Fracture behavior and lifetime performance of thermal barrier coatings in thermally graded mechanical fatigue environments

Abstract

The effects of bond coat species on the fracture behavior and lifetime performance were investigated in thermal barrier coating (TBC) systems through thermally graded mechanical fatigue (TGMF) tests. Two types of process, air-plasma spray (APS) and high-velocity oxygen fuel (HVOF), were employed to prepare the bond coats of about 300 μm thickness, and then the top coat of about 600 μm thickness was coated on the both bond coats by APS process. The TGMF tests with two tensile loads of 100 and 150 MPa were performed until 900 cycles at a surface temperature of 850 and 1100 °C for a dwell time of 10 min, and then the sample was cooled at the room temperature for 10 min at each cycle. When the tensile load applied in TGMF tests was 100 MPa at 850 °C, the TBC with APS bond coat showed delamination phenomena at the interface between the top and bond coats and small cracks on the surface after about 250 cycles, while the TBC with HVOF bond coat showed a long crack at interface between the top and bond coats without delamination phenomena until 900 cycles. As the tensile load in TGMF tests was increased to 150 MPa at 850 °C, delamination and/or cracks were created at the relatively low cycles, after about 130 and about 279 cycles for the TBCs of the APS and HVOF bond coats, respectively. When the tensile load applied in TGMF tests was 100 MPa and the temperature increase to 1100 °C, the TBC with APS and HVOD bond coats were delaminated after about 65 and about 110 cycles, respectively. These evidences indicate that the TBC with HVOF bond coat is more efficient in improving lifetime performance than that with APS bond coat in the thermal and mechanical environments.