Termomechaniczne aspekty przemiany fazowej w stopie TiNi z pamięcią kształtu indukowanej naprężeniem

摘要

Experimental investigations of thermomechanical couplings related to stress-induced martensite transformation in shape memory alloy (SMA) are presented in the paper. TiNi shape memory alloy specimens were subjected to uniaxial tensile tests carried out with various strain rates on an MTS testing machine (Fig. 1). The temperature changes, accompanying the process of stress-induced martensite transformation were recorded with use of a thermovision camera. It was shown that the martensite forward and reverse transformation, related to the SMA pseudo-elastic behavior, can occur and develop in inhomogeneous way in Liiders-like bands [3-5]. Nucleation and development of the phase transformation fronts in the SMA recorded by infrared camera were studied. Narrow bands of considerably higher temperature corresponding to the martensitic phase, starting from the central part of the specimen and developing towards the specimen grips, were recorded. Next, the upswing region was observed, manifested by the more advanced and more homogeneous stage of the phase transformation, accompanied by the more uniform temperature distribution. The inclined bands of heterogeneous temperature distribution were observed also during the unloading process of the SMA, while the reverse transformation accompanied by the temperature decrease took place [14]. The martensite transformation heterogeneity was confirmed by infrared technique and by photographs of the SMA specimen surface relief (Fig. 2). Thermomechanical aspects of the exothermic martensitic forward and the endothermic reverse transformations for various strain rates were analyzed.%W pracy przedstawiono wyniki badań sprzężeń termodynamicznych zachodzących podczas indukowanej naprężeniami przemiany fazowej w stopach TiNi z pamięcią kształtu. Wykazano, że przemiana martenzy-tyczna wprost i odwrotna, zachodząca podczas pseudosprężystego odkształcania tych stopów, ma charakter niejednorodny. Makroskopowo rozwija się w zlokalizowanych cienkich pasmach, podobnych do pasm Ludersa, w dwóch prawie prostopadłych kierunkach, co udokumentowano stosując metodę badań w podczerwieni oraz fotografując relief na powierzchni próbki.