Fabrication, microstructure and properties of chemical vapour deposited AIN/Mo laminated composites

The synthesis of AlN/Mo multilayer composites was investigated. Laminates of this type are used as ceramic-metal units in electrical and vacuum devices. Appropriate chemical vapour deposition (CVD) technologies have been developed for AlN/Mo laminated composites. The extreme behaviour of the thermodynamic and technological parameters as a function of CVD reactor temperature was studied and several types of AIN coating microstructures were observed. The highest AIN crystallization rate and the best properties were obtained in the ''bimodal'' type microstructure. The mechanisms for the different types of deposited microstructures are discussed. The temperature dependence of the thermal resistance and the long-term thermal stability in a vacuum and in caesium vapour media were studied for AlN/Mo three-layer laminates. Only the laminates with a ''bimodal'' type AlN microstructure were found to be satisfactory. Fully dense laminates of this type were characterized by high electrical and corrosion resistance for a minimum of 5000 h. It was concluded that the laminated composite based on molybdenum/aluminium nitride is an excellent alternative to the presently existing niobium/corundum laminates.