円管横坮縮による溶射皮膜の曲げ強度の簡便・高効率評価法の考案

摘要

発電用ガスタービンプラントではタービン入口温度rnの高温化が熱効率の向上につながる．新材料や冷却技rn術の開発と伴にその温度は年々高温化され，現在rn1500℃に至っている．超合金基材単独の使用では耐rn熱限界を超えるため，熱遮蔽皮膜（TBC）や耐熱・耐食rn皮膜MCrAlY（MはCoやNi）は必要不可欠なものとなrnっている．%Protective coating, MCrAlY, is used to isolate a super alloy substrate from oxidation and/or corrosion. The mechanical properties of the coating give the significant influence on the thermo-mechanical fatigue strength of the substrate. However, there are few proper and simple methods to evaluate the mechanical properties of the thin coatings used in actual systems. Authors have developed the lateral compression method of circular tube specimen and applied to evaluation of high temperature mechanical properties and fatigue strength in plasma spray coatings. The circular tube specimen has great merits, easy to make and easy to load. The specimen has further great merit that the test piece breaks 4 times in only one test piece. In this study, beam models were proposed to evaluate the strength of 4 locations. Loading with two plates was proposed because loading was easy and stable. However, in the case of loading with two plates, the beam model was apt to disagree with the actual deformation if the coating had low stiffness. It was because intensive load converted to distributed load and the loading point moved from original point. Then, the applicable range of thickness and Young's modulus was examined by FEM elastic contact analysis. It was found that the bending strength of thin coating is able to be obtained accurately by selecting the proper radius of circular tube specimen. It was also found that the method does not depend on materials if the Young's modulus is greater than 50 GPa. These results were also confirmed experimentally using CoNiCrAlY coatings.