High temperature strength and ambient temperature fracture toughness of Nb3Al/Nbss in-situ composites

摘要

To improve high temperature strengthand ambient temperature fracture toughness ofNb3Al/Nbss in-situ composites, solid solutionhardening of monolithic Nb3Al and Nb solidsolution (Nbss) as well as Nb3Al/Nbss in-situcomposites was measured at ambient temperature.Nb3Al polycrystals prepared by HIPing ofprealloyed powders deform plastically above 1400K,and are strengthened by alloying with W, Mo and Ta.Nbss single crystals grown in an electron-beamfloating zone furnace are solid solution hardenedat ambient temperatures by alloying with Mo, butnot by alloying with Ta. Yield strength of a Nb-Taalloy decreases rapidly with increasingtemperature, while that of a Nb-Mo alloy exhibitsconsiderably high strength at temperatures up o 1700K.Mo- or Ta-alloyed Nb3Al/Nbss in-situ compositesprepared by isothermal forging of cast alloyspossess high yield strength at elevatedtemperatures when the Nb3Al volume percent is high.With increasing Nbss volume percent, yield strengthof Ta-alloyed Nb3Al/Nbss in-situ compositesdecreases remarkably and solid solution hardeningdisappears at Nbss volume percent over 0.5. Mo-alloyed Nb3Al/Nbss in-situ composites exhibithigher yield strength than binary Nb3Al/Nbss in-situ composites even over Nbss volume percent of0.5. These results can be explained by the solidsolution hardening of Nb3Al and Nbss.