Materials Science Forum Vol. 1181

Abstract: Face-centered cubic (FCC) medium-entropy alloys (MEAs) are known for their excellent ductility and fracture toughness, but they suffer from relatively low mechanical strength. Alloying elements are added in FCC MEA matrix to promote the formation of hard secondary phase or intermetallic compounds that improve the mechanical performance of the alloys. In this study, the effect of chromium (Cr) and niobium (Nb) additions on the microstructural and corrosion characteristics of the CoNiV MEA matrix was investigated. A scanning electron microscope coupled with energy dispersive spectroscopy was used to analyse the microstructure and composition of the developed alloys. The corrosion properties of the alloys were evaluated using linear polarization. The alloys exhibited a dendritic microstructure with the presence of secondary phases, which is consistent with slow cooling associated with arc melting and the presence of elements with large atomic radii that upset the crystal lattice. Alloy containing Cr possessed better anti-corrosive properties than its Nb counterpart, signalling formation of a more stable Cr₂O₃ passive film. This layer creates a boundary between the corrosive medium and the alloy substrate to prevent further interaction.

Abstract: NiTi alloy has desired engineering properties with many applications, such as biomedical, aerospace, automotive, etc, where several researchers have investigated the development of ternary and quaternary alloying of NiTi to further enhance its performance for demanding technological applications. However, there are limited studies on the effects and synergy of Re and Mo on the nanomechanical properties of NiTi alloy, despite the highly recommended effect of Re on the mechanical properties of Ni-based superalloys. Therefore, this study bridged this gap by developing NiTi-Re-Mo alloy via the spark plasma sintering technique and investigating its nanomechanical properties in relation to NiTi, NiTi-Re, and NiTi-Mo alloys. It was noted that NiTi-Re-Mo has better nanomechanical responses than other developed NiTi-based alloys. For instance, the hardness and elastic modulus of NiTi-Mo-Re increased to about 28236.7 MPa and 483.4 GPa from 4460.7 MPa and 122.5 GPa for NiTi alloy, respectively. These significant increments were credited to the synergy effect of Re and Mo, the solution and hard phase precipitation strengthening of the NiTi system, which also contributed to the reduction of dislocations and improved mechanical locking of the NiTi system. This makes the alloy desirable for high mechanical strength applications.

Abstract: The research focuses on cored blades made from the MAR-M247® Ni-based superalloy, which were manufactured through directional solidification with varying withdrawal rates of either 3.4 mm/min or 5.0 mm/min, and shell mold temperatures of 1510 °C or 1566 °C after undergoing solution heat treatment. The characterization of four variants of the cored blades was conducted using several analytical techniques: X-ray diffraction (XRD), light microscopy (LM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX). The XRD analysis identified the presence of the γ matrix, the intermetallic γ' phase, MC carbides, and M₅B₃ phases. The dendritic regions of the cored blades consist of secondary γ' precipitates surrounded by a γ matrix, with a mean size ranging from 0.264 to 0.272 μm, depending on the fabrication parameters.

Abstract: This research investigates the impact of heat treatment and high-temperature oxidation on the phase transformation and performance of AlCrFeCuNi-Nb high-entropy alloys (HEAs). The alloys were produced using laser deposition and methodically heat-treated to enhance their structural stability. X-ray diffraction (XRD) was employed for phase analysis to examine phase alterations resulting from Nb addition and thermal exposure. Results indicate that Nb boosts phase stability, facilitates the production of protective oxide layers, and increases resistance to high-temperature oxidation. The enhanced alloy demonstrated exceptional oxidation resistance and mechanical properties. These findings underscore the promise of Nb-doped HEAs for engineering applications that necessitate resilient, high-performance materials capable of enduring harsh temperatures and corrosive conditions.

Abstract: Welding is a widely used and effective method of joining metals. However, serious challenges are often encountered in the process due to welding distortion. Distortions result from the thermal expansion and shrinkage of metals during the welding process. This review paper focuses on the mechanisms associated with welding distortion and various mitigation techniques adaptable by fabrication industries. Whereas full prevention of distortion is unattainable with a finite geometric accuracy, it can essentially be controlled to minimize the undesired impact of distortion on the geometric integrity, hence increasing the manufacturing efficiency and decreasing the production cost. This paper categorizes distortions into out-of-plane and in-plane deformation modes and describes the factors which influence distortions - welding parameters, sequences, and material properties. Furthermore, a review of traditional and novel mitigation strategies, such as the optimization of welding parameters and improved determination and prediction of the welding sequence schedule. In this review, based on the synthesis of current publications, efforts have been made to guide fabrication industries in determining appropriate procedures and parameters to be selected according to job requirements, with the sole aim of offering better weld quality and lowering of manufacturing cost.

Abstract: The limited thermal stability of starch-based bioplastics restricts their application in high-temperature environments necessitates the need to reinforce them with thermally robust fillers. This study explores calcined eggshell (CES) and silica as potential bio-based and inorganic fillers to enhance the thermal and structural performance of starch-derived bioplastics. Both materials were characterized using the Brunauer–Emmett–Teller method (BET), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis, and a Scanning Electron Microscope equipped with Energy Dispersive X-ray Spectroscopy (SEM-EDX). BET analysis revealed mesoporous structures in CES and silica, with pore diameters of 2.8 nm and 2.7 nm, and pore volumes of 0.125 cm³/g and 0.132 cm³/g, which favors filler–matrix interactions. FTIR confirmed the presence of hydroxyl and carbonate groups in CES and silanol groups in silica, which promotes compatibility with hydrophilic polymers. Thermal analysis showed both materials to be stable above 600°C, with CES decomposing into thermally inert CaO and silica, exhibiting minimal mass loss post-dehydration. SEM–EDX analysis confirmed high surface area morphologies and dominant Ca and Si elemental compositions for CES and silica, respectively. The findings support the suitability of CES and silica as effective fillers for thermally stable bioplastics, offering environmentally friendly and cost-effective alternatives to conventional additives.

Abstract: The decline in conventional oil recovery efficiency necessitates the development of advanced tertiary methods such as Enhanced Oil Recovery (EOR). This study investigates a hybrid nanofluid composed of acetylated cassava starch and silica nanoparticles for application in chemical EOR. Acetylated starch was synthesized to enhance viscosity and thermal stability, while silica nanoparticles were incorporated for their interfacial activity and wettability alteration capabilities. Comprehensive laboratory experiments were conducted to evaluate the hybrid fluid’s physicochemical, rheological, and recovery performance. Characterization using FTIR, XRD, SEM, and TGA confirmed successful functionalization and improved thermal resilience. Rheological tests demonstrated shear-thinning behavior with high viscosity retention. The hybrid fluid also achieved a 57.7% reduction in interfacial tension and altered sandstone wettability from oil-wet to strongly water-wet conditions. Core flooding tests revealed a recovery factor of 68.9%, outperforming starch-only, silica-only, and brine controls. The synergy between the polymer and nanoparticles enhanced colloidal stability, flow performance, and oil displacement efficiency under simulated reservoir conditions. The use of cassava starch as a biodegradable and locally sourced material underscores the environmental and economic viability of the formulation. These findings support the potential of acetylated starch–silica nanofluids as sustainable, high-performance EOR agents.

Abstract: —Borassus palm or aethiopium palmyra is a palm species tree, widely spread in sub-Saharan Africa but its fruits don’t have any economic value therefore considered as waste. This study investigated the potential of Borassus fruit fibers (BFF), extracted manually from the underutilized fruit, for various applications by examining their hygroscopic properties. Scanning electron microscopy (SEM) revealed the fibers' unique features, including a relatively large diameter and high affinity for water vapor. A Dynamic Vapor Sorption (DVS) analysis with exposure time varying from 1, 2, 4 until 72h and varied Relative Humidity (from 0 to 90%) with 10% increment was carried out to examine the Sorption-desorption behavior. The characteristic hysteresis behavior of natural fibers was observed, with significant moisture uptake, particularly above 70% RH. The sorption and desorption processes were quantified, revealing a linear relationship between mass change and relative humidity. Furthermore, an Ensemble learning approach, specifically a Gradient Boosting Regression (GBR) model, was developed to predict the hygroscopic behavior of BFF. Trained on the experimental sorption-desorption data, the GBR model demonstrated excellent predictive accuracy, achieving a high R² value of 91.7% and low CV, MSE, and RMSE values (6.9 and 2.6, respectively). These findings highlight the significant influence of relative humidity on BFF moisture content and demonstrate the effectiveness of GBR as a powerful tool for accurately predicting the complex hygroscopic behavior of these fibers. Keywords—Machine Learning techniques, Ensemble Learning, Natural fiber, Hygroscopic properties, sorption/desorption

Abstract: In this paper, the effects of seawater exposure on the bending and damping properties of fibre-reinforced sandwich structures were investigated experimentally and analytically using the residual property model (RPM). Glass fiber reinforced plastics facesheets with PVC foam core, exposed to seawater exposure until saturation was subjected to flexural and dynamic mechanical analysis tests. Key mechanical properties were used to develop an analytical residual property model. Results indicated that after exposure, while the flexural strength and modulus reduced by 20% and 19% respectively, the storage, loss moduli and tan delta increased by 7%, 20% and 12% respectively. Furthermore, the accuracy of property degradation was demonstrated for the predicted properties, thereby establishing the suitability of RPM as a cost-effective means for material property determination.