsed electric field treatment. The prediction of the impact of pulse current parameters on the repair effect will help to enhance and optimize the repair process, thereby providing a scientific basis for pulse current repair processing.

Over the past few years, the Cu element has attracted much attention in duplex stainless steels. It undoubtedly holds advantageous in regulating the two-phase proportion and austenite stability and is also one of the crucial factors affecting the corrosion resistance. However, the systematic research on the impact of Cu addition to lean duplex stainless steels remains insufficient. In this study, a novel Cu-alloyed Mn-N-type 20Cr lean duplex stainless steel was developed and the effect of Cu on the strain hardening capacity and corrosion resistance was analyzed. The results show that the Cu addition increases the volume fraction and stability of the austenite, retards the martensitic transformation, and extends the transformation-induced plasticity effect to a wider strain range. Compared to the Cu-free steel, the plasticity of Cu-containing steel can be increased by ~ 26%. Additionally, the addition of Cu redistributes the Cr and N elements in the ferrite and austenite phases, thereby improving the corrosion resistance of the lean duplex stainless steel.

Different from full-Heusler compounds, four vacancies in the face-centered cubic crystal structure provide extra sites for enhancing the thermoelectric properties of half-Heusler compounds (HHs). Herein, excess Ag is introduced to the Ni-site vacancies of ZrNiSn to optimize thermoelectric properties. The ZrNiAg_xSn (x = 0, 0.01, 0.02, and 0.03) samples were synthesized by levitation melting and spark plasma sintering. Remarkably, the introduction of excess Ag significantly improves the Seebeck coefficient of ZrNiAg_0.01Sn, and a peak power factor of ~ 4.52 mW/(m K²) is achieved in ZrNiAg_0.01Sn at 923 K, which is enhanced by 22.8% than that of pristine ZrNiSn. As a result, the figure of merit zT of pristine ZrNiSn is enhanced from ~ 0.60 to ~ 0.72 of ZrNiAg_0.01Sn at 923 K. Additionally, grain refinement effectively increases the Vickers hardness of ZrNiAg_0.01Sn, which is enhanced by 32.8% than that of pristine ZrNiSn. These results demonstrate a viable doping strategy for designing ZrNiSn-based HHs with excellent thermoelectric and mechanical properties.

This work presents the modified precipitation behavior of the β phase in a Mg-8.0Al-0.5Zn-0.2Mn-0.4Ce alloy (wt%, designated as AZ80 + 0.4%Ce), which has been subjected to room-temperature pre-compression and a subsequent dual-stage aging treatment, thereby imparting it with the pronounced basal texture. It was found that the synergistic application of pre-compression and dual-stage aging protocol markedly accelerates the age-hardening response and architecture of the continuous precipitates (CPs) in the present AZ80 + 0.4%Ce alloy. Consequently, this alloy achieves an exceptional balance between strength and ductility, boasting a yield strength of approximately 229.0 MPa alongside an elongation of around 7.0%. A series of microstructural characterizations reveal that high-density intragranular dislocations introduced by pre-compression serve as catalysts for the preferential formation of CPs over the discontinuous precipitates, effectively suppressing the latter. Notably, this also facilitates static recrystallization, which refines the grain structure and alleviates the residual stresses induced by deformation, further enhancing the mechanical properties. This research contributes a novel perspective to the thermomechanical processing design of precipitation-hardened lightweight alloys, offering a pathway to optimize their performance through tailored thermomechanical strategies.