Journal of Advanced Materials and Processing
Year:2010 | Volume:2 | Issue:3|Papers Count:8

In this study the effect of in situ Si3N4 formation in the microstructure of a Cordierite-Si3N4 composite using micro and nano silicon particles was investigated. It was found that micro and nano silicon particles have different reaction with the nitrogen in the matrix of cordierite at various temperatures. Result showed that using nano size silicon powder and increasing surface area formation of silicon nitride bonding will be increased which should be related to Si3N4 formation in low temperature and prevent to reacting with cordierite to form liquid phase during sintering. Additionally it was found that, it is possible to synthesis high porosity cordierite- Si3N4 composite with a good thermal shock resistance.

One of the bellows producing methods is hydro forming process. Some factors of hydro forming process such as internal pressure and velocity of die close, can affect final characteristic of produced bellows such as thickness distribution. One of the most important parametersof control in bellows is wall thickness distribution. In this paper, the thickness distribution of produced bellows and the effect of hydro forming process parameterswas investigateusing  analytical and experimental methods together with finite element simulation using ABAQUS/Explicit FEM software.The results which are obtained from analytical, experimental and finite element methods showed good agreement with each other. Prediction of thickness distribution of bellows using applied FEM method in this research could be used as a basis of designing a new type of the metal bellows.

Techniques of severe plastic deformation have been of continual interest in the production of novel metallic microstructures. Among these, accumulative roll bonding has been extensively used to produce multi-layered composites. Multi-layered Al/Ti composites were produced by accumulative roll bonding (ARB) process using Al 1100 and commercial Ti sheets. Mechanical properties of these multilayer composites were evaluated at different passes of ARB process. During ARB, it was observed that as the strain increased with the number of passes, the strength and micro-hardness of produced composites increased as well.

Numerous research works have been carried out in resent years to investigate mechanical alloying and combustion synthesis processes for the synthesis of advanced materials. In this work, Al2O3-TiN composite were produced using mechanical alloying and combustion synthesis method. TiO2 and Al powders were used as raw materials to prepare Al2O3-TiN composite. Powders were milled under nitrogen atmosphere (5 at pressure). Combustion were performed in the tube furnace under nitrogen atmosphere. The results of mechanical alloying indicated a two step mechanism. Titatium oxide were reduced to Ti at the first step followed by reaction with nirogen to produce TiN. When Al/TiO2 molar ratio in the starting powder was 1.2 or 1.3, TiN was produced after 20 hrs of milling, as observed in the XRD results. The results of combustion synthesis experiments indicated that aluminum and titanium oxide powders were combusted at 900oC and titanium nitride was formed.

Semiconductor photocatalysts are becoming more and more attractive due to their excellent potential to solve environmental problems. Among them, nanosizedanatase-phase titanium dioxide (TiO2) is of great interest due to the strong oxidizing power of its holes, high photostability and redox selectivity. In this research, we have synthesized single-phase anataseTiO2 nanoparticles and investigated their photocatalytic activity. A sol-gel route was utilized to prepare the material and demonstrate the advantages of the low-temperature preparation. In the first step, we investigated the thermal behavior of the prepared sol by simultaneous thermal analysis (STA) to determine the proper heat-treatment conditions. The as-prepared powders were subsequently characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), and BET surface area measurement technique. The mean crystallite size, for each heat-treatment conditions, was also calculated based on the Scherer equation. The photocatalytic activity of the powders was investigated using both Methylene Blue and Rhodamine B as model organic compounds under UV light irradiation.

This paper aims at investigating on the influence of welding current on the quality of AISI304 resistance spot welds. Mechanical properties of the spot welds (peak load, failure energy and failure mode) were evaluated using tensile shear test. The relationships among welding current, weld fusion zone characteristics and failure behavior were studied. Generally, it was observed that increasing fusion zone size is accompanied by an increase in load carrying capacity and energy absorption capability. However, when expulsion occurs, despite of almost constant weld fusion zone size, energy absorption capability reduces significantly due to increase in electrode indentation depth. Considering the failure mechanism in the tensile shear test, minimum required fusion zone size to ensure the pullout failure mode was estimated using an analytical model.

Metal matrix composites reinforced with TiC have achieved a lot of attention in recent years due to their excellent mechanical properties and wear resistance. So production of  FeCo-TiC composite powder by mechanical alloying using two different raw materials, pure titanium and ferrotitanium, was the aim of this research work. Powder mixtures of ferrotitanium, cobalt, graphite and also mixtures of iron, titanium, cobalt, and graphitewere milled at various milling times. Milled powders were characterized by XRD and SEM. The results show that mechanical alloying method with two different mechanisms leads to the formation of TiC embedded in FeCo alloy. When ferrotitanium was used the first nucleus of TiC was formed after 5 hours of milling. Increasing the milling time resulted in progress of reactions. When pure titanium was used, TiC was not produced after 5 hours of milling. However, with increasing of milling time to 7 hours, reaction between Ti and C was completed. Microscopic evaluation of the samples indicated that with increasing of milling time to 80 hr homogeneous composite powder, with particle size of about 1 micron is produced.