DEVELOPMENT OF HIGH-TEMPERATURE EDGE-INFDENT APPARATUS THATENABLES IN-SITU MEASUREMENT OF HIGH-TEMPERATURE DELAMINATION STRENGTH OF CERAMIC COATING

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Increase in efficiency of jet engine and gas turbine has been important for energy saving and environment preservation. Along this line, thermal barrier coating (TBC) by ceramics spraying has been applied to blades of gas turbine and combustion chamber. However, TBC can be delaminated by long-time exposure at high temperature and thermal cycling due to the oxidation of interface between coating and substrate. The situation is almost the same for casting and forging dies coated by WC-Co cermet. The purpose of present research is to develop the apparatus by which in-situ evaluation of delamination strength can be carried out at high temperature.First, the TBC specimens coated by 8mass%Y_2O_3・ZrO_2 ceramics were kept at high temperature to obtain the information on the degradation of interface. At the same time, a testing machine was designed and fabricated. Main viewpoints of design were how to decide the indent position on coating exactly, turn back the indenter just before the indenter reaches substrate deeply, and protect the indenter and holder from high temperature (1027〜1273K).Secondly, various tests were carried out to examine the characteristics of the apparatus. The results were as follows : (1) Detecting of delamination load is difficult at high temperature because the kink point does not appear on load-displacement curve. However, the interruption method can be used to obtain the upper and lower limits of delamination load. (2) The loading speed does not influence the delamination load, so that the higher speed should be applied to avoid the damage of indenter and holder. (3) The delamination is easier when the top angle of SiC cone-shaped indenter is smaller. However the indenter with 80° is often broken, so that a larger angle will be necessary. Although the problems remained, the apparatus can be used to evaluate the high-temperature delamination strength effectively.