Weak-beam Transmission Electron Microscopy Study On Dislocations And Twins In Intermetallic Compounds

Intermetallic compounds have extensive prospects in the area of high-temperature structural materials. Therefore, studies of dislocations and twins in the y phase in superalloys and y-TiAl phase in titanium-aluminium alloys are important. In this dissertation, dislocations in the y phase in a SRR300D superalloy and twins, dislocations in a y-TiAl phase have been identified by the means of transmission electron microscopy and weak-beam imaging techniques.A series of weak-beam images have been obtained from zonal axes of [001] and [Oil], in order to identify Burgers vectors of dislocations in the Ni-based superalloy. The Burgers vector of a perfect dislocation is identified as 1/2[1-10] and that of a partial dislocation as 1/6[21-1].Twins and dislocations are abundant in the cast single crystaltitanium-aluminide. Dislocations are observed on the coherent twin boundaries. There exist ordinary dislocations of 1/2<110] and superlattice dislocations of [01-1] and 1/2[-112] in the intermetallic compound. The ordinary distocations are likely to climb and annihilate by cross slip, which results to prismatic bops. Dissociation of superlattice dislocations was observed in a diamond-shaped region enclosed by two sets of{111} twin lamellae, the reaction equation for this dissociation is [101]â†'1/2[1-10]+1/2[112].Twin lamellae are observed in the cast single crystaltitanium-aluminide. One sets of twin lamellae are parallel to each other, while the other sets cut through them at the intersection sites. Four sets of{111} twin lamellae were observed in a sample area and they are confirmed by selected area diffraction patterns. The intersection between two {111} twins and the movement of dislocations in the twin lamellae were observed in an impact deformed y-TiAl phase.