V. Karthik

Study of Microstructure and Property Changes in Irradiated SS316 Wrapper of Fast Breeder Test Reactor

This paper presents the results of a study on mechanical properties and microstructure in a SS316 wrapper irradiated in a 40MWt/13MWe fast breeder test reactor at Kalpakkam, India. Transmission electron microscopy (TEM) examination and mechanical property evaluation were carried out on the hexagonal wrapper subjected to different displacement damages up to a maximum of 83 dpa at an operating temperature of about 673 K. The steel irradiated to 83 dpa showed an increase in the yield strength and ultimate tensile strength, with a reduction in uniform elongation to about 8 %–10 % from about 20 % in the unirradiated material. Density measurements on the specimen from different portions of the irradiated wrapper showed a peak volumetric swelling of about 3.5 % at a damage of 83 dpa. TEM studies showed extensive void formation at 40 dpa and beyond in addition to extensive precipitation and formation of dislocation loops. The void density and size showed a progressive increase with displacement damage. The precipitates were identified to be of nickel and silicon enriched M6C type of η phase, while radiation induced G phase was also observed at 83 dpa. The increase in strength and reduction in ductility with increase in dpa is attributed to irradiation hardening, which is supported by the increase in defect density as observed from the dislocation substructure and increase in the void density and size. The paper would discuss the degradation in mechanical property in terms of the microstructural changes.

Small Specimen Test Techniques for Estimating the Tensile Property Degradation of Mod 9Cr-1Mo Steel on Thermal Aging

The degradation in mechanical properties of modified (mod) 9Cr-1Mo steel on thermal aging at 923 K has been studied using the small specimen test techniques—shear-punch and ball-indentation tests. Small volumes of material required for these test techniques make them unique tools for the assessment of service related degradation and failure analysis of structural components. A variety of heat treated microstructural conditions of mod 9Cr-1Mo steel is generated on which both conventional tensile test and shear-punch/ball-indentation tests are carried out. The relationship between conventional tensile properties and small specimen test results is established from these standardization experiments. Small specimens of Mod 9Cr-1Mo steel in the thermally aged conditions are tested using both shear punch and ball-indentation techniques and the tensile property changes are determined. Both these tests identically reflect and quantify the changes in the tensile properties with aging time which correlates well with the microstructural changes observed using optical and electron microscopic studies.

Miniaturized Testing of Engineering Materials

This book is a comprehensive overview of methods of characterizing the mechanical properties of engineering materials using specimen sizes in the micro-scale regime (0.3-5.0 mm). A range of issues associated with miniature specimen testing like correlation methodologies for data transferability between different specimen sizes, use of numerical simulation/analysis for data inversion, application to actual structures using scooped out samples or by in-situ testing, and more importantly developing a common code of practice are discussed and presented in a concise manner.