Abstract
Polycrystalline CrN/TiN superlattice films were deposited on M1 tool steel using unbalanced reactive magnetron sputtering with opposed cathodes. The Cr and Ti targets were sputtered in Ar-N2 mixtures with partial pressure control of the N2. As the N2 partial pressure was increased from 0.1 to 1.1 mTorr, TiNx films went from stoichiometric B1-cubic TiN to slightly overstoichiometric TiN, while CrNx films went from cubic Cr-N solid solutions to hexagonal Cr2N to B1-cubic CrN. Since the N2 partial pressure required to form stoichiometric CrN was ≈10 times that required to form stoichiometric TiN, nitrogen was inlet at the Cr target position to maximize the difference in N2 partial pressures. Two series of CrN/TiN superlattices, with TiN fractions of 0.4 and 0.6, were deposited with periods ranging from 2 to 60 nm. X-ray diffraction showed a very strong (111) texture with first-order satellite peaks around the (111) Bragg peak. Kinematical diffraction simulations of the superlattice x-ray patterns indicated a strong composition modulation and a significant fluctuation in d-spacing that was related to ion bombardment defects. Cross-sectional transmission electron microscope images showed a columnar film structure with well-defined superlattice layers. Nanoindentation of 2-μm-thick CrN/TiN samples showed a maximum hardness of 35 GPa at a period of 2.3 nm, compared to 25 GPa for TiN and 14 GPa for CrN films. The maximum superlattice hardness was thus ≈75% larger than the rule-of-mixtures value. The hardness enhancement mechanisms are discussed.
Original language | English (US) |
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Pages (from-to) | 2913-2918 |
Number of pages | 6 |
Journal | Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films |
Volume | 16 |
Issue number | 5 |
DOIs | |
State | Published - 1998 |
ASJC Scopus subject areas
- Condensed Matter Physics
- Surfaces and Interfaces
- Surfaces, Coatings and Films