Phase transformation mechanisms in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy after subsequent annealing at 800 degrees C
Phase transformation mechanisms in a quenched Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y alloy after subsequent annealing at 800 degrees C
复制标题
淬火 Ti-45Al-8.5Nb-0.2W-0.2B-0.02Y 合金在 800 摄氏度后续退火后的相变机制
DOI：
10.1016/j.jallcom.2016.08.238
复制
发表时间：
2017
影响因子：
6.2
通讯作者：
Li Jinshan
中科院分区：
文献类型：
--
作者：
Song Lin;Lin Junpin;Li Jinshan
在加工高含Nb的TiAl（Nb-TiAl）合金时，部件某些部分的冷却速度可能非常高，尤其是薄零件。此外，必须对TiAl合金进行退火处理以提高其力学性能。采用扫描电子显微镜（SEM）和透射电子显微镜（TEM）研究了淬火态Ti-45 Al-8.5 Nb-0.2 W-0.2 B-0.02 Y合金在后续退火过程中的相变机制。结果表明，淬火组织中β o、α 2和大量转变的γ相共存。淬火样品中的初生α 2相中有细小的γ板条形核。在800° C下退火1 h后，大量极细的γ板条在体相α 2中析出，并且只能使用TEM成像来识别。尺寸为0.5-1 μm的ω o颗粒沉淀在保留的β o相中，几乎消耗了所有的β o区域。更有趣的是，在片层团和β o（ω）区的边界处观察到一些真孪晶关系的粗化γ晶粒。β o（ω）与粗化γ的取向关系为：[110] β//[11 2 <$0] ω//[111] γ，（11 1 <$）β//（0001）ω//（1 1 <$0）γ。在800° C退火100 h后，β o相区转变为小的ω o颗粒和等轴γ晶粒，并仍遵循上述取向关系。α 2相仅以较薄的板条形式存在于片层组织中，体积分数很小。这些结果表明，ω o相在800° C下是稳定的。这些相变的可能机制进行了讨论。
During the processing of high Nb-containing TiAl (Nb-TiAl) alloys, the cooling rate at certain parts of the components can be very high, especially at thin parts. Moreover, annealing treatment must be applied to TiAl alloys to improve their mechanical properties. In this study, the phase transformation mechanisms in a quenched Ti-45Al-8.5 Nb-0.2 W-0.2 B-0.02 Y alloy during subsequent annealing were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The results show that β o, α 2, and massively transformed γ phases co-exist in the as-quenched microstructure. Some fine γ laths nucleated in the primary α 2 phase in the quenched samples. After annealing at 800° C for 1 h, numerous extremely fine γ laths precipitated in the bulk α 2 phase and could only be recognized using TEM imaging. The ω o particles at sizes of 0.5–1 μm precipitated in the retained β o phase and nearly consumed all of the β o areas. More interestingly, some coarsened γ grains in true-twin relationship were observed at the boundaries of the lamellar colony and β o (ω) regions. The orientation relationship between β o (ω) and coarsened γ was confirmed to be the following:[110] β//[11 2¯ 0] ω//[111] γ,(11 1¯) β//(0001) ω//(1 1¯ 0) γ. After annealing at 800° C for 100 h, the β o phase region transformed into small ω o particles and equiaxed γ grains and still followed the above-mentioned orientation relationship. The α 2 phase only existed as thin laths in the lamellar structures in a small volume fraction. These results indicate that the ω o phase is stable at 800° C. Possible mechanisms of these phase transformations are discussed.