Oxidation and fatigue behaviour of γ-TiAl coated with HIPIMS CrAlYN/CrN nanoscale multilayer coatings and EB-PVD thermal barrier coatings

CrAlYN/CrN nanoscale multilayer coatings were deposited on γ-TiAl substrate material using high power impulse magnetron sputtering technology. The nitride coating provided effective oxidation protection to γ-TiAl at 850°C for exposure time periods exceeding 2000 cycles of 1 h dwell time at high temperature in air. High oxidation resistance was also observed at 900°C. After exposure to air at 850°C for 300 h, coated tension specimens exhibited a reduction in fatigue strength of about 70 MPa compared to the bare γ-TiAl alloy. Zirconia topcoats produced by electron-beam physical vapour deposition were well adherent to the CrAlYN/CrN coating with an oxy-nitride overcoat. When thermally cycled at 900°C, the lifetime of this thermal barrier coating system on γ-TiAl exceeded 1000 1 h cycles. Below cracks in the nitride coating, the substrate was oxidised and protrusions of an outer oxide scale with columnar structure formed.