Journal of Materials Processing Technology最新文献

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.

Continuous fiber reinforced metal matrix composites (CFMMCs) offer higher specific strength, specific modulus, and operating temperature than matrix metals due to the unique enforcement mechanism of the one-to-one scale arrangement of matrix and reinforced phases. Due to the heterogeneous characteristics between the plastic matrix and brittle fibers, the removal mechanism of CFMMCs during processing is exceptionally complex. Ultrasonic vibration-assisted grinding (UVAG) shows great advantages in machining difficult-to-cut materials (i.e., ceramics and composites) by changing the motion trajectory between grains and workpieces, effectively reducing grinding force and improving machining quality. However, little is known about the removal mechanism of UVAG for CFMMCs composed of the ductile (i.e., metal matrix) and brittle (i.e., SiC fiber) phases with highly anisotropic structure characteristics. This raises the question of how CFMMCs with heterogeneous components perform under abrasive processing and how to predict their processing forces. Hence, UVAG and conventional grinding (CG) experiments with single CBN grain were carried out on SiC fiber reinforced TC17 matrix composites (SiC_f/TC17) in this work. A grinding force model considering both phases and materials structure from energy aspect was proposed. A theoretical model for suppressing SiC fiber damage has been proposed, which is expected to guide low-damage processing of brittle materials. According to the results, the removal models of CFMMCs are revealed including: i) macro fracture of SiC fiber, ii) neat fracture of SiC fiber, and iii) TC17 matrix massive adhesion on the SiC fiber. Besides, no cracks crossing fibers are observed on the subsurface of SiC fiber under both UVAG and CG due to the good support of the TC17 matrix on SiC fibers. The grinding force predicted model error decreases as a_p increases. When a_p is 50 μm, the errors between predicted and experimental values are 7.8 % and 9.1 % for normal forces (F_n) and tangential forces (F_t), respectively. Ultrasound suppresses the severe wear behavior of grains, thereby improving the tool life. This paper aims to comprehensively reveal the characteristics of abrasive processing of CFMMCs from various aspects (surface morphology, subsurface features, grinding force prediction, and tool wear), which will promote the industrial application of CFMMCs.

To precisely control the melting of two base metals, laser offset welding is an effective method for managing the interfacial microstructure in dissimilar metal welds. Macrosegregation exhibits a markedly different morphology near the steel-nickel fusion line, which plays an important role in premature creep failure. In this study, it was found that an offset of the laser beam towards the nickel correlated with an increase in macrosegregation. When the laser beam was biased towards the steel, the partially mixed zone (PMZ) and transition zone (TZ) of 9Cr steel were identifiable within the macrosegregation, displaying a distinct solidification mode. Lath martensite and fine austenite formed in the PMZ, with alternating distributions of martensite and austenite observed in the TZ. Conversely, when the laser beam was biased towards the nickel, the unmixed zone (UMZ) of 9Cr steel was observed within the macrosegregation. Nanoindentation tests revealed that the maximum nanohardness in macrosegregation reached 5.90 GPa in the PMZ due to the formation of lath martensite, while the minimum nanohardness was 1.30 GPa in the TZ due to reduced martensite formation. Additionally, the TZ exhibited a significant reduction in resistance to plastic deformation. The various microstructures of macrosegregation were attributed to the solidification process and the dilution rate of 9Cr steel. When the liquidus temperature of WM exceeded 1455℃, a wide TZ formed in the macrosegregation due to adequate mixing. In contrast, when the WM had a significantly lower liquidus temperature than the 9Cr steel, only UMZ and PMZ formed in the macrosegregation due to preferential solidification and insufficient mixing. To minimize macrosegregation and eliminate the softening TZ, a laser beam offset towards the steel between 0.1 mm and 0.2 mm is recommended.

The formation of wavy interface is one of the distinctive features of high-velocity impact welding. It is known that the geometric parameters of waves (amplitude $a$ and length $\lambda$) depend not only on the impact conditions, but also on the mechanical properties of the materials being welded. However, until now, the impact of mechanical properties on the formation of waves has only been explored in a limited number of studies. To address this issue, in this paper, we use extensively a numerical simulation. First, we demonstrate that the numerical model, in conjunction with the smooth particle hydrodynamics (SPH) solver, effectively replicates the outcomes of a carefully controlled high-velocity impact welding experiment. Secondly, based on the validated model, we conducted a systematic study of the influence of strength on the wave formation process. Using numerical simulations with Johnson-Cook and ideal elastic-plastic strength models, we show that various characteristics of strength have a profound influence on the wave formation process. Furthermore, it is crucial to consider not only the yield strength of a material, but also factors such as strain and strain-rate hardening, along with thermal softening, to fully understand the wave formation during high-velocity impact welding.

The uneven metal flow and inhomogeneous microstructure on the cross-section of the extruded bar are mainly induced by the uncoordinated deformation during the traditional extrusion process, which seriously restricts its production and application. These defects are more prominent for the dual-phase Mg-Li alloy due to the phase transformation and the difference in flow between soft and hard phases. In order to solve the uncoordinated deformation in traditional extrusion, the reciprocating rotary extrusion (R-RE) process based on harmonic oscillation of die is proposed. The experiment and numerical simulations of the reciprocating rotary extrusion process were carried out at rotating frequency of 2.5 and 5 Hz, extrusion velocity of 1 mm/s, forming temperature of 290℃, die extrusion ratio of 12 and die rotating angle of ±6°. The coordinated deformation mechanism from macroscopical flow and microstructure in reciprocating rotary extrusion was investigated deeply. Meanwhile, a novel theoretical method was proposed to describe coordinate deformation characteristics quantitatively. The results indicated that the reciprocating rotary extrusion significantly reduces the forming load and accumulates more strain. The more uniform metal flow contributes to coordinated deformation. The extrusion deformation factors are proposed to reveal the coordinated deformation mechanism. In addition, the deformation body characteristic zone is novelly divided into six zones by combination of flow pattern and microstructure evolution.