Strength Estimation and Residual Stress Analysis of Thermal Barrier Coatings by Synchrotron Radiations.

将NiCoCrAlY作为粘结涂层，等离子喷涂在Ni高温合金基体上，采用空气等离子喷涂方法在试样表面喷涂一层涂层。来自同步加速器源的高能x射线具有较大的穿透深度。研制了专门的高温地应力测量炉。该炉在SPring-8中连接在光束线BL02B1上的4圆测角仪上。利用72keV的高能x射线，通过顶部涂层对粘结层的内应力随温度的升高进行了无损测量。在1073 K或更高的温度下，由于粘结层的软化，粘结层中的内应力被释放。粘结层内应力随温度的变化可以用粘结层与顶层膨胀的热失配来解释。提出了一种新的评价剥落应力的混合方法。热障涂层的面内应力可用实验室x射线测量，面外应力可用高能同步x射线测量。结合低能x射线和高能x射线测得的应力，评价了剥落应力的分布。为了氧化试样，试样在1373 K的空气中保存0,500,1000和2000h。用扫描电镜观察各氧化试样的横截面。热生长氧化物（TGO）由氧化铝层和复合氧化物层组成。暴露500h后，氧化铝层厚度停止增加，复合氧化层厚度单调增加。TGO在粘结层的凸部生长，并向上推顶。结果，在凸部附近产生了剥落裂纹。利用实验室x射线和高能同步加速器x射线获得的应力数据，采用混合方法估计了各氧化试样的剥落应力。未氧化的表面涂层不存在剥落应力。氧化试样的剥落应力在表面以下较小，在顶部与粘结层交界面附近急剧增大。界面附近的剥落应力约为200 MPa。暴露1000h时的剥落应力分布与暴露500h时相似。TGO促进了顶层涂层的剥落，剥落应力的分布与观测到的剥落裂纹位置相对应。少

As a bond coating, NiCoCrAlY was plasma sprayed oh the substrate of Ni super alloy and a top coating of the specimen was made by air-plasma spraying. High energy X-rays from a synchrotron source has a large penetration depth. A special furnace was made for the in-situ stress measurement in high temperature. This furnace was attached on a 4-circle goniometer at a beam line BL02B1 in SPring-8. Using high energy X-rays with 72keV, the internal stress of the bond coating was measured nondestructively through the top coating with the increase in temperature. At 1073 K or higher, the internal stress in the bond coat was released due to softening of the bond coat. The change of internal stresses in the bond coat with temperatures was explained by thermal mismatch of expansion between top and bond coats.A new hybrid method was proposed to evaluate a spalling stress. The in-plane stress in the thermal barrier coatin can be measured with laboratory X-rays, and the out-of-plane stress can be meas … More ured with high energy synchrotron X-rays. Combining these stresses obtained by the low and high energy X-rays, the distribution of the spalling stress was evaluated. To oxidize the specimen, the specimens were kept in air at 1373 K for 0,500,1000 and 2000h. The cross section of each oxidized specimen was observed with a scanning electron microscope. The thermally grown oxide(TGO) consists of the alumina layer and the composite oxide layer. The thickness of alumina layer stopped to increase after 500h exposure, while the thickness of the composite oxide layer incresed monotonically. The TGO grew at the convex part of the bond coating, and pushed up the top coating. As a result, the spalling crack was initiated near the convex part. The spalling stress for each oxidized specimen was estimated by the hybrid method using the stress data obtained by laboratory X-rays and high energy synchrotron X-rays. The top coating without the oxidization did not have the spalling stress. For the oxidized specimen, the spalling stress was small beneath the surface, and steeply increased near the interface between the top and the bond coating. The spalling stress near the interface was about 200 MPa. The distribution of the spalling stress for the case of the 1000h exposure was similar to that for the case of 500h. The TGO promotes the spallation of the top coating, and the distribution of the spalling stress corresponds to the observed position of spalling cracks. Less