Development of Monitoring Technique for Creep Deterioration in High Temperature Materials Using Miniaturized Specimens -Establishment of a New SP Creep Testing Method and Its Application-

小型冲压蠕变（SP-C）测试方法使用尺寸为10mm × 10mm × 0.3mm的小型化试样，用于评估高温下长期使用造成的蠕变特性和机械劣化。这种测试方法包括在试样周围区域施加集中的中心载荷，并在给定载荷和温度下确定中心变形随时间的变化曲线。SP-C方法应用于几种高温锅炉和汽轮机材料，包括钨合金9Cr铁素体钢、316型不锈钢和ni基超级合金。实验结果表明，SP-C试验获得的蠕变曲线总体形状与常规单轴蠕变试验获得的蠕变曲线在质量上相似，清晰地划分了初级、次级和三级蠕变阶段。弯曲是主导初级蠕变区的主要变形方式，而薄膜拉伸是主导二级和三级蠕变区的主要变形方式。根据应力（载荷）指数和蠕变表观活化能确定了与单轴蠕变的相关性。特别是，SP-C法得到的表观活化能与单轴蠕变试验结果接近。破裂数据是从使用Larson-Miller参数对旧材料进行的SP-C试验中推断出来的。结果表明，SP-C测试方法可以确定高温材料降解对蠕变性能的影响。上述试验证据表明，SP-C测试技术为评估在役构件的蠕变性能退化提供了一种有用的工具。

A small punch creep (SP-C) testing method using a miniaturized specimen with a dimension of 10mm by 10mm by 0.3mm has been demonstrated for evaluating creep properties and mechanical deterioration due to long-term service operations at high temperatures. This testing method involves the application of a concentrated central load to the specimen rigidly supported at its surrounding region, and determines a central deformation vs. time curve for a given load and temperature. The SP-C method was applied to several types of high temperature boiler and turbine materials, including tungsten-alloyed 9Cr ferritic steel, 316 type stainless steel, and Ni-based super alloys. Experimental results revealed that the overall shapes of the creep curves obtained SP-C tests were qualitatively similar to those obtained from conventional uniaxial creep tests, which clearly delineate primary, secondary, and tertiary creep stages. Bending was a dominant mode of deformation governing the primary creep region, while membrane stretching was dominant mode in the secondary and tertiary creep regions. A correlation with uniaxial creep was determined in terms of stress (load) exponent and apparent activation energy for creep deformation. In particular, the apparent activation energy obtained from the SP-C method was close to that determined from uniaxial creep tests. The rupture data was deduced from the SP-C tests conducted on the used materials using the Larson-Miller parameters. The results demonstrated that the SP-C testing method enables us to determine the effects of the high temperature materials degradation on the creep properties. The above experimental evidence suggests that the SP-C testing technique provides a useful tool for evaluating degradation of creep properties for structural components in-service.