Experimental characterization of stress corrosion cracking sensitization in austenitic stainless steel using nonlinear ultrasonic Rayleigh waves

This thesis examines the use of nonlinear ultrasound to evaluate sensitization, a precursor to stress corrosion cracking in austenitic stainless steel. Ultrasonic Rayleigh surface waves are generated on a specimen; as these waves pass through sensitized material, second harmonic generation (SHG) increases. In austenitic stainless steel with oven-induced sensitization, this increase is due only to the formation of chromium carbide precipitates, key products of the sensitization process. Weld-induced sensitization specimens demonstrate additional increases in SHG, likely caused by increased residual stress and dislocation density as a result of uneven heating. Experimental data are used to calculate the acoustic nonlinearity parameter, which provides a single value directly related to the quantity of micro- and nano-scale damage present within any given sample. Using this procedure, the effects of weld- and oven-induced sensitization are compared. Results demonstrate the feasibility of using nonlinear Rayleigh waves to detect and monitor stress corrosion susceptibility of welded material.M.S

Recent Progress on Nonlinear Ultrasonic Testing for Materials Aging in Nuclear Applications

Materials in nuclear power plants are subjected to a variety of time-dependent aging phenomena, depending on their environmental conditions. In many cases, such phenomena cause microstructural changes in the materials before the development of macro scale damage or, eventually, component failure. Nonlinear ultrasonic testing has the potential to probe microstructural characteristics of materials that have undergone aging related changes and can potentially be used to establish structure-property relationships or predict where macro scale damage (e.g., cracking) is likely to occur. In this talk, recent work relating measured material nonlinearity to microstructural changes encountered in nuclear power applications is presented, specifically radiation damage in ferritic steels and weld sensitization in austenitic stainless steels. In the case of radiation damage, it has been established that the formation of BCC Cu nanoprecipitates and changes in dislocation density affect the material nonlinearity. In nonlinearity measurements in the case of weld sensitization (migration of Cr to grain boundaries in the heat affected zone, affecting the local corrosion resistance), it is thought formation of M23C6 carbides at the grain boundaries affects the measured material nonlinearity. Preliminary results are presented

Recent Progress on Nonlinear Ultrasonic Testing for Materials Aging in Nuclear Applications

Materials in nuclear power plants are subjected to a variety of time-dependent aging phenomena, depending on their environmental conditions. In many cases, such phenomena cause microstructural changes in the materials before the development of macro scale damage or, eventually, component failure. Nonlinear ultrasonic testing has the potential to probe microstructural characteristics of materials that have undergone aging related changes and can potentially be used to establish structure-property relationships or predict where macro scale damage (e.g., cracking) is likely to occur. In this talk, recent work relating measured material nonlinearity to microstructural changes encountered in nuclear power applications is presented, specifically radiation damage in ferritic steels and weld sensitization in austenitic stainless steels. In the case of radiation damage, it has been established that the formation of BCC Cu nanoprecipitates and changes in dislocation density affect the material nonlinearity. In nonlinearity measurements in the case of weld sensitization (migration of Cr to grain boundaries in the heat affected zone, affecting the local corrosion resistance), it is thought formation of M23C6 carbides at the grain boundaries affects the measured material nonlinearity. Preliminary results are presented.</p