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R Rachbauer1, A Blutmager, D Holec
1Department Physical Metallurgy and Materials Testing, Montanuniversität Leoben, A-8700 Leoben, Austria.
Surface & Coatings Technology
|February 10, 2012
Summary
Hafnium alloying in titanium aluminum nitride (TiAlN) coatings enhances high-temperature performance by delaying the formation of undesirable wurtzite AlN. This improves hardness and oxidation resistance for demanding applications.
Area of Science:
- Materials Science
- Thin Film Technology
- Computational Materials Science
Background:
- Titanium aluminum nitride (TiAlN) coatings are crucial for high-temperature applications due to their mechanical and thermal properties.
- Age hardening in cubic TiAlN increases hardness with temperature, but is limited by the formation of brittle wurtzite AlN at elevated temperatures.
- The transition to wurtzite AlN significantly degrades the mechanical properties of TiAlN coatings.
Purpose of the Study:
- To investigate the effect of hafnium (Hf) alloying on the thermal stability and phase transformation of TiAlN coatings.
- To determine if Hf alloying can increase the temperature at which wurtzite AlN forms, thereby improving high-temperature performance.
- To evaluate the impact of Hf on the mechanical properties and oxidation resistance of TiAlN films.
Main Methods:
- Computational modeling (ab initio predictions) to study phase stability and decomposition products in quaternary TiAlHfN and related ternary systems.
- Fabrication of TiAlHfN films with up to 10 at.% Hf.
- Vacuum annealing treatments at temperatures ranging from 600 to 1100 °C to study phase evolution and mechanical properties.
Main Results:
- Hf alloying shifts the formation of dual-phase c-Ti(1-z)Hf(z)N and w-AlN to approximately 200 °C higher temperatures compared to Hf-free TiAlN.
- TiAlHfN coatings maintain a hardness of ~40 GPa up to ~1100 °C, whereas Hf-free TiAlN reaches its maximum hardness (~38 GPa) at ~900 °C.
- Annealing experiments show a substantial improvement in oxidation resistance with increasing Hf content in TiAlHfN films.
Conclusions:
- Hafnium alloying effectively enhances the high-temperature stability of TiAlN coatings by suppressing the detrimental wurtzite AlN formation.
- The improved thermal stability translates to retained hardness at significantly higher temperatures and enhanced oxidation resistance.
- TiAlHfN coatings represent a promising advancement for protective coatings in extreme high-temperature environments.