ULTRAFINE GRAINED MOSI2 WITH ULTRAFINE HFC DISPERSOIDS FOR IMPROVED SUPERPLASTIC FORMABILITY

THE DOE IS SEEKING RESEARCH DIRECTED TOWARD SIGNIFICANT MATERIALS ADVANCES IN AREAS SUCH AS PROCESSING OR FORMING OF CERAMICS IN THE SUPERPLASTIC STATE, PLASTIC BEHAVIOR AND PROPERTIES OF MONOLITHIC AND COMPOSITE SYSTEMS BASED ON HIGH MELTING CARBIDES, NITRIDES, BORIDES, ETC. WE PROPOSE TO PROCESS MONOLITHIC MOSI2 WITH ULTRAFINE GRAIN SIZE (1MUM)STABILIZED BY AN UNIFORM DISTRIBUTION OF ULTRAFINE (0.01-0.1MUM) HFC DISPERSOIDS WHICH WILL EXHIBIT SUPERPLASTIC FORMABILITY. THE APPROACH THAT IS PROPOSED IS TO PROCESS MOSI2 WITH APPROPRIATE MICROSTRUCTURAL CHARACTERISTICS TO INDUCE SUPERPLASTICITY. THE ULTRAFINE GRAIN SIZE IN MOSI2 PROCESSED VIA ADVANCED MELT SPINNING WILL SHOW ENHANCED STRAIN RATE SENSITIVITY LEADING TO SUPERPLASTIC FLOW. THE UNIFORMLY DISTRIBUTED ULTRAFINE HFC DISPERSOIDS WILL RETAIN THE FINE GRAIN SIZE AS WELL AS INHIBIT CAVITATION DURING SUPERPLASTIC FLOW BY VARIOUS RECOVERY MECHANISMS OCCURRING IN THE VICINITY OF THESE INCOHERENT PARTICLES. SUCH A MICROSTRUCTURE WILL LEAD TO ENHANCEMENT OF GRAIN-BOUNDARY SLIDING AND INHIBITION OF SLIP CREEP LEADING TO EASY SUPERPLASTIC FLOW. WE WILL EXAMINE THE MICROSTRUCTURES TO DETERMINE THE GRAIN SIZE AND THE SIZE, GEOMETRY, COMPOSITION AND DISTRIBUTION OFTHE DISPERSOIDS AS WELL AS THE DISLOCATION STRUCTURE USING TEM. THE SUPERPLASTIC BEHAVIOR OF THE MATERIALS WILL BE INVESTIGATED BY MECHANICAL TESTING AT TEMPERATURES FROM 1300-1600 K AND AT STRAIN RATES OF 10(-1) TO 10(-5) S(-1).