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Ti1-xAlxN thin films have been widely studied and proven to be effective multicomponent wear resistant tool coatings because of their high hardness, outstanding resistance to high-temperature oxidation, and beneficial age-hardening behavior. Analogous Hf1-xAlxN is likely to perform even better as a tribological hard coating however, because HfN is harder and more thermodynamically stable than TiN. Moreover, stronger driving forces for segregation during growth and aging are expected due to the increased lattice mismatch between HfN and AlN. Here, we present an initial investigation into the growth and physical properties of epitaxial and nanocrystalline Hf1-xAlxN. Hf1-xAlxN layers with 0≤x≤0.49 were grown on MgO (001) substrates at 550°C by UHV reactive magnetron sputter deposition in 90%Ar+10%N2 discharges at 7mTorr. HRXRD and TEM results showed that B1-NaCl structure layers grow epitaxially with a cube-on-cube orientational relationship. The lattice parameter decreased linearly from 0.453 nm to
0.444 nm with x=0.50, compared to 0.432 nm expected from the linear Vegard¡¯s rule. We found a metastable single phase field that is remarkably broad given the large lattice mismatch between the two alloy components. Alloying HfN with AlN leads to an increase in hardness (~25% to 39GPa), as well as nanostructured compositional modulations due to the onset of spinodal decomposition.
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