Characterization of the Induced Plastic Zone in a Single Crystal TiN(001) Film by Nanoindentation and Transmission Elect
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Characterization of the induced plastic zone in a single crystal TiN(001) film by nanoindentation and transmission electron microscopy Magnus Od´en Division of Engineering Materials, Department of Mechanical Engineering, Link¨oping University, S-581 83 Link¨oping, Sweden
Henrik Ljungcrantz and Lars Hultman Thin Film Physics Division, Department of Physics, Link¨oping University, S-581 83 Link¨oping, Sweden (Received 3 April 1996; accepted 19 February 1997)
≠ Æ The slip system of TiN at room temperature has been determined to be h110j 110 by Burgers vector analysis using transmission electron microscopy and slip trace analysis of indents made on a TiN(001) film deposited on a MgO(001) substrate. Both small indents (0.4 mN maximum load) and large indents (40 mN maximum load) were used to study the dislocation structure in TiN. The nucleation of dislocations was investigated using small indents. Further development of the plastic zone was studied using large indents and microhardness indents (1.6 N). The critical resolved shear stress evaluated at the load when pop-in occurs was estimated to be 3.7 GPa, assuming a Hertzian elastic contact. Indents made with a 0.4 mN maximum load show a complex dislocation pattern with loops and straight segments that belong to the same slip system. Dislocations of mixed screw and edge type are dominant. The cascade of dislocations generated during pop-in is likely to nucleate from loops. For larger indents, the plastic zone extends more than three times the diameter of the imprint. The straight dislocations outside the large imprint are arranged in arrays along the k100l and k110l directions. A scanning force microscopy study of the surface outside a microhardness indent revealed a raised surface along k110l and formation of troughs along k100l.
I. INTRODUCTION
TiN is used extensively in different applications, including wear-resistant coatings on mechanical components such as cutting tools. Knowledge about its properties such as plastic deformation mechanisms is limited mainly due to the problems associated with fabricating stoichiometric bulk NaCl structure TiN. High-quality single-crystal TiN thin films can, however, be grown on MgO substrates and used for studies of the plastic behavior of TiN.1 Materials with NaCl structure having a pronounced covalent bonding, e.g., TiC, VC, and ZrC, slip on the h111j planes, while more ionic materials of the same crystal structure like LiF, NaF, MgO, and NaCl have h110j as the primary glide planes.2 Even h001j has been observed as the glide plane for ZrC, but it is not favored. The Burgers vector of the dislocations for these materials is ay2k110l (a is the lattice parameter). ≠ The Æ slip system for TiN has been inferred to be h110j 110 in earlier studies. Wokulski3 deduced the slip system from anisotropic microhardness behavior of single crystal TiN whiskers and Hultman et al.4 from slip steps on the surface around a microhardness imprint. 2134
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