CVD CRB2 FIBERS FOR METAL MATRIX COMPOSITES

EVER-INCREASING DESIGN AND PERFORMANCE REQUIREMENTS ARE PLACING INCREASINGLY SEVERE DEMANDS ON MATERIALS PROPERTIES FOR GAS TURBINE APPLICATIONS. THE OPERATIONAL CAPABILITIES OF THE SUPERALLOYS HAVE ACHIEVED DRAMATIC INCREASES IN THE LAST DECADE, BUT FURTHER INCREASES CAN BE ACHIEVED ONLY THROUGH THE ADDITION OF SECOND-PHASE REINFORCEMENTS. ACCEPTABLE REINFORCEMENTS, HOWEVER, ARE NOT YET AVAILABLE, DUE TO DRAWBACKS SUCH AS HIGH DENSITY, LOW THERMAL EXPANSION, AND POOR OXIDATION RESISTANCE. CHROMIUM DIBORIDE (CRB2) HAS A CTE MATCHING THAT OF SUPERALLOYS, GOOD OXIDATION AND CORROSION RESISTANCE, HIGH MODULUS, REASONABLE DENSITY, AND POTENTIALLY HIGH STRENGTH SUITABLE FOR SUPERALLOY REINFORCEMENT. IN THIS PHASE I PROGRAM, ULTRAMET PROPOSES TO DEMONSTRATE THE FEASIBILITY OF PRODUCING CONTINUOUS HIGH-STRENGTH CRB2 MONOFILAMENTS BY CHEMICAL VAPOR DEPOSITION (CVD) ON A SUITABLE WIRE SUBSTRATEAND EVALUATE ITS STABILITY IN CONTACT WITH VARIOUS SUPERALLOYS THROUGH THE USE OF DIFFUSION COUPLES. SPECIFIC PROGRAM GOALS INCLUDE DEVELOPING A FINE-GRAINED MICROCRYSTALLINE CRB2 MONOFILAMENT WITH A STRENGTH IN THE 100-200 KSI RANGE AND EVALUATING ITS THERMAL AND MECHANICAL PROPERTIES.