Molecular dynamics (MD) simulations are applied to elucidate the anisotropic characteristics in the material responses for crystallographic nickel substrates with (100), (110) and (111) surface orientations during nanoindentation. The strain energy of the substrate exerted by the tip is stored by the formation of the homogeneous nucleation, and is dissipated by the dislocation sliding of the {111} plane. The steep variations of the indentation curve from the local peak to the local minimums are affected by the numbers of slip angle of {111} sliding plane. The pile-up patterns of the three nickel substrates prove that the crystalline nickel materials demonstrate the pile-up phenomenon from nanoindentation on the nanoscale. The three crystallographic nickel substrates exhibit differing amounts of pile-up dislocation spreading at different crystallographic orientations. The effects of surface orientation in material properties of F.C.C. nickel material on the nanoscale are observable through the slip angle numbers of {111} sliding planes which influence hardness values, as well as the cohesive energy of different crystallographic surfaces that indicate Young¡¦s modulus. Furthermore, the multiscale simulations are performed on the (100) monocrystal nickel substrate by using nanoindentation, compensating for MD limitation of a large specimen simulation without significant increase in the size of the problem. This study examines the accuracy of the coupling method for the multiscale model by means of the indentation curve and the deformation profile.
Nanoindentation-induced mechanical deformation in GaN thin films prepared by metal-organic chemical-vapor deposition (MOCVD) was investigated using the Berkovich diamond tip in combining with the cross-sectional transmission electron microscopy (XTEM). By using the focused ion beam (FIB) milling to accurately position the cross-section of the indented region, the XTEM results demonstrate that the major plastic deformation was taking place through the propagation of dislocations. The present observations are in support of attributing the pop-ins appeared in the load-displacement curves to the massive dislocation activities occurring underneath the indenter during loading cycle. The absence of indentation-induced new phases might have been due to the stress relaxation via substrate and is also consistent with the fact that no discontinuity was found upon unloading.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-1024107-135247 |
| Date | 24 October 2007 |
| Creators | Wang, Chung-ting |
| Contributors | T. N. Shiau, Hsieh, Shou-Shing, Chien, Chi-Hui |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-1024107-135247 |
| Rights | unrestricted, Copyright information available at source archive |
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