Variation in the structure of the amorphous NiTi-based alloys during mechanical vibrations

Abstract

The aim of the present work is to study the influence of the vibration temperature, frequency and amplitude on the structure of amorphous NiTi-based shape memory alloys. The Ti40.7Hf9.5Ni44.8Cu5, Ti40.7Hf9.5Ni41.8Cu8 and Ti50Ni25Cu25 melt-spun amorphous thin ribbons were subjected to low-frequency mechanical vibrations in a Dynamical Mechanical Analyser or ultrasonic vibrations in anvil. The results of the study have shown that the mechanical vibrations lead to a structural relaxation and initiate the beginning stage of the crystallisation in the amorphous NiTi-based shape memory alloys. During the vibrations with an amplitude of 4 μm, crystalline clusters, with a size of 4–6 nm, appear in the amorphous matrix. On an increase in the vibration temperature or frequency, the size of the crystalline clusters hardly changes. The clusters that form during the vibrations do not influence the crystallisation temperature but decrease the crystallisation enthalpy.