Mechanical properties of Ir-Nb alloys containing Ni and Al

Two alloys made by adding 5 or 10 at. pet, respectively, of Ni-18.9 at. pet Al to an Lt-15 at. pet Nb alloy were investigated, The microstructure and compressive strength at temperatures between room temperature and 1800 degr eesC were investigated to evaluate the potential of these alloys for ultra- high-temperature use. Their microstructural evolution indicated that the tw o alloys formed fee and L1(2)Ir(3)Nb two-phase structures. The fee and Lit two-phase structures were examined by transmission electron microscopy (TEM ) and scanning electron microscopy (SEM). The 0.2 pet flow stresses were ab ove 1000 MPa at temperatures up to 1200 degreesC, about 150 MPa at 1500 deg reesC, and over 100 MPa at 1800 degreesC, The strength of the quaternary Ir -base alloys at 1200 degreesC was even higher than that of Ir-base binary a nd ternary alloys. And the strength of quaternary Ir-Nb-Ni-Al was equivalen t to that of the Ir-15 at. pet Nb binary alloy at 1800 degreesC, The compre ssive ductility of quaternary (around 20 pet) was improved drastically comp ared with that of the Ir-base binary alloy (lower than 10 pet) and the tern ary Ir-base alloys (about 11 pet). An excellent balance of high-temperature strength and ductility was obtained in the alloy with 10 at. pet Ni-18.9 a t, pet Al. The effect of Ni and Al on the strength of the Ir-Nb binary allo y is discussed.