I. El-Mahallawi

Mechanical Properties and Wear Resistance of Semisolid Cast Al2O3 Nano Reinforced Hypo and Hyper-eutectic Al–Si Composites

The present investigation studies the prospects of using nanoparticles as reinforcement ceramic powders to gain improved performance of hypo and hyper eutectic Al cast alloys. A series of castings were prepared using A356 and A390 as the matrix alloy and alumina nano-powder in 40 nm size as the reinforcement. The nanoparticles were added to the molten slurries with stirring with different fraction ratios ranging from (0, 1, 2 and 4 wt%) in the mushy zone using a constant stirring time for one minute. To evaluate the results, the alloys were further characterized by various tribological and mechanical characterization methods. The results showed higher strength values with improved ductility compared to the monolithic alloys under the same casting conditions. The results also showed improvement in the wear resistance of the nano-reinforced alloys. The scanning electron microscopy of the fracture surface and the wear surface revealed the presence of nanoparticles in the interdendritic spacing and this confirmed with EDX analysis of these particles. The data obtained from the experimental work in this study together with previous published work by the authors were statistically analyzed using analysis of variance (ANOVA) to define the significant factors on both ultimate tensile strength and ductility and their level of confidence, using the orthogonal array L8. Response surface methodology (RSM) was used to build a model relating the type of matrix and nanoparticles addition to the ultimate tensile strength (UTS). The results have shown that the percent of the nanoparticles additions have a significant effect on the tensile properties of the alloys.

The Effect of Heat Treatment on the Properties of Friction Stir Processed AA7075‐O with and without Nano Alumina Additions

In this study, four passes friction stir processing (FSP) were applied on AA7075-O with and without the incorporation of alumina nano-particles (Al2O3) of average size 40nm. FSP parameters were constant at 500rpm and 40mm/min speed with tilt angle of 30. FSP rotation direction applied on clockwise and then counters clockwise direction every two passes. The friction stir processed (FSPed) materials were section and solution treated at 515C for 1.5hrs that followed by age hardening at 120C for 12, 24 and 36hrs. The effect of heat treatment regimes on the microstructure and hardness were examined. The microstructure and hardness after HT were compared with that of as FSPed material in each case. It has been found that in case of as FSPed material without any HT the effect of nano-alumina particles is significant in hardness increase relative to the one without powder. However, applying heat treatment regime has resulted in a slighter difference in the hardness between the two cases with and without nano particles additions.

Effect of Nano-Graphite Dispersion on the Thermal Solar Selective Absorbance of Polymeric-Based Coating Material

The basic part of solar water heaters is the collector and the main functional part of the collector is the absorber layer. In this work, a commercial locally available black painting (PACEN code 10382 colour 890), used for swimming pools solar heating, was modified by adding nano-graphite dispersion. The effect of nano-graphite particles percentage on the spectral absorbance of the material was examined on samples containing two values of 1.5 and 2.5% nano-graphite particles by weight. Fourier transform spectroscopy (FTIR) analysis was also used to identify the functional groups in the developed material. A simple experimental setup was designed to evaluate the performance of the developed nanodispersed selective coating polymeric based material, by measuring the increase in temperature of circulating water. It was shown that adding 1.5–2.5% nano-graphite particles to a polymer based black coating causes an increase in the optical absorptance, and an increase in the circulating water temperature.

Microstructure and Hardness of Subzero Quenched and Heat Treated Ti-6Al-4V Alloy

Titanium is one of the most important materials nowadays with promising lightweight demanding applications. However, despite its high strength-to-weight ratio, high temperature stability and high corrosion resistance, it has relatively low hardness. It is shown in this work that enhanced hardness values could be obtained for Ti-6Al-4V Alloy after heat treatment consisting of subzero quenching in a medium made up of dry ice and alcohol, followed by an aging treatment. The proposed heat treatment resulted an increase of 25% in the hardness of the alloy, compared to 5% reported in literature.

Thermoelectric Behaviour of Polyvinyl Acetate/CNT Composites

In this work an organic polymer/carbon nanotubes composite is introduced for low cost, versatile, nontoxic, light weight and high performance thermoelectric materials. Organic polymers have low thermal conductivity which is desirable for thermoelectric field. Composite films of polyvinyle Acetate and multi wall carbon nanotubes (MWCNT) are demonstrated as a new candidate material for thermoelectric application. MWCNT wt. percentage ranging from 1 to 70 wt% were manufactured and tested for thermopower and electrical conductivity. Dioctyl sodium sulfosuccinate is used as the wetting agent in ratios of 2, 25 and 100% of CNT weight content. A study of the effect of the dispersantto CNT ratio on the electrical conductivity and thermopower of the composite was also carried out. The composite thermoelectric properties were measured as a function of CNT concentration at room temperature.

Effect of Heat Treatment on Friction-Stir-Processed Nanodispersed AA7075 and 2024 Al Alloys

Friction stir processing (FSP) is gaining wide recognition in producing surfaces with high hardness and enhanced properties for light weight transportation application and armored vehicles. This work compares the effect of T6 peak-aging heat treatment on the toughness properties and the aging precipitation behavior of friction stir processed and nanodispersed AA2024 and AA7075 alloys. Plates of aluminum alloy AA7075-O with and without the addition of alumina nano-particles (Al2O3) of average size ~40 nm were FSP. The AA2024 nanodispersed alloys were prepared by casting, then were FSP. Combining nanodispersion and friction stir processing with peak-aged condition has shown to be an effective route in enhancing the elongation % of AA2024 alloy to double that of the T6 peak aged condition, and improving the impact toughness of AA7075 by 35% compared to the peak aged condition. The presence of nanodispersions affects the precipitation behavior of both AA2024 and AA7075 in peak aged condition, where the precipitates attach themselves to the nanoparticles and spinel type precipitates form resulting de-acceleration of the aging process.

Welding-associated failures in power boilers

This chapter provides a review on some important welding considerations that need to be considered to minimize chances for in-service failures of three of the most important steels (austenitic, duplex, and creep-resistant steels) used in manufacturing parts of power boilers. The service conditions for power boilers provides the three necessary conditions (susceptible microstructure, state of stress, and corroding environment) causing stress-corrosion cracking to end the life of parts. The review shows how failure is an end result of wrong material selection, or wrong welding conditions that do not count for possible metallurgical changes. In addition to proper material selection, the study highlights the significance of considering and understanding metallurgical related issues before adopting the welding route and the selection of the welding parameters.