采用压缩和单边缺口三点弯曲实验,研究了Mo₅SiB₂ (T2相)合金试样在真空条件和不同温度下的压缩行为和断裂行为,利用XRD, SEM－EDS和TEM等对试样变形后的微观组织、位错组态和断口形貌进行了分析和观察.结果表明, T2相的脆－韧转变温度为1000－1200℃.在外加切应力的作用下, [010](001)和<110>{110}等多个滑移系开始开动,导致试样发生明显的塑性变形. 由于刃型位错比螺型位错或混合型位错活跃,表现为[010]刃型位错深入到滑移面{110}, 与<110>位错发生交互作用,形成大量位错节点, 导致加工硬化. 随温度升高,试样断裂模式从单一解理断裂向穿晶解理－沿晶混合断裂转变,在1000℃时, 试样断口处能清晰地观察到滑移带.

The ordered intermetallic Mo₅SiB₂ (T2 phase) is a promising elevated－temperature structural material because of its high melting temperature, and excellent resistance to oxidation and creep. T2 phase has a body－centered tetragonal D8₁ structure (I4/mcm),with 20 Mo, 4 Si and 8 B atoms situating in layered arrangements along the c axis.This structure has been regarded as the obstacle to plastic deformation or dislocation activity especially at ambient temperature. However, like most intermetallic compounds, it undergoes a brittle－to－ductile transition (BDT) up to high temperatures, where the increased ductility is companied by microstructure changes. The feature of high－temperature applications makes it necessary to investigate the BDT behavior. The analysis of microstructure, dislocation configuration and fracture surfaces were carried out by compression and three－point bending tests, coupled with XRD, SEM－EDS and TEM methods. The result suggested that BDT happened over a wide temperature range of 1000－1200℃. At the BDT temperature above, multiple slip systems such as the [010](001) and <110>{110} could be activated under an applied stress, resulting in obvious plastic deformation. Since the edge dislocation displayed more activity than screw and mixed ones, the edge dislocation with b=[010] interacted with the <110>－type dislocation via slipping into its plane of {110}. Therefore, the work hardening was caused by the formation of lots of dislocation nodal points during the subsequent compression process. With temperature increasing, the fracture mode underwent a conversion from transgranular cleavage at ambient temperature to a mix of transgranular cleavage and intergranular failure.