Slip systems and dislocation emission from crack tips in single crystal TiC at low temperatures
- Case Western Reserve Univ., Cleveland, OH (United States). Dept. of Materials Science and Engineering
Low temperature (20--90 0C) plastic deformation in TiC{sub 0.91} single crystals has been studied using microindentations on (111), (001) and (110) surfaces, the dislocation structures around microindents being characterized by transmission electron microscopy (TEM). Deformation occurs primarily by {l_brace}111{r_brace}<1{bar 1}0> and {l_brace}110{r_brace}<1{bar 1}0> slip, with the favored slip system determined by crystal orientation. Indentations below 300 C produced distinct dislocation half loops-hexagonal loops arising from {l_brace}111{r_brace} slip and elongated loops from {l_brace}110{r_brace} slip. At 500 C, much more extensive plastic deformation occurred, accomplished mainly by the motion of edge dislocations from these same systems. The dislocation configurations suggest a relatively high mobility of edge segments and a large Peierls stress for screw dislocations. Thermal activation apparently increases the mobility of screw segments, and results in dislocation structures containing mixed dislocations with no preferred orientation; this signals the onset of the brittle-ductile transition between 700 and 900 C. Cleavage cracks around indents on {l_brace}111{r_brace} and {l_brace}110{r_brace} surfaces introduced below 500 C, but not those on {l_brace}001{r_brace}, arrested with dislocation emission at the crack tips. The emitted dislocations were coplanar dislocation half loops, arising from {l_brace}001{r_brace}<110> slip, and resulted from mode II or mode III loading of the cleavage crack. The local mode II and mode III stress intensity factors must have been sufficiently high to activate {l_brace}001{r_brace} slip, even though this slip system has not, to date, been reported in macroscopic tests.
- OSTI ID:
- 271771
- Journal Information:
- Acta Materialia, Vol. 44, Issue 6; Other Information: PBD: Jun 1996
- Country of Publication:
- United States
- Language:
- English
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