Structure and mechanical properties of polycrystalline CrN/TiN superlattices

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.

Wear and corrosion resistance of CrN/TiN superlattice coatings deposited by a combined deep oscillation magnetron sputtering and pulsed dc magnetron sputtering

“…Further increasing V s to -100 V, Cr, Ti and N element concentration showed a slight decrease to 12.6 at%, 36.2 at% and 51.2 at%, respectively, as a result of increasing γ sput . With an increase in V s , the increased ion bombardment resulted in the resputtering effect of Cr and Ti with increasing γ sput at higher V s than -60 V [34]. The Cr/(Cr+Ti) and (Cr+Ti)/N ratios slightly increased from 0.277 and 0.859 to 0.294 and 0.972, and then decreased to 0.258 and 0.953, respectively.…”

“…The Cr/(Cr+Ti) and (Cr+Ti)/N ratios slightly increased from 0.277 and 0.859 to 0.294 and 0.972, and then decreased to 0.258 and 0.953, respectively. The (Cr+Ti)/N ratio (Me/N ＜ 1) indicates that stoichiometric CrN and TiN cubic phases were probably obtained in the coatings at such a high N content (higher than 50%) [34][35][36]. TiN layers [37].…”

“…As V s was increased to -100 V, the peaks from LAXRD patterns became sharper and had a higher intensity. It clearly indicates that the obviously flatter and better defined interfaces between the CrN and TiN layers are gradually formed in CrN/TiN superlattice coatings, which are benefited from the increased ad-atom mobility and suppressed interfaceroughening effects due to the increased ion bombardment [34,35,[37][38][39]. The  of the coatings was calculated using the modified Bragg law [40].…”

Nanostructured Coatings

“…This increased hardness effect has been observed for many other nitride/nitride multilayer systems [6,7], but also for nitride/metal systems, where the materials have different crystal structures [8,9]. Figure 24.3 shows an example of the dependence of the hardness on the modulation period for TiAlN/Mo multilayers.…”

Dry Sliding Wear Model of Nanometer Scale Multilayered TiN/CrN PVD Hard Coatings

“…Recently, a new generation of thin films, named superlattices, consisting in nanometric scale multilayers, is particularly studied to extend the lifetime of cutting tools. Increase in hardness when compared to monolayered coatings has been often reported [1][2][3][4][5][6][7][8] and some explanations of this hardening are based on the Hall-Petch effect, on the variations of shear modulus or on internal stresses [9][10][11][12][13][14][15][16]. This hardening could be at the origin of the enhancement of wear resistance of superlattices, whereas for other authors, the key parameter would be rather the ratio of hardness (H) of the layer over its elastic modulus (E) [17][18][19][20].…”