Structure and mechanical properties of polycrystalline CrN/TiN superlattices
- Department of Materials Science and Engineering, Northwestern University, Evanston, Illinois 60208 (United States)
- Advanced Coatings Technology Laboratory, Northwestern University, Evanston, Illinois 60201 (United States)
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{endash}N{sub 2} mixtures with partial pressure control of the N{sub 2}. As the N{sub 2} partial pressure was increased from 0.1 to 1.1 mTorr, TiN{sub x} films went from stoichiometric B1-cubic TiN to slightly overstoichiometric TiN, while CrN{sub x} films went from cubic Cr{endash}N solid solutions to hexagonal Cr{sub 2}N to B1-cubic CrN. Since the N{sub 2} partial pressure required to form stoichiometric CrN was {approx}10 times that required to form stoichiometric TiN, nitrogen was inlet at the Cr target position to maximize the difference in N{sub 2} 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 {ital 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-{mu}m-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 {approx}75{percent} larger than the rule-of-mixtures value. The hardness enhancement mechanisms are discussed. {copyright} {ital 1998 American Vacuum Society.}
- OSTI ID:
- 641611
- Journal Information:
- Journal of Vacuum Science and Technology, A, Vol. 16, Issue 5; Other Information: PBD: Sep 1998
- Country of Publication:
- United States
- Language:
- English
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