TOUGHENING OF MOSI2 WITH A DUCTILE (NIOBIUM) REINFORCEMENT

The effect of interfacial reactions and Y2O3 coatings on toughening of MoSi2 by ductile phase Nb reinforcements has been investigated. In the absence of coating the interfacial reaction layer exhibits parabolic growth with Mo5Si3, (Mo, Nb)5Si3, (Nb, Mo)5Si3 and Nb5Si3 phases forming. In precracked laminates subjected to tensile loads the ductile phase deformation is partially constrained, with debonding occurring within the interfacial reaction zone. Dense Y2O3 coating inhibits interdiffusion and results in more extensive debonding. In either case, significant toughening is expected with measured work of rupture values-chi almost-equal-to 5.7 to 6.3. Bulk composite MoSi2 reinforced with 20 vol.% Nb particles subjected to a chevron-notched three point flexure test had a work of rupture almost five times larger than the unreinforced MoSi2 matrix.