Calorimetric and ultrasonic investigation of the R-phase formation in a TiNi:Fe alloy

The authors report a systematic calorimetric study of the formation of the R-phase in a polycrystalline TiNi:Fe alloy, conducted using a high-sensitivity scanning device. Thermograms performed at very slow heating/cooling rates always appear as an overlap of two peaks. The high-temperature peak does not present any hysteresis and is associated with a continuous transition to the intermediate incommensurate phase. Extrapolation at zero heating/cooling rates gives a value of 1.8 K for the intrinsic thermal hysteresis of the second peak at lower temperatures, ascribed to the first-order transition from the incommensurate to the R-phase. The paper also reports ultrasonic measurements on this alloy. Elastic anomalies in both longitudinal and shear elastic constants and in the ultrasonic attenuation have been detected in the same temperature region as the overall thermal effect.