SPRAY FORMING RESEARCH AT DREXEL-UNIVERSITY

R&D programs in spray forming at Drexel University are profiled; these include thermal spraying and spray forming in the Osprey mode. Therma l spray techniques in use are low pressure plasma; air plasma, reactiv e plasma, wire-are, high velocity oxy-fuel, and flame spray. Applicati ons include the plasma spray forming of refractory metals and function ally gradient materials and the reactive plasma spraying and synthesis of a broad range of materials. The latter include high nitrogen steel s, Ti/TiN and Ti/TiC composites, Al2O3/SiAION composites, and Mo/MoSi2 composites. The primary focus of the programs on spray forming in the Osprey mode is on modeling for process optimization and the in-situ f abrication of discontinuously reinforced metal matrix composites. A co mplete integral model has been developed which delineates allowable wi ndows for processing parameters and materials properties in order to o ptimize the spray cast microstructure. Two adaptations of the basic Os prey technology have been evaluated for in-situ composite processing: the injection of benign particles into the spray and reactive spray fo rming involving gas-liquid and solid-liquid reactions. One example of inert spray forming is the injection of W or Al2O3 into a Cu spray. Sp ray farming of Fe-Al with a partial pressure of oxygen in the nitrogen atomizing gas and the injection of Fe-C particles into a Spray of Fe- Ti are examples of reactive spray forming. It is concluded that inert and reactive spray forming in the osprey mode are viable approaches fo r the fabrication of discontinuously reinforced metal matrix composite s. The review concludes with a brief description of the educational co mponent of the program.