Complex-shaped Components Research Articles

On the development of gelcasting process for tungsten and its alloys

Gelcasting technique has been successfully used for the preparation of porous tungsten. Gel forming monomer (methacrylamide (MAM)) and Cross-linker (NN’-Methylenebisacrylamide (MBAM)) dissolved in water were used for gelcasting of green compacts of tungsten with 39% solid loading. Appropriate quantity of dispersant, initiator, and catalyst were used in order to obtain a uniform dispersion of tungsten particles and also control the polymerization process. Several issues related to dispersant selection, de-airing, de-bindering, sintering, and selection of mold material have been addressed in order to obtain a defect-free product. Theoretical density of the porous sintered tungsten pellets produced by gelcasting process is ∼85%. The average pore diameter and mean pore area are 3 µm and 16 µm2, respectively, which are specifically required for the cathode application. Complex shape components of pure tungsten have been successfully made using gelcasting technique for the first time.

Post-processing of additively manufactured microstructures using alternating-magnetic field-assisted finishing

Complex-shaped components with unique microstructural features are becoming more and more important in the section of the optics and aerospace industries. Currently, additive manufacturing (AM) has been acknowledged as a potential technology to fabricate complex-shape components for the industrial application. However, the poor surface quality limits the performance of the AM components. This work was focused on the post processing for the 316L rectangular microstructures fabricated by the selective laser melting (SLM) technique. A novel alternating-magnetic field-assisted finishing (A-MFAF) method was proposed to improve the surface quality of rectangular microstructures while maintaining the surface profile accuracy. The magnetic field generator was designed to integrate two permanent magnet poles with different magnetization directions and a slotted magnetic pole holder. The alternating magnetic field of the finishing tool was thus achieved in the finishing zone. Finite element analysis (FEA) was utilized to verify the feasibility of the magnetic field generator. The material removal principle of the A-MFAF method was introduced in detail. Mathematical models of the material removal ratio (MRR) were established. The effects of finishing parameters on surface roughness were evaluated quantitatively. Experimental results showed that the 316L materials were uniformly removed from the top to the bottom surface of the rectangular microstructures. The SLM-generated surface defects were removed as well. Surface roughness (Sa) of the top and bottom surfaces was reduced from initial 9.79 μm to 0.85 μm and 3.12 μm, respectively. After finishing, the residual stress was converted from tensile to compressive states.

Evaluation of boronized steel for corrosion resistance enhancement of tubing in soultz-sous-forets and rittershoffen geothermal plants

Advanced iron boride protective coatings on carbon steels were tested and evaluated, for the first time, in actual corrosion conditions in the geothermal Rittershoffen and Soultz-sous-Forets sites (France) with positive results. Moreover, large size boronized spools demonstrated high performance in geothermal corrosive flows of NaCl-KCl-CaCl2-rich brines and significant CO2 contents at 150 °C. The coating's high performance is related to chemical inertness of crystalline iron borides and to well-consolidated double-layer structure. The proposed boronizing thermal diffusion technology is well suited for inner surface protection of piping and complex shape components. It could be a cost-effective solution to enhance equipment performance for geothermal applications.

Fabrication of highly transparent AlON ceramics by fast formed direct aqueous slip casting green body

By using a copolymer of isobutylene and maleic anhydride (Isobam-104) as dispersant to prepare slurries of high solid loading, aluminum oxynitride (AlON) green bodies were fast formed by direct aqueous slip casting. Based on the experiments on solid loading and dispersant amount, the optimal sample pressureless sintered at 1880[Formula: see text]C for 2.5 h showed the highest transmittance of 80.1%. The slurry drying time in mold was effectively reduced to only 2 h by increasing solid loading, which is more adaptive to fabricate complex-shaped and/or large-sized AlON components of high transparency.

Superior superplasticity and multiple accommodation mechanisms in TiB reinforced near-α titanium matrix composites

Superplastic forming is a promising technique for producing complex-shaped components of hard-to-deform titanium matrix composites (TMCs). Superplastic tensile tests were performed on hot-rolled TiB/near-α Ti matrix composites with different reductions to investigate the effects of matrix microstructural characteristics and whisker orientation on superplastic deformation behavior. The results showed that the composite with initial BT-type texture and finer matrix grains at a rolling reduction of 80% exhibited lower flow stress and larger elongation than the composite with initial T-type texture at a rolling reduction of 40%, and superior elongation of 682% was achieved in the former. Significant randomization of crystal orientation and dynamic grain growth phenomenon occurred in the matrix alloys during deformation. The originally misaligned TiB whiskers gradually rotated to the tensile direction and simultaneously rotated circularly around the [010] axis during superplastic tensile deformation, which would accommodate the matrix deformation and share more load transferred from the matrix. Another important accommodation mechanism of TiB whiskers was to accelerate the dynamic recrystallization of the surrounding matrix by particle-stimulated nucleation. TEM and EBSD observations together with GND-distribution analysis confirmed that the primary superplastic deformation mechanism of TiB/Ti composites is grain/phase boundary sliding accommodated by dislocation slip and dynamic recrystallization.

Capability to detect and localize typical defects of laser powder bed fusion (L-PBF) process: an experimental investigation with different non-destructive techniques

Additive manufacturing (AM) technologies, generally called 3D printing, are widely used because their use provides a high added value in manufacturing complex-shaped components and objects. Defects may occur within the components at different time of manufacturing, and in this regard, non-destructive techniques (NDT) represent a key tool for the quality control of AM components in many industrial fields, such as aerospace, oil and gas, and power industries. In this work, the capability of active thermography and eddy current techniques to detect real imposed defects that are representative of the laser powder bed fusion process has been investigated. A 3D complex shape of defects was revealed by a µCT investigation used as reference results for the other NDT methods. The study was focused on two different types of defects: porosities generated in keyhole mode as well as in lack of fusion mode. Different thermographic and eddy current measurements were carried out on AM samples, providing the capability to detect volumetric irregularly shaped defects using non-destructive methods.

Enhanced superplasticity achieved by disclination-dislocation reactions in a fine-grained low-alloyed magnesium system

Superplastic forming, as an advanced manufacturing method, is especially important for producing complex-shaped components for Mg-alloys. Superplasticity can be achieved through grain boundary sliding at elevated temperatures in high-alloyed Mg systems, with a typical grain size < 10 μm stabilized by high densities of intermetallic precipitates. However, it is difficult to stabilize small grains and facilitate grain boundary sliding in low-alloyed systems due to insufficient precipitates. Here, by utilizing a distinctive design strategy, i.e. introducing solute segregation to enhance stability of the fine-grained structure, we obtained an Mg-1Zn-0.2Ca-0.2Zr-0.1Ag (wt.%) alloy achieving ∼450% superplastic strain. Through quasi-in-situ Electron Backscatter Diffraction analyses, we investigated systematically microstructure evolutions during superplastic deformation of the alloy at different strains. It has been found that superplasticity is achieved through the absorption of intragranular dislocations by grain boundaries, which are associated with stress-driven grain boundary migration mediated by disclination-dislocation reactions. By using a theoretical description based on stress-driven grain boundary migration and disclination-dislocation reactions, our model can capture multiple superplasticity mechanisms (e.g., grain boundary sliding and grain rotation), which establishes a fundamental relationship between the evolution of microstructural defects and the strain accommodation during superplastic deformation. Our results not only suggest an effective way to achieve superplasticity in low-alloyed Mg systems, but also provide a new insight to elucidate the nature of superplasticity mechanism by revealing the intrinsic correlation between stress-induced grain boundary migration and disclination/dislocation motion.

Towards lab-based X-ray scattering tensor tomography with circular gratings

Reinforcement of the polymer matrix in injection-molded plastics with fibers of various kinds can improve their mechanical properties. The resulting polymer composite material provides exceptional load-bearing capabilities with flexibility in the molding of complex-shaped components. Mechanical properties of short-fiber-reinforced polymers are highly dependent on the fiber orientation in the matrix. Lack of maturity of injection molding simulation frameworks limits prediction of the complex flow patterns during injection molding, while the requirement for resolving individual fibers in conventional imaging methods significantly restricts the imaged field-of-view. Here we demonstrate 3D characterization of the fiber orientation in a complete FRP component enabled by a novel technique of X-ray tensor tomography. The obtained fiber orientation reconstruction can be efficiently used in reverse engineering applications, serving as a reference for simulations.

Application of hybrid additive manufacturing technology for performance improvement of martensitic stainless steel

Additive manufacturing (AM) is considered to be an attractive technology that offers tremendous advantages in rapidly producing complex-shaped components close to their final/net shape. However, uncontrolled metallurgical defects (pores, cracks, and inclusions), deleterious tensile residual stresses (RS), as well as scattered and unsatisfactory material performance have hindered its applications. In this study, layer-by-layer ultrasonic micro-forging treatment (UMT) was combined with directed energy deposition (DED) to substantially improve the mechanical performance (e.g., strength-ductility synergy, and fatigue behavior) and corrosion resistance of as-built 15–5PH stainless steel (SS). The surface RS distribution, mechanical properties, corrosion resistance, and microstructural properties of the non-UMT and UMT specimens were analyzed. In particular, focused ion beam (FIB) was employed to prepare the specimen for transmission electron microscopy (TEM) observations of the surface severe plastic deformation (SSPD) zone after UMT. The results indicated that the process with UMT resulted in higher surface compressive stress (~−750 MPa), reduced oxide inclusions, and refined martensite blocks (23.8% finer than that of the non-UMT specimen). The improvement of these characteristics induced by UMT further led to a comprehensive increase in the strength, elongation, fatigue resistance, corrosion resistance, and surface hardness of the DED fabricated parts. This work demonstrated the tremendous potential of integrated DED technology for tailoring the microstructure, controlling the quality, and producing martensitic SS with excellent mechanical performance and corrosion resistance.

Selective laser melting of Al–Si–10Mg alloy: microstructural studies and mechanical properties assessment

Additive Manufacturing (AM) technique is widely recognized by aerospace sectors for its potential to fabricate complex shape components directly from a Computer-Aided Model data (CAM). Selective Laser Melting (SLM) is an innovative method high degree of adaptability among different AM techniques. SLM is one of the AM techniques adopted to produce the three-dimensional complex shape components. Current research work focuses on fabricating an Al–Si–10Mg aluminium alloy by SLM process which is studied for the influence of scanning speed and build orientation on the mechanical strength and surface finish of the as built component compared with as casted specimen. The importance of the sample studied for the scanning speed and built direction is relatively essential exclusively for dynamic applications. The as-built samples surface micrographs was surprisingly refined with a progressively reduced grain size diameter from 7.2 μm to 5.5 μm by increasing scanning speed compared to that of AlSi10Mg parts (∼9.1 μm). The mean layer thickness increased from 20 μm to 30 μm by decreasing the scanning speed from 500 mm/s to 200 mm/s. Attractive advantage of the Orowan mechanism, fine grain strengthening, and the graded interfacial layer, a considerably-high microhardness (135 ± 3.1HV), and enhanced mechanical properties were achieved.

Biaxial formability and microstructure of an Al-Mg-Si alloy sheet post solution heat treatment

Hot forming-quenching integrated process was developed to fabricate aluminum alloy complex-shaped components by taking advantage of the enhanced formability at the temperature close to solution temperature. But, it is very difficult to evaluate the formability under biaxial tension state and continuous cooling conditions. A measuring method was proposed to evaluate the biaxial formability by combining solution heat treatment and hot gas free bulging test. The effects of temperature and pressurizing rate on the bulging ability and thickness uniformity of an Al-Mg-Si alloy sheet were clarified. The deformation mechanism was revealed by microstructure observation. It is found that excellent formability can be obtained under the high temperature with less heat loss and rapid pressurizing conditions. The limiting strain under rapid pressurizing condition decreases from 1.13 at 500 ℃ to 0.81 at 400 ℃, being at a high strain level. Thickness uniformity can be obviously improved at a higher deformation temperature accompanied by rapid loading due to the remarkable strain-rate hardening effect. Dynamic recovery is the main restoration mechanism, resulting in numerous substructures and unchanged grain size. The obtained biaxial formability closer to actual forming condition can provide fundamental guidance for forming aluminum alloy complex-shaped component by hot forming-quenching integrated process.

3D printing floating modular farms from Plastic Waste

As demographic growth and climate change effects increase, agriculture intensifies its pressure on the natural ecosystems from which life on Earth depends. In recent years, novel designs and resource-efficient manufacturing methods have been studied to alleviate the impact of food production, many of them incorporating farms into the urban context. However, farming in freshwater bodies remains largely unexplored and constitutes a great opportunity for innovation when land is scarce. Physical requirements for floating farming demand water barrier, solid, inert, and food-grade material with sufficient natural light transmittance, and lightweight, large-scale, complex-shaped components. Therefore, Polyethylene Terephthalate (PET) is presented in this paper as an ideal material for the fabrication of deployable floating farm modules, and Fused Deposition Modeling (FDM) is selected as the most appropriate manufacturing process for the required geometries. Today, recycled polymers in 3D Printing have progressed as a more sustainable feed for small-scale applications. However, there are limited built examples of Additive Manufacturing (AM) using recycled polymers in large-scale real-life applications. This project explores digital designs and fabrication approaches to large-scale manufacturing using PET obtained from single-use bottles to produce empirical prototypes tested in real-life conditions. The research prompted the digital design of a one-meter diameter translucent dome and a flotation platform, their fabrication using large-scale FDM, the assembly of the printed elements, and the monitoring of the farming module performance during operation. The paper covers the state of the art of related 3D printing technologies and their application in food production devices, details the design process of the floating module, explains the selected printing processes and interfacing strategies, and discusses the empirical evidence on the benefits and drawbacks of large-scale AM applied to the cultivation of food. Overall, the research demonstrates the possibilities of 3d Printing using recycled polymers, adding novel insights from a fully-functional project to the incipient body of research on digital manufacturing in food production.

Correlation between mechanical behaviour and microstructural features of AISI 316L produced by SLM

The Additive Manufacturing (AM) process is nowadays considered a valid alternative to produce complex shape components in AISI316L stainless steel. Although many manufacturers consider additive manufacturing a fast and economical production method compared to traditional ones, there are still problems regarding the mechanical behaviour of components obtained with rapid prototyping. The purpose of this work is to investigate the difference in mechanical behaviour between AISI316L obtained with the traditional method and that obtained by Selective Laser Melting. In order to obtain a correlation among mechanical behaviour and microstructure, static tensile tests, monitoring the energy release of the material, were performed. Failure analysis was carried out by means of optical and scanning electron microscopy with energy dispersive spectrometry (SEM/EDS). Furthermore, the composition and crystal structure were analysed by XRF and XRD. Differences between traditional and AM material were highlighted, both from energy release and microstructure point of view.

Superplastic deformation behavior of Mg alloys: A-review

The magnesium alloys are the next-generation lightweight metal materials; however, the production of the complex shape components of thermo-mechanical processed magnesium alloys is very limited in comparison to their die-casted counterparts. Both high strain rate and low-temperature processing are required to save time and cost for the project. Uniaxial tensile testing has been vastly used for determining the plasticity of magnesium alloys at elevated temperatures. Therefore, this review article sheds light on superplastic behaviors under the uniaxial tensile loading of different magnesium alloys. This review also emphasizes low and high-temperature superplasticity, high strain rate superplasticity, deformation mechanism, thermal stability, texture evaluation, and fracture mechanism of extruded/rolled and severe plastic deformed magnesium alloys. At the end of the review, some technical issues have been addressed which can be beneficial for further enhancement in the superplasticity of magnesium alloys.

Investigation of the tensile behaviour of PolyLactic Acid, Acrylonitrile Butadiene Styrene, and Polyethylene Terephthalate Glycol materials

Additive Manufacturing (AM) provides numerous advantages like material waste reduction, dimensional control, and simplified production processes compared to conventional manufacturing techniques. The additive manufacturing techniques are capable of producing complex-shaped components with ease. Out of the several available 3D printing techniques, Fused Deposition Modelling (FDM) is widely used, because of its flexibility in the fabrication of large components. PolyLactic Acid (PLA), Acrylonitrile Butadiene Styrene (ABS), and Polyethylene Terephthalate Glycol (PETG) are some of the commonly used thermoplastic filaments in the FDM process. It is essential to understand the tensile property of such polymers before selecting them for a requirement. In this regard, the tensile behaviour of the PLA, ABS, and PETG materials is studied in this work. The tensile specimens are modelled in Solidworks modelling software in accordance with the ASTM standards. The specimens are 3D printed using the FDM process and tested in a universal tensile testing machine. The tensile results show that PETG material has high elongation and tensile strength whereas ABS has high stiffness compared to the other materials. PLA is stronger than ABS in terms of tensile strength and is analogous to PETG material. It is evident from the comparison that the PETG filament is suitable for applications like hooks, brackets, etc. which require high tensile strength.

Repair of damaged parts using wire arc additive manufacturing in machine tools

Mechanical parts manufactured using additive manufacturing (AM) processes are used in various fields, such as the aerospace, automobile, and machine tool fields. Recently, many researchers have been actively researching AM processes, owing to their advantages in fabricating complex-shaped components that are difficult to process using conventional processes such as rolling, forging, and casting. One of the AM processes, wire arc additive manufacturing (WAAM), is widely used for manufacturing and repair. Mechanical parts usually suffer from severe damage, such as wear and cracks, during operation. Therefore, research on the damaged parts is often required for repairs. This study was performed to investigate the repair of damaged parts using WAAM in machine tool remanufacturing. In general, these parts are often damaged owing to falls of the workpieces and the inexperience of workers; the cross slide is one of the parts damaged most often in a lathe. Accordingly, this study used the cross slide as an example. First, the damaged area was partially cut flat. Second, it was filled with a metal wire using WAAM. Third, post-processing was performed to adjust the surface quality and shape accuracy. Then, the microstructure, chemical composition, and mechanical property of the repaired part were analyzed. Finally, the repaired cross slide was used to replace damaged parts. In general, this method can be applied to various mechanical parts such as impellers, turbine blades, and machine tools.

Comparative evaluation of 3D printed components for deviations in dimensional and geometrical features

Additive Manufacturing technology is an emerging and a rapidly growing technology that has its roots spread almost in each and every field. This research investigates the components 3D printed two widely used 3D printing technologies, namely Fused Deposition Modelling and Stereolithography Apparatus. Fused Deposition Modelling is a process where a thermoplastic material is extruded through an extruder with a nozzle that travels, in a predefined path, over a heated bed platform along a part’s geometry. Stereolithography Apparatus is the most promising approach for producing simple to complex-shaped components due its great accuracy, flexibility, and efficiency. In this technology, Masked Stereolithography Apparatus is the recent technology in which the resin is cured with the help of an LED light source guided by LCD screen. Dimensional Deviation and Geometric Tolerance Deviation offered by the components produced on different 3D printers are important to be analyzed. This study mainly emphasizes on development of benchmark component and 3D printing of that component on Fused Deposition Modelling and Masked Stereolithography Apparatus 3D printer and making a comparative evaluation. For this, the benchmark component is evaluated for dimension and geometric tolerance deviation by measuring it with the help of Co-ordinate Measuring Machine.

Resonant Airborne Acoustic Emission for Nondestructive Testing and Defect Imaging in Composites

A new version of an acoustic emission mode which is different from its traditional counterpart is discussed in view of applications for nondestructive testing. It is based on the effect of acoustic waves generation from the defect area in ambient air by local standing wave vibration developed in this area at the defect resonant frequency. Another approach which does not require preliminary knowledge of local defect-resonance frequency is one that uses wideband acoustic activation by a noise-like input signal. The acoustic emission field from the defect area is a “fingerprint” of the radiation source, and thus is applicable to defect detection and imaging. This enables the use of commercial microphone scanning for detecting and imaging various defects in composites. An improvement in the acoustic-emission scanning mode based on a multiple-axis robot is studied to applications to complex shape components. A rapid, full-field imaging of the acoustic-emission field is implemented by means of an array of microphones (acoustic camera). Numerous case studies validate the potential of the resonant acoustic-emission modes for integration in the defect imaging system based on inexpensive, fully acoustic instrumental components.

Sulfidation-Oxidation Resistance of Thermal Diffusion Multi-Layered Coatings on Steels.

The high-temperature sulfidation-oxidation corrosion resistance of protective coatings deposited on carbon and 316L steels was studied. The coatings obtained via the thermal diffusion process had multi-layered architectures and consisted of aluminides, iron borides, or iron boride–TiO2 layers. The protective coatings experienced a minimal rate of mass changes, insignificant scale formation, and no delamination and surface micro-cracking after 504 h of exposure in 1% (Vol.) H2S-air atmosphere at 500 °C. Furthermore, the coatings demonstrated a high degree of integrity compared to bare 316L stainless steel. Aluminized steels demonstrated the highest performance among the studied materials. The developed thermal diffusion coatings are promising candidates due to their enhanced stability in H2S–air atmosphere; they may be employed for protection of inner and outer surfaces of long tubing and complex shape components.

Innovative Joint for Cable Dome Structure Based on Topology Optimization and Additive Manufacturing.

Aiming at the problems of a low material utilization rate and uneven stress distribution of cast-steel support joints in cable dome structures, topology optimization and additive manufacturing methods are used for optimization design and integrated manufacturing. First, the basic principle and calculation process of topology optimization are briefly introduced. Then, the initial model of the support joint is calculated and analyzed by using the universal software ANSYS Workbench 2020R2 and Altair OptiStruct, and the optimized joint is imported into Discovery Live to smooth the surface. The static behaviors of three types of joints (topology-optimized joints, joints after the smoothing treatment, and joints from practical engineering) are compared and analyzed. Finally, the joints are printed by using fused deposition modeling (FDM) technology and laser-based powder bed fusion (LBPBF) technology in additive manufacturing. The results show that the new support joint in the cable dome structure obtained by the topology optimization method has the advantages of a novel shape, a high material utilization rate, and a uniform stress distribution. Additive manufacturing technology can allow the manufacture of complex shape components with high precision and high speed. The combination of topology optimization and additive manufacturing effectively realizes the advanced design and integrated manufacturing of support joints for cable dome structures.