The Praparation And Chemical Mechanism Of Functional Graded Materials Using Metal Organic Chemistry Vapour Deposition

Functionally Graded Material(FGM) is a new generation of composites in which the composition of a dispersion phase is gradually and spatially varied, and thus the properties/microstructure relationships have continuous characteristics. FGM has many superior properties such as eliminating interface crack between the two materials, reducing the thermal and residual stress, thermal barrier, thermal shock resistance, anti-corrosion, increasing the bonding strength and toughness, high-temperature strength (to 2000 C) etc., as compared with traditional composite materials. The applications field of FGM include aerospace , electron, chemistry, biology and medicine fields; The composition change also from metal/ceramic to metal/metal, metal/alloy, non-metal/non-metal and non-metal/ceramic. Moreover, various methods including Powder Metallurgy, Self-propagating High-temperature Synthesis(SHS), Chemical and Physical Vapor Deposition (CVD and PVD), Electrodeposition, Laser Cladding Method, Plasma Sputtering and Sol-Gel Method have been studed. Metal Organic Chemical Vapor Deposition (MOCVD), using Chemical Vapor Deposition of metal organic compounds, is an effective method for acquiring special function materials and membrane. With MOCVD film technology, film chemical composition is easier to control, deposition temperature lower, deposition speed higher, deposited film more compact, homogenous and flat.In this paper, firstly, the study of FGMs ,the study of CVD and MOCVD, and the nucleation mechanism have been introduced. Secondly, the fabracations of metal/metal and metal/ceramic FGMs have been reported. Based on the experiment and analysis, the optimum conditions for preparation of Si02 films have been studied. Furthermore, using the inverse designing idea of FGMs, Fe/Mo and Mo/SiO2 FGMs have been successfully prepared. Finally, the composition and microstructure of the materials have been measured by X-ray Debey Powder Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Scanning Electon Microscope (SEM), Step Instrument and Metallgical Microscope.The main points of our studies are as following:(1).The preparation of SiO2 films on the substrate of Al2O3, using cold-wall reactor (MOII) and Chemical Vapor Deposition of Si(OC2H5)4, has been studied. Based on the analysis of relationship between the deposition rate and the deposition conditions (the main factor : substrate tenperature, TEOS temperature and deposition time), it is proved that the maximum deposition rate and the optimum surface state, structure of thin films are to be gotten, when the temperature of substrate is 500 to 600 C, the pressure of the reactor is 260 to 400 Pa, the temperature of TEOS is about 60 C, current is 1ml.s-1. The longer deposition time is, the deeper films are.(2).According to the inverse design system, the structure optimization of FGMs is obtained. Based on the physical properties calculated and the thermal residual stress simulated, it is found that the optimum property parameters and the minimum thermal residual stress are to be gotten when the component distribution exponent P=l.(3).The Fe/Mo FGMs have been successfully carried out, when the current of Fe(CO)5 and Mo(CO)6 is controlled, the temperature of substrate is 500 C, the pressure of the reactor is 150 to 200 Pa, the temperature of Fe(CO)5 and Mo(CO)6 is 15 C and 60-70 C. The results showed that the materials are consisted of two phases: Fe and Mo solid solution, in which the compositons are of compact texture, with their parculates being uniformed in distribution, fine grains being small. Furthermore, the compositons of the Fe/Mo FGMs are gradually varied and conformed the law of the gradient materials.(4).The Mo/SiO2 FGMs have been developed using MOCVD with Mo(CO)6 and Si(OC2H5)4. By adjusting the temperature and current of the reactors, the most suitable conditions for preparation of the materials appear that the temperature of substrate is 500 to 600掳C, the pressure of the reactor is 170 to 350 Pa, the deposition time is 60min for every layer.