TY - JOUR
T1 - Dislocation shielding and flaw tolerance in titanium nitride
AU - Kumar, S.
AU - Wolfe, D. E.
AU - Haque, M. A.
N1 - Funding Information:
M.A. Haque gratefully acknowledges the support from the Center for Nanoscale Mechatronics & Manufacturing of the Korea Institute of Machinery & Materials and the National Science Foundation, USA (CMMI # 0625650).
PY - 2011/5
Y1 - 2011/5
N2 - Titanium nitride is a very brittle and flaw sensitive ceramic material at temperatures below 750 °C. In this study, we present experimental evidence of room temperature dislocation-based plasticity in the material as well as insensitivity to flaws in form of single edge notches. We performed in-situ fracture experiments inside the transmission electron microscope on 150-300 nm thick, 5 μ wide freestanding films fabricated from titanium nitride/titanium multi-layers with titanium nitride as the notched and titanium as un-notched layers. The calculated stress concentration factor for the 800 nm to 1.5 μ long notches were greater than 8, however, the terminal cracks always nucleated at the un-notched edge of the specimens and not at the notch tip. To explain such remarkable flaw tolerance, we observe motion of dislocations (pre-existing and nucleated away from the notch) towards the notch tip. We suggest that the room temperature dislocation activities are facilitated by the residual stresses in the multi-layer specimens and the thickness dependence of image forces, which reduces the effective shear modulus to promote dislocation motion. The migration of dislocations towards the notch tip shields it from stress concentration to manifest the flaw tolerance in 150 nm specimens, which is observed real time in the microscope.
AB - Titanium nitride is a very brittle and flaw sensitive ceramic material at temperatures below 750 °C. In this study, we present experimental evidence of room temperature dislocation-based plasticity in the material as well as insensitivity to flaws in form of single edge notches. We performed in-situ fracture experiments inside the transmission electron microscope on 150-300 nm thick, 5 μ wide freestanding films fabricated from titanium nitride/titanium multi-layers with titanium nitride as the notched and titanium as un-notched layers. The calculated stress concentration factor for the 800 nm to 1.5 μ long notches were greater than 8, however, the terminal cracks always nucleated at the un-notched edge of the specimens and not at the notch tip. To explain such remarkable flaw tolerance, we observe motion of dislocations (pre-existing and nucleated away from the notch) towards the notch tip. We suggest that the room temperature dislocation activities are facilitated by the residual stresses in the multi-layer specimens and the thickness dependence of image forces, which reduces the effective shear modulus to promote dislocation motion. The migration of dislocations towards the notch tip shields it from stress concentration to manifest the flaw tolerance in 150 nm specimens, which is observed real time in the microscope.
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U2 - 10.1016/j.ijplas.2010.09.003
DO - 10.1016/j.ijplas.2010.09.003
M3 - Article
AN - SCOPUS:79953856897
SN - 0749-6419
VL - 27
SP - 739
EP - 747
JO - International journal of plasticity
JF - International journal of plasticity
IS - 5
ER -