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Tungsten copper and molybdenum copper composites, with weight percent copper in the range of 20% - 40%, have been produced using the spark plasma sintering (SPS) technique. Other specimens having similar compositions were also developed using the conventional techniques of Liquid Phase Sintering (LPS) and Infiltration. Electrical conductivity measurements showed that the specimens produced by the SPS process had substantially higher levels of electrical conductivity than those produced by the other methods. Relative density measurements showed that the SPS specimens achieved very high densification, with relative densities in the range of 99.1% - 100%. On the other hand, the specimens produced by LPS and infiltration had relative densities in the range of 88% - 92% and 96% - 98% respectively. The superior conductivity of the SPS specimens has been attributed to the virtually full densification achieved by the process. The effect of porosity on electrical conductivity has been discussed and three standard models were assessed using results from porous sintered skeletons of pure tungsten and pure molybdenum.

The fatigue properties of AMCs are affected by low ductility, poor toughness, and resistant to crack growth which is attributed to the reinforcement particles, sizes, and shapes, because the crack growth rate behavior of the composite displays a markedly higher sensitivity to the applied stress intensity (K) than observed in most metals. The use of nano-sized ceramic particles has been reported to strengthen the metal matrix, while maintaining good ductility, high temperature creep resistance, and better fatigue. Based on this background, fatigue properties of Al-Si-Mg/palm kernel shell ash nanoparticles (PKSAnp) was investigated. Sol-gel method was used in the production of the PKSAnp; 4 wt% of PKSAnp was added to Al-7%Si-0.3%Mg alloy to produce A356/4 wt% PKSAnp composites; fatigue properties were determined as per ASTM E466; microstructure of the composite was determined using a scanning electronic microscope; ANSYS bench work software was used determined the factor of safety and fatigue life. The presence of PKSAnp in the alloy has great influences that alter the number of cycles obtained for the composite even at higher temperature. The presence of PKSAnp shifted the curve to a higher number of cycle before failure. The result shows that failure of the alloy will occur before the design life is reached since the minimum value obtained for the alloy is less than one.

Mild steel is the most extensively used carbon steel for numerous industrial applications, where it is exposed to various service environments containing acids, bases and salt solutions. From industrial point of view, plastic deformation and heat treatment are among the essential manufacturing steps in mild steel processing and these steps can implicate its corrosion behaviour. This work investigated the effect of cold plastic deformation and subsequent high temperature heat treatment on the microstructure and corrosion behaviour of mild steel in two different concentrations (0.5M and 1.0M) of sulphuric acid (H2SO4), using the weight loss method. Mild steel samples were cold pressed to thickness reduction of 20%, 40% and 50% and subsequently heat treated at 700oC and 900°C and then air-cooled. The test duration lasted for 25 days and the weight loss measurements were taken at intervals of 5 days. It was observed that corrosion rates of the samples were generally higher in the 1.0M than in 0.5M acid solution. The as-received and heat-treated mild steel samples exhibited higher corrosion rates than the cold-pressed and heat-treated samples. The results indicated strongly that cold working accompanied by heat treatment improves corrosion resistance of mild steel in acidic media.

Photoelectrochemical (PEC) water splitting is a process of separating water into clean hydrogen and oxygen gases using photocatalysts. The major challenge in PEC water splitting is the development of photocatalysts with appropriate properties for efficient and cost-effective practical production of hydrogen. The use of nanocrystalline metal oxides as photocatalysts is one of the promising routes of producing hydrogen fuel efficiently and cheaply. However, the transition metal oxides (TMOs) used today still have tremendous limitations of high cost, low visible light harvesting capacities, inefficient charge separation and transportation, and poor stability in water. The solution to these limitations is being sought by energy materials researchers by exploiting a variety of uncommon properties of TMOs through synthesis and combination of TMOs to form various mixed transition metal oxides (MTMOs) thin films and MTMOs architectures. Thus, this work focused on the review of various TMOs and MTMOs and the strategies attempted to improve the efficiency of two basic reactions of evolution hydrogen and oxygen evolution in PEC water splitting. The major outcomes of this survey are: (a) major research efforts in this direction focused on adjusting the chemical composition and modifying morphologies of the materials using nanotechnology processing routes that led to the creation of thin thicknesses, high surface areas and active sites, and enhanced electrocatalytic activities of the metal oxides; (b) despite advances in finding a cheaper and more efficient alternative to Pt cathode, the electrocatalytic activity of TMOs is still much lower to the state-of-the-art Pt cathode, and therefore simple and effective strategies are still required to develop effective metal oxide-based photocathode for hydrogen production.

Characterization is an indispensable tool for understanding the structure–property-processing relationship in all material classes. However, challenges in self-healing materials characterization arise from the preparation routes, material types, damage mechanism and applications. Here, the discourse surveys the exploits, advances and challenges encountered within various characterization methods that have been exploited to reveal the damage-restoring processes in some material classes, namely metals, polymers, ceramics, concretes and coatings. Since there is no unified characterization procedure for the different classes of materials displaying self-repairing capabilities, the outcome of this discourse contributes to the advancement of knowledge about understanding self-healing testing procedures. An overview of methods, challenges and prospects toward self-healing property standardization at different length scales has been discussed.

The corrosion and surface characterizations of aluminium alloys reinforced with mussel shell powder (MSP) were studied. Different weight percentages of 3, 6, 9, 12 and 15 wt% MSP were used to develop metal matrix composites for the investigations. The (MSP) was characterized by X-ray fluorescent (XRF). The alloy and the composites were subjected to corrosive medium at various concentrations (1, 1.5, 2, 2.5 and 3 M) of HCl using gravimetric-weight loss and potentiodynamics polarization techniques. Characterizations of the alloy/composites by scanning electron microscopy (SEM) and Energy-dispersive X-ray (EDS) were used to show the degree of attack of acidic solutions on their surfaces. The temperature and time were varied in the range of 30–60 °C at 10 °C interval, and 24 to 144 h at 24-h interval, respectively. The corrosion rate of the composites increases with increase in the reinforcement of mussel shell powder, temperature and the acid concentrations and was in the sequence of 333 K > 323 K > 313 K > 303 K. The unreinforced alloy exhibited slightly superior corrosion resistance when compared to composites in HCl at various concentrations. This was due to the reinforcements that constitute different compounds such as CaO, SiO and FeO, which may become anodic/cathodic to the matrix, thereby increasing the corrosion rate of the composites. The icorr of the composites increase with increase in the reinforcements. Pits formations were seen on the coupons which indicated intergranular corrosion attack by the acidic medium and increase as the acid concentrations increase. The results of weight loss were in good agreement with those of characterizations and electrochemical techniques. The result of the work lead to the following conclusion that the composite cannot be used either for holding HCl solution or as a structural material where HCl solution is found. This is because it will selectively dissolve the composite, leaving behind an altered residual structure based on the results of weight loss, and the potentiodynamics polarization.

2 Abstract: Although martensitic stainless steel materials are not used in large quantities compared to austenitic and ferritic grades, they play a huge and often unseen part in our modern world due to their combination of strength, toughness and moderate corrosion resistance. However, after welding the martensitic stainless steel tend to lose their mechanical/microstructural integrity. In this study, the microstructures and mechanical properties of a welded AISI 410 martensitic stainless steel after different heat treatments were studied, with aims to restore the hardness and improve grain refinement of the materials. The results show that the structures of the steel after austenitizing treatment at 1020°C are of lath martensite mixed with a small amount of retained austenite. Apart from TP2 specimen, where martensite phase was transformed into ferrite structure, the structures of the tempered steel are mixtures of tempered martensite, carbides and reversed austenite dispersed in the martensite matrix. The result indicated that the tempering regimens (500, 600 and 700°C) carried out improved the hardness and grain refinement leading to the existence of finely distributed carbides in the materials. TheTP3 specimen experienced secondary hardening phenomenon, displays the best comprehensive mechanical properties and has the highest hardness value of 370.7 HV close to the parent metal after tempering at 700 °C.

Nanoscale materials have larger surface areas than similar masses of bulk materials. As surface area per mass of a material increases, a greater amount of the material comes into contact with the surrounding materials, thus affecting reactivity. The benefit of a greater surface area and improved reactivity in nanostructured materials is that they help to create better catalysts and support the “functionalization” of nanoscale material surfaces for applications ranging from drug delivery to more affordable modes of producing and storing energy. Electrochemical methods offer one of the best approaches to such characterization, and there is a growing need for practical exercises that illustrate fabrication and facilitate the electrochemical analysis of nanomaterials and nanostructured surfaces. Here, we describe the basic principles and significance, techniques, and challenges of characterizing nanomaterials by electrochemical method.

Iron-based biodegradable metals have been shown to present high potential in cardiac, vascular, orthopaedic and dental in adults, as well as paediatric, applications. These require suitable mechanical properties, adequate biocompatibility while guaranteeing a low toxicity of degradation products. For example, in cardiac applications, stents need to be made by homogeneous and isotropic materials in order to prevent sudden failures which would impair the deployment site. Besides, the presence of precipitates and pores, chemical inhomogeneity or other anisotropic microstructural defects may trigger stress concentration phenomena responsible for the early collapse of the device. Metal manufacturing processes play a fundamental role towards the final microstructure and mechanical properties of the materials. The present work assesses the effect of mode of rolling on the micro-texture evolution, mechanical properties and biodegradation behaviour of polycrystalline pure iron. Results indicated that cross-rolled samples recrystallized with lower rates than the straight-rolled ones due to a reduction in dislocation density content and an increase in intensity of {1 0 0} crystallographic plane which stores less energy of deformation responsible for primary recrystallization. The degradation resulted to be more uniform for cross-rolled samples, while the corrosion rates of cross-rolled and straight-rolled samples did not show relevant differences in simulated body solution. Finally, this work shows that an adequate compromise between biodegradation rate, strength and ductility could be achieved by modulating the deformation mode during cold rolling.

A high strength-ductility combination is a critical mechanical property requirement for biodegradable metals such as pure iron (Fe) deployed for cardiovascular implant applications. However, improving strength and ductility simultaneously is a very challenging task because strength and ductility are mutually exclusive. The main target of this work was to achieve homogeneous and fine grain structure in pure iron (Fe) that would enable adequate strengthductility combination via thermomechanical process of cold rolling and recrystallization annealing. Pure Fe samples were subjected to various degrees of cold rolling followed by recrystallization annealing at 550°C, 670°C, 800°C and 900°C, microstructural examination and the mechanical property evaluation. Thermomechanical processing restored ductility, refined microstructure reducing grain size from 29.6 µm to 14.6 µm and 13.8 µm, which led to 44.7% and 48.2% increase in yield strengths for the pure Fe cold rolled to 75% and 85% reduction and annealed at 550°C, respectively.Keywords: grain size evolution, mechanical properties, pure iron, thermomechanical processing, biodegradable.

In the present study, the structural modification of sand cast Al-12wt%Si alloy with sulfur/sodium and its effect on mechanical properties were investigated. Different addition levels of sulfur and sodium were used to modify and produce castings of the same shape and size from the alloy. The results indicated that the addition of sodium or sulfur to eutectic Al-Si alloy can modify the Al-Si eutectic morphology from needle-like eutectic silicon structure to fine-scale eutectic silicon structure with significant improvement in mechanical properties of the alloy. The optimum levels of modification by sodium flux (60% NaF and 40% NaCl) and sulfur were found to be 0.6% - 1.0% and 0.02% - 0.05% of the weight of the alloy respectively. The alloy modified with 0.6% Na flux had the best mechanical properties closely followed by the one modified with 0.02% sulfur. Over modification of the alloy with sodium produced over modification band which consisted of aluminum dendrites and coarse silicon particles in the microstructure of the alloy. Increase in concentration of sulfur decreased the degree of fineness of the eutectic silicon structure with significant decrease in mechanical properties of the alloy and this is suggested to be as a result of the presence of a brittle sulfur compound at the grain interfaces of the alloy.

The development and characterisation of new metallic biomaterials that contain non-toxic and non-allergic elements but possess low elastic modulus and low biodegradation rates, has become a topic of serious investigation in orthopaedic implant application. The lowering of elastic modulus and improving of corrosion resistance can be achieved by specific chemical alloying and super-elasticity effects, associated with a stress-induced phase transformation from the BCC metastable beta phase to the orthorhombic α″ martensite. Using this framework, this paper focuses on the effect of Nb and/or Zr micro-additions on the elastic modulus/yield strength balance and discusses microstructure, and the mechanical and electrochemical behaviour of four new β-Ti-8Mo-xNb-xZr (x=2-5) alloys, using tensile tests, X-ray diffraction, SEM characterisation, ultrasound technique and potentiodynamic polarisation methods. The results reveal that the alloys exhibit a pronounced microstructural sensitivity response, with alloying elements and excellent agreement between β-stability and high mechanical strength, with increasing Nb additions. Although all the alloys possess excellent corrosion resistance and low Young׳s modulus, Ti-8Mo-4Nb-2Zr alloy, which consists of β+α'' phases, exhibits a low Young modulus of 35GPa, which is lower than those of the commercial alloys already used in biomedical implantation. The significant corrosion resistance, nontoxicity and better mechanical compatibility are properties pertinent to preventing stress shielding and bone resorption in orthopaedic implant applications.

Pure iron has been demonstrated as a potential candidate for biodegradable metal stents due to its appropriate biocompatibility, suitable mechanical properties and uniform biodegradation behavior. The competing parameters that control the safety and the performance of BMS include proper strength-ductility combination, biocompatibility along with matching rate of corrosion with healing rate of arteries. Being a micrometre-scale biomedical device, the mentioned variables have been found to be governed by the average grain size of the bulk material. Thermo-mechanical processing techniques of the cold rolling and annealing were used to grain-refine the pure iron. Pure Fe samples were unidirectionally cold rolled and then isochronally annealed at different temperatures with the intention of inducing different ranges of grain size. The effect of thermo-mechanical treatment on mechanical properties and corrosion rates of the samples were investigated, correspondingly. Mechanical properties of pure Fe samples improved significantly with decrease in grain size while the corrosion rate decreased marginally with decrease in the average grain sizes. These findings could lead to the optimization of the properties to attain an adequate biodegradation-strength-ductility balance.