针状Ti-55511合金热变形及后续退火过程中组织演变及其力学性能

Microstructure Evolution and Mechanical Properties of Lamellar Ti-55511 Alloy During Hot Rolling and Annealing

对针状Ti-55511近β钛合金进行750℃热轧和600℃/1 h退火,研究合金在热轧及退火中组织演变及力学性能。结果表明,热轧时,针片α相将发生动态再结晶(DRX),与β相的Burgers取向关系(Burgers orientation relationship)发生破坏,进而形成细小的等轴α相,使合金强度及塑性提高。后续退火过程中,α相通过静态再结晶(SRX)进一步发生球化和长大,次生α相析出,β相发生再结晶,合金的强度提高,塑性降低。在变形初期,针片α相内产生2种孪晶变体(交叉状孪晶),随着α相球化程度增加`,α相内将产生3种孪晶变体(针织状孪晶)。在后续退火过程中,这些孪晶将逐渐缩短,进而分解消失,表现在退火样品中α晶粒内存在纳米级孪晶(孪晶缩短)与层错(孪晶分解)。

750 °C hot rolling and subsequent 600 °C/1 h annealing was conducted on lamellar Ti-55511 near-beta Ti alloy to investigate the microstructure evolution and mechanical properties. The results show that the Burgers orientation relationship between α and β phase is broken down owing to dynamic recrystallization(DRX) of lamellar α phase during hot deformation, forming fine and equiaxed α plates, which leads to the increase of the tensile strength and elongation. During annealing, secondary α grains are precipitated from β matrix, resulting in higher strength but lower elongation. Meanwhile, further spheroidization and growth of α phase happen via static recrystallization(SRX) during annealing. The recrystallization of β phase only happens in subsequent annealing rather than in hot rolling. At the beginning of the deformation, two twin variants can be found in lamellar α phase. With an increase of deformation, three twin variants are formed in α phase. The nano-scaled twins and stacking fault are formed resulting from twins decomposing during annealing.