Effects of grain size on acoustic emission of nanocrystalline superelastic NiTi shape memory alloys during fatigue crack growth

摘要

Acoustic emission of nanocrystalline superelastic NiTi alloys with different grain sizes (GS) of 10 nm, 60 nm and 235 nm during fatigue crack growth is investigated. The acoustic emission responses among the three characteristic regimes of fatigue crack growth exhibit significant differences for all GS specimens. Such differences due to the increase of elastic wave emission with the driving force reveal the correlation between acoustic emission responses and fatigue crack growth. The total accumulated acoustic energy (AAE) over the whole fatigue process is monotonically decreased by more than 10 times when the GS is decreased from 235 nm to 10 nm. Such significant decrease in AAE originates from the rapid decrease of elastic wave emission induced by phase transition, martensite variants evolution and dislocation motion with GS reduction. The work suggests a nondestructive approach to monitor the damage of NiTi in practical applications. (C) 2019 Elsevier B.V. All rights reserved.