International Journal of Machine Tools & Manufacture最新文献

Directed energy deposition (DED) with a coaxial wire-laser configuration has gained significant attention in recent years for the production of large-scale metallic components because of its low directional dependence, fast deposition rate, high feedstock efficiency, and low manufacturing costs. This work studies the coaxial wire-laser DED process of Inconel 718 alloy under a stable deposition condition with a relatively low input volumetric energy density (55.5 J/mm³). Post characterization reveals a cluster of refined grains at the center-bottom region of the as-printed track. Operando high-energy synchrotron X-ray experiments and multi-physics modeling are applied innovatively to study the fundamental mechanism responsible for the formation of this microstructure. The X-ray diffraction experiment provides direct evidence, which is supported by the simulation, that the feeding wire can reach the melt pool bottom and release solid particles (primarily carbides) near the mushy zone owing to insufficient melting. Consequently, these sub-micron sized particles suppress the growth of large columnar grains and cause the formation of unique microstructural heterogeneity. This discovery offers new opportunities for tailoring the solidification microstructure by controlling the melting state of the feedstock wire in DED process, in addition to commonly known factors such as the thermal gradient and solidification velocity.

Although the intermittent contact by the ultrasonic vibration-assisted cutting explained the machinability advantages, there exists a research gap in concentrating the effects of high-frequency ultrasonic vibration-assisted cutting (HFUVAC). This work clarified the differences of the micro/nano incremental material removal mechanisms between conventional cutting (CC) and high-frequency ultrasonic vibration-assisted cutting of 316 L stainless steel. The machinability advantages and microstructure features were compared and analyzed through the ultra-precision cutting experiments. Compared with the continuous contact mode of the conventional cutting, the incremental effect of the high-frequency ultrasonic vibration-assisted cutting achieved superior machinability, which included cutting force decreasing, tool wear reduction, surface defects suppression, and chips undergoing from discontinuous quasi-shear state to continuous multiple-shear state. As the nominal cutting speed increased in the high-frequency ultrasonic vibration-assisted cutting, the surface defects and surface roughness showed an increasing trend, which was indispensable to control the normal cutting speeds below 5 m/min, or the cutting stroke in each vibration cycle less than 800 nm to obtain the defect-free surface. The grain refinement and severe elongation deformation were observed at the chip bottom and machined surface of the conventional cutting due to strong mechanical friction loads. While the microstructure features of chips and the machined surface in the local deformation layer were the results of friction reduction, dynamic recrystallization, and twinning/stacking formation induced by the incremental effects of the high-frequency ultrasonic vibration-assisted cutting. The results help to improve surface quality and optimize the ratio of cutting speed to vibration frequency to enhance the efficiency.

Linear friction welding is a solid-state, near-net shape manufacturing method for metallic alloys which is characterised by complex deformation and metallurgical actions at the weld interface. However, a lack of understanding of the welding parameter interaction and subsequent welding mechanisms is hindering the joint integrity enhancement of dissimilar linear friction welding. In this study, we investigated the influence of various process parameters on macro/micro-formation, microstructural evolution, and properties to establish optimal welding conditions for the sound linear-friction-welded joint integrity of dissimilar superalloys, IN718, and the powder metallurgy FGH96. Increased oscillation frequency or decreased applied pressure promoted continuous dynamic recrystallisation and grain refinement, although discontinuous dynamic recrystallisation remained dominant. Enhanced dissolution of the strengthening phases (γ′ phase on the FGH96 side and δ phase on the IN718 side) was observed from the thermomechanically affected zone to the interface. The subsequent correlation between the microstructure and mechanical properties indicated that solid–solution strengthening was the dominant mechanism for enhancing interfacial bonding, which was promoted by mutual material deformation on both sides. Accordingly, to achieve synergistic plastic deformation in dissimilar linear friction welding, an optimisation strategy of welding parameter combination was proposed and validated by investigating hot compressive dissimilar Ni-based superalloys. The results of simulations of sub-size workpieces showed that using linear friction welding to manufacture bimetallic bladed disks, from conception to completion, was feasible. The paper offers an integrated solution for the full-scale manufacturing of an IN718/FGH96 blisk using linear friction welding based on microstructure–property interactions and relevant simulations, which can ideally serve as the basis for future bimetallic bladed disk manufacturing.

Grain refinement and arrangement is an effective strategy to enhance tensile and fatigue properties of key metallic components. Laser shock peening (LSP) is one of surface severe plastic deformation methods in extreme conditions, with four distinctive features, namely, high pressure (1 GPa–1 TPa), high energy (more than 1 GW), ultra-fast (no more than nanosecond scale), and ultra-high strain rate (more than 10⁶ s⁻¹), and generates a deeper compressive residual stress (CRS) field and the formation of a gradient nanostructure in the surface layer to prevent the crack initiation of metallic materials and alloys, which is widely used in aerospace, overload vehicle, ocean engineering, and nuclear power. Despite some investigations of LSP on surface integrity, microstructural evolution, and mechanical properties of metallic materials and alloys, there is a lack of a comprehensive perspective of LSP-induced microstructural evolution, mechanical properties for metallic materials and alloys in the last two decades. Furthermore, the relationship between the mechanical properties of metallic materials and alloys and the LSP processing parameters is presented. In particular, LSP-induced featured microstructure and grain refinement mechanisms in three kinds of crystal structures, for instance, face-centred cubic, body-centred cubic, and hexagonal close-packed metals, are present and summarised for the first time. In addition, some new emerging hybrid LSP technologies and typical industrial applications as important chapters are shown. Finally, the faced challenges and future trends in the next 10–20 years are listed and discussed. Results to date indicate that LSP, as an emerging and novel surface modification technology, has been increasingly used to surface layer of metallic components. These topics discussed could provide some important insights on researchers and engineers in the fields of surface modification and advanced laser manufacturing.

Single-crystal silicon carbide (SiC) is one of the most attractive materials for electronics and optics but extremely difficult to cut owing to its hard and brittle properties. While in previous studies, the focus has been placed on machining flat surfaces, in this study, the mechanisms of tool-workpiece interaction in cutting curved microstructures on 4H–SiC (0001) were explored through the ultraprecision diamond turning of micro-dimples. The surface/subsurface of both machined workpieces and used diamond tools were characterized, and the machining characteristics, such as chip formation and cutting forces, were also investigated. It was found that microcracks occurred easily in the feed-in/cut-in area of the dimples, which is caused by a large friction-induced tensile stress due to a large thrust force. The dimples located on the secondary cleavage directions <10−10> (S-dimples) were easy to produce crack-free surfaces, while the dimples located on the primary cleavage directions <−12−10> (P-dimples) were very prone to cause cracks on surfaces, even though the chips were formed in a ductile mode. The dimples located on the in-between direction (I-dimples) were moderately prone to surface cracking. It was also found that although the S-dimple has a crack-free surface, it has the thickest subsurface damage (SSD) layer containing a disordered layer, dislocations, and stacking faults; the SSD layer of the P- and I-dimples do not contain stacking faults; and the SSD layer of the I-dimple is the thinnest. Flank wear with nanoscale grooves on the diamond tool was significant without edge chipping and diamond graphitization detected. By optimizing the cutting conditions, a crack-free micro-dimple array was fabricated with nanometric surface roughness. The findings from this study provide guidance for the manufacture of curved SiC parts with high surface integrity, such as molds for replicating microlens arrays and other freeform surfaces on glass.

To meet the various and critical manufacturing requirements including high precision, low cost, good manufacturability, and more demanding from product service and performance aspects such as high performance, light-weight, less energy consumption and low carbon emissions in today's era of rapid product development with short product life circle, it is crucial to re-innovate and re-invigorate metal forming technologies and enable it to play an even more important role in manufacturing arena. Historically, introducing new kinds of energy fields into the forming process drives the innovative advance and rejuvenating of forming technologies due to the physically interactive mechanisms of energy field and certain material deformation behaviors such as thermal-mechanical coupling effects. In this paper, a classification of energy-aided metal forming processes is orchestrated and presented, and three kinds of energy-assisted metal forming technologies, viz., electrically-assisted forming, ultrasonic vibration assisted forming, and electromagnetic field supported forming, are reviewed and delineated as they are currently receiving a widespread attention with promising application potentials. In this paper, the physical essence and the effects of these introduced energy fields on deformation behavior, process performance, microstructure evolution are elucidated and analyzed. The constitutive modeling of these forming processes is recapitulated, and the newly established energy field assisted metal forming technologies are exemplified and discussed. Based on the advantages and limitations of these unique metal forming processes assisted by additional energy fields, the process capacity and application potentials are unraveled and examined. Finally, from the aspects of exploring physical mechanisms, establishing high-fidelity models, coupling the multiple energy fields, and developing intelligent equipment and realizing these forming processes, the current challenges and future prospects were discussed, summarized and articulated in such a way to present a panorama of the research, development and application of the energy-assisted forming technologies.

Microstructural features are an important factor in the evaluation of machined surface integrity. In particular, twins and twin boundaries have a significant impact on the physical and mechanical properties of components. This study investigates twin boundary evolution mechanisms in the machined surface during orthogonal cutting of oxygen-free-high-conductivity copper with cutting speeds ranging from 125 m/min to 2000 m/min. Pertinent features including twin boundaries, grain morphologies, textures, etc. Are characterized by electron backscattered diffraction and transmission electron microscope. The results show that the machined surface is divided into the refined layer, the deformed layer, and the matrix. An abnormal gradient distribution of a 60°<111> twin boundary is discovered for the first time. Specifically, the annealing twins mostly diminish in the deformed layer and regenerate in the refined layer. In the refined layer, a temperature-dominated process of twin formation and dynamic recrystallization occur. In the deformed layer, the resolved shear stress along the twin system is calculated through a novel approach, which reveals the stress-induced detwinning mechanism. The results of this research are beneficial for understanding both the deformation mechanism of medium stacking fault energy face-centered cubic metal under extreme loading conditions and the underlying effects of twins on the mechanical properties of machined surface.

The process of Hot Form and Quench of aluminum alloys, called Direct HFQ®, has been developed and applied to manufacture high-strength panel components, in which aluminum alloy sheet is heated to solution heat treatment temperature, quickly transferred to cold press dies, simultaneously formed and quenched, and subsequently artificially aged. For Direct HFQ, however, forming occurs at high temperatures, which results in high workpiece/die friction and wear, and hence high tooling and maintenance costs. In the present study, a novel Indirect HFQ for aluminum alloys has been proposed, in which alloy sheet in the O temper is formed at room temperature, then heated to solution heat treatment temperature, and quickly transferred to cold press dies for shape calibration and quenching, followed by artificial aging. In order to compare Indirect HFQ with Direct HFQ, AA6082 sheet specimens have been deformed uniaxially using the two HFQ techniques to a given strain or fracture. Mechanical properties of the deformed specimens have been measured, and differences in mechanical properties after the two HFQ processes have been quantified. Their microstructures have also been characterized to explain those differences. In addition, both HFQ techniques have been applied to form a B-pillar sectional component. It has been found that grain growth occurs in alloy deformed uniaxially to a strain higher than or equal to 10% during Indirect HFQ process, and the degree of grain growth decreases with increasing deformation. The grain growth during Indirect HFQ leads to a lower yield strength (up to ∼8%) and tensile strength (up to ∼12%) than that of the alloy processed using Direct HFQ. In addition, the alloy has a lower ductility and formability during Indirect HFQ than Direct HFQ.

The powder–melt pool interaction behavior is crucial in laser-based directed energy deposition (LDED). Partially melted particles, which are formed as a result of this interaction, significantly influence on the microstructure and mechanical performance of multi-material and metal-matrix composites fabricated via LDED. However, the presence of partially melted particles is a contentious issue that has been overlooked in single-material LDED studies. Furthermore, the investigation of partially melted particles is hindered by the difficulties in direct observation. To overcome this obstacle, this study was conducted using a single-bead Ti–6Al–4V printing experiment with a relatively high oxygen content to distinguish partially melted particles directly. The formation mechanism of the partially melted particles was revealed through experimental studies combined with numerical analysis using a self-established model. Additionally, the influence of partially melted particles on the grain structure of LDED–fabricated parts was investigated in a low–oxygen environment. The partially melted particles tend to survive close to the surface of the deposited layer. As the penetration depth increased, the particle size decreased and the aspect ratio increased. The formation of partially melted particles collectively depends on the laser power, scanning velocity, powder size and powder feed speed, differing from the common conclusion that an insufficient input energy results in poor powder melting behavior. Furthermore, a Ti–6Al–4V sample with high–fraction equiaxed grains was fabricated using optimized processing conditions. The partially melted particles significantly affected the solidification behavior. In addition to the heterogeneous nucleation mechanism caused by the partially melted particles, a novel seed crystal mechanism was proposed to support the abnormal formation of equiaxed grains. This study highlights the importance of partially melted particles in LDED, and provides useful insights into in-situ microstructural control in LDED.

In the laser powder bed fusion (LPBF), the grains grow in preferential directions depending on the scanning strategies, which results in layer-by-layer builds of particular crystallographic textures. The unique microstructure formed by LPBF results in anisotropic properties of the built structure at both macro and micro levels. To understand the grain deformation of the textured alloy fabricated by LPBF in the high-strain-rate shear process, Alloy 718 was used as an example in this work. Bulk samples with different metallurgical textures were deliberately fabricated by LPBF via three laser rotation angles, namely 0°, 67° and 90°, and then four thin slices obtained from bulks were subjected to “quasi-in-situ” grain deformation investigation through orthogonal cutting (a simple shear loading condition). The evolution of crystal orientations and morphologies, including size and shape, were traced before and after shear deformation. A full-field crystal plasticity simulation was used to quantify the stress status for grains obtained from EBSD data. This for the first time reveals the crystallographic level deformation history for hundreds of microns during a high strain rate shear removal deformation. Due to the carefully retained deformation history (i.e., typical bulges and slip bands) on the surface, a repeated deformation pattern was observed, attributing to the non-homogeneous deformation of typical build-directional blocks. The most active slip trace of deformed grain was calculated and verified based on the dominated slip bands within individual grains. The slip trace direction and intensity were quantified for different textured Alloy 718. Since the slipping-based deformation for an orientated grain is represented by its most active slip trace, a deformation tendency map is obtained by combining the shear direction, slip system and grain morphology. It reveals that grains in high texture intensity workpieces generally follow the macro shear-based deformation, while with the decrease in texture intensity, the plastic anisotropy is significant at the grain scale. Grains with similar orientations may also result in localised deformation anisotropy due to the different morphologies.