Creep and Evolution of Dynamic Recrystallization in single Crystals of Ti-48 at percent Al with Different Orientation between Stress Axis and #gamma# Lamellar Plate

摘要

Creep deformation of Ti-48 at percent Al PSTcrystals with various lamellar orientation angles ? with respectto the stress axis has been investigated at 1148 K under thestress of 68.6 MPa. The specimen with a lamellar orientationnearly parallel to the stress axis (Φvalence 3 deg) shows thesmallest creep rate and the extended transient creep stage,whereas the specimen with Φvalence 63 deg exhibits thelargest creep rate and the shortest rupture life. The formerexhibits no macroscopic change in the lamellar morphologyeven after creep tested for 5200 h. However, the specimenwith the Φvalence 63 deg ruptured only after 920 h showsmany bent lamellar plates and dynamically recrystallized grainsnear the middle of the specimen. The dynamicrecrystallization is caused by the following sequence: (1)breakup of lamellar plates, (2) formation of subboundariesrunning parallel to the stress axis, (3) further collapse anddistortion of the lamellar plates, (4) occurrence of dynamicallyrecrystallized grains along the subboundaries. The orientationdependence of the occurrence of dynamic recrystallization isassociated with the rotation of the lamellar plates, and can beinterpreted in term of the difference in mode of slip deformation.