| Zr1-xAlxN layers have been deposited in the full compositional range (x = 0...1) by adjusting working point and pulse times for reactive pulsed magnetron co-sputtering of aluminium and zirconium targets. Whereas ZrN is known to be a hard coating material with properties similar to the well established TiN, yet a higher oxidation resistance, no enhanced hardness is found for Zr1-xAlxN in a range x=0.3...0.9, as it is the case for Ti1-xAlxN with x = 0.5...0.7. However, films with a fraction of only a few atomic percent aluminium exhibit enhanced hardness up to 30 GPa, which is well above the hardness of pure ZrN or pure AlN (25 GPa both) deposited by reactive pulse magnetron sputtering. XRD investigations reveal the nanocrystalline nature of the coating with a grain size of 10 nm for the cubic structure ZrN with a (100) preferred orientation. It is believed that Al acts as an impurity which limits the grain growth and initiates frequent re-nucleation of ZrN-crystallites. Thereby, the nanocrystalline structure is formed with a maximum in hardness for an optimum Al concentration of approximately 5 at.%. |
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