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Investigation of structural and microstructural properties of the components through ultrasonic non-destructive characterisation helps to prolong the life of the devices. Temperature-dependent ultrasonic velocity and attenuation measurements were used to explore the temperature-dependent structural/phase transitions, initiation and growth of fatigue-induced damages and life-limiting fatigue crack during the aging of materials.An indigenously designed experimental set-up was designed and fabricated for on-line measurement of ultrasonic velocities and attenuation over a wide range of temperature from 300 to 1200 K. The ultrasonic velocity/attenuation measurements carried out on M250 grade maraging steel was used to explore the recovery of martensite, formation of coherent intermetallic Ni3(Ti,Mo) precipitations, dissolution of Ni3(Ti,Mo), formation of Fe2Mo precipitation, dissolution of Fe2Mo, austenite revision and transformation of martensite to austenite. Further, the ultrasonic velocity/attenuation measurements carried out in nanoperovskite and ferrite samples(Nd1-xSrxMnO3, Sm1-xSrxMnO3 Pr1-xSrxMnO3andBaPrxFe2-xO4)were used to explore the phase transition temperature (TC), charge ordering Temperature (TCO) and Jahn-Teller temperature (TJT). The nanocrystalline nature of the perovskites was explained based on the observed anomalies at transition temperature. The advantages of the on-line ultrasonic characterisation were compared with other methods. The first derivative of temperature dependent ultrasonic parameters was used to reveal the precise information to detect the early stages of microstructural and substructure variations in material.
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