Modified 9Cr-1Mo ferritic steel (T91/P91) has been subjected to a series of heat treatments consisting of soaking for 5 minutes at the selected temperatures, starting from the ␣ -phase region (1073 K) to the ␥ ϩ ␦-phase region (1623 K), followed by oil quenching. Hardness measurements, microstructural features, and grain-size measurements by the linear-intercept method have been used for correlating them with the ultrasonic parameters. Ultrasonic velocity and attenuation measurements, and spectral analysis of the first backwall echo have been used for characterization of the microstructures obtained by various heat treatments. As the soaking temperature increased above Ac 1 , the ultrasonic velocity decreased because of the increase in the volume fraction of martensite in the structure. There were sharp changes in the ultrasonic velocities corresponding to the two critical temperatures, Ac 1 and Ac 3 . Ultrasonic longitudinal-and shear-wave velocities were found to be useful in identifying the Ac 1 and Ac 3 temperatures and for the determination of hardness in the intercritical region. However, ultrasonic attenuation and spectral analysis of the first backwall echo were found to be useful to characterize the variation in the prior-austenitic grain size and formation of ␦ ferrite above the Ac 4 temperature. The scattering coefficients have been experimentally determined for various microstructures and compared with the theoretically calculated value of the scattering coefficients for iron reported in literature.

The deformation and damage mechanisms in wrought, double-aged, Inconel718 superalloy (AMS 5663D) tested under monotonic tensile strains of 2% and lo%, fully-reversed fatigue, and tensile strain (2% or 10%) followed by fully-reversed fatigue conditions were investigated by examining the microstructures of representative specimens. All tests were conducted in air at room temperature. The specimens were sectioned and examined by transmission electron microscopy to reveal typical microstructures as well as the active deformation and damage mechanisms. Specific mechanistic features addressed include the type of slip, interaction of dislocations with y", y' and the carbides (precipitated during solidification and the subsequent heat treatment received by the superalloy), twinning, and microcracking. In all cases the microstructure of the as-received superalloy is employed as the reference to establish the nature and distribution of the secondary phases before the superalloy is subjected to different types of mechanical loading. Results of the investigation and comparisons of the mechanisms of deformation and damage observed under monotonic tensile strain, fully-reversed fatigue, and tensile strain followed by fully-reversed fatigue in Inconel 718 superalloy are reported.Superalloys 718,625,706 and Various Der~at~ves

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Ultrasonic velocity measurements have been carried out across the weld line in two perpendicular sections of modified 9Cr–1Mo ferritic steel weldments, in the as welded and post-weld heat treated (PWHT) conditions. The ultrasonic velocity plot is correlated with the weld profile in both the sections and with the associated microstructural features in different regions of the weldments for the two conditions investigated. The present study reveals that the weld profile can be imaged and the adequacy of the PWHT can also be assessed in modified 9Cr–1Mo ferritic steel weldments using ultrasonic velocity measurements.

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