ISSN:
1662-9752
Source:
Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Martensitic transformations in NiTi shape memory alloys (SMAs) strongly depend on themicrostructure. In the present work, we investigate how martensitic transformations are affected byvarious types of ultra-fine grained (UFG) microstructures resulting from various processing routes.NiTi SMAs with UFG microstructures were obtained by equal channel angular pressing, highpressure torsion, wire drawing and subsequent annealing treatments. The resulting material stateswere characterized by transmission electron microscopy and differential scanning calorimetry(DSC). The three thermomechanical processing routes yield microstructures which significantlydiffer in terms of grain size and related DSC chart features. While the initial coarse grained materialshows a well defined one-step martensitic transformation on cooling, two-step transformations werefound for all UFG material states. The functional stability of the various UFG microstructures wasevaluated by thermal cycling. It was found that UFG NiTi alloys show a significantly higherstability. In the present work, we also provide preliminary results on the effect of grain size on theundercooling required to transform the material into B19’ and on the related heat of transformation
Type of Medium:
Electronic Resource
URL:
http://www.tib-hannover.de/fulltexts/2011/0528/02/19/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.584-586.852.pdf
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