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tial3 grain structure observed during annealing at different temperatures
The nucleation and growth phenomenon of tial3 phase at the Ti/tial3 and Al/tial3 interfaces were analysed by orientation imaging microscopy (OIM) using electron backscattered diffraction (EBSD). Results showed that the resulting tri-modal tial3 grain structure was found to be consisting of fine grains near Ti/tial3 interface, coarse grains at the centre part and relatively small grains at the Al/tial3 interface.
During the annealing process, the fine grains of tial3 phase were nucleated at the Ti/tial3 interface and remained in this region for a longer time due to the low interfacial energy. On the other hand, the fine grains of tial3 nuclei on the Al/tial3 interface were shifted towards the Al side during the annealing process. This can be attributed to the fact that Al diffuses faster than Ti and so the mass transport from Al to Ti side is high.
This leads to the formation of a tri-modal tial3 grain structure between Ti and Al sheets with nearly nano-sized tial3 grains/nuclei near Ti/tial3 interface, fine tial3 grains adjacent to the region of minimal growth shifted towards Al side (Region D) and coarse and intermixed regions B and C at the centre part. The grain size of tial3 at the Ti/tial3 surface is significantly larger than that at the Al/tial3 surface.
The presence of tial3 in the reaction product was demonstrated through X-ray diffraction (XRD) and direct thermal analysis (DTA). DTA curves of samples containing tial3 showed that the melting point of tial3 phase at 670.0 degC was offset by peaks at 1 388.4 degC and 1 340.4 degC respectively.