A Comparative Study of Creep in Ti-52Al and Ti- 48Al-2Cr-2Nb-1B Intermetallics

摘要

Creep strength and microstructure of pure#gamma#-phase Ti-52 at percent A1 and two microstructuralmodifications of #gamma#/#alpha#_2 two-phase Ti-48A1-2Cr-2Nb-1B (in at percent) intermetallics are investigated andcompared. Data obtained in tension and compression attemperatures 973-1150K and in the applied stress range 50-300MPa are presented. The pure #gamma#-phase Ti-52A1 crept intension at 1100K is brittle once the applied stress exceeds 150MPa. On the other hand, a fully lamellar modification of Ti-48A1-2Cr-2Nb-1B alloy exhibits a remarkable ductility atconsiderably lower temperatures. The improved ductility of thefully lamellar modification is also superior when compared tothe equiaxed fine grain modification of Ti-48A1-2Cr-2Nb-lBalloy. However, the equiaxed fine grain modification exhibitsthe highest creep strength which is associated with sharp creeprate minima observed on creep curves of equiaxed grainmicrostructures. A conventional light microscopy, SEM andTEM were used to quantify the microstructure of the alloysbefore and after creep. Contrary to a grain growth, observedduring creep of Ti-52A1 alloy, a grain refinement due torecrystallization was found after creep in Ti-48A1-2Cr-2Nb-lBalloy. The difference in creep behaviour of the investigatedalloys is attributed to a different intensity of dislocation glide,twinning and recrystallization. It is suggested that the incrementof creep strength and the decrement of ductility observed inequiaxed alloys is associated with the lack of plasticdisplacements parallel to the c-axis of the tetragonal L1_0 latticeat the beginning of creep.