Slip systems and dislocation emission from crack tips in single crystal TiC at low temperatures

Journal Article · Sat Jun 01 00:00:00 EDT 1996 · Acta Materialia

DOI:https://doi.org/10.1016/1359-6454(95)00360-6· OSTI ID:271771

Chien, F R; Ning, X J; Heuer, A H ^[1]

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1. 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, Journal Name: Acta Materialia Journal Issue: 6 Vol. 44; ISSN XZ504Y; ISSN 1359-6454
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
BRITTLE-DUCTILE TRANSITIONS
CRACKS
DEFORMATION
DISLOCATIONS
EDGE DISLOCATIONS
FRACTURE PROPERTIES
ORIENTATION
SCREW DISLOCATIONS
SLIP
STRESS INTENSITY FACTORS
STRESSES
TEMPERATURE DEPENDENCE
TITANIUM CARBIDES
TRANSMISSION ELECTRON MICROSCOPY