Advances in Science and Technology Vol. 154

Abstract: High-entropy alloys (HEAs) have excellent properties that are being explored for potential applications in many engineering fields. Their excellent properties strongly depend on their phases. The vastness of alloy compositions that can be synthesized makes it extremely challenging to experimentally investigate all the possible HEA types. To mitigate these challenges, more efficient and systematic computational techniques can be applied to the existing experimental data to accelerate HEA design and discovery. Therefore, this study developed three soft computing classification models based on artificial neural network, k-nearest neighbor (kNN), and support vector machine (SVM) to classify solid solution, amorphous and intermetallic phases in HEAs. Empirical studies showed that hyperparameter optimization improved classification accuracies of the classifiers with kNN (92%) outperforming ANN (86%) and SVM (90%) using all five predictive features. Feature selection did not improve the classification accuracy of any of the model. This studied demonstrated the importance of applying soft computing techniques and hyperparameter optimization for enhancing the classification accuracies of models to predict the phases in HEAs.

Abstract: High strength 7xxx series aluminium alloys are widely utilized in the aerospace, automotive and other manufacturing industries due to their low cost, high specific strength, high stiffness strength and fracture toughness. Additive manufacturing presents new opportunities in producing 7xxx series aluminium alloys such as reduced material waste, shorter lead time, and increased design freedom. This paper reviews the current progress in Wire Arc Additive Manufacturing (WAAM) of 7xxx series aluminium alloys, a technology that offers benefits such as better energy absorption than alternative laser-based processes, high deposition rates, and unrestricted build size. A classification of the AM processes utilized to fabricate aluminium alloys and WAAM process variants for fabricating aluminium alloys are introduced. Also, some common defects including porosity, solidification cracking and volatile elements loss encountered during the WAAM process of 7xxx series aluminium alloys are discussed. Whilst porosity remains a major issue in 7xxx series aluminium alloys produced via WAAM, several opportunities to minimize or eliminate the defects through process selection and alloy development are presented.

Abstract: This paper integrated two severe plastic deformation methods, namely frictional extrusion, and friction stir spot welding to obtain synergetic benefits and create a friction extrusion spot welding (FESW) process. The FESW process was carried out with the use of AA1xxx Al alloy by interchanging the location of the predrilled extrusion hole (between the upper and bottom plates). The microstructure, tensile-shear load, and fracture behaviours of the welds were investigated. The results revealed the presence of no weld discontinuities/flow-aided defects while the FESW process was effective in filling the extrusion holes irrespective of the location of the predrilled holes. An inverse relationship was found to ensue between the tool’s rotating speed and the tensile-shear load of the bottom plate hole-friction extrusion spot welded joint joints while a direct correlation occurred between the tensile-shear load and the rotational speed (up to 1100 rpm) in the top plate hole-friction extrusion spot welded joints. The difference in the tensile and fracture behaviours of the two weld categories is attributed to the disparity in the hole-filling mechanisms. The maximum tensile shear load of 3.1 kN (at 710 rpm) and 3.3 kN (at 1100 rpm) were obtained in the bottom plate hole-and top plate hole-FESW joints respectively.

Abstract: Wire arc additive manufacturing (WAAM) has gained significant attention in recent years as a cost-effective and efficient method for fabricating complex geometries. This study investigates the effects of cold forging and annealing on mechanical properties of AISI 308LSi wall fabricated using an automatically controlled gas metal arc welding on a CNC machine. The multilayer WAAM wall manufactured at an optimized parameters was first machined to a fairly smooth surface. Thereafter, the wall samples were differently subjected to annealing at 930°C and cold forging processes to improve the mechanical properties. Microstructural characterization of the post-processed and as-deposited samples were performed using optical and scanning electron microscopy while the tensile and hardness properties were investigated using Instron universal testing machine and Vickers hardness tester respectively. Annealing process was found to improve the tensile properties while the cold forging improved hardness of the deposited WAAM wall. These findings offer valuable insights into optimizing post-processing techniques for WAAM parts, especially 308LSi stainless steel and contribute to the advancement of this technology for industrial applications.

Abstract: The widespread corrosion of critical oil and gas infrastructure requires development of innovative and environmentally sustainable solutions. This research considers the repurposing of hitherto un-useful expired drugs to meet this challenge and to do so in ways that also puts stop to the menacing and illegal circulation of expired pharmaceuticals in developing economies. The corrosion inhibitory potential of expired paracetamol was evaluated for mild steel in acidic environment. Electrochemical analysis revealed that the corrosion current decreased from for the mild steel immersed in the blank/uninhibited 0.5M HCl environment to in the case of the sample in the 8g/l environment. The concentration of dissolved ions of iron in the acidic environment also followed this trend supported by the results obtained from the gravimetric analysis. Optical microscopy showed gradual covering of the corroding surface by a layer of inhibitor film with increasing concentration of the additive in the acidic environment. The corrosion inhibition efficiency increased with increasing concentration of the expired drug, reaching a maximum of 73.24% for 8.0 mM of expired paracetamol directly dissolved in the acid. Expired paracetamol acted as a mixed-type inhibitor for mild steel in 0.5M HCl and the corrosion inhibition process was spontaneous. All analyses agreed that expired paracetamol drug is capable of inhibiting corrosion of mild steel in HCl and that the corrosion inhibition is achievable without prior pretreatment. The research is fundamental as it attempts to lay some groundwork for further research towards developing viable and marketable product from this category of materials.

Abstract: This research evaluates the performance of hot mix asphalt modified with fly ash and waste foundry sand for road development. Preliminary tests were conducted to determine material properties. Hot mix asphalt samples with varying percentages of granite, sand, stone dust, and bitumen (5%, 5.5%, 6%, 6.5%, and 7%) were produced using ASTM D6927 Marshall mix design. The optimum bitumen content (OBC) was found from the mix to be 5.7%. Using the same mix design, bituminous mixtures were created with waste foundry sand as a partial replacement for fine aggregate (10% - 50% at 10% intervals), along with granite, stone dust, and 5.7% bitumen (OBC). The mix with 40% replacement performed optimally. A new mixture, incorporating granite, sand, fly ash (10% - 60% replacement for filler material, at 10% intervals), and 5.7% bitumen (OBC), was produced. The optimal replacement percentage was 50%. A combination mix of the materials, based on derived optimums, achieved a stability value of 26.09 kN, meeting the Asphalt Institute's criteria. Microstructural analysis indicated a densely packed agglomeration of particles, implying good strength properties. This research demonstrates the viability of waste foundry sand and fly ash as alternative materials, enhancing the strength and flexibility of hot mix asphalt. Reusing these waste materials in road construction is a positive step towards sustainability.

Abstract: Concrete is a construction material that is widely embraced worldwide with a major disadvantage of environmental unfriendliness arising from the production process of cement, one of its vital components. Recent studies have found that replacing cement with pozzolans increases compressive strength, durability, and occasionally workability, although at a low replacement percentage. The low replacement level obtained can be improved upon with the use of superplasticizer to further enhance the workability and the compressive strength. Therefore, the primary objective of this study is to determine the effects of adding Costamix 200 superplasticizer and partially replacing cement with sawdust ash (SDA) for cement on the mechanical properties of the resultant concrete. Waste sawdust was collected, dried, and then burnt in a furnace for 60 minutes at 700°C. Concrete samples were made using 150 x 150 x 150 mm³ rectangular and 100mm cylindrical molds using a 1:2:4 mix ratio, 0.55 water cement ratio, a constant dosage of 1.8% superplasticizer (Costamix 200), and SDA at 0%, 5%, 10%, 15%, 20%, and 30% SDA respectively. The concrete samples were tested at 7, 14, 21, and 28 days for bulk density, split tensile strength, and compressive strength were carried out. The outcomes of the research show that the presence of costamix 200 and SDA at 0%, 5%, 10%, 15%, and 20% cement substitution resulted in compressive strength range of 18.91 N/mm² to 25.00 N/mm² at 28 days. The optimum value of 25.00 N/mm² was recorded for 15% replacement making it ideal for use in structural applications such as beams, slab and column.

Abstract: This study focuses on eliminating cracks partially in structures by adopting bacteria-based fibre and steel reinforced self-healing concrete. Two bacteria of the genus Bacillus were used, one was cultured from soil, while the other was cultured from parkia. These were subcultured using an algae medium to produce 13500 ml of washed bacteria cells, which were immobilized in 1,500 ml of silica gel. A nutrient solution was also prepared by mixing 171 g of yeast extract, 1710 g of urea, and 1710 g of calcium lactate in water. Water, polyvinyl alcohol (PVA), bacteria cells, and silica gel contributed to the total water content at a ratio of 0.22, 0.03, 0.225, and 0.225 respectively. 81 concrete cubes of and 72 reinforced beams of were cast using 1:2:4 mix ratio. Cracks were created on the surface of the cubes after casting with a 0.6 mm steel plate and were cured for 7, 14, and 28 days. After curing the reinforced beam for 14 days, cracks were created on 36 beams (healed specimen) out of which 18 numbers were cured for 7 days and the remaining were cured for 14 days. 18 beams out of the remaining 36 beams (sound specimen) were tested at 7 days while the remaining 18 were tested at 14 days. The compressive strength, water absorption, and sorptivity results showed that Bacillus spp. (from soil) performed better than the control and Bacillus spp. (from parkia).

Abstract: The characterisation and insulating efficiencies of sawdust and rice husk in glass shavings reinforced termite clay-based (GSRTC) composite has been compared. Termite clay was unearthed from the Federal University of Technology, Akure (FUTA) campus in Ondo State. It was processed to obtain 150 μm undersize. Glass shavings were processed to obtain 106 μm undersize. The glass shavings were then mixed with the termite clay in a constant weight proportion of 10%. Sawdust and rice husk were processed to obtain 150 μm undersize. The prepared blended GSRTC powder was mixed with the sawdust, and the rice husk in 2, 4, 6, 8, and 10 wt.%. The resulting mixtures were compacted into cylindrical-shaped samples. The samples were dried and fired in a furnace at 1000°C for 2 hours. The chemical composition of GSRTC composite constituents was studied prior to the production of the composite. The control sample with only 10 wt.% of glass shaving possessed the highest: compressive strength; linear and volumetric shrinkage; bulk density; and thermal conductivity, while the sample with 10 wt.% of sawdust in GSRTC possessed the lowest: compressive strength (1.62 MPa); linear and volume shrinkage; bulk density (0.68 g/cm³); thermal conductivity (0.23 W/m-K).. Conclusively, the additive proportion and type affect composites' physical properties. An increase in additive proportion is accompanied by an increase in porosity, a reduction in porosity and bulk density. The compressive strength and thermal conductivity decreased with increasing additive content. GSRTC composites with sawdust additive possessed better insulating performance. However, GSRTC composite with rice husk additive displayed higher compressive strength.