Journal of Materials Processing Technology最新文献

In present work, three press-hardened steel (PHS) sheets were designed for three typical manufacturing processes: cold-rolling (CR) process with about 1.5 km, thin slab continuous casting and rolling (TSCR) process with about 300 m, and Castrip process with about 50 m. Despite the similar constituents of mixed ferrite and pearlite, there were different microstructure characteristics and chemical distributions of these three PHS sheets. The press-hardened steel by Castrip process contained ultrafine pearlite lamella of about 198 nm, accompanying with high-density dislocations (∼10¹⁴ /m²). It was coarse pearlite lamella of 503 nm for press-hardened steel by TSCR process, while it was spheroidized pearlite with the average cementite particle size of 464 nm for press-hardened steel by CR process. The dislocation densities were ∼10¹³ and ∼10¹² /m² for press-hardened steels by TSCR and CR process, respectively. Subsequently, three press-hardened steel sheets were reheated to simulate the hot stamping process. From thermodynamics, press-hardened steel sheet by Castrip process could induce the earliest reversed austenite transformation due to more C and Mn. Kinetically, the high-density dislocations and ultrafine-lamella pearlite together created the fastest rate for reversed austenite transformation. Meanwhile, the mechanical properties of Castrip sheet could firstly reach 1500 MPa grade under the short-time heating condition (below 2 min). Furthermore, compared to the traditional one (900–950 °C for 3–5 min), the optimized hot stamping process of 930 °C × 2 min were performed on Castrip sheet by industrial plat die quenching process and real hot stamping part, which still reached 1500 MPa grade.

Compacted Graphite Iron (CGI) represents a unique combination of the characteristics of grey and spheroidal cast irons, sparking significant interest over the past two decades, particularly as a favoured material in several automotive industry applications, including engine components and heavy-duty vehicle parts. Despite its growing prominence, the full potential of CGI remains underutilised, primarily due to its lower productivity rate compared to grey cast iron. This paper comprehensively reviews existing research on CGI machining, emphasising the challenges and exploring opportunities for development in this field. A detailed comparison between the machining of compacted graphite iron, grey cast iron and spheroidal graphite cast iron is provided, highlighting the unique characteristics associated with CGI. The influence of microstructure and chemical composition on machining processes is thoroughly examined and deliberated. Moreover, this review delves into the effects of various process variables on CGI machining, including cutting tools, lubrication, and cooling methods. The paper concludes by discussing potential future trends and innovations in CGI machining, offering a prospective outlook on how these developments could bridge the productivity and literature gap and enhance the utilisation of CGI in industrial applications.

High carbon pearlitic steel wires are widely used in the industry, such as for producing tyre cords and steel cables due to its excellent mechanical properties. Cold drawing is a crucial step in steel wire production. Due to the loading state during the cold drawing process, pearlitic wires tend to exhibit a <110> fiber texture. The non-uniform texture distribution on the cross-section of steel wires has been observed experimentally. The mechanisms yielding this non-uniformly distributed texture are carefully investigated in this study using a multi-scale computational approach. Firstly, a macroscale finite element model is established to simulate the deformation behaviour of pearlitic steel wires during cold drawing, with the aim of thoroughly investigating the inhomogeneous elastic-plastic deformation behaviours. Secondly, the macro mechanical responses are incorporated into the mesoscale representative volume element model as boundary conditions to comprehensively study the effect of inhomogeneous deformation characteristics on texture formation. The results present a significant advancement by revealing that the non-uniform texture distribution in a steel wire can primarily be attributed to the multiaxial stress state on the cross-section. Notably, at the center of the steel wire, the maximum principal stress aligns with the drawing axis, resulting in a dominant <110> fiber texture. Conversely, at the subsurface, the maximum principal stress progressively shifts towards the circumferential direction, yielding an evolving texture characterized by a {110}<110> circumferential texture. Furthermore, the research uncovers a crucial finding that it is the {110}<110> circumferential texture that significantly weakens the torsion ability of the wires. This is due to the limited activation of slip systems, marking a key advancement in understanding the mechanical properties of steel wires.

Coating adhesion and friction properties are critical for the utilization and maintenance of de-painted surfaces. This study utilized the "low-temperature processing" characteristic of ultraviolet picosecond lasers for the nondestructive removal of coatings on aluminum alloys, facilitating environmentally friendly paint stripping and subsequent applications. By adjusting laser fluence, surface morphology, chemical properties, and interface characteristics were evaluated, and temperature monitoring during the cleaning process was conducted to elucidate the cleaning mechanism. The results indicated that a laser fluence of 1.30 J/cm² is the threshold for complete coating removal. The fully stripped substrate exhibited surface roughening, slight oxidation, and polarization, which enhance wettability. This improved wettability, in turn, increases coating adhesion and wear resistance. Temperature monitoring results revealed a minimal photothermal effect during the ultraviolet picosecond laser cleaning process, ensuring the substrate remains intact. The de-painting mechanism primarily relies on the photochemical effect, enabling paint removal at low temperatures.

Metal lattice structures with lightweight and multifunctionality characteristics have attracted increasing attention in recent years owing to their good mechanical properties, which can further be improved by applying nanoparticle-modified aluminum alloys to lattice structures. However, current manufacturing technologies limit the development of large-size and complex aluminum alloy lattice structures. Herein, a novel unsupported additive manufacturing method based on wire arc-directed energy deposition (WA-DED) was explored for the fabrication of lattice structures. This method realized the continuous forming of unsupported lattice struts by controlling the arc heat input based on the established theoretical models. The models consisted of a heat transfer model taking into account both heat conduction and heat convection for molten pool temperature stabilization, as well as a force model to ensure molten pool force stabilization. Process windows of heat input of unsupported struts were then developed based on the theoretical models followed by validation by numerical simulation. Unsupported nanoparticle-modified aluminum alloy lattice struts with different diameters and angles were fabricated using WA-DED technology, which exhibited refined microstructures with grain sizes smaller than 20 μm and excellent mechanical properties with ultimate strengths and breaking elongation exceeding 400 MPa and 7 %, respectively. Finally, high-quality pyramid lattice structures were efficiently fabricated using the unsupported additive manufacturing method. Overall, the proposed method fills the gap in the efficient preparation of large-size aluminum alloy lattice structures. The developed model can also broadly be extended to the unsupported additive manufacturing of other materials, such as titanium, steel, and magnesium alloys.

Heterogeneous W-steel joining components will produce brittle intermetallic compounds (IMCs) and significant residual stress in the interface. Adding a Cu interlayer serves as an effective solution. Nevertheless, the strengthening of W-Cu-steel joints is restricted because W-Cu and Cu-steel are members of binary immiscible and finite solid solution systems. Thus, accomplishing interface alloying by overcoming the positive generating energy of insoluble systems and opening up interatomic diffusion channels is a crucial issue to be addressed. In this work, casting and brazing technologies were incorporated into bonding W-Cu-steel to provide a high temperature field, as well as the dissolving and wetting of Cu-based liquid phase to refractory W. It is shown that the superior tensile strength of the W/Cu castings-steel brazed joints (∼264 MPa) was achieved, and the joint survived 1000 cycles of thermal fatigue under 1 MW/m². To assess the effects of brazing and casting on the W-Cu-steel joint, a detailed analysis was conducted on the mechanism of atomic diffusion in the joint interface. It is considered that in W-Cu joining, casting provided a higher thermodynamic driving force than brazing, thus achieving better interatomic diffusion and a wider microalloying region. Cu-steel joining achieved good alloying and forming dendritic extensions by intergranular diffusion. Based on the process optimization results, the feasibility of preparing the U-shaped first wall (FW) mock-up with W armor using brazing technology was verified. This study provides a new technological path, offering a major design and manufacturing guide for plasma facing components (PFCs).

Generally, in a laser hardfacing process, a mixture of ceramic and metal powder is used to clad a hard surface, resulting in enhanced wear characteristics of metal parts. This study proposes an efficient hardfacing process that uses a single and minimal amount of ceramic powder (0.079 g/min in this work). This process, named as Laser Directed Energy Deposition of Minimal Ceramic Powder (LDED-MCP), features that the melt pool is generated inwardly because only the substrate participates in forming the melt pool. Furthermore, due to the minimal powder flow rate used and sparse particle-melt pool collision events, ripple formations leading to the convective melt pool flow and inhomogeneous microstructures would be suppressed. Consequently, the produced layer is nearly flat and free of incompletely melted metallic particles, thus minimizing post-machining. For a 316 L substrate and SiC powder material combination, a crack-free layer about 560 μm thick with an average hardness of about 417 HV was created through process parameter optimization. This layer showed a eutectic structure composed of γ-austenite and chromium carbides, partially melted SiC particles between dendrites, and in-situ synthesized SiC nanoparticles decorating the cell walls. Through this work, near-net-shape hardfacing of stainless steels is realized through LDED-MCP process minimizing powder pre-processing and post surface machining.

Laser powder bed fusion, while promising, faces hurdles in certifying fabricated parts due to cost and complexity, with in-process monitoring emerging as a potential solution. Existing models focus on predicting defects at a given location using the monitoring signals from solely that same location. Hence, these models treat each track or layer independently of the previous and subsequent ones, neglecting potential interdependencies. This study proposed an in-situ, photodiode-based monitoring approach considering inter-hatch and inter-layer effects on porosity formation - factors often overlooked in existing research. Two Ti-6Al-4 V cuboids (10×10×5 mm³) were built with optimized process parameters, with the melt pool continuously monitored at 20 kHz via a co-axially mounted photodiode. The monitoring system captured the integral radiation in the near-infrared spectrum within a field of view centered on the melt pool. The porosity is assessed by X-ray computed tomography (X-CT), serving as ground truth to build supervised machine learning (ML) models. This study considered physical phenomena occurring during the printing process, including remelting of lack of fusion pores by the subsequent layer, keyholes penetrating the current layer hence introducing pores in the layer below, and overlap between adjacent scan tracks. These considerations are critical for a holistic understanding of pore formation mechanisms. Photodiode signals and computed tomography volumes were cropped using windows of four sizes to test the model's pore localization capability. A machine learning model, specifically a Convolutional Neural Network (CNN) - Long Short-Term Memory (LSTM) network, was trained to predict porosities using these window sequences. The CNN extracted spatial features from photodiode signals, addressing inter-hatch effects, while the LSTM captured temporal dependencies across layers, addressing inter-layer effects. The results, with the Area Under the Receiver Operating Characteristic curve (AUC) of 0.91 for pores exceeding 8000 μm³ in volume and 100 μm² in cross-sectional area, demonstrate the feasibility of the proposed model in detecting pores-level defects. This high defect prediction and positioning accuracy are essential for process control, providing real-time status of the region of interest and informing the controller of pore positions, thus facilitating intra-layer or inter-layer correction.

Aluminum-copper dissimilar welding is a highly demanded connection process; however, welding defects and the excessive growth of intermetallic compounds (IMCs) cause pose challenges for its application. This study uses an adjustable ring-mode (ARM) laser technology to achieve lap welding of ultra-thin Al-Cu plates. Lap-welding experiments were conducted using three laser modes—fixed core power, fixed ring power, and varying welding speed—to investigate the evolution of material mixing, intermetallic compound distribution, and joint strength under different modes. Our results indicate that the high energy density of the core laser is beneficial for increasing the penetration depths of joints, whereas the large action area of the ring laser is beneficial for improving the stabilities of melt pools. The joint action of the adjustable ring-mode (ARM) laser increased the melting width and depth of the joint, and the mixing of Al and Cu was controlled in the Al-Cu mixed zone at the upper part of the weld, to limit element mixing in the Cu-rich zone of the weld interface and suppress the distribution of intermetallic compounds. In addition, the ring laser induced the aluminum in the upper part of the molten pool to invade from both sides of the interface to the bottom, forming a certain Al invasion depth. This limited the accumulation of intermetallic compounds at the interface, optimized the path of shear fracture propagation, and improved the shear strength of the joint. This study provides a research basis for further exploring the material flow mechanism and optimizing the intermetallic compound distribution during the Al-Cu adjustable ring-mode (ARM) laser dissimilar welding process.

As the utilization of composite materials flourishes in commercial aircraft, the use of Invar alloy with low coefficient of thermal expansion (CTE) for fabricating composite molds has gained prominence. The large-size composite molds can be fabricated by Wire-arc Directed Energy Deposition (Wire-arc DED), due to its high deposition efficiency and ability to form optimized topologies. However, the Wire-arc DED Invar components still exhibit heterogeneous microstructure, low strength and non-tunable CTE. To address these challenges, this study explores the integration of an ultrasonic energy field during the deposition process to systematically investigate its effects on microstructural evolution, mechanical properties and CTE of Invar alloy. The results reveal that the ultrasonic vibration-assisted deposition significantly refines the grain structure, resulting in a decrease of 81.04 % in grain size compared to the reference state. Moreover, the components fabricated by ultrasonic vibration assisted Wire-arc DED exhibit exceptional properties, with a yield strength (YS) of 408 ± 11.37 MPa, ultimate tensile strength (UTS) of 645 ± 7.61 MPa, and elongation (EL) of 31.3 %. Additionally, the correlation between grain size and CTE was established. The effectiveness of introducing an ultrasonic energy field in improving the mechanical properties and modulating the CTE of the components is further validated by rigorous theoretical calculations. This research provides a promising way to fabricate high performance Invar alloy composite molds.