報告書番号

Q04017

タイトル（和文）

ガスタービン遮熱コーティングの耐熱サイクル特性評価手法の開発 -－TBCの損傷過程並びに耐熱サイクル特性向上方策－-

タイトル（英文）

Development of Evaluation Method for Resistance to Thermal Cycling of Thermal Barrier Coatings for Gas Turbine-Damage Process of TBC and Improvement of Resistance to Thermal Cycling-

概要 （図表や脚注は「報告書全文」に掲載しております）

高熱流束加熱試験装置を用いて、ガスタービン定格時における温度負荷および熱応力負荷を模擬した熱サイクル試験を行った。その結果、トップコート深さ方向のき裂（縦き裂）が発生し、それがボンドコートとの界面付近にまで成長すると、界面方向に成長するき裂（横き裂）が発生した。さらに、この横き裂が近傍の横き裂と合体することでトップコートのはく離が生じると考えられる。また、トップコートの気孔率を分析した結果、焼結による気孔率の減少が観察された。トップコートの焼結によって増加した引張応力が、熱サイクルに伴う熱疲労とともに、縦き裂の発生と成長を促進していると考えられる。さらに、気孔率を増加させるとともに不純物濃度を低減させたトップコートを用いたTBC試験片の熱サイクル試験では、同じ熱流束、基材表面温度の条件下において、縦き裂の成長速度が小さく、横き裂の合体も少なかった。

概要 （英文）

In order to clarify a damage process of a topcoat of a thermal barrier coating (TBC) for gas turbines under heat flux, thermal cycle tests were performed by means of a high heat-flux heating apparatus. TBC (Yttria stabilized Zirconia (YSZ)) specimens were heated by plasma gas flow and its back was cooled by water. The experimental observation clarified the damage process of the TBC specimens as follows. At first, cracks were initiated in the direction of coating thickness (vertical crack). When they reached at the vicinity of the boundary between a topcoat and a bond coat, cracks growing along the boundary (transverse cracks) were initiated in the vicinity of the boundary. The transverse cracks were coalesced each other, and they can lead to the topcoat delamination. After the thermal cycle test, the porosity of topcoat decreased due to sintering. The tensile stress increased by the topcoat sintering, as well as the thermal fatigue due to thermal cycles, promotes the initiation and growth of vertical cracks. In thermal cycle tests by means of a more porous TBC with smaller concentration of impurities such as SiO2 in sprayed particles of YSZ, growth rates of vertical cracks was smaller and coalescence of transverse cracks was rarer compared with the denser TBC including more impurities. The tensile stress on topcoat surface decreases by the following reasons:① The porosity of the latter TBC was larger than that of the former one at the same number of cycles. The porosity, moreover, decreased due to sintering during the thermal cycling test and its decrease saturated. The saturated porosity of the latter was also lager than that of the former. These results in the decrease of Young’s Modulus.The decrease of thermal conductivity due to the higher porosity increases the temperature gradient in the topcoat. As a result, the restraint of topcoat surface is increased.

報告者

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