You should be able to answer these questions without too much difficulty after studying this TLP. If not, then you should go through it again!
Why is a martensitic transformation often termed "displacive"?
Which of the following statements are correct concerning displacive (martensitic) and diffusional phase transformations?
Martensitic transformations often exhibit hysteresis - for example, the temperature must be taken considerably above that at which the two phases have the same free energies during heating, in order for the transformation to go to completion, whereas it needs to be cooled well below that temperature in order for it to fully reverse. Which of the following explanations for this effect is correct?
Unlike loading and unloading of a specimen to and from its conventional elastic limit, doing this to a superelastic material, to and from its superelastic limit, leads to energy being (permanently) absorbed within the specimen, despite the fact that the original specimen shape has been recovered. Assuming "ideal" superelastic behaviour, which of the following could happen to this energy?
The following questions require some thought and reaching the answer may require you to think beyond the contents of this TLP.
A component, to be made from a NiTi Shape Memory Alloy, must be superelastic under service conditions. Thermal cycling, while monitoring the phases present, gave the plot below. Thermodynamic calculations indicate that the stress level to stimulate martensite formation rises with temperature at 1 MPa K−1. The flow stress (for dislocation glide) is 100 MPa at 20 °C and falls with increasing temperature at 0.3 MPa K−1. Calculate the maximum use T.
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