Electron-backscattered diffraction and transmission electron microscopy study of post-creep Ti_3SiC_2

摘要

The post-creep microstructures of coarse-grained (100-200 mu m) and fine-grained (3-5mu m)Ti_3SiC_2 samples - both loaded in air at 1000 deg C, under a tensile stress of 80 MPa were studied by electron backscatter diffraction, EBSD, and transmission electron microscope, TEM. The CG sample ruptured after approx = 100 h, with a strain to failure of approx = 2.5 PERCENT that was mostly concentrated near the fracture plane. Analysis of more than 35 grains in the undeformed grip area indicated that the maximum misorientation, MO, angle within each grain was < 2 deg. In the deformed area, roughly 1.2 mm below the fracture surface, the MO's - again within each grain - varied dramatically; in some grains, MO's of the order of 10 deg in narrow spatial range - attributed to kink boundaries - were observed; in others, the MO was < 2 deg, i.e. they were un-deformed. Further analysis of the grains with large MO's revealed two types of deformed grains. Ones in which the kink boundaries - responsible for the MO - alternated in angle, or sign, forming a herring-bone like structure, and others in which they were all in same direction, causing bending of the basal planes. The latter deformation mechanism was confirmed by TEM. The TEM, on both fine and coarse-grained samples revealed the presence of dislocation arrays, low angle grain boundaries, as well as triple point cavities.