Journal
INTERNATIONAL JOURNAL OF FATIGUE
Volume 88, Issue -, Pages 166-177Publisher
ELSEVIER SCI LTD
DOI: 10.1016/j.ijfatigue.2016.03.023
Keywords
Nanostructured materials; NiTi shape memory alloy; Grain size effects; Fatigue
Funding
- DGA of France
- HongKong Research Grant Council (RGC) through the GRF Grant [16214215]
- 973 Program of China [2014CB046902]
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The effects of grain size (GS) on tensile fatigue life of nanostructured NiTi superelastic shape memory alloys (SMAs) with GS = 10 nm, 42 nm and 80 nm are investigated. Macroscopic stress-controlled tensile fatigue tests, acoustic energy measurements and fracture surface observations were performed. It is shown that low-cycle fatigue life (under sigma(max) = 450 MPa) of nanostructured NiTi polycrystalline SMA increases significantly when GS decreases from 80 nm to 10 nm. However, there is no significant effect of GS on the intermediate-cycle fatigue life (under (sigma(max) = 300 MPa). It is found that accumulated acoustic energy can be used to distinguish the three stages of fatigue: slow crack propagation, fast crack propagation and final fracture. Micro cracks were found on fracture surfaces of all GS specimens under intermediate-cycle fatigue and on fracture surfaces of 10 nm GS specimen under low-cycle fatigue, while micro voids were found in 42 nm and 80 nm GS specimens under low-cycle fatigue. The results of the paper indicate that grain refinement down to nanoscale has potential in developing high fatigue resistance SMAs. (C) 2016 Elsevier Ltd. All rights reserved.
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