Schichtentwicklung zum Oxidationsschutz von Titanaluminiden mittels HS-PVD

• Coating development for the oxidation protection of titanium aluminides by means of HS-PVD

Liang, Tiancheng; Bobzin, Kirsten (Thesis advisor); Oechsner, Matthias (Thesis advisor)

Düren : Shaker Verlag (2020)
Book, Dissertation / PhD Thesis

In: Schriftenreihe Oberflächentechnik 62
Page(s)/Article-Nr.: xiv, 143, Seiten : Illustrationen, Diagramme

Dissertation, RWTH Aachen University, 2020

Abstract

The demands for efficiency improvement and emission reduction in the aerospace industry are constantly increasing. Here, the use of lightweight construction materials offers a promising approach to increase the engine efficiency by reducing the mass inertia while minimizing the CO2 emissions. Presented as a new class of advanced engineering materials, the gamma titanium aluminide alloys have been attracting increasing interest in the recent years due to their low density of ρ ≈ 3.9 g/cm3, promising high-temperature strength as well as high oxidation and corrosion resistance up to the temperatures of T ≈ 750 °C. Hence, the γ-TiAl alloys have been considered as a competitive replacement for conventional Ni-based alloys, particularly in the production of moving parts for high-temperature applications. However, additional oxidation protective measures are required for higher application temperatures T > 750 °C.The objective of the present work is the development of high-temperature oxidation protective coatings for γ-TiAl alloys using high speed physical vapor deposition (HS-PVD). This variant of PVD process is characterized by high deposition rates, dense plasma and stable process control during reactive sputtering. These characteristics are of great interest, particularly for the synthesis of oxidation-resistant PVD coatings. In the first part of the work, the process development is presented, which builds the basis of the subsequent coating development. For this purpose, reference coatings with systematically varying parameter combinations are synthesized and characterized in order to determine an appropriate process window. In the second part of the work, novel coating systems are developed by means of HS-PVD. A total of four coating systems based on (Cr,Al)ON, CrAl, SiAl and SiAlY are developed and evaluated with regards to their suitability for the oxidation protection of γ-TiAl alloys. The oxidation resistance and the interdiffusion behavior of the coated samples are investigated by isothermal and thermo-cyclic oxidation tests at an application-relevant temperature T = 950 °C. Moreover, a new in situ post-annealing process consisting of vacuum annealing and pre-oxidation in the coating chamber is presented. The results show that the coatings produced by HS-PVD in combination with the applied in situ post-annealing represent a promising solution for the high temperature oxidation protection of γ-TiAl alloys.