Abstract In this paper the occurrence of twinning parallel to the lamellae during compression at 700 °C of a polycrystalline nearly lamellar commercial γ-TiAl alloy, Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB 2 , has been studied and shown to lead to the formation of cracks at colony boundaries. However, the occurrence of this longitudinal twinning mode was less common by at least a factor of ten in tests at room temperature. Furthermore, the debonding of colony boundaries caused by the shear strain of longitudinal twinning is exacerbated when the same γ-TiAl variant favourably oriented for twinning occurs repeatedly in the lamellar structure. This effect was caused by the preferential nucleation of certain γ-TiAl variants in the presence of TiB 2 boride reinforcement. It is shown that the boride additions increase the probability of double, triple or even higher order multiply stacked γ-variants. This increases the resulting shear strain that must be accommodated and hence the probability of crack nucleation.

中文翻译：

---

多晶TiAl合金中硼化物与纵向孪晶的相互作用

摘要 本文研究了多晶近片状商用 γ-TiAl 合金 Ti-45Al-2Nb-2Mn(at%)-0.8 vol% TiB 2 在 700 °C 压缩过程中平行于片晶的孪晶发生。并表明会导致在菌落边界处形成裂缝。然而，在室温下的测试中，这种纵向孪晶模式的发生率至少降低了 10 倍。此外，当相同的 γ-TiAl 变体有利于孪晶取向时，在层状结构中重复出现时，由纵向孪晶的剪切应变引起的菌落边界的剥离会加剧。这种效应是由某些 γ-TiAl 变体在 TiB 2 硼化物增强体存在下优先成核引起的。结果表明，硼化物的添加增加了双倍的概率，三重或什至更高阶的乘积γ-变体。这增加了必须适应的最终剪切应变，从而增加了裂纹成核的可能性。