高温曝露されたEB-PVD遮熱コーティングの残留応力と組織

Residual stresses structure of EB-PVD thermal barrier coatings exposed at high temperature

鈴木 賢治*; 菖蒲 敬久  ; 和田 国彦*; 松原 秀彰*

Suzuki, Kenji*; Shobu, Takahisa; Wada, Kunihiko*; Matsubara, Hideaki*

ガスタービンエンジンの主要技術である遮熱コーティングに関して、高温大気曝露を施した試験片における残留応力及び組織観察を行い、曝露前との比較することによる材料挙動を検討した。高エネルギー放射光X線による非破壊応力測定の結果、コーティング表面から中間層において圧縮応力が開放されつつあり、組織観察からその原因は焼結による羽毛状組織の凝集が影響していると考えられる。また、ボンドコーティングとの界面付近のトップコーティング初期層では残留応力が解放されずに圧縮の面内残留応力が残っており、これはボンドコーティングと基材との熱膨張係数のミスマッチが影響していると考えられる。

Thickness of the bond coating was about 0.18 mm, and the thickness of the top coating was about 0.12 mm. The rotation speeds of specimens in the EB-PVD process were 5 rpm, 10 rpm and 20 rpm. The specimens were oxidized at 1273 K for 200 h. The in-plane residual stress was measured by a conventional X-ray method, and the out-of-plane residual strain was measured by a strain scanning method with hard synchrotron X-rays. For the specimens with 5 rpm and 10 rpm, the in-plane compressive residual stresses were released by the oxidization. For the specimen with 20 rpm, the in-plane residual stress did not change by the oxidization, because it was very small before the oxidization. The in-plane residual stresses were large compression near the interface. For the specimens with 5 rpm and 10 rpm, the out-of-plane stresses were small from the coating surface but became a compression near the interface. Both in-plane and out-of-plane residual stresses of the specimen with 20 rpm were very small. In the effect of decreasing the residual stress, the rotation speed of 20 rpm was the excellent condition. According to the observation with a scanning electron microscope, the featherlike columnar structure decreased after the oxidization. This volume decrease caused the release of the in-plane residual stresses.