Power plant metallic components working at high temperature and stress in the creep range undergo material degradation due to intrinsic damage caused by microstructural deterioration and grain boundary voids. These aspects are considered for designing such components for a definite period, for example 200, 000 h. At the end of designed life the components cannot be retired since useful remaining life exists in most cases [1]. The remaining life of the component is decided to a large extent by microstructural damage assessment involving nondestructive in-situ metallography, replication and evaluation of the replicas in microscopes [1, 2]. To improve the quality of microstructural characterization after creep damage it was thought that the analysis of area-wise invariant multilayers at discrete depths without translational and rotational errors can help significantly. The multiple layers are assembled to get a 3-D picture using a software. The data generated from multiple layers will enhance the accuracy and reliability of damage assessment as compared to conventional one layer replication. The actual work was accomplished by in-situ abrasive lapping followed by electropolishing using CEPIN and APINE [3, 4]. Two or three close in-situ Vickers hardness impressions were made to identify the spot for repeated photomicrography and also for measuring the depth. The successive diagonal measurement of the Vicker's diamond indentor after polishing and etching will give a measure of depth of dissolution as the ratio of depth to diagonal is 1: 7 The replicas were taken after each successive layer removal and etching, and the depth of each layer removed was known from successive diagonal reduction. These replicas were gold sputtered and examined in light optical microscope and in SEM. Series of photomicrographs were obtained at various depths without translational and rotational errors. These photomicrographs at various depths were used as inputs for data processing. The results will be presented and discussed. REFERENCES
- R. Viswanathan, " Damage Mechanisms and Life Assessment of High Temperature Components", ASM International, OHIO, 1989.
- B. Neubauer and V. Wedel, " ASME Int. Conf. In Advances in Life Prediction Methods", Albany, U. S. A., pp. 307-313, 1983.
- G. Venkataraman, "Non-Destructive Testing 92", Proc. 13th WCNDT, Brazil, pp. 1223-1227, 1992.
- G. Venkataraman, "Life Assessment of Power Plant Components at Difficult Locations by Improved In-Situ Metallography", J. of Non Destructive Evaluation, Vol. 14, No. 1-4, pp. 24-27, 1994.
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