Austenitic stainless steels have a major problem during solution annealing or welding in the temperature range of 500-800 &deg / C due to the formation of chromium carbide, which causes chromium depleted areas along grain boundaries. This means that the structure has become sensitized to intergranular corrosion. Susceptibility to intergranular corrosion can be determined by means of destructive acid tests or by nondestructive electrochemical potentiokinetic reactivation (EPR) tests. The EPR test, which provides quantitative measurements, can be practiced as single loop or double loop. Single loop EPR method for AISI 304 and 304L type stainless steels was standardized / however double loop EPR (DLEPR) method has not been validated yet. In this study, the degree of sensitization was examined in AISI 304L and 316L type steels by DLEPR method whose experiments have been carried out on sensitive and nonsensitive steels to examine and determine the detailed parameters / solution temperature, concentration and scan rate of the DLEPR method. In order to determine the degree of sensitization, oxalic acid, Huey and Streicher tests were carried out and revealed microstructures and measurements of weight loss by the acid tests were then correlated with DLEPR method results, as a first step towards standardization of DLEPR method for 316L steels. Best agreement was provided with test parameters which are 1M H2SO4 + 0.005M KSCN at 3 V/hr scan rate with 30 &deg / C solution temperature. It was concluded that specimens can be classified as step, dual and ditch, if the Ir:Ia ratios were obtained to be between 0 to 0.15, 0.15 to 4.0 and 4.0 to higher respectively.

The major aim of this study was to investigate various leaching methods for the recovery of zinc and lead from blended neutral leach residues of &Ccedil / inkur having a composition of 12.59 % Zn, 15.21 % Pb, 6.45 % Fe, 0.054 % Cd. Initially water leaching tests were performed at various conditions of leaching temperature, reaction time and particle size. The optimized conditions for water leaching were found to be 2 h, 95&amp / #61616 / C and 250 g/l pulp density with a final pH of 5.9. However, the zinc recovery value of 10.26 % was not adequate for industrial scale operations itself. In acid leaching trials / acid concentration, temperature, reaction time and particle size were the chosen variables. At the optimized condition of 150 g/l H2SO4, 95&amp / #61616 / C, 2 h at 250 g/l pulp density with a final pregnant solution pH of 4.2, the extraction values were determined as 74.87 % for Zn and 39.59 % for Fe. These recovery values were evaluated as suitable for industrially feasible operations while creating a secondary leach residue of a composition of 4.10 % Zn, 19.17 % Pb, 5.52 % Fe and 85 ppm Cd that would not be suitable for pyrometallurgical lead production. After recovering zinc in considerable amount by hot sulphuric acid leaching, NaCl leaching experiments for the extraction of lead were done on the secondary leach residue by taking temperature, time and pulp density into account. The most promising conditions of brine leaching for lead recovery were found as 300 g/l NaCl, 20&amp / #61616 / C, 15 minutes and 20 g/l pulp density that gave approximately 82 % lead recovery with a final residue of 7.87 % Pb, 6.86 % Zn, 8.79 % Fe.

In this study, production and properties of titanium diboride particle reinforced aluminum matrix composite were investigated. TiB2 particles form in-situ through the reaction of TiO2 and H3BO3 and Na3AlF6 in aluminum melt. The results showed that the in-situ TiB2 particles formed were spherical in shape and had an average diameter of 1mm .Moreover, the distribution of TiB2 particles in the matrix were uniform. The ultimate tensile strength, yield strength, flexural stress and hardness were found to while reduction in area and elongation were found to decrease with increase in reinforcement content in the matrix.

Mica based glass - ceramics have been produced by subjecting the glasses in the SiO2 , Al2O3 , CaO , MgO, K2O , and F system to a controlled heat treatment called crystallization. TiO2 was added into the batch in the amount of 1 wt% of the glass as nucleating agent. B2O3 additions in the amounts of 1, 2, 4 and 8 wt% of the glass have been made in the batch to see and evaluate the effects of B2O3 additions on the texture of the mica glass ceramics. Crystallization was accomplished in two steps, nucleation and crystal growth. Nucleation temperature was 650 &amp / #61616 / C. Crystal growth temperatures were 850 and 1000 &amp / #61616 / C. The time for holding the specimens at the temperatures was 8 hours. The X-Ray diffraction analysis revealed that resultant glass ceramics possessed not only synthetic fluormica crystals called phlogopite which provide machinability, but also wollastonite crystals which provide biocompatibility. The scanning electron microscopy examinations have indicated that the amount and distribution of the crystalline phases varied as a function of B2O3 content and heat treatment schedule applied.

ABSTRACT TRIBOLOGICAL PROPERTIES OF A TIGHTLY WOVEN CARBON/CARBON COMPOSITE Karaveli, Keriman M.Sc., Department of Metallurgical and Materials Engineering Supervisor: Prof. Dr. Abdullah &Ouml / zt&uuml / rk June 2005, 77 pages Tribological properties of a tightly woven Carbon/Carbon (C/C) composite were assessed experimentally in accord with the ASTM pin on disk technique. The C/C composite used in this study was a commercial material (K-Karb) obtained in a panel form. The composite consists of graphite fiber reinforced graphite matrix developed for aerospace applications. The fiber reinforcement was in a plain weave woven fabric form. The tests were conducted by sliding zirconia ball against the C/C composite. The friction coefficient and wear rate were determined as functions of applied load, sliding speed, sliding distance and lubrication in ambient laboratory conditions. Mean friction coefficient of the composite was 0.135 &micro / when tested at ambient atmosphere and 0.113 &micro / in lubricated environment at a load of 5 N, sliding speed of 0.5 cm/s, and sliding distance of 100 m. The wear volumes determined from surface profile traces obtained on the wear tracks after completion of the tests were used for calculations of the specific wear rates. The specific wear rates of the composite were 0.754 x 10-4 mm3/N.m at ambient atmosphere and 0.437 x 10-4 mm3/N.m in lubricated environment at the load of 5 N, sliding speed of 0.5 cm/s, and sliding distance of 100 m. The specific wear rate of the composite decreased with increasing sliding distance, sliding speed, applied load and also, decreased in lubricated environment. Keywords: C/C composite, tribology, friction, wear, lubricant.

The oxidation of three different steels used in the construction of petroleum refineryheaters was investigated by using thermogravimetric analysis technique (TGA). C-5,P-11, and P-22 steel samples were tested in two different oxidizing environments / air and CO2+N2+H2O (that simulates the combustion products of natural gas) at two different temperatures / 450oC and 500oC. In air oxidation P-22 had the best oxidation resistance among the three steels at two temperatures. In CO2+N2+H2O environment,C-5 possessed better oxidation resistance than P-22 and P-11. Analyses of oxidation products by using optical microscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were carried out to correlate TGA results to oxide composition and morphology. Lower oxidation rate of P-22 in air was explained with reference to the formation of Cr-O phase. Analytical rate equations showed that all the steels obeyed parabolic rate equation during oxidation and no transition was observed

A series of AlSi9Mg alloys were prepared and tested to reveal the effect of addition sequence and timing of grain refiner and eutectic modifier. AlSr10 master alloy was used as an modification reagent, and also for grain refiner AlTi5B master alloy was used. The depression at the eutectic temperature due to the addition of modifier and decrease in the amount of undercooling at the liquidus due to the presence of grain refiner were examined by the cooling curves which were obtained by the Alu-Therm instrument, which is the aluminum thermal analyzer of the Heraeus Electro-Nite. The alloys that were both modified and grain refined were subsequently poured as tensile test specimen shapes in permanent die casting mould for four times at 60 minutes time intervals, meanwhile thermal analysis of the alloys were also made. In this work the effect of grain refinement and modification agent, also the determination of the optimum time to pour after adding these agents were studied by aluminum thermal analyzer. The parameters obtained from this analyzer are compared with the microstructures / to see the effect of these agents on mechanical properties, hardness, tensile strength and percent elongation values were investigated. In this study the possibility of predicting the mechanical properties prior to casting by thermal analysis method was examined by regression analysis method. By this method relationship between thermal analysis parameters and mechanical properties was established.

This thesis aims to examine the possibility of using Magnetic Barkhausen Noise technique in characterizing the ferritic-martensitic microstructure of hypoeutectoid steels quenched from the intercritical temperature range. For this purpose, rectangular specimens were prepared from SAE 1020, 1040 and 1060 steels. The specimens were heated at different temperatures within the intercritical temperature range and then quenched into water. Microstructures of the specimens were characterized by metallographic examinations and hardness measurements. The measurements of the Magnetic Barkhausen Noise (MBN) were performed by using both Rollscan and &amp / #956 / SCAN sensor connectors. It was seen that, for specimens having identical carbon content, Barkhausen emission decreased as the heating temperature increased. Moreover, in specimens heated at the same temperature, Barkhausen emission decreased as the carbon content of the specimen increased. In both cases, the decrease in Barkhausen emission is associated with the increase in martensite content. The results indicate that MBN is inversely proportional to hardness and that MBN is very sensitive to the microstructural condition of the material. It has been shown that using MBN is a powerful tool for evaluating the microstructure of hypoeutectoid steels quenched from the intercritical temperature range and that the use of this technique could be extended to characterize industrial dual phase steels.

ABSTRACT A study is carried out on the production of aluminum foams via powder processing. The study deals mainly with the effect of TiH2 particle size on the process of foaming. Mainly two TiH2 particle sizes were used / namely 27,5 &amp / #61549 / m and 8,5 &amp / #61549 / m. Foaming experiments were carried out at temperatures between 675oC &ndash / 840oC. The viscosity of the system is adjusted by controlled addition of Al2O3. The study shows that choice of foaming agent size is influential in the foaming process. With the use of fine foaming agent, temperatures in excess of 800oC would be required for successful foaming. The study further showed that the relation between foaming and viscosity was also dependent on the particle size. Viscosity of 2.3 mPa.s was found to be a limiting value for successful foaming with fine foaming agent. This value appears to increase with increasing particle size. An analysis is presented with regard to temperature dependence of foaming which takes into account the effect of particle size.

In this study an experimental spray-rolling set-up is designed in order to produce rapidly solidified Al-Fe-V-Si flat product. Al-Fe-V-Si alloys produced by rapid solidification powder metallurgy (RSP/M) methods are mostly used in high temperature applications in aerospace and automotive industries. The RSP/M technique used is spray deposition, which is desirable because of the high cooling rates achieved, as a result fine silicide dispersoids and intermetallics are observed in the microstructure which are known to contribute to the mechanical properties i.e. high strength at elevated temperatures, thermal stability, fracture toughness, corrosion resistance. Since spray deposition is a droplet consolidation process a considerable amount of porosity is expected in the final product. In this work, spray rolling process, which consists of spray deposition and subsequent hot twin-rolling stage, is designed and developed by interpreting the results obtained from SEM, XRD, tensile, three point bending and hardness tests of the specimens formed in several design stages. Two original intermetallic phases characterized in this study are V3Si and V2Mg3Al18 .