常规铸造定向层片TiAl合金持久加载中的组织退化及改善途径

Microstructural degradation during creep loading and improvement methods for a directional lamellar TiAl alloy prepared by conventional casting

摘要:

基于常规铸造定向层片组织TiAl合金与PST晶体的组织差别，详细讨论这些组织差别对常规铸造定向层片组织TiAl合金持久加载过程中组织退化的影响，并探讨降低这些不利影响的微合金化途径。结果表明：定向层片组织与PST晶体的差别主要包括存在层片团界和小角度取向差、Al元素成分偏析以及α2相体积分数高于热力学平衡状态，同时，后续热等静压导致等轴γ晶粒析出和层片间距增加也是另外的明显差别。这些组织差别对定向层片组织持久加载过程中的组织退化造成不同程度的不利影响。其中，Al元素成分偏析和α2相体积分数过高促进了定向层片组织铸态试样的组织退化，热等静压试样中的等轴γ晶粒进一步加剧了其组织退化，这些均对定向层片组织持久寿命造成不利影响。而层片团界对组织退化的不利影响作用较小。此外，探讨了Zr、C、Si微合金化抑制持久加载过程中组织退化进而改善持久性能的思路。

Abstract:

microstructure differences between the polysynthetically twinned crystal and the directional lamellar structure prepared by conventional casting for TiAl based alloy were analyzed, in order to detail discuss their influence on the microstructural degradation during creep loading. And micro-alloying methods were proposed to decrease the adverse effect. The microstructural differences mainly included colony boundary, Al segregation and excess α2 phase. Additionally, equiaxed gamma grain precipitation and lamellar coarsening during hot isostatic pressing were also other differences. These differences had adverse influence on the microstructure degradation of directional lamellar structure prepared by conventional casting during creep loading. Al segregation and excess α2 phase promoted the microstructural degradation for as-cast sample, and the equiaxed gamma grain precipitated during hot isostatic pressing aggravated the microstructural degradation. They caused significant reduction of creep rupture life. The effect of the former was less than that of the latter. The colony boundary had a little adverse effect on the microstructural degradation. Additionally, the methods that minor addition of Zr,Si,C improved the creep rupture properties by inhibiting microstructural degradation were also discussed.