Complex-shaped Components Research Articles

A New Approach to Characterize Superplastic Materials from Free-Forming Test and Inverse Analysis

For about 60 years, the aerospace industry has been strongly interested in superplastic forming processes to produce extremely light and complex-shaped components. Superplastic characteristics are found in lightweight metallic materials such as titanium-based, aluminum-based, and, more recently, magnesium-based alloys. Since the high ductility exhibited by superplastic materials is two orders of magnitude higher than that of conventional materials, complex-shaped components can be obtained. If made with conventional materials, they require expensive assembly operations. The behaviour of superplastic materials is summarized by a constitutive equation commonly obtained via tensile testing that subjects the tested material to a one-dimensional stress state. On the contrary, free-forming tests allows us to test the material by subjecting it to a stress state similar to that determined during a real superplastic-forming process. The aim of this work is to define the characteristic parameters of superplastic materials by free-forming tests. The behaviour of superplastic materials is commonly modelled using a power law which puts the material into a stress-to-strain-rate relationship. This law needs to identify two parameters characterizing superplastic materials: the strain rate sensitivity index and the strength coefficient. In this work, a new procedure is presented that implies the two material parameters vary with strain. It allows for a reduction in the number of constants needed to determine the material constitutive equation, thus requiring low simulation time compared to models that adopt the multiple-objective optimization based on genetic algorithms (GAs). It is more suitable to be used in the industrial field. Furthermore, the proposed procedure is compared with a conventional procedure which is also based on the inverse analysis carried out through the use of a finite element analysis. The results of the conventional procedure, based on the inverse analysis, which is conducted through the use of a finite element analysis, are used to calculate the material constants, and are compared with those coming from the procedure proposed in this work. The proposed procedure appears equally simple and gives more accurate results compared to the conventional procedure. In fact, the maximum percentage error, regarding the prediction of the forming times of a free-forming process, was reduced from 20% to 8%. The development of the proposed procedure, as well as the comparison of the results with a conventional procedure, required the development of an experimental activity. This activity consists of free-forming tests conducted at a constant pressure (the pressures employed vary from 0.2 to 0.4 MPa), at a temperature of 753 K, and on circular sheets (thickness 1.0 mm and radius 40 mm) in superplastic magnesium alloy AZ31.

Exploring the Impact of Heat Treatment on Residual Stress, Microstructure, and Mechanical Behavior of Laser Powder Bed Fusion Additively Manufactured Ti-6Al-2Sn-4Zr-2Mo Alloy

In the field of additive manufacturing (AM), a promising alloy that is gaining attention is the near-α Ti-6Al-2Sn-4Zr-2Mo (Ti6242) alloy. This alloy is known for its remarkable resistance to creep and corrosion at elevated temperatures. However, the production of Ti6242 components via Laser-based AM technologies faced with several challenges, such as the formation of residual stress in the as-built state that originates from the nature of these processes. Therefore, this study has a dual objective: first, to evaluate the microstructure and residual stresses in the as-built Ti6242 produced through laser powder bed fusion. Secondly, to investigate the impact of a promising post heat treatment on mitigating residual stresses, inducing alterations in the microhardness of the Ti6242 alloy and its ductility, phase transformations and microstructure evolution. The as-built specimen exhibited a significant residual stress of 1357 MPa, which was caused by the pronounced temperature gradients experienced during the fabrication process. It is interesting to note that this promising post heat treatment was highly effective in eliminating 99% of the residual stress. After heat treatment, the amount of α' present in the as-built specimen decreased. This resulted in the activation of diffusion of elements such as molybdenum, causing a proportion of the α' to decompose into the more ductile α+β structure. Additionally, it is revealed that the microstructural changes and relieved stresses from the heat treatment process caused a lower microhardness and a higher ductility under compressive loading, as the elongation and toughness reached 20.5% and 23.255 kJ/mm3 in the heat-treated samples, respectively. The outcomes of this work facilitate the use of this alloy in the production of complex shape components through laser-based AM technologies.

On the feasibility to obtain CuCrZr alloys with outstanding thermal and mechanical properties by additive manufacturing

The CuCrZr alloy combines high thermal conductivity and mechanical strength with stability at high-medium temperatures, making it a promising heat sink material for the EU-DEMO divertor and limiters. Additive Manufacturing (AM) technologies have proven effective in developing complex-shaped components with almost no constraints on geometry and minimal machining and welding requirements. This makes them particularly suitable for the production of heat exchangers featuring complex cooling channels with intricate inner structures.This study demonstrates the feasibility to obtain dense CuCrZr via Electron Beam Powder Bed Fusion (EB-PBF) with high thermal conductivity and enhanced mechanical strength compared to conventional routes. Gas atomization was used to produce spherical powders with a composition close to ITER specifications. By optimising the EB-PBF process parameters, relative density values of 99.7 % were achieved after HIP treatment, that removes the eventual residual porosity. The results underscore the importance of meticulous powder manufacturing to mitigate oxidation and microstructural defects in the final components. Achieving high relative densities in the EB-PBF process requires a focus on adopting high-energy absorption rates in the powders. This strategy can be accomplished by reducing the scanning speed and consequently the building rate of the process. The microstructural characterization revealed a complex hierarchical microstructure composed of grains and grain boundaries, solidification-enabled cellular-like subgrains elongated along the building direction and an ultra-fine precipitate state (already present in the as-built condition) mainly consisting of Cr-rich nanoprecipitates, although Zr-rich precipitates were also found at the melt pool boundaries. The thermal conductivity, hardness, mechanical strength at room temperature and high-medium temperatures were measured and correlated with the EB-PBF process parameters and the microstructure obtained after HIP treatment. The results indicate that it is possible to obtain CuCrZr with improved mechanical behaviour compared to conventional manufacturing technologies, while maintaining the thermal conductivity requirements for EU-DEMO.

Visual Strain Sensors Based on Fabry-Perot Structures for Structural Integrity Monitoring.

Strain sensors that can rapidly and efficiently detect strain distribution and magnitude are crucial for structural health monitoring and human-computer interactions. However, traditional electrical and optical strain sensors make access to structural health information challenging because data conversion is required, and they have intricate, delicate designs. Drawing inspiration from the moisture-responsive coloration of beetle wing sheaths, we propose using Ecoflex as a flexible substrate. This substrate is coated with a Fabry-Perot (F-P) optical structure, comprising a "reflective layer/stretchable interference cavity/reflective layer", creating a dynamic color-changing visual strain sensor. Upon the application of external stress, the flexible interference chamber of the sensor stretches and contracts, prompting a blue-shift in the structural reflection curve and displaying varying colors that correlate with the applied strain. The innovative flexible sensor can be attached to complex-shaped components, enabling the visual detection of structural integrity. This biomimetic visual strain sensor holds significant promise for real-time structural health monitoring applications.

The Impact of Surface Roughness on Conformal Cooling Channels for Injection Molding.

Injection molding technology is widely utilized across various industries for its ability to fabricate complex-shaped components with exceptional dimensional accuracy. However, challenges related to injection quality often arise, necessitating innovative approaches for improvement. This study investigates the influence of surface roughness on the efficiency of conformal cooling channels produced using additive manufacturing technologies, specifically Direct Metal Laser Sintering (DMLS) and Atomic Diffusion Additive Manufacturing (ADAM). Through a combination of experimental measurements, including surface roughness analysis, scanning electron microscopy, and cooling system flow analysis, this study elucidates the impact of surface roughness on coolant flow dynamics and pressure distribution within the cooling channels. The results reveal significant differences in surface roughness between DMLS and ADAM technologies, with corresponding effects on coolant flow behavior. Following that fact, this study shows that when cooling channels' surface roughness is lowered up to 90%, the reduction in coolant media pressure is lowered by 0.033 MPa. Regression models are developed to quantitatively describe the relationship between surface roughness and key parameters, such as coolant pressure, Reynolds number, and flow velocity. Practical implications for the optimization of injection molding cooling systems are discussed, highlighting the importance of informed decision making in technology selection and post-processing techniques. Overall, this research contributes to a deeper understanding of the role of surface roughness in injection molding processes and provides valuable insights for enhancing cooling system efficiency and product quality.

Optimization of the grain boundary network and tensile properties of powder metallurgy-hot isostatic pressed Ni-based alloy Inconel 625

Powder metallurgy-hot isostatic pressing (PM-HIPing) is an advanced manufacturing technology for large-sized and complex-shaped components for nuclear applications. In the present study, a novel PM-HIPing strategy was proposed to optimize the grain boundary network and tensile properties of Ni-based alloy Inconel 625, and it was verified by a series of experiments. Samples with 69 % and 74 % of coincidence site lattice (CSL) grain boundaries were obtained when the narrow-size ranged powder was consolidated at 1140 °C and 1180 °C, respectively. The fraction of CSL grain boundaries was further increased to ∼78.5 % after a high temperature solution treatment. Room temperature yield strength and ultimate tensile strength of PM-HIPed alloy 625 were comparable to that of the wrought specimens, elongation of the specimens was ∼56–60 %, the samples all featured with dimple ductile dominant fracture mode.

Finishing of additively manufactured stainless steel features by the eco-friendly electrolyte: Plasma and surface interaction science

Many industries, including the chemical, food, medical, and aerospace sectors, use complex-shaped components fabricated by additive manufacturing. The usage of additively manufactured components in end-user applications is challenging due to their higher surface roughness. Finishing processes are necessary to reduce the surface roughness. Electrolytic hot plasma polishing is a newly developed finishing process. For this process, an eco-friendly electrolytic solution is prepared and used to finish any shape of the component that is to be conductive. Salts and distilled water are used while preparing the eco-friendly electrolytic solution, which is used to finish stainless steel. Initially, the prepared solution was used to finish cast stainless steel components, and subsequently, it was employed for finishing additively manufactured stainless steel components. Voltage–current characteristics of the cast and additively manufactured components resulted in a similar pattern. As a result, the range of the input process parameters for cast components was chosen for the input of central composite rotatable design to finish the additively manufactured stainless steel components. The surface roughness of additively manufactured stainless steel features was reduced to 95.6 % of the original surface roughness of 12.45 μm. Scanning electron microscopy was used to examine surface morphology and material removal mechanisms.

Modelling the weld cladding process to predict weld clad position and shape error

Wire arc additive manufacturing (WAAM) is one of the most productive metal additive manufacturing methods. One of its most promising applications holds in the manufacturing of difficult-to-cut materials where production costs can be reduced with minimizing the time of machining and total tool costs. To develop a correct WAAM, technological processes for manufacturing complex-shaped components welding torch path corrections and welding power corrections have to be made especially in critical sections such as corners and sharp edges. A predictive mathematical model of the material cladding during the WAAM process has been developed for the purposes of generating an optimal toolpath of the WAAM clads. This predictive mathematical model is simplified to reflect the important physical phenomena in the weld pool but also to optimize computing time. In this paper, the principle of the mathematical model is described, and its functionality is verified by the welding experiments with five different welding power settings. For the initial calibration of the model parameters single straight-line weld clads with 5 different welding power settings (wire feeds) ranging from 5.0 to 8.6 m/min were investigated. 3D scans of these welded samples are used for the verification. With the calibrated simulation model, it was possible to predict the precise shape with a maximum deviation circa 0.20 mm. The start portions of the weld clads seem more complex having the deviation circa 0.30 mm. These are valuable results as the WAAM technology is generally considered to be reasonably rough.

Additive manufacturing-assisted sintering: Low pressure, low temperature spark plasma sintering of tungsten carbide complex shapes

Tungsten carbide (WC), renowned for its exceptional hardness and wear resistance, plays an essential role in various industrial applications (cutting tools, abrasives, and wear-resistant components). While traditional methods involve hot pressing, Spark Plasma Sintering (SPS) combined with Additive Manufacturing (AM) offers a cutting-edge approach, utilizing high-voltage electric current and mechanical pressure for rapid densification, particularly advantageous for fabrication of complex shape components made from challenging materials like nanosized binderless tungsten carbide. The study encompasses the entire spectrum of the powder's characterization, extending to the development of an intricate finite element simulation tailored for SPS sintering. Sintering cycles underscore the exceptional quality of the powder, demonstrating full density microstructures even under low-temperature (1550 °C) and low-pressure (50 MPa) conditions. The nanosized powder exhibits minimal microstructural coarsening, reflecting the high quality of the initial pure tungsten carbide nano powder. The core of this study revolves around the methodology employed for deriving constitutive parameters, following the Skorohod-Olevsky theory of continuum sintering. The derivation methods include variations in temperature, heating regimes, and stepwise pressure application during SPS. Additionally, a grain growth model is formulated based on microstructural analysis. Critical parameters, including the apparent sintering activation energy (800 kJ/mol) and the creep law stress exponent (n = 4.0), are discussed. The article concludes with the integration of the mechanical sintering model into finite element method (FEM) software, considering thermal and electrical aspects for a comprehensive SPS-AM modeling approach and its application to complex shape production. The research aims to enhance the understanding of SPS for tungsten carbide, providing insights for its application in manufacturing cutting-edge components in challenging environments.

Surface Plastic Deformation of Monocrystalline Alloy Components of Complex Shape

Surface Plastic Deformation of Monocrystalline Alloy Components of Complex Shape

Surface characteristic of Ti-6Al-4V alloy fabricated by Electron Beam Melting prepared by different surface post treatments

Metal additive manufacturing (AM) is a technique in constant growth that offers freedom in design in the production of complex shape components. However, it is well documented that most types of material failures in the AM parts are very sensitive to their surface properties. Hence, in this work, some surface post-treatments such as grinding, drag finishing and Surface Mechanical Treatment (SMT) are used as post-treatment processes to improve the performance of Ti-6Al-4V samples fabricated by the Electron Beam Melting technique. The influences of different post-treatment were investigated on the surface properties. The outcomes demonstrated that the SMT has- the highest efficiency in the surface treatment and could reduce surface roughness, increase hardness and improve wettability. This work demonstrates the potential of SMT to achieve favourable surface properties of AM metallic components.

Simultaneous improvement of strength and ductility of laser additively produced Ti6Al4V by adding tantalum

Laser additive manufacturing (LAM) technique can efficiently fabricate Ti6Al4V components of complex shapes, but often show poor mechanical properties. In this study, tantalum (Ta) was added into Ti6Al4V as an alloying element to improve the overall mechanical performance using a laser cladding system. It was found that Ti6Al4V–4Ta (corresponding to 4 wt% Ta) exhibited excellent mechanical performance with the yield stress of 956 MPa, ultimate tensile strength of 1042 MPa and the elongation of 10.8 %, meeting the ISO 7209 requirements for titanium and titanium alloys. The synergistic improvement of strength-ductility of Ti6Al4V–4Ta was attributed to the microstructure refinement, weakened α-variants selection, Ta solid solution, modified dislocation density and β phase content. Further quantitative analysis demonstrated that the strength increase was mainly contributed from the additional grain boundary, solid solution and dislocation induced by Ta elemental alloying. This study established Ta elemental alloying as an effective method to simultaneously enhance the strength and ductility of Ti6Al4V alloy using LAM technology.

Laser powder bed fusion of an ultrafine microstructural in-situ TiB2/Al composite with excellent mechanical properties and thermal stability at elevated temperatures

Additive manufacturing of lightweight and heat-resistant aluminum-based materials has received ever increasing interest for obtaining high specific strength and complex-shaped components serving at elevated temperatures in aerospace industry. In this study, an in-situ TiB2 particle reinforced Al–Cu–Mg–Fe–Ni (Al2618) alloy was additive manufactured by laser powder bed fusion (L-PBF) with excellent printability. The as-printed TiB2/Al2618 composite presented a fully equiaxed and remarkably refined grain structure with an average size of ∼1 μm. The intermetallic phases in the Al matrix exhibited an ultrafine cellular structure owing to the rapid solidification by L-PBF. The ultrafine microstructure showed excellent thermal stability at elevated temperatures due to the synergic effects of TiB2 particles and Fe, Ni-rich coarsening-resistant intermetallic phases. The L-PBF TiB2/Al2618 composite has shown superior mechanical performance at elevated temperatures both in tensile strength and in strength retention after thermal exposure among typical L-PBF and wrought Al alloys. This work inspires the design of heat-resistant metal matrix composites (MMCs) with advanced high-temperature mechanical performance enabled by additive manufacturing for potential industrial applications.

Role of 3D printed customized implants in periarticular fractures: a narrative review

“3D printing” is a common term used for a number of technologies which operate on the principle of converting a computer-generated 3D image into a physical model. Advantage of 3D printed parts is that they can assume complex shape, with solid and porous components that can be combined to provide the best combination of strength and performances and can help visualize the complex fractures which are difficult to apprehend with conventional imaging. Presently, the primary applications for 3D printing are the production of anatomical models for planning and surgery simulation, patient-specific instruments and custom-made prosthesis which have transformed how orthopedic problems are addressed now. This review aims to describe the utility and future directives into the application of this technology in orthopedics.

Ultra-Broadband Flexible Thin-Film Sensor for Sound Monitoring and Ultrasonic Diagnosis.

Small-scale and flexible acoustic probes are more desirable for exquisite objects like human bodies and complex-shaped components than conventional rigid ones. Herein, a thin-film flexible acoustic sensor (FA-TES) that can detect ultra-broadband acoustic signals in multiple applications is proposed. The device consists of two thin copper-coated polyvinyl chloride films, which are stimulated by acoustic waves and contact each other to generate the triboelectric signal. Interlocking nanocolumn arrays fabricated on the friction surfaces are regarded as a highly adaptive spacer enabling this device to respond to ultra-broadband acoustic signals (100Hz-4MHz) and enhance sensor sensitivity for film weak vibration. Benefiting from the characteristics of high shape adaptability and ultrawide response range, the FA-TES can precisely sense human physiological sounds and voice (≤10kHz) for laryngeal health monitoring and interaction in real-time. Moreover, the FA-TES flexibly arranged on a 3D-printed vertebra model can effectively and accurately diagnose the inner defect by ultrasonic testing (≥1MHz). It envisions that this work can provide new ideas for flexible acoustic sensor designs and optimize real-time acoustic detections of human bodies and complex components.

Enhanced deep drawing formability and deformation mechanism of aluminum alloy at cryogenic temperature

In this paper, a novel deep drawing forming technique, which involved cooling dangerous areas with high plastic deformation using liquid nitrogen, was introduced to enhance the formability of complex-shaped aluminum alloy components. Uniaxial tensile tests were conducted on Al-Cu series alloys at different temperatures, demonstrating that decreasing the temperature from room temperature (RT) to cryogenic temperature (CT) increased the uniform elongation by over 50%. A deep drawing numerical simulation model was established for a complex-shaped component used in aircraft body opening frame, and a set of forming molds that can control the cooling areas was designed based on the strain distribution. The results of the forming experiment showed that the new deep drawing technique successfully fabricated the component without cracks, whereas the conventional cold forming technique resulted in large-scale cracks at the bottom of the component. The mechanism behind the enhanced ductility of aluminum alloys was analyzed using dislocation slip, grain deformation, serrated flow, and fracture observations.

In-situ generated particle synchronous enhancement of strength and toughness in pressureless sintered Ti3AlC2 layered ceramics

Ti3AlC2 as a typical MAX phase has attracted extensive attention due to its advantages of both metals and ceramics. However, the decomposition of Ti3AlC2 during pressureless sintering leads to a low density, which restricts its application in complex-shaped components. To address this challenge, MgO, CeO2, Y2O3, and La2O3 were employed as additives to fabricate Ti3AlC2 ceramics with minimal decomposition via pressureless sintering. It was observed that these oxide additives reacted with aluminum and oxygen, forming MgAl2O4, CeAlO3, YAlO3, and LaAlO3, respectively. These in-situ generated aluminate particles effectively impeded the outward diffusion of aluminum and the inward diffusion of oxygen, thereby inhibiting the decomposition of Ti3AlC2. Furthermore, the thermal expansion mismatch between the in-situ generated particles and the matrix induced beneficial residual stresses. These combined effects contributed to the synchronized enhancement of both strength and toughness. Among the four additives, CeO2 displayed the best efficiency. Ti3AlC2-1.0 wt%CeO2 reached a flexural strength of 680.74 MPa and fracture toughness of 7.82 MPa m1/2, equivalent to those by pressure assisted sintering. The calculated toughness considering the residual stress was approximately 7.71 MPa m1/2, in good agreement with the measured value.

Microstructure and mechanical properties of additively manufactured γ-TiAl with dual microstructure

The latest research on electron beam powder bed fusion (PBF-EB), additive manufacturing (AM) process, reveals the possibility of establishing a dual microstructure and differing mechanical properties inside a complex-shaped component made of titanium aluminides (TiAl). The functionally graded material (FGM) parts are processed with two different, well-adjusted AM process parameter sets leading to a significant change in localized aluminum (Al) loss via evaporation during PBF-EB. By heat treatment, the as-built microstructure, containing two different levels of Al, is transformed into customized microstructures: fully lamellar (FL) and nearly lamellar (NL + γ). This study aims to determine the microstructural and mechanical characteristics of PBF-EB processed 4th generation TiAl alloy TNM. Tensile and creep tests are performed for single (FL or NL + γ) and dual microstructure specimens with two orientations. The element distribution of aluminum is determined, the microstructures are characterized, and the fracture-inducing defects are identified. The presented new FGM processing route is a groundbreaking benefit from the PBF-EB process and is necessary for superior mechanical performance. The stress-strain and the creep properties of the dual microstructure specimens are situated between the single microstructure specimens. The mechanical characterization shows that the interface between FL and NL + γ does not cause any weakening of the specimens. The failure always takes place in the weaker microstructure (tensile: FL; creep: NL + γ). For the first time, AM components such as TiAl turbine blades can consist of creep-resistant airfoil sections and high-strength root sections taking advantage of new microstructural FGM design possibilities.

Quantification of structural response and edge orientation of Chopped Tape Thermoplastic Composites in net-shaped specimens

Chopped Tape Thermoplastic Composites (CTTCs) offer high formability and performance for complex-shaped components in the aerospace and automotive industries. However, the mesoscopic discontinuity leads to spatial variabilities and correspondingly high scatter in the elastic properties of CTTCs due to the random orientations of chopped tapes and chopped tape-cavity edge interactions. Here we propose a new approach to investigate the effect of mould cavity edges on chopped tape orientation and hence the mechanical properties of CTTCs. Based on this approach, a Set Voronoi tessellation was implemented to represent the variability of local Young’s Modulus and chopped tape-cavity edge interactions occurring during the manufacturing process. It was confirmed that the chopped tapes align along the edges, and progressively transition to a random orientation towards the middle of the specimen. The results were validated on moulded specimens and demonstrated the ability to deconvolute the edge interaction.

Comparative study on the formability and microstructure evolution of different tempered Al–Cu–Li alloy sheets during room and cryogenic temperature forming process

High strength aluminum alloy sheets with excellent formability are necessary for the successful fabrication of complex-shaped components in order to prevent cracking during the forming process. To address this issue, this study investigated the formability of annealed (O) and water-quenched (WQ) Al–Cu–Li alloys at both room and cryogenic temperatures. Our results reveal a significant increase in the forming limit curve, with a 40% enhancement observed as the forming temperature decreased from 298 K to 113 K. Additionally, a 30% increase in formability was observed when transitioning from the O temper to the WQ temper. Thickness measurements reveal that WQ pre-treatment and cryogenic forming promoted continuous work hardening, thus improving deformation homogeneity. The mechanism responsible for the higher work hardening ability was elucidated by examining the microstructure evolution in different regions of the components. The results show that coarse particles in the O tempered alloys accelerated cross slip, resulting in the formation of recovered microstructures (i.e., dislocation cells and Cube texture) while simultaneously hindering dislocation movement and inducing local stress concentration. Conversely, for the WQ tempered alloy deformed at cryogenic temperature, the dissolution of particles and decreased stacking fault energy at low temperature suppressed cross slip and resulted in well-arranged dislocations within the slip system. Consequently, the combination of WQ pre-treatment and cryogenic forming demonstrates enhanced formability in high strength aluminum alloys, offering a novel method for manufacturing complex-shaped components.