Application of CuCoMnO (x) coat by sol gel technique on aluminum and copper substrates for solar absorber application

Solar thermal heaters are used widely in domestic and industrial applications. The main part of solar thermal heaters is the absorber surface which must have a maximum absorptivity (alpha) and minimum emissivity (epsilon) of solar radiation. This is achieved by application of selective coating on the absorber surface. In the present work, solar selective CuCoMnO (x) spinel films are deposited by sol gel technique using a dip-coating technique on copper and aluminum sheets. The precursor's ratio Co:Cu:Mn applied is 1:3:3. Different precursor molar ratios were combined with a fixed amount of solvents for the coating process. Process parameters such as withdrawal rate, heat treatment, and substrate materials on the coat characteristics and optical properties were studied. The coated metallic samples were heat treated at 450A degrees C for 30 min in the case of aluminum and at 200A degrees C at different times in the case of copper. Optical properties of the coatings, namely absorptivity (alpha) and emissivity (epsilon) were measured and the deposition process parameters were optimized in order to produce the maximum selectivity (alpha/epsilon) values. The deposition parameters were found to influence both the thickness and surface roughness of the coatings. As the coating thickness decreases, the absorptivity increases while the emissivity decreases irrespective of the substrate material. It was also observed from the results that when applying the coat on aluminum substrates, a maximum selectivity value of (alpha/epsilon) = 31 was realized while for the copper substrates a maximum value of (alpha/epsilon) = 81.8 was obtained. The deposited coatings were analyzed using SEM, XRD, and AFM

Microstructure of plasma-sprayed cast iron splats with different particle sizes

The superior wear-resistant property of cast irons is closely linked with their microstructure, in which graphite formation in plasma-sprayed cast iron coatings causes distinct characteristics owing to its self-lubricating property. Since the solidification rate generally affects graphite formation, the optimum in spray parameters such as substrate temperature, ambient pressure, particle size and spray distance is required to slow down the solidification rate, as well as to improve the adhesive strength of splats. In this study, cast iron splats were induced on an aluminum alloy substrate by plasma spraying using alloyed cast iron powder high in silicon and aluminum in a low pressure argon atmosphere. Then, the effects of particle size on the microstructure and adhesive strength of splats were investigated by introducing the correlation between the solidification rate and the microstructure. Spraying with large particles leads to an increase in the number fraction of disk splats and a slight decrease in their adhesive strength. Cross-sectional observations reveal fine graphite growing in splats nearly perpendicular to the substrate surface

Characterization of the hard anodizing layers formed on 2014-T3 Al alloy, in sulphuric acid electrolyte containing sodium lignin sulphonate

The properties of hard anodizing layers formed on 2014 Al alloy in sulphuric acid electrolyte containing sodium lignin sulphonate were investigated. The corrosion behavior of 2014 Al alloy has been studied using potentiodynamic polarization technique. Anodic layers morphology and composition were examined by scanning electron microscope, energy dispersion X-ray (EDX), X-ray diffraction (XRD) and Fourier infrared spectroscopy (FTIR). The results showed that the corrosion resistance has been enhanced after hard anodizing of 2014 Al alloy. Addition of lignin sulphonate to the sulphuric acid electrolyte significantly improved the corrosion resistance of the anodized 2014 aluminum alloy by adsorption on copper-intermetallic phases. Adsorption of sodium lignin sulphonate on oxide surface has been confirmed by SEM, EDX, and FTIR. Phenolic and carboxylic groups in sodium lignin sulphonate are functional groups, which are responsible of complex formation on oxide surface. The morphology of the hard anodizing layer is non-homogenous due to the high copper content of 2014 Al alloy. Addition of sodium lignin sulphonate resulted in the formation of anodic layers with more homogeneity and fewer cracks. Keywords: Hard anodizing, Al-Cu alloy, Corrosion, Potentiodynamic polarization, FTIR, Sodium lignin sulphonate, Green inhibitor, SE

Study of the Isochronal Annealing of High Pressure Die-Cast Magnesium Alloy AZ91 by Positron Annihilation Lifetime Technique

Key words: Positron lifetime; isochronal annealing; AZ91 alloy; microhardness; microstructure INTODUCTION Magnesium alloys (light alloys) are of increasing attention for transport applications in the automotive and aerospace industry. The most popularly used magnesium alloys are those based essentially on the Mg-Al system, such as AZ91, AM60B and AM50A. In addition, the poor elevatedtemperature properties of low-cost magnesium alloys have now become a critical issue for widespread applications of magnesium alloys [1] . Several investigations have been performed using positron annihilation lifetime (PAL) for studying defects in magnesium and magnesium alloys [2-6]. Positron Annihilation Lifetime (PAL) is a specific technique for the detection of open volume defects such as vacancies, vacancy clusters, dislocations, grain boundaries in materials (metals and alloys) and free volumes for polymers Mg, 9%Al -and 1%Zn (AZ91) alloy is the most widely used commercial Magnesium alloy and has a good combination of castability, mechanical strength and ductility. Currently, AZ91 alloy is used mainly in the high pressure die-casting (HPDC) form for structural components in the automobile industry. HPDC is a well established process, which is of high efficiency and low cost. However, the HPDC components contain a substantial amount of porosity due to gas entrapment during die-filling and hot tearing during the solidification in the die cavity. Such porosity not only affects mechanical properties, but also denies the opportunity for property enhancement by subsequent heat treatmen

Mechanical behavior and corrosion properties of Ti-7Mo-8Nb alloy for biomedical applications

The present study investigates the microstructural, mechanical and corrosion properties of Ti-7Mo-8Nb alloy manufactured through powder metallurgy. The performance of the developed alloy is benchmarked against cast Ti-6Al-4V. Microstructure examination of Ti-7Mo-8Nb revealed a Widmanstätten structure containing equiaxed β grains along with acicular α phase. In regards to the mechanical properties, Ti-7Mo-8Nb possessed higher compressive yield strength, higher hardness but lower elastic modulus than Ti-6Al-4V. The elastic modulus of Ti-7Mo-8Nb was almost 44.9 GPa, approaching the usually desired value of 30 GPa for cortical bone. Wear test revealed also a lower wear rate for Ti-7Mo-8Nb. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) experiments were carried out for both Ti-7Mo-8Nb and Ti-6Al-4V immersed in Hank’s solution as a simulated body fluid at a temperature of 37 °C. Both experiments revealed higher corrosion resistance for Ti-7Mo-8Nb manifested by lower corrosion and passivation current densities, higher negative phase angle, higher impedance modulus and larger Nyquist semicircle diameter as compared to Ti-6Al-4V alloy. The superior corrosion properties of Ti-7Mo-8Nb are indicative of the development of a more stable passive layer on the surface. The fitting of EIS data into an equivalent circuit suggested the formation of a double oxide layer consisting of an inner compact base passive film along with an external porous layer. The presented combination of high strength, high corrosion resistance along with low elastic modulus puts forward the Ti-7Mo-8Nb alloy as a good candidate for orthopedic biomedical applications

Corrosion and High Temperature Oxidation Behavior of 316L Stainless Steel Joined with Cu-Ag Based Braze Alloys

316L samples of various geometries were joined under Argon atmosphere using Cu-Ag based braze alloys. Following joining, elemental and phase composition across the braze and parent metal interface was characterized with optical microscopy and SEM with EDS. Baseline electrochemical testing was performed on each of the braze alloys in the fired and unfired condition. Additionally, metal-to-metal braze specimens were prepared in order to expose the braze interface to 0.6 M NaCl electrolyte where the free corrosion potential was monitored. Following exposure to the aggressive solution, the corrosion damage morphology was characterized to determine the mode of attack and likely initiation areas. The critical potential for localized corrosion initiation was also investigated for the braze alloys when connected galvanically to 316L samples to determine the impact of brazing on localized corrosion. Initial results indicate dissimilar metal driven corrosion attack at the braze metal interface into the parent 316L as well as preferential dissolution of the Cu rich phase within the braze alloy when exposed to 0.6 M NaCl

Effect of Mg Addition and PMMA Coating on the Biodegradation Behaviour of Extruded Zn Material

Although zinc (Zn) is one of the elements with the greatest potential for biodegradable uses, pure Zn does not have the ideal mechanical or degrading properties for orthopaedic applications. The current research aims at studying the microstructure and corrosion behaviour of pure Zn (used as a reference material) and Zn alloyed with 1.89 wt.% magnesium (Mg), both in their extruded states as well as after being coated with polymethyl methacrylate (PMMA). The grafting-from approach was used to create a PMMA covering. The “grafting-from” method entails three steps: the alkali activation of the alloys, their functionalization with an initiator of polymerization through a phosphonate-attaching group, and the surface-initiated atom transfer radical polymerisation (SI-ATRP) to grow PMMA chains. Electrochemical and immersion corrosion tests were carried out in a simulated body fluid (SBF), and both confirmed the enhanced corrosion behaviour obtained after coating. The electrochemical test revealed a decrease in the degradation rate of the alloy from 0.37 ± 0.14 mm/y to 0.22 ± 0.01 mm/y. The immersion test showed the ability of complete protection for 240 h. After 720 h of immersion, the coated alloy displays minute crevice corrosion with very trivial pitting compared to the severe localized (galvanic and pitting) corrosion type that was detected in the bare alloy