TiAl合金全片层组织的热稳定性研究

研究了Al含量、冷却速率和添加硼元素对TiAl合金全片层组织在1150℃的热稳定性的影响。研究表明：Al含量在46％～48％（原子分数，下同）范围的二元TiAl合金的Al含量越高，γ偏析程度越严重，铸造片层组织的热稳定性越差；Ti-48AI合金α单相区固溶处理后炉冷的粗片层组织的稳定性远远优于空冷的细片层组织，空冷细片层组织容易在晶界处发生不连续粗化转变，并且空冷片层晶粒内的魏氏片层（LW）与基体的界面往往与晶界一同成为片层组织发生分解的起始部位；Ti-48A1合金中添加0．8％B因晶界TiB2相的存在能有效抑制细片层组织的晶界不连续粗化，但γ相从TiB2／基体界面和晶界重新形核生长可使片层组织转变为均匀的细晶近γ组织。

Thermal Stability of Fully Lamellar Microstructures in TiAl Alloy

The effects of Al content, continuous cooling rate and boron addition on the thermal stability of fully lamellar （FL） microstrncture in TiAl alloys at 1150 ℃ were investigated. For the binary TiAl alloys with 46% - 48% Al, the richer the Al content is, the heavier the y dendritic segregation is and the more instable the as-cast FL microstrncture is. The thermal stability of coarse lamellar microstructure in Ti-48Al alloy formed after solution treatment in α single phase field by furnace cooling is superior to that of fine lamellar microstructure formed by air cooling. For the fine lamellar microstructure, the lamellae discontinuous coarsening is apt to occur at the grain boundaries and the interfaces between the Widmanstatten lamellar colonies in the grains and the lamellar matrix. Addition 0. 8% boron into the Ti-48Al alloy results in that the TiB2 particles at grain boundaries restrain the lamellae discontinue coarsening effectively. Meanwhile, the new γ grains can nucleate at the TiB2/matrix interfaces and grain boundaries, as a result, the fine lameUar microstructure transforms into the homogeneous and fine near γ microstructure after a long time anneal.