AN EVALUATION OF THE PROPERTIES OF CR3SI ALLOYED WITH MO

The properties of a Cr3Si alloy designed for the high temperature, high velocity gas dow conditions typical of the operating environment within an aircraft engine are discussed. The alloy composition was obtained by macroalloying Cr3Si with Mo to improve its high temperature oxidation resistance. Detailed cyclic, isothermal and low temperature ''pest'' oxidation studies conducted between 773 and 1673 K revealed that the alloy has excellent oxidation properties due to the formation of dual protective oxides scales of Cr2O3 at low temperatures and SiO2 at high temperatures. Preliminary burner rig tests conducted at 1473 K in a 0.3 mach combustion flame indicated that the alloy life is expected to exceed 100 cycles. The alloy exhibits a compressive brittle-to-ductile transition temperature of about 1500 K. The compression strengths vary between 650 MPa at 1500 K and 50 MPa at 1700 K. Preliminary results suggest that the compressive creep strength of the as-cast alloy is equal to or better than MoSi2-reinforced with either SiCp or SiCw, while that of the powder metallurgically-processed alloy is comparable only to the unreinforced MoSi2. The room temperature fracture toughness of the alloy was determined to be between 2.0 and 3.0 MPa m1/2.