High Entropy Alloys for Aerospace Applications

In the aerospace industry, materials used as modern engine components must be able to withstand extreme operating temperatures, creep, fatigue crack growth and translational movements of parts at high speed. Therefore, the parts produced must be lightweight and have good elevated-temperature strength, fatigue, resistant to chemical degradation, wear and oxidation resistance. High entropy alloys (HEAs) characterize the cutting edge of high-performance materials. These alloys are materials with complex compositions of multiple elements and striking characteristics in contrast to conventional alloys; their high configuration entropy mixing is more stable at elevated temperatures. This attribute allows suitable alloying elements to increase the properties of the materials based on four core effects , which gives tremendous possibilities as potential structural materials in jet engine applications. Researchers fabricate most of these materials using formative manufacturing technologies; arc melting. However, the challenges of heating the elements together have the tendency to form hypoeutectic that separates itself from the rest of the elements and defects reported are introduced during the casting process. Nevertheless, Laser Engineering Net Shaping (LENS™) and Selective Laser Melting (SLM); a powder-based laser additive manufacturing process offers versatility, accuracy in geometry and fabrication of three-dimensional dense structures layer by layer avoiding production errors

Microstructural, mechanical and pozzolanic characteristics of metakaolin-based geopolymer

The use of cement contributes to global CO2 emission and this leads to the depletion of ozone layer,causing global warming. The quest to reduce or eliminate this problem has resulted in the discovery of metakaolin-based geopolymer as an alternative to the use of cement in construction work. In this study, metakaolin obtainedas a result of kaolin calcination from some deposits in Nigeria; Ogun (Imeko), Edo (Okpela), Ondo (Ifon)and Ekiti (Isan-Ekiti) were characterized and used to determine the compressive and flexural strength of metakaolin-based geopolymer concrete (Mk-GPC). Cubes of 150 × 150 × 150 mm were used for the compressive strengthtest and reinforced concrete beams of size 150 × 250 × 2160 mm were produced to test for flexural strength. A water-absorption test was also carried out on Mk-GPC and the effect of ball-milling was assessed on the strengthproperties. The results from the various tests showed that 800°C for 1 hour of calcination of kaolin gives bestcombination of performance properties due to the presence of amorphous silica in metakaolin. Mk-GPC gavehigher compressive strength and at an early age than ordinary Portland cement (OPC) concrete. The water absorptioncapacities of Mk-GPC were higher than the control samples. In the flexural strength test, the reinforcedbeams failed in flexural-shear mode and the shear capacities at 28-, 56- and 90-day curing age of the beams werebetween 0.656 and 0.938 MPa for Mk-GPC beams and between 0.563 and 0.844 MPa for the control beams. Themoment capacities for the beams were between 19.25 and 33.25 (×10³ kgm²/s²) for Mk-GPC beams and were between22.75 and 28.0 (×10³ kgm²/s²) for the control beams. The study has revealed that metakaolin-based geopolymercan serve as an alternative to cement for sustainable construction in the Nigerian construction industry

Effect of Calcination Temperatures of Kaolin on Compressive and Flexural Strengths of Metakaolin-Concrete

The incorporation of pozzolanic materials in concrete construction is progressively increasing. This is due to technological advancement and climate change problems associated with carbon emissions resulting from the large-scale manufacturing of cement and its usage for concrete production. In this study, metakaolin obtained was used to partially substitute cement in metakaolin-concrete. Calcination temperatures of kaolin were varied from 500oC to 800oC at an interval of 100oC for 60 minutes. The metakaolin obtained was used to partially replace cement at 0, 5, 10, 15, 20 and 25 % by weight using a mix ratio of 1:2:4 and 0.4 water-cement ratio. Compressive strength test was carried out at curing ages of 7, 28 and 90 days, while the flexural strength test was performed at curing ages of 28 and 90 days. For both compressive and flexural strengths, 15 % by weight replacement with metakaolin gave the best strength values at all temperatures. An Increase in temperature led to a significant increase in the strength of metakaolin-concrete. ANOVA showed all factors significantly affected the flexural strength (P < 0.1), whilst the calcination temperature was significant (P < 0.1) to the compressive strength. This study showed that metakaolin is a supplementary cementitious material (SCM) and is a potential alternative to cement and can be used in the construction industry.  Also, the calcination temperature of kaolin has a significant effect on the properties of the resulting metakaolin-concrete produced from it

Mechanical and Microstructural Characteristics of Rice Husk Reinforced Polylactide Nano Composite

The application of polylactides in tissue engineering is attracting significant interest. Using renewable; low cost; health and environmental friendly agro waste as reinforcement in electrospun polylactide nano composite fibres reduces the need for petroleum based fillers and enhances the strength of polylactides. In this paper, the morphological, mechanical and water permeability properties of electrospun treated and untreated rice- husk reinforced polylactide- nano- composite fibres are presented. The treated rice- husk particulates were ground, subjected to steam explosion and chemical treatment to remove its lignin and hemi-cellulose contents so as to increase the crystallinity of the filler. The addition of 4wt. and 6 wt. % untreated rice- husk filler increased the tensile strength by 95% and 43% respectively. Young’s modulus, fracture stress, water permeability and other properties are also enhanced. This work shows that; the mechanical properties and biodegradability of scaffolds for tissue engineering can be improved by reinforcing polylactide with rice-husk instead of petroleum- based polymeric- nano- fiber composites

A Morphological Characterization of High Yield Chitin from Periwinkle Shells

Research on obtaining chitin from periwinkle shell is scarce due to the very low yield of chitin from this kind of shell. Thisstudy reports a method of processing periwinkle shells to obtain high yield, bio-medically suitable chitin. The experimentwas designed using IM and 2M concentrations of HCl for demineralization and a 1M NaOH concentration for deproteinization. FTIR, SEM, XRD and DTA analytical tools were used to characterize the extracted chitin. The FTIR spectral, XRD patterns and SEM analysis, revealed the complete removal of calcium carbonate by the acid concentrations used. The particle-like form of periwinkle shell was transformed to sheet-like fiber and globular-like fiber of α-chitin by increasing the concentration of HCl from1M to 2M respectively. The crystal size increased from 11.2Å (1M HCl) to 13.4Å (2M HCl). The yield of chitin from periwinkle shell also increased from 52% to 71% using 1M and 2M HCl respectively. Thus, acid concentrations can be used to alter the structure of chitin with different mechanical properties

Mechanical Strength and Biocompatibility Properties of Materials for Bone Internal Fixation: A Brief Overview

An ideal bone internal fixation material does more than just fracture union. It ensures the preservation of Bone Mineral Density (BMD) and body-bone’s integrity. This has been a major fight in osteosynthesis from the ancient time till date. Animal skeletons that were first used as internal fixations though had some desirable mechanical properties comparable to bones, their usage resulted in mild pus formation, difficulty with resorption of sterile bones and non-union. A shift to metallic bone implants resulted in corrosion and bio-incompatibility, stress shielding, imaging and radiotherapy interference, temperature sensitivity, revision surgery with extreme difficulty, growth restriction, metal-in tissue accumulation, bone-metal elastic modulus mismatch to mention but a few. Advances in osteosynthesis have, however, led to great improvement on metallic bone fixations, yet leaving some fundamental issues unresolved. Exploration of biodegradable polymers and their composites is fast solving most of the problems encountered through the use of skeletal and metallic fixations. Their low Young's moduli and excellent biocompatibility, non-carcinogenicity and bioresorbability have made them viable materials for bone fracture healing. This brief overview covers the biomechanical properties of popular biological materials, metallic fixations and polymeric scaffold

Crab (Brachyura) shell Acid and Alkali Treatments: Influence on Thermal and Structural Properties of Isolated Acetamide-Rich Natural Polymer

Exoskeleton of crab comprises a dominating mineral (calcium carbonate, CaCO3), protein and a natural polymer (chitin). Chemical treatments have been employed at different instances to isolate pure chitin from different sources. It is thus necessary to investigate how this treatment will influence the features of chitin isolated from the same source (crab). In this study, 0.4, 0.8 and 1.2 M hydrochloric acid (HCl) were separately used to demineralize crab shell particles and this was followed by deproteinization with 0.4 and 1.2 M sodium hydroxide (NaOH) at 100 0C.  Results showed that chitin properties were influenced by concentrations of reagents. Fibrils of different forms and surface appearance were observed via Scanning Electron Microscopy (SEM). The highest crystallinity index of 71% was possessed by chitin extracted using 0.4 M HCl and NaOH while 65.5% remained the least displayed by chitin extracted with 1.2 M HCl and NaOH. This trend was similar for chitin’s thermal stability where Thermogravimetric analysis (TGA) results informed that using the highest concentrations of 1.2 M HCl and NaOH provided chitin with 80.12 kJ/mol activation energy. On the other hand, 112.54 kJ/mol was calculated for chitin isolated with the minimum demineralization and deproteinization reagents used in this study

Comparative effects of organic and inorganic bio-fillers on the hydrophobicity of polylactic acid

The use of Polylactic acid (PLA) has been limited in the biomedical field because of its slow degradation profile which is traceable to its degree of hydrophobicity. In this work, 16.67 wt. % of chitosan (Ch), chitin (Ct) and titanium (Ti-6Al-2Sn-2Mo-2Cr-0.25Si) (Ti) powders weremelt blended with PLA and the resulting composites examined using Fourier Transform Infrared Spectroscopy (FTIR). Chitosan was found to reduce the hydrophobic peak due to δs(CH3) in PLA by 13.92%, chitin by 10.65% and titanium by 8.04%. Summarily, the organic biofillers produced more hydrophilic PLA composites than the inorganic filler. The percentage reduction in hydrophobicity renders the developed composites more suitable for orthopaedic applications

Parametric Effects of Fused Deposition Modelling on the Mechanical Properties of Polylactide Composites: A Review

Polymers are generally inferior in mechanical properties to metals which are the current orthopaedic material for osseointegration in many parts of the world today. This assertion also applies to poly(lactic acid) (PLA), a polyester that has been recently found applicable in tissue remodelling. To improve on its mechanical properties, several processing techniques, inclusive of fused deposition modelling (FDM) also branded as fused filament fabrication (FFF), have been used. FDM has been endeared to many researchers because a range of parameters can be combined to bring about widely different mechanical properties. Although the influence of FDM parameters on the mechanical properties of PLA is clear, the tensile, compressive and flexural strengths obtained so far are inferior to human cortical bone. The need to improve on this production technique for improved mechanical properties is apparent in all the works examined in this revie

The Strength characteristics of Chitosan‐ and Titanium‐ Poly (L‐lactic) Acid Based Composites

The problem of bone fracture and the need to avoid revision surgery in osteosynthesis are the critical reasons for the gradual shift from the use of metallic fixations to the polymeric scaffold in the orthopaedic applications. However, the mechanical properties of polymers that have become a substitute for metals need to be improved upon. An attempt was made to improve the mechanical properties of poly(L‐lactic) acid (PLLA), a biopolymer, by loading it with 1.04, 2.08, 4.17, 8.33 and 16.67 wt.% of chitosan (an organic filler) and Ti‐6Al‐2Sn‐2Mo‐2Cr‐0.25Si (an inorganic particle). Melt blend technique was the processing technique. Hardness, compressive modulus and fracture toughness of virgin PLLA improved significantly while the resulting composites were found to be less ductile than unreinforced PLLA. Titanium reinforced PLLA displayed superior mechanical properties over the neat and chitin reinforced PLLA. Compressive modulus values of the developed composites were much lower than the modulus of cortical bone, they were, however, mechanically compatible with the properties of cancellous bone. Optical microscopy images also show the formation of pores which are a catalyst for cell proliferation and cell differentiation