Journal of Advanced Processes in Materials Engineering
Year:2010 | Volume:4 | Issue:1 (12)|Papers Count:8

In this research, titanium carbide and TiC-Al2O3 nanocomposite was produced by MASHS method from rutile as an inexpensive material, Aluminum and graphite. Phase analysis of the products was carried out using XRD and microstructure of the product was also studied by SEM. Primary mixture was milled in a planetary ball mill at 8h, 10h, 20h and 60h milling time. The XRD analyses showed that after10h, peaks corresponding to TiC and Al2O3 phase appeared on XRD patterns. The crystallite sizes of TiC and Al2O3 were determined by Williamson-Hall method. Whit increasing the milling time to 20h peaks corresponding to TiC broadened slightly and diminished in intensity, which are the results of the fineness of the crystallites. The crystallites size was on the scale of nanometer. For samples 20h milled, TiC-Al2O3 nanocomposite was heat treated at 800°C and 1200°C. No significant phase change was observed after heating of the synthesized TiC-Al2O3 powder. And grain sizes remained at scale of nanometer.

Maraging Steels are a group of steels having high strength and toughness. Presence of inclusions in these steels is harmful for their strength and toughness. Also, there are some active elements within these steels. Therefore, application of advanced melting, refining and casting processes such as vacuum processes are used greatly in production of maraging steels. In this research two C300 maraging steel with 0.65 and 1 wt% Ti were casted firstly in VIM furnace. Then samples subjected to VAR process in order to study the effects of this process on mechanical proerties, inclusions content and gas atoms within the steel. The results show that during VAR process of the bars casted in VIM furnace, the total N and O gases reduced up to 14%, ductility and resistane to impact increased up to 30% and 47% respectively. Comparison of these two steels that produced by VIM+VAR showed that titanium increasing from 0.65 to 1 wt% causes marginal increasing in strength and hardness and marginal decreasing in ductility and resistance to impact of steel.

In this research, metal cored wire including ferroalloy materials was used and cladded by FCAW process with different shielding gases (as nitrogen and argon) on steel substrate. The chemical analysis examination showed that the nitrogen absorbed in sample that was fabricated with nitrogen gas shielding. Consequence of XRD pattern indicated that the Carbonitride phase (TiCN) precipitations appeared in weld metal (nitrogen gas) and titanium carbides (TiC) precipitate in (argon gas) samples. SEM examination results, revealed that the fine particles of TiCN and TiC precipitations sited in ferrite microstructure and the mapping of elements explained the homogeneously precipitates of elements and phases in microstructure. Also, the hardness value sample that fabricated with argon gas was lower than the sample that fabricated with nitrogen gas. The wear test (ASTM G65) result indicated that sample was being consist of TiCN had higher abrasive wear resistance than the other (TiC).

In lost foam casting, pattern and gating system prepared form gasifiable pattern (mainly polystyrene) and coated pattern embedded in unbounded sand. Pattern thermal degraded and under go out from the mold while the molten metal enter the mold. In steel lost foam casting, molten metal has high temperature then foam pattern decompose mainly to the gaseous products and escape from the mold. Back pressure of the decomposed products changes the flow pattern in the mold. In aluminum lost foam casting less heat reaches to the foam pattern and less decomposition occurred and decomposed products mainly in liquid form escape the mold. In this research flow pattern and gas gap length in aluminum and steel lost foam casting investigated using photography technique. Pressure measurement results indicate that back pressure increased with coating thickness, foam density and spure height increscent. Comparison between photography results of aluminum and steel indicate that with increasing metal temperature from aluminum to steel temperature, reaction intensity and the gaseous products volume increased.

In this research, nanopowder alumina was produced by sol-gel method. Boehmite sol was prepared from aqueous solution of aluminum nitrate in pH = 8 and 80°C. In the first section of the research, some amount of this sol was transformed to gel after heating at 100°C. Post heat treatment on the dried gel was in 1100°C for 2 hours. Alpha alumina was synthesized with specific surface area of 12 m2/g, particle size average of 450 nm and crystal size 35 nm. In the second section of the research, microwave was used for transformation of the starting sol into gel. alpha alumina was synthesized by heating the dried gel in microwave for 20 minutes. Specific surface area of 35 m2/g and of crystal size of 25 nm was attained by this method.

In this investigation, combustion synthesis and the mechanochemical synthesis of chromium carbide (Cr3C2) were studied using chromium oxide, aluminium and carbon powders. XRD technique was used to characterize the product. Without any mechanical activation, ignition of the raw mixture only resulted in aluminothermic reduction of chromites. When the raw powders were mechanically activated for 2 hours, combustion reactions were completed and Cr3C2 was produced. Results of the mechanochemical process indicated that the aluminothermic reduction of chromites proceed with time and is almost completed after 5 hours. Further milling results in dissolution of carbon in chromium and after 7 hours of milling, distinguished peaks for Cr3C2 appeared in XRD results. No peaks for alumina, a by product of the process, were observed in the XRD pattern which means this phase is amorphous. This was confirmed by annealing of the sample at 1100°C for 1 hr which resulted in a sharp peak for alumina in addition to chromium carbide.

In the present work, in situ production of Alumina-Spinel composite by gelcasting method is investigated. For this purpose, two different raw materials, magnesium hydroxide and magnesium acetate, were used and their properties were studied separately. The results of the sedimentation test show that the amount of dispersant agent in the suspension containing magnesium acetate was smaller than the suspension containing magnesium hydroxide. Also, the segments produced by magnesium hydroxide had higher mechanical properties than the ones produced by magnesium acetate. The effect of sintering time on the spinel phase constitution is examined by XRD. Finally, the existence of further porosities in the segments containing magnesium acetate was proven by SEM.

API 5CT T95 has wide range of applications in oil industries. According to local production of this kind of steel in Iran, research and study about this subject is very important. This steel after melting, casting and forging will heat treated to reach the required mechanical properties. The heat treatment cycle is quenching and tempering. This research has done to draw the tempering graph. This kind of information is not available. To draw it some tensile test samples of the API 5CT T95 steel have prepared. All samples austenitized at 890°C and then quenched in water. Finally each sample have tempered in constant temperature including 570, 600, 620, 635, 650, 660, 670, 680 and 700°C. After hardness and tensile tests the tempering graph for this steel that will be the main reference of the heat theaters, have drawn.