Metamorphic testing and its applications

The phases in magnetic materials can be studied ultrasonically. Magnetic phase transition points can be determined from discontinuities in ultrasonic velocity as a function of temperature. Conventionally this is done using piezoelectric transducers (normally quartz) pulsed with a tone burst generator. Very accurate velocity measurements are required as the change in velocity is typically 1 part in 104 [1]. A common problem experienced with contacting transducers is the fracturing of the acoustic couplant bond at low temperatures. Non-contacting acoustic techniques have no problems with bond failure, electromagnetic acoustic transducers (EMATs) can be used for measurements on rare earth magnetic materials