Growth of single-crystal TiN/VN strained-layer superlattices with extremely high mechanical hardness

Abstract

Single-crystal TiN/VN strained-layer superlattices (SLS’s) with layer thicknesses lTiN =lVN =λ/2 (where λ is the period of the superlattice) ranging from 0.75 to 16 nm have been grown on MgO(100 ) substrates by reactive magnetron sputtering. Cross-sectional transmission electron microscopy (TEM) and x-ray diffraction examinations showed that the films were single crystals exhibiting coherent interfaces and several orders of superlattice reflections. There was no evidence in either plan-view or cross-sectional TEM analyses of misfit interfacial dislocation arrays. The primary defects observed were dislocation loops with a diameter of 8–10 nm extending through several layers and small defects with a diameter of 1–2 nm that were confined within single layers. Microindentation hardness values H, measured as a function of λ in films with a total thickness of 2.5 μm, increased from 2035±280 kg mm−2 for Ti0.5V0.5N alloys (i.e., λ=0) to reach a maximum of 5560±1000 kg mm−2 at λ=5.2 nm and then decreased rapidly to 3950±550 kg mm−2 at λ=7.5 nm. Further increases in λ resulted in a slower decrease in H to 3640±550 kg mm−2 at λ=32 nm. The large error bars in the H values for the SLS samples were due to the difficulty in measuring such extremely high hardnesses in thin films. (H for pure single-crystal TiN and VN films were 2200±300 and 1620±200 kg mm−2, respectively.) SLS samples grown with constant λ=6.5 nm, but different lTiN /λ ratios, exhibited a maximum hardness at lTiN /λ≂0.3.

Fretting wear analysis of TiC/VC multilayered hard coatings: experiments and modelling approaches

“…This shows that no direct correlation can be drawn between the micro-hardness properties and the sublayer inter-diffusion phenomena. Such a tendency was previously confirmed on TiN/NbN superlattices by Yashar and Sproul [7] and by other authors [8,9] for different carbide and nitride PVD deposited superlattice coatings. Anderson and co-authors also observed a similar micro-hardness evolution for metallic structure like Cu/Ni multilayers [10].…”

“…4) leads to the following general expression associated to a mean "composite" friction coefficient. (8) Applied to the bi-layer system, the following simplified formulation is then deduced. …”

Phase transformations in nanocomposite ZrAlN thin films during annealing

“…8 Also two-phase nanocrystalline materials in the form of multilayers exhibit an increased hardness compared to their constituents due to the difference in elastic properties between the layers that hinder dislocation motion, 9 most clearly seen in nanoscale multilayers. 10,11 The decomposition of metastable single-phase films can also act to improve the hardness at elevated temperature as a two-phase structure is formed. The most studied of these is the TiAlN system where age hardening upon annealing of thin films was first observed.…”

Solid particle erosion mechanisms of protective coatings for aerospace applications

“…In studies on the TiN/VN [40] and TiN/NbN [41] systems, maximum hardness enhancement can be observed for a periodicity between 4 and 8 nm, as illustrated in Figure 2.6 taken from [42]. The hardness enhancement mechanism was found to be the hindering of dislocation movement across sharp interfaces by a mismatch between the elastic moduli of the layers [42].…”