Microstructure And Mechanical Properties Of Ti-44Al-8Nb-0.2W-0.2B-Y Alloy

High Nb containing TiAl alloys are the typifiers of newly-developedhigh-temperature and high-strength TiAl alloys, which have a high potentialapplication in the aerospace industry with their attractive properties, such as highspecific strength and modulus, good creep resistant, and good high temperatureoxidation resistance. It is difficult to prepare large-size high Nb containing alloyingot due to refractory of high melting point and serious element segregation. It canreduce element segregation and intermal stess and eliminate casting defects byβ-phase solidification and hot isostatic pressing. The high Nb containing TiAl alloysingot with nominal composition of Ti-44Al-8Nb-0.2W-0.2B-Y (at%) is preparedusing three remelting VAR technology and then canned forged at1250℃bytwo-step forging with50%deformation; and heat treated under the conditon of1310℃/15min and1250℃/2h by means of furnace cooling and air cooling. Themicrostructure and mechanical properties of as-cast, as-forged, and as-heat treatedhave been investgated systematically in this paper.As-cast Ti-44Al-8Nb-0.2W-0.2B-Y alloy shows a typical fully lamellarstructure and its room tensible strength is499Mpa and elongation is less than0.1%.The component distribution of HIPed is more uniform and the lamelar becomescoarser. The lamellar microstructure of as-forged becomes bended forming mixedstructure between a small amout of β/B2and a large number of γ phases in the grainboundary with944Mpa room tensible strength and1.3%elongation. With theincrease of temperature, the high-temperature tensible strength decreases and theenlongation increases. The elongation is up to64%for900℃tensible.Fully lamellar obtained by the heat treatment of1310℃/min is mainlycomposed of fine lamellae colony; duplex microstrutrue obtained by the heattreatment of1250℃/2h is composed of fine equiaxed γ grains, fine lamellae as wellas residual lamellae. Duplex microsruture obtained by air cooling has the highestroom-temperature tensile strength-1008MPa; while the fully lamellar obatained byfurnace cooling has good comprehensive mechanical property and best ductility. thetensile properties of duplex is superior to the fully lamellar at750℃, and the duplexhas the highest tensile strength and elongation.