Key Engineering Materials Vol. 1060

Abstract: Titanium aluminide (Ti-Al) has attracted attentions for applications in aerospace and automotive industries due to their unique properties such as low density, high stiffness and high specific strength at ambient and elevated temperatures. However, the ubiquitous manufacturing of components by conventional processing techniques is hindered by the inherent brittleness of TiAl-based alloys at ambient temperature making it difficult to process this type of alloy, thus, restricting their wider application. Moreover, the direct energy deposition (DED) is amenable to surface modifications and manufacturing of near-net shaped part of difficult-to-process materials. Therefore, this study examines Ti-Al-Si-x(Mo+V) alloys produced from elemental powders via laser in-situ alloying through DED technique using the laser engineered net shaping (LENS) machine. The focus of this investigation was to examine the influence of heat treatment on the alloys at varied Mo+V feed rates after laser in-situ alloying. Isothermal annealing heat treatment, was performed at 1150 °C for 15 min, 30 min, and 60 min, and at 1200 °C, 1300 °C, and 1400 °C for 60 min and furnace cooled (FC), followed by homogenization heat treatment at 950 °C for 6 hours and FC. It was observed that the microstructure revealed relatively large β₀-phase precipitates within the lamellae and α₂+γ lamellae colony boundaries. It was deduced that the presence of ζ-Ti₅Si₃ causes an increase in the alloys’ microhardness, which is notable after heat treatment at 1150 °C and 1200 °C, with microstructures of columnar and duplex phases, respectively.

Abstract: This study systematically investigates the microstructure and high-temperature performance of plasma-sprayed La₂Zr₂O₇/NiCoCrAlY (LZO/NAY) thermal barrier coatings (TBCs) with double-layer, three-layer, and five-layer gradient architectures. To address interfacial stress accumulation caused by mismatches in thermal expansion coefficients between ceramic and metallic layers, multilayer compositional gradients were introduced. Microstructural characterization was performed using SEM, EBSD, and TEM, while finite element modeling was used to evaluate thermal insulation and stress distribution. The five-layer gradient coatings exhibited the smoothest compositional transition and most uniform stress distribution, significantly reducing interfacial stress concentration and residual stresses. Thermal shock resistance tests at 1200 °C demonstrated that the five-layer coatings withstood 24 cycles, a marked improvement compared to 18 and 3 cycles for three-layer and double-layer systems, respectively. Isothermal oxidation tests at 1000 °C further showed that gradient coatings maintained superior structural integrity, with thinner thermally grown oxide layers than the conventional system. The findings provide both theoretical and experimental evidence that compositional gradient design markedly enhances the durability and thermal stability of TBCs, offering practical strategies for advanced thermal protection in high-temperature applications.

Abstract: Zinc-aluminum (Zn-Al) alloys are widely applied in engineering due to their strength, corrosion resistance, and castability. Among them, ZA-12 (hypereutectic) offers microstructural characteristics distinct from Zamak 5 (hypoeutectic), yet its response to microalloying has not been fully characterized. In this study, ZA-12 was produced by green sand casting and evaluated before and after titanium-boron (Ti-B) microalloying to examine changes in mechanical and microstructural behavior. Compression testing and hardness measurements were performed alongside grain size analysis to assess the influence of Ti-B additions. The results show that Ti-B treatment refines the microstructure of ZA-12 and produces measurable variations in hardness and compressive strength. When compared with previously characterized green sand-cast Zamak 5, ZA-12 displays noticeable differences in the extent of property changes under Ti-B addition, reflecting the influence of alloy composition and solidification type. This comparative assessment contributes to a better understanding of how hypereutectic and hypoeutectic Zn-Al alloys respond to Ti-B microalloying and supports ongoing efforts to tailor these alloys for engineering applications.

Abstract: Glass-enamel coated reactors are essential in chemical and pharmaceutical production, yet repairing local enamel defects remains difficult without risking further damage. This work introduces a non-destructive repair concept using a custom 3D-printed tantalum patch that magnetically adheres to the curved reactor surface. The patch, produced by powder bed fusion and equipped with a silicone gasket and embedded neodymium magnets, was tested in a glass-lined laboratory reactor under 18 combinations of temperature, pressure, and mixing speed. A pH-indicator paper placed beneath the patch verified sealing performance in a mildly acidic medium. No liquid penetration occurred under any tested condition, demonstrating that the magnetically fixed tantalum patch provides effective temporary repair of enamel defects. The results support its potential industrial applicability and highlight future development needs in gasket optimization and magnetic clamping design.

Abstract: This study investigates the applicability of several statistical learning regression and classification methods for analyzing fused filament fabrication (FFF) printing parameters and their relationship to resulting mechanical properties reported in different papers. The research questions are the following. RQ1: Identify which algorithms perform best on relatively small dataset with moderate dimensionality. RQ2: Investigate that secondary data extracted from publications are sufficiently uniform for reliable modeling, considering the potential influence of unreported printing parameters, environment variables. Data were collected using a python-based extraction process to retrieve data from the literature, followed by manual refinement, cleaning. Feature selection and engineering were applied to standardize input features and address missing datapoint values, resulting in a dataset of approximately 500 samples with eight input features and three output mechanical properties. Various regression methods were tested like linear regression with regularization, local regression, random forest regression, and gradient boosting regression, while classification methods include logistic regression, random forest classifier, gradient boosted trees, and support vector machines. Models were examined using standard regression and classification metrics, including residual analysis, confusion matrices, and cross-validation. Results show that missing features significantly influence model performance. The study shows the challenges and potentials of applying machine learning to secondary data in additive manufacturing.

Abstract: The primary focus of this paper is reverse engineering, a methodology that plays an increasingly important role in modern industry, particularly in situations where an existing component must be re-documented and reproduced despite the absence of original technical documentation. The aim of the research is to digitally reconstruct a gear with 11 teeth and a module of 5 mm using three-dimensional scanning and subsequently manufacture the component through additive manufacturing. A RangeVision Neo 3D scanner was employed for the digitization process, while Bambu Lab X1E and P1S printers were used for fabrication. During the experimental phase, the dimensional accuracy of the reproduced parts was evaluated by comparing the original gear with its 3D-printed counterparts. The study assumes that mechanical components can be successfully reproduced even without prior design documentation. The results demonstrate accuracy and precision achievable through 3D scanning and additive manufacturing technologies. Furthermore, the paper highlights the industrial relevance of reverse engineering and its cost-effective potential for the reproduction of mechanical components.

Abstract: The aim of the research was to statistically model the geometric accuracy and surface roughness of parts manufactured using the FDM (Fused Deposition Modeling) 3D printing process. Data were collected using various measurement methods (caliper, micrometer, 3D scanner, roughness tester). Based on the measurement results, several tables were created in which the deviation of the measured values from the nominal values was characterized using statistical metrics. From these, various summary tables were created, which were then used to examine the deviations and make comparisons. Deviations from the CAD model and shape tolerances were determined using 3D-scanned geometry software. The aim is to establish recommended maximum tolerances for the 3D printing technology examined in the research based on the geometric deviations.

Abstract: This research evaluates a waste K⁺-rich bentonite from the Polycanthos quarry in Cyprus for its application in water-based drilling fluids. Although bentonite is generally known for its exceptional swelling and colloidal properties, this specific waste material possesses a unique composition. It is dominated by K⁺-rich montmorillonite and beidellite derived from illite/smectite mixed-clay layers. This composition renders conventional Na₂CO₃ activation insufficient to meet American Petroleum Institute (API) standards due to inadequate colloid formation. To overcome this limitation, polymer additives were incorporated to form composites with the Na₂CO₃-activated bentonite. Of the two polymer groups tested, Xanthan Gum and Carboxymethyl Cellulose (CMC), at a concentration of 1.5 g per 22.5 g of bentonite in 350 mL of fluid, yielded the most favorable results. These composite systems were subjected to dynamic thermal aging for 16 hours to assess their rheological stability under prolonged high-temperature conditions. Rheological properties, including viscosity, plastic viscosity (PV), and yield point (YP), were measured using Couette viscometry. Both composites satisfied API requirements, and the CMC-bentonite composite exhibited superior colloidal stability at temperatures up to 100°C. This study concludes that polymer additives can effectively enhance the performance of the waste bentonite for drilling applications, including under extreme thermal conditions. This enhancement method allows the waste bentonite to meet industrial standards while simultaneously supporting circular economy principles, thus contributing to environmental and economic sustainability.

Abstract: Bentonite is widely used in water-based drilling fluids (WBF) due to its strong colloidal properties in aqueous systems, provided API standards are met. Conventionally, bentonite performance is enhanced through Na₂CO₃ activation; however, this approach may be inadequate for bentonites with uncommon mineralogical compositions. Building on our previous work, which involved modifying a K⁺-rich bentonite with a unique composition activated by Na₂CO₃ and further modified with polymers to achieve API-compliant WBF. Among all polymers tested, Xanthan gum and CMC exhibited the most promising performance and were subjected to dynamic thermal aging at high temperatures. Filtration tests were conducted, and the resulting filter cakes were characterized using TGA/DTG to evaluate thermal stability. The composite with CMC exhibited a higher final residue (83.5%) compared to xanthan gum (78.41%), indicating enhanced thermal stability, stronger polymer-clay interactions, and reduced polymer volatilization. This investigation emphasizes the contribution of bentonite to environmental sustainability.