부산대학교 도서관

The major effort during this report period was to elucidate the hardening mechanisms in polycrystalline superlattices. Since the last progress report, the authors have been working on theoretical modeling of hardening mechanisms in superlattices and have carried out detailed studies of two new polycrystalline superlattice coatings, NbN/VN and CrN/TiN, which were produced using an opposed, dual-cathode, high-rate, reactive, unbalanced-magnetron sputtering system. Significant hardness enhancement the above rule-of-mixture hardness value was found for the CrN/TiN, but not for the NbN/VN. Correlating these results with prior results for TiN/NbN and TiN/VN shows that the major hardening mechanism in polycrystalline superlattices is the difference in layer elastic moduli, which is minimal in the NbN/VN case. The modulus difference provides a barrier to dislocation flow across the layers. In the absence of modulus-difference hardening in NbN/VN, it was found that other hardening mechanisms such as coherency strains and the small grain sizes observed in the superlattices play a minor role. The results achieved in this report period are described in this paper along with publications and presentations.