Fatigue Crack Initiation in the Iron-Based Shape Memory Alloy FeMnAlNiTi
- PDF / 1,650,543 Bytes
- 9 Pages / 595.276 x 790.866 pts Page_size
- 17 Downloads / 187 Views
SPECIAL ISSUE: A TRIBUTE TO PROF. DR. GUNTHER EGGELER, INVITED PAPER
Fatigue Crack Initiation in the Iron-Based Shape Memory Alloy FeMnAlNiTi R. Sidharth1 • W. Abuzaid2 • M. Vollmer3 • T. Niendorf3 • H. Sehitoglu1
Ó ASM International 2020
Abstract The newly developed FeMnAlNiTi shape memory alloy (SMA) holds significant promise due to its desirable properties including ease of processing, room temperature superelasticity, a wide superelastic window of operation, and high transformation stress levels. In this study, we report single crystals with tensile axis near h123i exhibiting transformation strains of 9% with a high transformation stress of 700 MPa. The functional performance revealed excellent recovery of 98% of the applied strain in an incremental strain test for each of the 40 applied cycles. Concomitantly, the total residual strain increased after each cycle. Accumulation of residual martensite is observed possibly due to pinning of austenite/martensite (A/M) interface. Subsequently, under structural fatigue loading with a constant strain amplitude of 1%, the recoverable strains saturate around 1.15% in local residual martensite domains. Intermittent enhancement of recoverable strains This invited article is part of a special issue of ShapeMemory and Superelasticity to honor Prof. Dr.-Ing. Gunther Eggeler. This special issue was organized by Prof. Huseyin Sehitoglu, University of Illinois at Urbana-Champaign, and Prof. Dr.-Ing. Hans Jurgen Maier, Leibniz Universitat Hannover. & R. Sidharth [email protected] H. Sehitoglu [email protected] 1
Department of Mechanical Science and Engineering, University of Illinois At Urbana-Champaign, 1206 W. Green St., Urbana, IL 61801, USA
2
Department of Mechanical Engineering, American University of Sharjah, PO Box 26666, Sharjah, United Arab Emirates
3
Institute of Materials Engineering, University of Kassel, Mo¨nchebergstraße 3, 34125 Kassel, Germany
is observed due to transformation triggered in previously untransformed domains. Eventually, fatigue failure occurred after 2046 cycles and the dominant mechanism for failure was microcrack initiation and coalescence along the A/M interface. Thus, it is concluded that interfacial dislocations, which play a crucial role in the superelastic (SE) functionality, invariably affect the structural fatigue performance by acting as the weakest link in the microstructure. Keywords Functional fatigue Structural fatigue Crack initiation Superelasticity Residual martensite Shape memory alloys
Introduction NiTi-based shape memory alloys (SMAs) are the most widely used SMAs to date due to their large transformation strains and good functional stability when subjected to cycling loading [1–3]. However, extended commercial usage of NiTi is still hindered by the relatively low transformation stress levels and high cost of production. Thus, various Iron-based SMAs have gained a lot of attention owing to better workability and lower processing costs. Febased SMAs are particularly attractive for load bearing applications,
Data Loading...
