An Approach to Synthesize Thick α‐ and γ‐Al₂O₃ Coatings by High‐Speed Physical Vapor Deposition

Crystalline α‐ and γ‐Al₂O₃ exhibit in many applications high wear resistance, chemical resistance, and hot hardness, making them interesting materials for production engineering. To synthesize α‐Al₂O₃ with high coating thickness of s ≥ 10 μm, chemical vapor deposition at temperatures T > 1000 °C is well established. However, there are almost no studies dealing with the synthesis of thick α‐Al₂O₃ by physical vapor deposition (PVD) at high temperatures T > 700 °C. High‐temperature deposition of thick coatings can be realized by means of the dense hollow cathode plasma, combined with the transport function of the plasma gas in high‐speed (HS) PVD. Herein, crystalline α‐ and γ‐Al₂O₃ films are deposited on cemented carbides at substrate temperatures T _s ≈ 570 °C and T _s ≈ 780 °C by HS‐PVD. These coatings exhibit a thickness up to s = 20 μm. Moreover, phase analysis presents α‐phases in coatings synthesized at substrate temperature of T _s ≈ 780 °C with significant higher hardness than films by T _s ≈ 570 °C. These release the potential of HS‐PVD to synthesize α‐Al₂O₃ coatings with high thickness. Thereby, a higher thickness of these coatings is beneficial for the wear protection of turning and die casting tools.