Degradation of TiNi-based shape memory alloys (SMAs) during thermo-mechanical cycling

Haenschke, Titus Paul (2013). Degradation of TiNi-based shape memory alloys (SMAs) during thermo-mechanical cycling. University of Birmingham. Ph.D.

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Abstract

This thesis is aimed at the identification of causes for the instability of TiNi-based shape memory alloys during thermomechanical cycling. To assess the macroscopical and microstructural
behaviour several techniques were employed.

Thermo-mechanical tests (TMT) revealed that TiNi did not stabilise under the tested conditions. In contrast,
TiNiCu showed a more stable behaviour. Whereas the maximum testing temperatures were found to be detrimental for the strain output in TiNi, none such influence could be found in TiNiCu. In TiNiCu increasing
stresses seems to prevent the material stabilisation.

During in-situ TMTs under high energy X-ray radiation in a synchrotron, microstructural factors influencing the stability of the material were assessed. No hint on a negative influence of remnant or intermediate phases and texture or variant selection was found. Instead increasingly negative strains build up in austenite possibly causing instabilities.

In TiNiCu differences in the processing where found to cause changes in the phase transformation temperatures.
These could be linked with differences in the chemical composition and in the level of inhomogeneity of precipitates.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):