Thermal Stability of cubic and nanocrystalline arcevaporated TiCrAlN coatings
(TixCryAlz)N coatings were deposited on WC-Co substrate using cathodic arc evaporation technique to investigate phase transformation, thermal stability, and high temperature mechanical properties. Two compositions Ti0.34Cr0.33Al0.33N and Ti0.24Cr0.02Al0.74N were studied and compared with industrial standard hard TiAlN coating. These compositions were annealed at 800 oC up to 1100 oC. X-ray diffractogram showed a mixture of cubical and hexagonal phases in as-deposited state for high Al content composition. Differential scanning calorimetry showed that spinodal decomposition starts late compared to TiAlN coating. The results from nanoindentation did not show age hardening in Ti0.34Cr0.33Al0.33N composition while composition Ti0.24Cr0.02Al0.74N showed a significant increase in hardness compared with TiAlN coating. Also the Ti0.24Cr0.02Al0.74N retains its hardness over a wide temperature range while TiAlN coating hardness decreases after annealing at 900 oC. Upon annealing at 1400 oC, the coating decomposes into equilibrium phases i.e., c-TiN and h-AlN while Cr found to be in oxides form. HRTEM results revealed that the coating consists of nanocrystalline grains with defects rich regions.
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