Investigation of high temperature synthesis of Al2O3 and ZTA coatings by HSPVD

• Applicant: Professorin Dr.-Ing. Kirsten Bobzin
• Subject Area: Coating and Surface Technology
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 532907407

Due to the special properties of nickel-based alloys and the associated requirements for machining this material, coated carbide tools are used. In addition to a low adhesion tendency and a high abrasion resistance, the tools must have a high temperature stability and oxidation resistance. In particular, crystalline α-alumina (Al2O3) produced by high temperature chemical vapor deposition (HT-CVD) offers high potential as a wear protection layer for cutting tools. However, in contrast to the numerous studies on the synthesis of PVD-Al2O3 at temperatures T ≤ 700 °C, there are only a few studies dealing with the synthesis of Al2O3 using HT-PVD processes T > 700 °C. In the case of HT-synthesized α-Al2O3 coatings, the investigation of the deformation behavior, the residual stress state and the crack resistance, which represent important property criteria under the conditions of use of these coatings on cutting tools, are also ignored. The disadvantages of pure Al2O3 coatings include brittle coating behavior and low crack resistance. Therefore, in the field of high-performance ceramics, attempts have been made to develop new oxide ceramics with the aid of additional phases, of which ZrO2 has proved to be very promising, and thus to overcome the limitations of α-Al2O3. In zirconia-reinforced alumina (ZTA), the addition of ZrO2 to Al2O3 leads to an increase in crack resistance. In the research on PVD-ZTA coatings, however, only a few investigations have been carried out. High-speed (HS) PVD is based on the principle of hollow cathode gas flow sputtering (HK-GFS) and also enables HT coating processes at temperatures up to T = 950 °C. Preliminary work has shown that HS-PVD technology in particular offers great potential for the development of oxide wear-resistant coatings. The overall objective of the research project now applied for is to investigate thick (s > 15 µm) crystalline α-Al2O3 coatings by means of HT-PVD, 700 °C ≤ T ≤ 900 °C, and to gain knowledge about the influence of high process temperatures on the coating properties. In particular, the HS-PVD technology is used for coating development, which enables the production of thick PVD coatings at high temperatures. A process window for the deposition of crystalline α-Al2O3 at higher process temperatures will be investigated. Various analyses will be carried out to determine the influence of high process temperatures on coating properties. Furthermore, the influence of ZrO2 on crack resistance of ZTA-HS-PVD coatings will be investigated. As a result of the analyses carried out, the residual stress state in the HS-PVD coatings and the interactions between the coating parameters and the residual stresses will be fundamentally researched and adjusted with regard to machining.

• DFG Programme: Research Grants