Journal of Advanced Processes in Materials Engineering
Year:2010 | Volume:4 | Issue:3 (14)|Papers Count:8

Alumina is an important material in industrial applications. In the present article, an Al2O3 nanopowder was synthesized by a wet chemical method using AlCl3· 6H2O and aluminum powder. The effect of pH on the structural evolutions and morphological characteristics of the nanopowder were investigated by X-ray diffractometry, scanning electron microscopy, thermal analysis and Brunauer-Emmett-Teller surface area measurement. The results showed that an amorphous powder and AlOOH were formed at pH values of 2 and 9 respectively. The surface area of synthesized powders at pH value of 2 and calcined at 800oC was 55 m2/g. The surface area of the powder increases to 170 m2/g, by increasing the pH value up to 9. Nanopowders in alkaline solution were finer than acidic solution.

Metal matrix composites reinforced with TiC have achieved a lot of attention in recent years due to their excellent mechanical properties and wear resistance. Thus combustion synthesis of FeCo-TiC was studied in this research work. Powders of graphite, Cobalt and ferrotitanium (rather than elemental Ti which is very expensive) were used as starting materials. Raw materials were mixed and compacted into pellets. Samples were ignited in a tube furnace under flow of argon. The products were characterized by SEM and XRD. The results show that combustion synthesis of the powders leads to the formation of fine TiC embeded in FeCo alloy. The presence of cobalt in the sample resulted in a decrease in ignition temperature. Further reduction in ignition temperature (less than 1080oC) was obtained by milling powder mixtures for 5 minutes. Maximum hardness of explosived products with 23% porosity was 760 HV0.1.

In this research accumulative roll bonding (ARB) process has been used for pure copper (99.9%). The ARB process up to 6 cycles was performed under unlubricated conditions. Texture and microstructure evolution during accumulative roll bonding (ARB) of samples has been investigated. The grain size after six pass is 310 nm. The results indicate that with increasing the number of cycles, the overall texture intensity increases even up to the six rolling pass and a strong texture develops. The main textural components are the brass, TC and Dillamore of which the intensities increase with increasing number of cycles. Grain refinement is slightly decreased after 4 cycles. Evolution of strong texture with very sharp components during the ARB leads to the formation of a band-like structure and prevents the full grain refinement.

9Cr-1Mo steel known for its improved mechanical properties such as low thermal expansion, excellent irradiation resistance to void swelling, high strength and good creep resistance and etc. are widely used for chemical, petrochemical, power generation and nuclear technology. The aims of this research were casting a kind of this steel in laboratory scale and modify its casting microstructure. After casting, for modifying the inhomogeneous and large grain structure, the samples were preheated at 1150oC followed by hot forge at 650oC with a strain about 1.5. Then deformed samples were annealed in g, g+α and α regions for different times. The effect of deformation and annealing parameters on micro structural characterizations and mechanical properties were studied with microscopically observation and mechanical testing. The optimum heat treatment conditions after deformation for reach to fine and homogenous microstructure with desirable mechanical properties were annealing temperature about 900°C and anneling time about 120 minutes.

In this investigation, NiCrAlY coating was deposited on steel substrate using high velocity oxy-fuel (HVOF) process. Different spray parameters such as spray distance and powder feed rate were applied and the hot corrosion behaviour in molten salt (Na2SO4- 60%V2O5) environment at 900oC was studied. Optical microscope and scanning electron microscopy/energy dispersive spectroscopic analysis (SEM/EDS) techniques were used to analyse the corrosion products. The analysis of the results indicates that the spraying distance and the powder feed rate have a significant effect on the properties of NiCrAlY coatings such as oxygen content and porosity. The coatings prepared by 20 cm spraying distance and 32gr/min powder feed rate have the best corrosion resistance, because of the less oxides.

In this investigation standard Y blocks from Ductile Iron with different percentage of Silicon have been casted in CO2 Silicate Sodium molds, then standard impact samples were machined and heat treated in different conditions. In the first stage samples were Austempered and impact tested was done at room temperature, test samples Austenitization at 875oC in 60 min, and then Austempered at 375oC in 6 different periods of time. Impact test results show that with an increase in silicon content the impact energy were decreased in a specific time. The best impact energy gained in 2.42-2.81 silicon content in 90 min. In the second stage all samples were Austenitization at 875oC in 60 min and Austempered at 375oC in 90 min. Then charpy impact tests carried out in different temperature, the result shown that DBTT were increased with an increase in silicon content.

Cu-Cr alloys with high electrical and thermal conductivity, high strength and good resistance to fatigue and corrosion, as well as good ductility have many applications in industry. These alloys are capable of being age-hardened. As Cr-content in solution before aging increases, their strength increases since more fine particles can be produced in the matrix during ageing stage of hardening. Therefore intensive works have been done to increase Cr solubility in Cu especially by rapid solidification of molten copper containing chromium. In the present work attempts have been done to introduce a method for production of Cu-Cr alloy with acceptable Cr-content with reasonable cost. Results show that maximum solubility of Cr in Cu matrix about 1.12 wt.% can be achieved.

Cu1-xCoxFe2O4 (x=0–1) ferrite nanoparticles were prepared using reverse micelle process. X-ray diffraction patterns demonstrated that single phase spinel ferrites are obtained. The results obtained from vibrating sample magnetometer (VSM) confirmed that with an increase in cobalt content, the saturation magnetization increases. The compositional dependence of blocking temperature was measured using Superconducting Quantum Interference Device (SQUID). Magnetic dynamics of the samples was studied by the measurement of AC magnetic susceptibility versus temperature at different frequencies. The phenomenological Néel-Brown and Vogel-Fulcher models were employed to distinguish between the interacting and noninteracting system. Results exhibited that there is strong interaction among fine particles.