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-

点击翻译按钮获取中文摘要

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.