Arc travel across the surface of a weld pool melt enables a wide range of thermal impacts on the solidifying metal during the formation of a thermal and wear-resistant nickel aluminide-based alloy. The formation of a homogeneous thermal field in the weld pool at an arc oscillation frequency of 3 Hz decreases the solidification rate. Under these conditions, the structure ratio of the relatively viscous γ-solid solution (Hv of 4700–4900 MPa) is highly alloyed (up to 14 wt%) with iron and other elements to nickel–aluminium martensite, and the composition of the Ni2Al-phase (Hv of 4400–4700 MPa) is close to optimal (approximately 50/50). The metal deposited in this structure indicates higher thermal resistance during temperature cycling within a temperature range from 20 °С to 1150 °С compared to that of the γ + γ'(Ni3Al) alloy structures formed at low arc oscillation frequencies. When the two composite wires are separated by a distance of 12 mm, the thermal impact of the arc on the weld pool melt becomes an impulse with an arc transition frequency of 11–13 Hz between the electrodes. The thermal cycle formed under these conditions provides the highest cooling rates of the melt near the solidification front, which reduces the size of the structural components and allows for the microalloying of the deposited metal with titanium diboride. The TiB2 particles in the structure enable the formation of strengthening phases, such as borides, with a high content of refractory elements (Cr, W, Mo, Ta). This increases the resistance of the deposited metal to gas abrasive wear at temperatures up to 1000 °С.

Fine blanking is used in industrial processes for mass production of high accuracy sheet metal parts. The process characteristic leads to a strain hardening of the sheared surface. Utilization of the process-immanent surface hardening can reduce time and energy consumption of downstream heat treatment processes like case hardening. Substituting High Strength Low Alloy (HSLA) steels by High Manganese Steels (HMnS) increases strain hardening during fine blanking and may replace the necessary heat treatment. This work investigated the mechanism-driven behavior of HMnS (1.7401) during fine blanking and its influencing factors, changing the part properties. Based on a characterization of the material properties of HMnS, the influence of the initial sheet temperature, blanking velocity and blank holder force on the sheared surface hardening and quality was analyzed. Due to enhanced strain hardening of HMnS, higher surface hardness with softer core was achieved compared to S700MC (1.8974) HSLA-steel. In addition, the sheared surface hardening was increased by a decrease in blanking velocity and an increase in blank holder forces. Taking into account the alloy design, fine blanking of HMnS offers the potential to achieve a high sheared surface hardening by targeted activation of the deformation mechanisms with simultaneous high quality and strength.

Oscillating bone sawing produces periodic exchange of tool rake and flank faces with high oscillating frequency, resulting in greater cutting forces with negative rake angles at small depths of cut and different speeds. However, only some studies have focused on these conditions, and various contradictory conclusions have emerged. This work, for the first time, observed and analyzed the unique serrated chip formation mechanism in orthogonal bone cutting at small depths of cut under different cutting conditions (i.e., positive and negative rake angles, high and low cutting speeds) using SEM (scanning electron microscope) images of bone chips and cutting process data with synchronized force data. The influence of bone viscoelasticity on new surface formation was confirmed through cutting force and average segment width measurements at different speeds. A cutting model that considers the new surface formation was proposed to explain the increase in shear stress with decreasing depth of cut, and a segment width prediction model incorporating the energy of the new surface formation and fracture toughness was developed. The predicted results, including shear force and segment width, agree well with the experimental findings. This work provides insights into chip formation in brittle materials like cortical bone. It offers the potential for predicting cutting forces in bone sawing or micro-cutting, even with varying cutting speeds.

Fabricating unsupported inclined rods using additive manufacturing poses significant challenges, limiting the design and manufacturing of lattice structures. This study introduces a method for controlling molten pool flow to successfully fabricate unsupported rods with varying diameters (4.6–9.3 mm) and inclination angles (−30 degrees to 90 degrees) using wire arc additive manufacturing. The key contributions of this research lie in enabling the fabrication of negatively inclined unsupported rods and investigating the influence of arc heat input on the deposition process, molten pool behavior, microstructure, and mechanical properties. By effectively controlling the molten pool flow, this method significantly reduces constraints on structural design, facilitating the fabrication of multi-angle lattice structures. It is observed that rod diameter negatively correlates with arc heat input per volume. Tensile strength initially increases and then decreases with diameter increment. Additionally, fabricating negatively inclined rods requires additional heat input, resulting in slightly inferior mechanical properties compared to positively inclined rods. The demonstrated applicability of the proposed method through the stable fabrication of screw rods and arc-curved rods showcases its potential for various lattice structure designs. Furthermore, the limitations of minimum rod diameter and inclination angle are discussed, determined by arc energy equipment, machine tool accuracy, and torch interference. This study advances additive manufacturing techniques by enabling the fabrication of unsupported inclined rods and expanding the design space for lattice structures.

A single track, as the basic unit of laser directed energy deposition (L-DED) process, plays a significant role in the dimensional accuracy and mechanical performances of the ultimate products. However, there is almost no systematic investigation on the formation process and three-dimensional characteristics of the internal pore defects. Here, we used a high-speed camera, laser scanning confocal microscope (LSCM), and synchrotron radiation X-ray computed tomography (SR-CT) to study single tracks of AlSi10Mg alloy fabricated by blue laser directed energy deposition (BL-DED). A comprehensive investigation is conducted on the impact of processing parameters on the sizes, shapes, and formation mechanism of pore defects. Three types of pore defects are examined in single tracks: Type I lack of fusion, Type II spherical gas pores and Type III large irregular pores. Besides, large irregular pores are the transition between other two types. In particular, the results of SR-CT show that porosity decreases gradually with the increment of laser power and scanning speed. Therefore, high laser power accompanying with fast scanning speed will reduce the porosity. The lowest porosity of 0.074% is achieved under the power at 1600 W with scanning speed at 1080 mm/min, which has an obvious improvement over the current infrared L-DED. In addition, the mapping relationship among laser power, scanning speed and pore defects is established, which will provide a fundamental understanding of the origin of the defect and strategies for controlling the defect in L-DED towards high-quality printing.

Ultrasonic assisted milling (UAM) has been demonstrated excellent cutting performance for nickel-based superalloy machining. However, the machining quality improvement achieved by traditional UAM is limited at high cutting speed. Rotary ultrasonic elliptical milling (RUEM) is an unconventional cutting method recently proposed for high quality and efficient machining of difficult-to-cut alloy, breaking the cutting speed limit for UAM. In order to verify the feasibility of this method in thin-walled curved surface machining, the ball end milling cutter was adopted in feasibility experiments of RUEM on Inconel 718 with the evaluation of cutting force, surface integrity and tool wear. The results indicate that compared with conventional milling (CM) without ultrasonic vibration assistance, the cutting force reduction reaches 31.33% in RUEM. The material strength enhancement was obtained in RUEM with the disturbed strengthening phases of Inconel 718. RUEM achieved − 728.65 MPa of surface compressive residual stress and 140 µm depth of compressive residual stress layer beneath the machined surface simultaneously, while CM provided tensile residual stress field near the machined surface. Moreover, the tool flank wear status was significantly improved in RUEM. These results demonstrate that various machinability benefits of Inconel 718 are obtained by RUEM, which is a promising method for nickel-based superalloy thin-walled structure finish machining.

In-situ additive manufacturing (AM) is well known for integrating of material synthesis and near-shaping fabrication. However, the insufficient metallurgy has become a widespread challenge owing to the molten pool’s short lifetime. Our previous research proved that employing alternating dual-electron beams can effectively manipulate the molten pool length, thereby prolonging its duration time. However, it is difficult for the preset alternating dual-heat source parameters under current open-loop operations to guarantee the desired molten pool length for the time-variation of the AM process. Therefore, this study further proposes a closed-loop control of alternating dual-electron beams to maintain a stable molten length, thereby ensuring internal metallurgical quality and external forming morphology. Specifically, based on a self-developed atmospheric-pressure vapor-prevention visual sensor, a machine-vision closed-loop control system for the molten pool length was established. The influence of the alternating dual-beam parameters on the molten pool length was studied and modeled, and the deflection voltage was selected as the controlled variable owing to its good dynamic performance and wide manipulation range. Given the nonlinearity and time variance of the AM process, a Fuzzy-PID controller with the ability to adjust control parameters in real-time was designed. The experimental verification results indicated that the developed controller could effectively control the molten pool to the expected length and exhibited good robustness in the disturbance test. Finally, a multi-layer multi-pass component was successfully fabricated with a closed-loop-controlled molten pool length of 24 mm. This study significant for promoting the industrial application and intelligent development of in-situ AM technology.

Incremental stretch flanging (ISF) has a more complex deformation process than conventional incremental forming, resulting in varying forming limits and strain characteristics. This work pointed out that Dt/D (Dt: tool diameter; D: flanging diameter) can be used as a dimensionless parameter to represent the flanging process, and proposed the incremental flanging forming limit (IFFL) test method. The IFFL test’s idea is to conduct incremental hole flanging experiments using different Dt and D, in which the opening diameter of the sheet metal is continuously reduced until a fracture occurs. The incremental flanging-fracture forming limit (IF-FFL) was obtained by fitting the ultimate strain points, which successfully predicted the occurrence of fracture in ISF, and its accuracy has been experimentally verified. In addition, the strain path in ISF can be divided into three zones, and the ratio β of the minor strain and the major strain in zone Ⅰ has an exponential relationship with Dt/D. The fracture may also occur at the edge or wall under different flanging parameters, and the critical flanging diameter Dc of the two fracture forms is obtained by using the membrane strain analysis model. Moreover, the theoretical variation of the process forming limit with Dt/D is studied, effectively supporting the industrial production practice.

The present study focuses on understanding the effect of scan strategy on the microstructure and mechanical properties of LDED fabricated IN718 built at optimized process conditions from single track analysis. Initially, single track studies were conducted by varying laser power, scan speed, and feed rate (3 levels) to optimize process parameters for bulk deposition. Based on the dilution, aspect ratio, track continuity and melt pool shape, best process parameter were chosen for depositing bulk structures. Bulk rectangular specimens were fabricated using the LDED process for different infill rotation (0°, 45°, 67°, and 90°) at optimized process conditions. Infill rotation did not show any significant change in the density of the samples. However, grain size measurement from EBSD and SEM micrographs revealed a substantial difference in grain size between samples without infill rotation (0°) and samples with infill rotation (45°, 67°, and 90°). XRD and EDS mapping revealed higher the formation of secondary laves phases with infill rotation as a result of higher cooling rate. Similarly, melt pool shape and arrangement showed significant variation with different infill angles. Samples with 0° and 90° infill rotation exhibited strong crystallographic texture along the build direction. There was a significant variation in the microhardness and tensile strength of the build with variation in infill rotation. This variation in mechanical properties were attributed to grain size, LAGB's fraction, secondary phases, and crystallographic texture.

The hole expansion test is an appropriate evaluation method for assessing the formability of automotive parts, where fracture prediction using simulated localized thickness is crucial. However, the accurate thickness prediction in the hole expansion test remains challenging. In this study, the selection of yield functions and calibration strategies were investigated to accurately predict the thickness of advanced high-strength steel subjected to the hole expansion test. An accurate description of the material anisotropy is important for thickness prediction because of the generation of various multiaxial stress states. To describe plastic anisotropy, a series of uniaxial tension, bulge, and in-plane biaxial tension tests were conducted on DP980 steel. Because conventional biaxial tension tests for DP980 steel showed a small strain range owing to its low ductility, a new laser-welding-reinforced biaxial tension test was developed to investigate the anisotropy of the plane strain at large strains. Differences in the ratio of the plastic strain rates were observed between the conventional and new tests. Finally, a hole expansion test and corresponding finite element simulations were conducted with different yield functions and calibrations for the Yld2000–2d yield function. The thickness strain profiles along the hole circumference and 3 mm inward were measured and predicted using simulations. In conclusion, both the yield stress and the ratio of plastic strain rates in the plane strain state were equally important for accurate thickness prediction during the DP980 hole expansion test. Furthermore, the crack location was inconsistent with the thinnest region in the experiment, which might be because of the shear fracture anisotropy encountered in DP980 steel.

Laser powder bed fusion (L-PBF) technique, as the mainstream technology in metal additive manufacturing, enables the fabrication of aluminum alloys and their composite components with high precision and design freedom, thereby advancing structural lightweighting in various application domains, such as aerospace and transportation. Nevertheless, aluminum powders present challenges including high laser reflectivity, high thermal conductivity, low melting point, and susceptibility to oxidation. Consequently, defects such as pores, solidification cracks, orientation anisotropy, and surface roughness commonly exist in L-PBFed aluminum alloy and composite parts. These defects severely compromise the mechanical performance and dimensional accuracy of L-PBFed parts. Thus, extensive research efforts have been focused on defect control in the L-PBFed aluminum alloys and their composites. However, a systematic summary and in-depth analysis of the formation mechanism and controlling strategy of various defects is still absent, which is the key to develop high performance aluminum alloys and their composites via L-PBF. In this review, a thorough analysis and summary of the causes of defects are provided, followed by an in-depth analysis and conclusion of defect control strategies and mechanism in L-PBF. Furthermore, we also present an outlook on the challenges and research opportunities in L-PBFed aluminum alloys and their composites in the last section, which we hope could inspire more new development of high-performance aluminum alloys and their composites via L-PBF.

Hot forming process is a potential route for manufacturing metallic bipolar plates with fine flow channel geometries and higher dimensional accuracy. To facilitate the design of the hot forming process for bipolar plates, effects of temperature, strain rate, and grain size on the flow behavior of ultra-thin 316 L austenitic stainless steel were investigated. Uniaxial tensile tests over 973–1173 K and 0.001–0.1 s−1 were conducted with digital image correlation techniques. Experiment results present the flow stress of ultra-thin 316 L stainless steel decreases with decreasing strain rate, increasing temperature, and increasing grain size. The flow behavior of ultra-thin 316 L stainless steel is significantly affected by strain rate, temperature, grain size, and their coupling effects. A new flow stress model incorporating strain rate, temperature, and grain size is developed to capture the complex deformation behavior of ultra-thin 316 L stainless steel. By comparing calculated flow stresses with experimental data, the reliability of the developed flow stress model is verified with an average absolute relative error of 4.5%, indicating that the developed flow stress model is capable of accurately describing the flow stress dependency of ultra-thin 316 L stainless steel on strain rate, temperature, and grain size.

A large-scale macro-micro multiscale surface structure processing technology has been proposed. A combination of high-precision abrasive belt grinding technology with micro offset forming of contact wheel surface contour and ultra fast laser surface micro texture technology has been developed. On the premise of ensuring surface accuracy requirements, form regular and large-scale surface micro nano structures. Thus enhancing the feasibility of metal surface micro nano manufacturing technology in engineering applications. Use laser belt machining equipment to process the surface. Clarified the positioning method and structural design method of laser and contact wheel. The results show that the laser belt machining technology can achieve high surface integrity machining of the macrostructure above 0.5 mm. Moreover, within the macroscopic structure, the morphology of the microstructure can be regulated. Based on the experimental results, control methods for microstructure morphology with different characteristics were designed. This study effectively combines two processing techniques to achieve efficient and high-precision processing of multi-scale surface structures and analyzes the regulatory effect of processing parameters on structural morphology.

To improve the machinability of silicon carbide (SiC) during machining, promoting surface plasticity is a classical strategy. In this study, it aimed to promote the surface plasticity of SiC by combining surface metallurgical reactions with femtosecond laser (fs laser) surface modification. Firstly, an Al/Ti coating was deposited on the fs laser modified surface. After heat treatment, experimental characterization revealed metallurgical reactions that produced an intermetallic compound containing Al and Ti. Nanoindentation tests showed the surface treated by fs laser and metallurgical reactions has over a 2x increase in deformation energy compared to different surface conditions. Furthermore, a scratch test demonstrated better lateral plastic flow and uniform scratch width in the treated surface, indicating improved plasticity promotion and machinability. To reveal the effect of Ti and Al during heat treatment, ab initio molecular dynamics simulations were conducted. This investigation provides a novel strategy to promote surface plasticity and improve the machinability of SiC.

The thermal fatigue effect on the microstructure and mechanical properties of the joints that form some components of the future fusion reactor is a concern within the scientific community. In this study, we analyze the metallurgical modifications caused by thermal fatigue and their impact on the mechanical properties of tungsten-EUROFER brazed joints (blocks measuring 6 × 6 × 4 mm). We conduct the analysis using an actively cooled mock-up subjected to steady-state thermal loads, which provides valuable information about the operating conditions of the reactor. Three different surface conditions of tungsten were evaluated: 600 ºC (2 MW/m2), 700 ºC (2.5 MW/m2), and 800 ºC (3 MW/m2), with varying numbers of applied cycles ranging from 100 to 1000. Throughout the tests, infrared cameras and pyrometers were used to analyze the thermal behavior of the W-EUROFER joint. At 600 ºC and 700 ºC target temperatures, no anomalies in the heating and cooling capacity of the W-EUROFER joint were observed. This represents an advancement compared to previous studies that employed Cu20Ti filler, as it demonstrates consistent and efficient cooling capabilities even at surface temperatures of up to 700 ºC, without any notable anomalies starting from the previous filler's 500 ºC. However, in the case of 800 ºC, the test had to be prematurely stopped. Microstructural analysis revealed the formation of cracks in some cases due to the stresses generated by the mismatch in the coefficient of thermal expansion between the materials used. These cracks affected the mechanical integrity of the joint.

In order to enhance the joint performance, the Cu/Sn58Bi-0.6B4C/Cu 3D structure was obtained by ultrasonic-assisted connection. The influence of ultrasound on the solder and its wettability, as well as the microstructure, interfacial IMC structure, and mechanical properties, was investigated. It is indicated that ultrasonic cavitation improves the crystal structure of the solder alloy by refining grain size and making the microstructure more uniform. The ultrasound also changes the preferred orientation of β-Sn and Bi phases, and increases the low-angle grain boundaries and local orientation differences for improved alloy strength. Additionally, the ultrasound promotes the molten solder spreading on the Cu substrate. The microstructure of the filler metal layer is improved by ultrasonic, and the Cu6Sn5 compounds floating in the solder matrix act as the strengthening phase. Cavitation bubbles erosion increases the contact area between the solder and Cu substrate. The audiogenic high temperature reduces the IMC thickness difference at both ends of the joint caused by the temperature gradient. Besides, the grain size in the solder matrix and interfacial IMC is refined with increased supercooling. The ultrasound strengthens joint shear strength significantly and improves the potential path for crack propagation. The appearance of dimples in the fracture alters its mode from being typically brittle to a mixed ductile and brittle fracture. The above enhancement will be further improved with the appropriate extension of ultrasonic time. We hope to strengthen joint performance by ultrasound, and provide reference for future research and application combining soldering with ultrasonic technology.

Oxygen-free copper components are widely used in high energy physics engineering, which are usually fabricated by the diamond machining process for achieving low roughness surface. However, the wear of diamond tool heavily affects the surface quality. In this work, the wear law of diamond tool in machining of oxygen-free copper is studied with consideration of the anisotropy of diamond strength. Firstly, the stress distribution on the tool face in machining is calculated. The results show that the cutting stress near the flank face is larger than that near the rake face. Secondly, the strength distribution of tool cutting edge is modeled. The theoretical prediction reveals that the anisotropy of diamond crystal leads to the great differences in the strength of cutting edge at different positions, and further affects the cutting edge wear resistance. Thirdly, the wear model of diamond tool is established with consideration of cutting stress distribution and tool edge strength, in which the mechanical wear is the dominant wear process. Finally, the variation of the surface roughness is analyzed on the basis of the tool wear through the cutting experiments. The experiment results indicate that the surface material deformation is closely related to the tool cutting edge wear transition area and results in different values of surface roughness. The obtained results can improve the understanding of the diamond tool wear law and estimate the diamond tool wear in machining of oxygen-free copper.

Fabrication of hole-free aluminum structures through metal droplet-based 3D printing is an important channel for high-performance aluminum parts in aerospace applications. Unfortunately, completely eliminating bottom hole defects has proven challenging due to the narrow printing temperature range and complex hole defect evolution rules. In this work, by tailoring the overlap ratio (η) and substrate temperature (Ts), we proposed a novel strategy to eliminate bottom hole defects of overlapping droplets in a broad temperature range. Combining the high-speed sequence images and the numerical simulation model, the evolution mechanism of bottom hole defects with distinct overlap ratios was revealed. The result demonstrats that the bottom hole defect evolution is dominated by the droplet spreading order and the competition of inertial and capillary forces. Moreover, a regime map was summarized, where the substrate temperature window for the hole-free region at the valley (η = 0) is expanded by 114% compared to the peak (η = 0.6). Finally, a simple and effective strategy was presented, which could enlarge the printing temperature range for eliminating bottom hole defects. This work might provide theoretical guidance for the low-cost and high-quality droplet printing of multitudinous metal components.

As driven by the need of structural integration and functionalization in modern society, functionally graded material (FGM) with multiple materials is highly demanded for rapidly growing industrial needs. FGMs with smooth gradients in composition and mechanical properties can prevent failure caused by mismatched interfaces and stress concentration. This work first investigates the effects of homogenization and aging heat treatment on the microstructure evolution and mechanical properties of 316 stainless steel (SS316)/ Inconel 718 (IN718) FGMs first. The FGMs fabricated with a decent gradient compositional control by laser-based directed energy deposition. The compositional evolution, the aging precipitation behaviors with different homogenization times, and the microhardness of FGMs were studied via microstructure characterization and high-throughput simulation, to elucidate their effects on gradient smoothing and mechanical properties. Homogenization not only eliminates the heterogeneity inherited from the additive manufacturing (AM) process but also provides a practical way to smooth the gradient of composition and microstructure for improved gradient properties. Furthermore, it directly affects the subsequent precipitation behaviors in the FGMs, which highly depends on the diffusion degree of the elements in the matrix and grain boundaries. This work also conducted a comprehensive study on the heat treatment of SS316/IN718 FGMs, which will provide a theoretical and practical basis for the further development and application of FGMs. Besides, the uncertainty of thermodynamic modeling is evaluated and quantified the prediction accuracy for further improvement in the future.

This paper proposes a novel impact welding method named water-augmented vaporizing foil actuator welding, in which liquid water is introduced to alter the foil’s vaporization process, thus altering the induced driving pressure and the final welding performance. A series of comparative experiments were performed to confirm the effectiveness of the process and to understand the underlying mechanism. The proposed process decreased the lower-bound required discharge energy by 58–69%, increased the peel strength by 30–60%, and significantly reduced the variability in the critical standoff distance at the lower bound of the weld window. In addition, the proposed process resolved the robustness issue by producing a much more regular and repeatable shape of the weld area compared to conventional VFAW. Furthermore, three potential mechanisms have been proposed to explain the process improvement: the added water 1) increased the electrical energy deposition, 2) introduced additional energy from the aluminum-water chemical reaction, and 3) provided a more efficient force-transfer medium. In summary, this paper introduces a novel impact welding method with much improved process capability and robustness compared to conventional vaporizing foil actuator welding. In addition, due to its simplicity, this method may be easily extended for other forms of impulse metalworking, which may stimulate a wide interest for the community of high velocity metalworking.