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-

一个小冲孔蠕变（SP-C）测试方法，使用一个尺寸为10 mm × 10 mm × 0.3mm的小型试样已被证明是评估蠕变性能和机械性能退化，由于长期的服务操作在高温下。该测试方法包括将集中的中心载荷施加到在其周围区域刚性支撑的试样上，并确定给定载荷和温度下的中心变形与时间的关系曲线。将SP-C法应用于几种高温锅炉和涡轮机材料，包括钨合金化9 Cr铁素体钢、316型不锈钢和镍基高温合金。实验结果表明，得到的SP-C试验的蠕变曲线的整体形状是定性相似的那些从传统的单轴蠕变试验，它清楚地描绘初级，二级和三级蠕变阶段。弯曲是一个主要的变形模式，而膜拉伸是主导模式，在第二和第三蠕变区。与单轴蠕变的相关性确定的应力（负荷）指数和蠕变变形的表观活化能。特别是，从SP-C方法获得的表观活化能接近单轴蠕变试验确定。断裂数据是从使用Larson-Miller参数对所用材料进行的SP-C试验中推导出来的。结果表明，SP-C测试方法使我们能够确定高温材料降解对蠕变性能的影响。上述实验证据表明，SP-C测试技术提供了一个有用的工具，用于评估在役结构部件的蠕变性能退化。

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.