Low-frequency Internal Friction Behavior Of Thermoelastic Martensitic Transformation

Shape memory alloy (SMA) has been one of functional materials deserved to studying due to its outstanding shape memory effect, pseudo-elasticity and high damping capacity. During the study of SMA's excellent property, people find the behavior of phase interface in the thermoelastic martenstic transformation (MT) determines its physical and mechanical properties. Therefore, the research of the behavior of phase interface during the thermoelastic MT and its law of evolution becomes the focus of the SMA' s studying.Cu-based SMA is selected for studying in this text, and the mechanism of thermoelastic MT is well and systematically studied by means of internal friction(IF) measurements. Cu-Al-Ni-Mn-Ti is a new improved polycrystalline SMA, which possesses well cold-hot treatment capability, best thermal-cycle performance, excellent structural stability, and high transition temperature.Firstly, complete phase transition measurement in the IF measurement is used for studying the common behavior of samples which includes the internal friction's dependence of the temperature, measuring frequency, temperature rate, strain amplitude and so on. Secondly, the partial reverse phase transformation measurement is used for doing the same thing. Lastly, the experiment results gained from these two measurements are compared each other to find some significant phenomenon.It's deserved to saying that two IF peaks are found in the thermoelastic MT by means of the partial reverse phase transformation measurement. The results of these experiments confirm that a single IF peak observed in a complete phase transition in fact is made up of two IF peaks, which are high-temperature IF peak and low-temperature IF peak.The low-temperature peak is relatively wide and smooth, and corresponds to the minimum of relative dynamic modulus (RDM). It has strong dependence on time, and is considered to arise from the soft mode effect caused by the viscous movement along phase interface during the thermoelastic MT. The high-temperature peak is narrow and sharp, and corresponds to the inflexion point of RDM. It is independence of soft mode effect, and is . considered to be attributed to the normal migration of phase interface due to the cooperative shearing motion of atoms at the phase interface. The low-temperature peak and the high-temperature peak are correspondent to different mechanism, so thermoelastic MT is aprocess that many mechanisms are interactive each other at the same time.