AVS 66th International Symposium & Exhibition
    Advanced Surface Engineering Division Thursday Sessions
       Session SE-ThA

Paper SE-ThA6
In situ Scanning Electron Microscopy based Uniaxial Compression of sub-micrometer-size NbC(100) Single-crystalline Pillars

Thursday, October 24, 2019, 4:00 pm, Room A215

Session: New Challenges and Opportunities in Surface Engineering
Presenter: Suneel Kodambaka, University of California, Los Angeles
Authors: A. Aleman, University of California, Los Angeles
K. Tanaka, University of California, Los Angeles
H. Zaid, University of California, Los Angeles
J.-M. Yang, University of California, Los Angeles
S. Kodambaka, University of California, Los Angeles
Correspondent: Click to Email
Cubic group 4 and 5 transition-metal carbides (TMCs), such as HfC and TaC, are hard (>20 GPa) and strong (moduli >270 GPa) solids with high melting points (> 2900 K) that exhibit superior strengths at elevated temperatures and excellent resistance to wear, ablation, and corrosion. They are attractive for applications in cutting tools, hard protective coatings, advanced propulsion systems, spacecrafts, rockets, and hypersonic jets that operate under extreme environments, e.g. at ultra-high temperatures (> 2000 K) and highly corrosive atmospheres. The realization of enhanced ductility, especially at low temperatures could potentially enable new applications for this class of materials. Our recent efforts have focused on understanding the mechanical behavior of group 5 TMC single-crystals, VC, NbC, and TaC.

Here, we report on the room-temperature mechanical behavior of 100-oriented NbC single-crystalline pillars of diameters between 330 and 830 nm. We prepared the pillars via focused ion beam milling of bulk, commercially-available, NbC single-crystals. We carried out uniaxial compression of the pillars using Hysitron PI-85 picoindenter in situ in a scanning electron microscope . We find that all the pillars exhibit plastic deformation with strains up to 26%. Load-displacement curves obtained during the compression tests reveal multiple displacement bursts, indicative of sustained slip. Interestingly, yield strengths vary non-monotonically with pillar diameter between 8 GPa and 12 GPa and by up to 40% among the pillars of the same diameter. From the post-compression images of the pillars, we identify {110}<110> and {111}<110> as the two likely slip systems operating within these pillars. We suggest that the observed size-dependence in NbC(100) pillars is a consequence of the activation of these two slip systems. We observe a similar size-dependence in VC(100) pillars based upon which we suggest that the observed mechanical behavior is characteristic of group 5 TMCs.