Search Results (45)

Three-dimensional concrete printing (3DCP) represents a paradigm shift in construction technology, enabling the automated, formwork-free fabrication of intricate geometries. Despite its rapid growth, successful implementation remains dependent on the precise control of material rheology and printing parameters. This review critically analyzes the foundational rheological properties of static yield stress, dynamic yield stress, plastic viscosity, and thixotropy and their influence on three core printability attributes, i.e., pumpability, extrudability, and buildability. Furthermore, it explores the role of critical process parameters, such as print speed, nozzle dimensions, layer deposition intervals, and standoff distance, in shaping interlayer bonding and structural integrity. Special emphasis is given to modeling frameworks by Suiker, Roussel, and Kruger, which provide robust tools for evaluating structural stability under plastic yield and elastic buckling conditions. The integration of these rheological and process-based insights offers a comprehensive roadmap for optimizing the performance, quality, and scalability of 3DCP. Full article

This review presents a comprehensive analysis of polypropylene (PP) fibre incorporation in three-dimensional printed concrete (3DPC), focusing on the material behaviour in both fresh and hardened states. PP fibres play a critical role in improving rheological properties such as buildability, flowability, and extrudability. While increased fibre content enhances interlayer bonding and shape retention through the fibre bridging mechanism, it also raises yield stress and viscosity, which may compromise extrudability. In the hardened state, PP fibres contribute to improvements in compressive and flexural strength up to an optimal dosage, beyond which performance may decline due to fibre clustering and reduced packing density. When aligned with the printing direction, fibres are particularly effective in mitigating shrinkage-induced cracking by redistributing internal tensile stress. However, their inclusion can lead to a slight increase in porosity and promote mechanical anisotropy. This review also discusses mix design parameters, fibre characteristics, and experimental protocols, while identifying key research gaps including the lack of standardized testing methods, limited understanding of fibre orientation effects, and insufficient exploration of hybrid fibre systems. Based on the synthesis of reported studies, optimal print quality and structural consistency have been associated with the use of 6 mm long fibres, nozzle diameters of 4 to 6 mm, and printing speeds ranging from 40 to 60 mm/s. Overall, PP fibre reinforcement shows strong potential for enhancing the structural integrity and dimensional stability of 3D-printed concrete, while emphasizing the need for further studies to optimize its use in practice. Full article

Plasma nitriding (PN) is often used to enhance the mechanical properties (surface hardness, wear and corrosion resistance) of bulk alloys. High-quality AlCrN hard coatings were obtained using high-power pulsed magnetron sputtering (HiPIMS) technology. This study proposes a combination of two surface treatment methods (plasma nitriding and hard coating deposition) in a continuous plasma process to optimize the application and service life of cutting tools. The main feature of this study is to verify the mechanical properties and adhesion strength of nitride tungsten carbide (WC-Co) bulk at a lower temperature (∼300 °C) and shorter time (0.5 to 1.5 h) of PN treatment. After 1.5 h of PN treatment on the WC-Co substrate without subsequent coating, the ultra-thin WN_x diffusion interlayer (thickness ∼11.5 nm) on the subsurface was directly observed via TEM analysis, and the types of chemical bonding were confirmed by XPS analysis. Vickers analysis indicated that the surface hardness of the nitrided WC-Co substrate was enhanced by PN treatment from 1534 to 2034 Hv. The AlCrN coating deposited on the nitrided WC-Co substrate significantly enhances the surface mechanical properties, including adhesion strength (increasing from 70 to 150 N), hardness (rising from 2257 to 2568 HV), and wear resistance (with the wear rate decreasing from 14.5 to 3.4 × 10⁻⁸ mm³/Nm). Composite surface technology has a high commercial application value because it enhances the value of products under the existing equipment of manufacturers. Full article

In the laser powder bed fusion (LPBF) process, the surface quality of intermediate layers impacts interlayer bonding and part forming quality. Due to the complex dynamic process inherent in LPBF, current monitoring methods struggle to achieve high-quality in situ online monitoring, which limits the in-depth understanding of the evolution mechanisms of the surface morphology of LPBF intermediate layers. This paper employs an optimized coaxial optical imaging method to monitor key LPBF processes and analyzes the intermediate layer surface morphology evolution mechanism considering heat, force, and mass transfer. Results indicate that LPBF intermediate layer surfaces are influenced by energy density, melt pool behavior, and previous layer morphology, forming complex topological structures. At a low energy density, insufficient powder melting causes balling, extended by subsequent melt pools to form a reticulated structure and local large-scale protrusions. Heat accumulation at a high energy density promotes melt pool expansion, reduces melt track overlap, and effectively eliminates defects from previous layers via remelting, with spatter becoming the main defect. Additionally, the melt pool wettability on the part contours captures external powder, forming unique, overhanging contour protrusions. This paper enhances understanding of LPBF intermediate layer surface morphology formation mechanisms and provides a theoretical basis for optimizing surface quality. Full article

With the rapid advancement of 3D printing technology in low-carbon construction, the constructability of 3D printing materials has increasingly garnered attention. The constructability of these materials is intrinsically linked to their rheological properties. Therefore, this paper investigates the impact of additives, specifically hydroxypropyl methylcellulose (HPMC) and polycarboxylate superplasticizer (PCE), on the rheological properties of materials. The findings indicated that HPMC significantly increased both shear stress and apparent viscosity while also enhancing the thixotropic loop area. In contrast, PCE was found to reduce viscosity and yield stress, thereby improving fluidity and plasticity. The judicious incorporation of PCE (less than 0.003) and HPMC (less than 0.002) can enhance the rheological properties of the printing material, thereby improving the stability and interlayer bonding characteristics of the 3D printing structure. However, an excessive amount will result in a reduction in fluidity and cohesion, adversely impacting the printing quality. At this stage, the occurrence of cracks increases, which is detrimental to interlayer adhesion. Therefore, the judicious control of the proportions of PCE and HPMC can enhance the fluidity and viscosity of the material, thereby improving interlayer bonding strength and print quality. Full article

Spark plasma sintering (SPS) is an effective technique for studying the diffusion bonding of diamond/Cu composites, and has the potential to advance the application of copper matrix composites. This study investigates the SPS diffusion bonding of diamond/Cu composites using a chromium (Cr) interlayer. The effects of process parameters on the microstructure and mechanical properties of the bonding interface were evaluated through shear strength testing and SEM analysis. The results show that shear strength increases with interlayer thickness up to a certain point, after which it decreases. As the bonding temperature, holding time, and bonding pressure increase, defects such as cracks and voids at the diffusion-bonded interface are reduced, resulting in improved shear strength. Under suitable conditions (10 μm interlayer, 810 °C, 60 min, and 10 MPa), the bonding interface is defect-free, achieving a maximum shear strength of 139.89 MPa and a thermal conductivity (TC) of 700.97 W/(m·K), indicating high-quality diffusion bonding. Full article

The drilling of State-of-the-Art printed circuit boards (PCBs) often leads to shortened tool lifetime and low drilling accuracy due to improved strength of the PCB composites with nanofillers and higher thickness-to-hole diameter ratio. Diamond coatings have been employed to improve the tool lifetime and drilling accuracy, but the coated microdrills are brittle and suffer from coating delamination. To date, it is still difficult to deposit diamonds on ultrathin microdrills with diameters lower than 0.2 mm. To avoid tool failure, the pretreatment was optimized to afford sufficient fracture strength and enough removal of cobalt. Further, the adhesion of the diamond coating was improved by employing an interlayer comprising SiC/microcrystalline diamond, which mitigates stress accumulation at the interface. By these means, microdrills with diameters of 0.8 and 0.125 mm were coated with adherent diamonds. In this context, the composite coating with the diamond/SiC interlayer and a nanodiamond top layer featured enhanced adhesion compared to single nano- or microdiamond coatings on the WC-Co microdrills. The composite diamond-coated WC-Co microdrills featured improved wear resistance, resistance to delamination of the diamond coating, and improved performance for drilling PCBs compared to micro- and nanodiamond-coated microdrills without interlayer. In addition, a higher hole quality was achieved when the diamond-coated microdrills were used. These results signify that the composite/nanodiamond coating features the highest bonding strength and best drilling performance. Full article

Due to its super plasticity, low weight, and high mechanical resistance properties, generally, Ti6Al4V is used for aeronautical applications. However, it has low resistance to plastic shearing. In addition, it has poor wear resistance. For these reasons, a lot of techniques have been developed to improve its wear resistance. Investigations of microstructure and interfacial reactions of diffusion bonding of Ni and Ti6Al4V materials have been performed experimentally. Ni samples were prepared with 50 ± 5 µm Ni powders in cylindrical shape. For diffusion bonding, Ag foil was used for improving the interlayer and connection quality. Nickel and its alloys can be joined by using some different processes, and the use of an interlayer can further facilitate the joining process and improve the joint quality. The experiments were carried out under the protected atmosphere. Argon gas was used for protection. The experiments were performed under 5 MPa pressure for 60 min duration at 850 °C, 900 °C, and 950 °C thermal conditions. Investigations of metallurgical structure occurring in the interface areas were examined by optic analysis of EDS, SEM, and X-ray. The strength of the joints was tested by lap-shear tests. From observations, the best quality of the coalescence at interfaces was indicated at elevated temperatures. Full article

Additive Manufacturing (AM) enables the automated production of complex geometries with low waste and lead time, notably through Material Extrusion (MEX). This study explores Large Format Additive Manufacturing (LFAM) with carbon fiber-reinforced polyaryletherketones (PAEK), particularly a slow crystallizing grade by Victrex. The research investigates how extrusion parameters affect the mechanical properties of the printed parts. Key parameters include line width, layer height, layer time, and extrusion temperature, analyzed through a series of controlled experiments. Thermal history during printing, including cooling rates and substrate temperatures, was monitored using thermocouples and infrared cameras. The crystallization behavior of PAEK was replicated in a Differential Scanning Calorimetry (DSC) setup. Mechanical properties were evaluated using three-point bending tests to analyze the impact of thermal conditions at the deposition interface on interlayer bonding and overall part strength. The study suggests aggregated metrics, enthalpy deposition rate and shear rate under the nozzle, that should be maximized to enhance mechanical performance. The findings show that the common practice of setting fixed layer times falls short of ensuring repeatable part quality. Full article

In this work, the PEEK/short carbon fiber (CF) composites were prepared, a new thermodynamic coupling (preheating and impact compaction) process of the FDM method is proposed, and the warp deformation mechanism was obtained by finite element simulation analysis. Results show that a new method could improve the forming quality of an FDM sample. The porosity of FDM samples of the PEEK/CF composite gradually decreased from 10.15% to 6.83% with the increase in impact temperature and frequency. However, the interlayer bonding performance was reduced from 16.9 MPa to 8.50 MPa, which was attributed to the influence of the printing layer height change from the printhead to the forming layer. To explain the above phenomenon, a thermodynamic coupling model was established and a relevant mechanism was analyzed to better understand the interlayer mechanical and porosity properties of PEEK/CF composites. The study reported here provides a reference for improving the forming quality of fabricated PEEK/CF composites by FDM. Full article

The manufacture of damping alloy parts with stable damping properties and high mechanical performances in the selective laser melting (SLM) process is influenced by temperature evolution and residual stress distribution. Choosing an appropriate scanning strategy, namely the specific trajectory along which the laser head scans powders within given area, is crucial, but clearly defined criteria for scanning strategy design are lacking. In this study, a three-dimensional finite element model (FEM) of the SLM process for manufacturing a WE43 alloy component was established and validated against the published experimental data. Eleven different scanning strategies were designed and simulated, considering variables such as scanning track length, direction, Out–In or In–Out strategy, start point, and interlayer variation. The results showed that scanning strategy, geometry, and layer number collectively affect temperature, melt pool, and stress outputs. For instance, starting scanning at a colder part of the powder layer could lead to a high peak temperature and low melt pool depth. A higher layer number generally results in lower cooling rate, a lower temperature gradient, a longer melt pool life, and larger melt pool dimensions. Changing the start point between scanning circulations helps mitigate detrimental residual stress. This work highlights the potential of analyzing various scanning strategy-related variables, which contributes to reducing trial-and-error tests and selecting optimal scanning strategies under different product quality requirements. This article can assist in the design of appropriate scanning strategies to prevent defects such as element loss due to evaporation, poor bonding, and deformation or cracking from high residual stress. Additionally, identifying stress concentration locations and understanding the effects of geometry and layer number on thermal and mechanical behaviors can assist in geometry design. Full article

Traditional resistance spot welding (RSW) has been unsuccessful in forming quality composite joints between steel– or aluminum–polymer-based composites. This has led to the development of spot welding variants such as friction stir spot welding (FFSW), ultrasonic spot welding (USW), and laser spot welding (LSW). The paper reviewed the differences in the bonding mechanisms, spot weld characteristics, and challenges involved in using these spot welding variants. Variants of RSW use series electrode arrangement, co-axial electrodes, metallic inserts, interlayers, or external energy to produce composite joints. FFSW and USW use nanoparticles, interlayers, or energy directors to create composite spot welds. Mechanical interlocking is the common composite joint mechanism for all variants. Each spot welding variant has different sets of weld parameters and distinct spot weld morphologies. FFSW is the most expensive variant but is commonly used for composite spot weld joints. USW has a shorter welding cycle compared to RSW and FFSW but can only be used for small components. LSW is faster than the other variants, but limited work was found on its use in composite spot weld joining. The use of interlayers in FFSW and USW to form composite joints is a potential research area recommended in this review. Full article

The field of protective coatings for industrial applications is continuously evolving, driven by a need for materials that offer exceptional hardness, enhanced wear resistance, and low friction coefficients. Conventional methods of coating development, such as physical vapour deposition (PVD) and chemical vapour deposition (CVD), often face challenges like the necessity of vacuum conditions, slow growth rates, and weak substrate adhesion, leading to inadequate interface bonding. This study introduces a novel approach utilising an integrated laser/sol–gel method for synthesising aluminium nitride (AlN) coatings on EN43 mild steel substrates which overcomes these limitations. The technique employs a high-intensity diode laser with optimal power and translation speeds to consolidate a pre-applied thin layer of sol–gel slurry consisting of aluminium hydroxide, graphite, and urea on the substrate. Chemical thermodynamic calculations were used to predict the slurry composition, along with identifying the critical temperature range and the essential enthalpy needed for the synthesis of aluminium nitride. A three-dimensional heat transfer model was developed to predict the important process parameters, such as scanning speed and laser power density, required to achieve the temperature ranges necessary for a successful deposition process. Optical and scanning electron microscopy techniques were used to examine the surface morphology and microstructure of the coating. Elemental energy-dispersive X-ray spectroscopy and an X-ray diffraction analysis confirmed the synthesis of an aluminium nitride coating with a thickness ranging from 4 to 5 µm. Furthermore, the detection of sub-micron crystalline aluminium nitride structures yielding a metal matrix composite interlayer was indicative of strong metallurgical bonding. Microhardness testing indicated a hardness value of approximately 876 HV. The coated samples with the highest quality exhibited a surface roughness, Ra, ranging from 1.8 to 2.1 µm. Additionally, the coatings demonstrated an exceptionally low coefficient of friction, recorded at less than 0.1. These results represent a significant step forward in this field, offering a cost-effective, efficient, and scalable solution for producing high-quality coatings with superior performance characteristics. Full article

Additive friction extrusion deposition (AFED) is a recently developed additive manufacturing technique that promises high deposition rates at low forces. Due to the novelty of the process, the underlying phenomena and their interactions are not fully understood, and in particular, the processing strategy and tool design are still in their infancy. This work contributes to the state-of-the-art of AFED through a comprehensive analysis of its working principles and an experimental program, including a representative sample component. The working principle and process mechanics of AFED are broken down into their individual components. The forces and their origins and effects on the process are described, and measures of process efficiency and theoretical minimum energy consumption are derived. Three geometrical features of the extrusion die were identified as most relevant to the active material flow, process forces, and deposition quality: the topography of the inner and outer circular surfaces and the geometry of its extrusion channels. Based on this, the experimental program investigated seven different tool designs in terms of efficiency, force reduction, and throughput. The experiments using AA 6061-T6 as feedstock show that AFED is capable of both high material throughput (close to 550 mm³/s) and reduced substrate forces, for example, the forces for a run at 100 mm³/s remained continuously below 500 N and for a run at 400 mm³/s below 3500 N. The material flow and microstructure of AFED were assessed from macro-sections. Significant differences were found between the advancing and retracting sides for both process effects and material flow. Banded structures in the microstructure show strong similarities to other solid-state processes. The manufacturing of the sample components demonstrates that AFED is already capable of producing industrial-grade components. In mechanical tests, interlayer bonding defects resulted in more brittle failure behavior in the build direction of the structure, whereas in the horizontal direction, mechanical properties corresponding to a T4 temper were achieved. Full article

To enhance the quality stability of 3D printing concrete, this study introduces a novel machine learning (ML) model based on a stacking strategy for the first time. The model aims to predict the interlayer bonding strength (IBS) of 3D printing concrete. The base models incorporate SVR, KNN, and GPR, and subsequently, these models are stacked to create a robust stacking model. Results from 10-fold cross-validation and statistical performance evaluations reveal that, compared to the base models, the stacking model exhibits superior performance in predicting the IBS of 3D printing concrete, with the R² value increasing from 0.91 to 0.96. This underscores the efficacy of the developed stacking model in significantly improving prediction accuracy, thereby facilitating the advancement of scaled-up production in 3D printing concrete. Full article