[en] Corrosion is a major concern in the industrial application of ferrous alloys due to enormous cost involved in damages, maintenance and corrosion control. Material scientists increasingly use statistical methods to speed up material design, due to the need for several process parameters in corrosion inhibition method. This study focuses on optimization of three main contributing parameters; inhibitor concentration, exposure time and temperature on the austenitic stainless steel (SS) Type 316 corrosion inhibited through a novel eco-friendly waste material. Response surface method (RSM) was used for evaluation of experimental process variables influencing SS corrosion. The effect of changes in the level of these variables on stainless steel corrosion was studied using Box Behnken design. The optimum levels of process parameters were studied using quadratic regression model coupled with desirability approach. The relationship between predicted and experimental values shows the accuracy of the developed model. Morphologies of the corroded surfaces are examined via scanning electron microscope equipped with energy dispersive x-ray spectroscopy (SEM/EDX). The study showed that RSM is an effective statistical method to predict optimum operating parameters of the inhibitor studied in acid solution required to reduce corrosion rate of stainless steel. (paper)

[en] Eggshell powder (ES) inhibitive effect on Type 316 austenitic stainless steel (SS) corrosion in sodium chloride and sulfuric acid solutions was studied using weight loss, linear polarization, scanning electron microscopy, and energy-dispersive X-ray spectroscopy (SEM/EDX) techniques. Experimental observation proves the inhibitor to be effective in both media with inhibition efficiencies of 99.99 and 94.74% owing to the inhibitive action of ES molecules in the chloride and acid solutions. Stainless steel samples in chloride solution have significantly lower corrosion rate values than stainless steel samples in sulfuric acid solution at all concentrations studied. The preferential adsorption of residue ES monomers in the inhibitor decreased the corrosion rate value. Polarization curve measurements show that ES is a mixed type inhibitor for SS corrosion in 0.5 M H₂SO₄ and 3.5% NaCl solutions. The ES inhibited the SS corrosion in both studied media and its inhibition depends on exposure time, concentration, and environment. Stainless steel ES adsorption follows Langmuir adsorption isotherm. SEM/EDX investigation shows less corroded surface, fewer pits for SS in NaCl/ES solution with slight deduction in the chromium composition percentage, and other alloying elements compared to SS sample in H2SO4/ES solution. The applied techniques explained that ES is an effective inhibitor for Type 316 SS in NaCl solution than in H₂SO₄ solution. Good agreement between linear polarization and weight loss results was observed.

[en] With everyday advancement in laser cladding technology, hard-faced materials have been considered as excellent candidates for tribological applications. In this study, Co–Ni intermetallics were synthesized on Ti–6Al–4V substrates using a 3 kW Rofin Sinar Ytterbium laser. Effect of the relationship between the laser parameters: powder composition, laser scan speed and laser power on the hardness values and tribological resistance of the coatings were studied. Microstructural examination and analysis were performed on resultant coatings using scanning electron microscope equipped with energy dispersive spectrometer. The coatings exhibited a good metallurgical bonding between the coatings and the substrate. Microhardness test was conducted on the coatings while the tribological behaviour of these coatings were also observed under a load force of 100 gf. The relationship between the microhardness and wear depth showed a tremendous benefit of the coatings to Ti–6Al–4V surfaces during abrasion. Phase analysis, using x-ray diffractometry, showed newly developed structures which may account for the increased microhardness values of the coatings as well as enhanced wear resistance. (paper)

[en] Heat transfer in materials during laser material processing serves as a key indicator to existing phases in the material, which governs the mechanical and chemical properties of the material during service. Without the knowledge of the property and behaviour of a material under service, loss of lives and values may be inevitable. This study presents the numerical modeling of the effect of laser parameters on the nature of phases present on the surface of Ti-6Al-4V alloy via heat transfer phenomenon. COMSOL 5.3a software was used to create a model of Ti-6Al-4V substrate, subjected to laser radiation during laser surface cladding. Boundary conditions were applied to the surfaces of the block samples while temperature distribution was measured with set boundary probes. Isothermal plots revealed that the material heating from the free surface was not sufficient enough to develop a large zone of phase change along the depth of the substrate. This was related to the high cooling rate of laser cladding. (paper)

[en] The influence of varied process parameters involving three levels of temperature, pressure, heating rate and dwell time on the microstructure, densification and microhardness of spark plasma sintered Ti-6Al-4V/h-BN binary composite was studied. Taguchi design method was adopted to randomize the SPS process parameter levels. The microstructure was analyzed by optical microscopy, densification was determined based on the principle of Archimedes and Vickers microhardness tester was used to evaluate the microhardness of the sintered composite. The consolidation of Ti-6Al-4V powder and nanoparticles of 3 wt.% of h-BN via SPS produced nearly full theoretical densification of 99.77% and the sintered composite gave a microhardness value of 710.37 HV which is more than 200% that of the monolithic alloy. The best combination of relative densification and microhardness were obtained at the sintering parameters of 1000 °C of temperature, 40 MPa of pressure, 100 °C/min heating rate and 15 min of dwell time. Generally, it was found that improved microstructure, densification and microhardness were influenced by the high temperature of sintering and low rate of heating that gave room for adequate diffusional mass transport resulting in solid bonding between the particles of the matrix and the ceramic reinforcement. (paper)

[en] High-temperature ceramic–metal (cermet) coatings are highly viable in engineering applications involving ablative influence of hot environments. Thus, the synthesis of two different compositions (75Ni:20SIC:5ZrB₂ and 70Ni:20SiC:10ZrB₂) of Ni–SiC–ZrB₂ cermet coatings on Ti–6Al–4V (Grade 5) alloy using laser cladding technique was successful in the present study. Phase analysis was conducted on the coatings to investigate the existing phases using x-ray diffraction, while scanning electron microscope (SEM) equipped with energy-dispersive spectrometer (EDS) was used to examine microstructural morphology of the cermet coatings. Wear and oxidation tests were performed on both the as-received sample and the laser cladded samples with the use of a CERT UMT-2 ball-on-disk reciprocating tribometer and PerkinElmer TGA 4000 thermal analyzer, respectively. High diffraction peaks of ZrSi₂, Ni₃Ti, and Ni₃B indicated micromigration and in situ reactions among elemental constituents between the coatings and the substrate. Friction coefficients and microhardness values of the coatings proved enhanced tribological and hardness properties in comparison with the Ti–6Al–4V substrate, accordingly. After oxidation, the as-received sample revealed oxide phases of TiO₂, SiO₂, and Al₂O₃, while the oxidized coatings showed protective oxides of ZrO₂, NiO, Ni₃TiO₅, and ZrSiO₄. Although the coatings were characterized with microcracks and intense dissolution of SiC particles, the coatings showed good metallurgical bond with the substrate.

[en] In the research study, incorporation of Cu with hard SiC and Ni micron-sized particles was applied in the fabrication of a multifunctional copper-based metal matrix composite using spark plasma sintering. The developed spark plasma-sintered Cu–xNi and Cu–xNi–xSiC composite charateristics were studied by conducting morphological analysis, electrochemical, microhardness, and densification tests. Analytical equipments used include scanning electron microscopy, equipped elemental dispersive spectroscopy, X-ray diffractometry, and Vickers hardness tester. Electrochemical characterizations using potentiodynamic polarization for the electrochemical stability of the sintered composite in 0.5 M H2SO4 was also carried out. 96% densification and 90.20% corrosion resistance were obtained. The Cu–Ni composite showed an increase in corrosion resistance as a result of Ni addition in H2SO4 environment, while Cu–xNi–xSiC composite showed a slight decrease in corrosion resistance with excess SiC. It can be inferred that Cu–xNi and Cu–NixSiC composites improves the hardness values and corrosion resistance for electrical application when applied.

[en] Improvement of wear behaviour and mechanical properties of polymers as bulk and surface coating materials for advanced engineering applications have been research interest. Improved wear resistance and mechanical properties were achieved in this study by incorporation of surface modified graphene and titanium dioxide nano-powder in poly (vinylidene fluoride) matrix via solution blending and melt compounding. The morphology of the nanocomposites was studied using scanning electron microscope (SEM). The nanocomposites showed significant reduction in wear volume and enhanced mechanical properties due to the presence of surface modified nanofillers. About 76.5% reduction in wear volume, 52% and 186.5% increase in tensile strength and Young modulus respectively were achieved in this study. The surface modification of the nanofillers was essential in dispersion of the nanofillers in the polymer matrix and the improved properties recorded. Such nanocomposites can find applications as protective surface coating materials for high frictional condition and bulk materials for automobile and aerospace components. (paper)

[en] The utilization of the hybrid reinforced aluminium metal matrix composites has over the time emerged as the leading promising composite materials due to their excellent enhanced properties. The corrosion performance and thermal behavior of aluminium based composite reinforced by hybrid Nano ceramic particulates have been very essential in most structural applications. The corrosion rate, polarization resistance, cathodic protection, and anodic dissolution remain the essential corrosion properties while the variation of material mass gain or loss as a function of the temperature determine the thermal stability of the composite materials. In this work, the investigation of the corrosion behavior in the acidic environment has been achieved for high-grade AA8011-ZrB₂ + Si₃N₄ composites under the ambient temperature condition, while the thermal response of the developed composites was examined in an inert nitrogen atmosphere with the heating rate ranging from 30 °C to 900 °C at 20 °C min⁻¹. AA8011 reinforced ZrB₂ + Si₃N₄ hybrid metal matrix composites were fabricated by liquid metallurgy technique. The corrosion features and thermal stability of the developed hybrid composites with varying percentage weight fraction of the Nanoceramic particulates have been examined. From the experiment, it was observed that the corrosion rate decreases with increase in the Nano reinforcement. The developed composites were stable under high temperature and the composite with 20% weight proportion of the Nanoparticulate was observed to be more thermally stable than the unreinforced alloy. (paper)

[en] Percolative polymer nanocomposites (PPNC) such as polymers reinforced with graphene and/or carbon nanotubes have attracted research attention on the effort to improve the energy storage capacity of polymeric materials. Such nanocomposites often associated with high energy dissipation and dielectric loss. Recently, research interests have shifted from increasing dielectric constant of PPNC to the reduction of dielectric loss associated with such nanocomposites. Various means have been employed in the suppression of energy dissipation and dielectric loss of PPNC via covalent and non-covalent modification of percolative nanofillers (PnF). For instance, chemical and mechanical (physical) techniques of insulating PnF have been employed in the reduction of current leakage, high mobility of charge carriers and direct contact of PnF in the polymer matrix. A significant reduction in the energy dissipation of PPNC has been achieved so far. However, there is still a need for further reduction of energy dissipation associated with such nanocomposites to realize their practical applications as dielectric energy storage materials. Therefore, this review summarised the various techniques employed by various studies in the reduction of energy dissipation associated with PPNC and results achieved using the techniques. The review was concluded with present challenges and the way forward to further address the challenges facing PPNC as dielectric energy storage materials.