PROCESSING AND PROPERTIES OF NB-TI-BASE ALLOYS

The processing characteristics, tensile properties, and oxidation resp onse of two Nb-Ti-Al-Cr alloys were investigated. One creep test at 65 0-degrees-C and 172 MPa was conducted on the base alloy, which contain ed 40Nb-40Ti-10Al-10Cr. A second alloy was modified with 0.11 at.% C a nd 0.07 at.% Y. Alloys were arc melted in a chamber backfilled with ar gon, drop cast into a water-cooled copper mold, and cold rolled to obt ain a 0.8-mm sheet. The sheet was annealed at 1100-degrees-C for 0.5 h . Longitudinal tensile specimens and oxidation specimens were obtained for both the base alloy and the modified alloy. Tensile properties we re obtained for the base alloy at room temperature, 400, 600, 700, 800 , 900, and 1000-degrees-C and for the modified alloy at room temperatu re, 400, 600, 700, and 800-degrees-C. Oxidation tests on the base allo y and modified alloy, as measured by weight change, were carried out a t 600, 700, 800, and 900-degrees-C. Both the base alloy and the modifi ed alloy were extremely ductile and were cold rolled to the final shee t thickness of 0.8 mm without an intermediate anneal. The modified all oy exhibited some edge cracking during cold rolling. Both alloys recry stallized at the end of a 0.5-h annealing treatment. The alloys exhibi ted moderate strength and oxidation resistance below 600-degrees-C, si milar to the results of alloys reported in the literature. The additio n of carbon produced almost no change in either the yield strength or ductility as measured by total elongation. A small increase in the ult imate tensile strength and a corresponding decrease in the reduction o f area below 600-degrees-C were observed. Carbon addition also served to marginally refine the grain size after annealing. The results of th is study and those of similar alloys reported in the literature sugges t that 40Nb-40Ti-10Al-10Cr forms a good base alloy suitable for alloyi ng for improvement in its oxidation and high-temperature strength prop erties.