Abstract
A new application which focuses on an artificial sphincter fabricated by Ni-Ti SMAs for human implantation is under investigation by applying the all-round shape memory effect with precise control of the phase transformation temperatures. In this study, a Ni51at.%-Ti alloy was fabricated by arc melting with fast solidification, followed by a proper strained aging which induces the two way shape memory effect needed for this particular application. Differential scanning calorimetry was used to investigate the thermal behavior and transmission electron microscopy was used for studying the microstructure of the alloys. With the latter the novel technique of automated crystal orientation microscopy is used and optimized to obtain phase and orientation mapping of the various structures.
Highlights
The effect of Ni4Ti3 precipitates on the all-round shape memory effect (ARSME) is mainly due to the particular growth and orientation of the precipitates during the training process
03022-p.2 mapping, (d) conventional bright field image of the same region, (e) and (f) selected area diffraction patterns, e from grain B and f from grain A in d, (g) and (h) uncorrected diffraction patterns acquired by ACOM-Transmission Electron Microscopy (TEM), g from grain B and h from grain A
The camera length (CL) calculation will be more accurate if the diffraction pattern is more close to a zone axis because this provides more spots with a homogeneous intensity for the software to detect and a reliable CL determination is a basic need for the quality of the orientation and phase mapping. This implies that the conditions optimized for the template matching, as mentioned in the previous paragraph, are not ideal for the calibration of the CL, which is further worsened for more complicated patterns such as the one with Ni4Ti3 superspots
Summary
The effect of Ni4Ti3 precipitates on the ARSME is mainly due to the particular growth and orientation of the precipitates during the training process. The difference in strain distribution directly causes a difference in preferential orientation of the Ni4Ti3 precipitates and these differences will guide the ensuing phase transformation. A quantitative study of such differences in this all-round shape memory alloy will help to improve the phase transformation performance.
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