NiTi Phases

Water comes in three phases: solid (ice), liquid, and gas (steam). NiTi has two different solid state phases. One way that we can learn about the differences between high and low-symmetry phases of nickel-titanium alloy is by studying the sound they make when dropped on a hard surface (their acoustic properties.)

Clicking a thumbnail on this web page (http://chemistry.beloit.edu/edetc/cineplex/sound/index.html) shows a movie of that demonstration.

Water changing phases.
Solid to liquid phase (left).
Liquid to gas phase (right).

NiTi has two solid phases with different acoustic properties.

NiTi changing from solid Austenite to solid Martensite phase.

Changing temperature.
Cooling (left).
Heating (right).

Austenite phase NiTi
Cooling (left).
Heating (right).

Martensite phase NiTi
Cooling (left).
Heating (right).

A bar of NiTi is cooled and then repeatedly dropped as it warms. Which phase is the final room temperature bar?

Can you solve a NiTi mystery?

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