Polycrystal CuAlNi shape-memory alloy

Here is the results of an experiment on polycrystalline CuAlNi, which is know to fail on grain boundaries, and it sure does!

Here is an example of the microstructure present in the specimen at room temperature:

click for a larger image

On heating the microstructure dissappears. The following movie shows a heating and cooling cycle.

Heating and Cooling of polycrystalline CuAlNi, no load

If you load this material it quickly fractures, as shown below:

This composite image covers the whole width of the 0.25 inch wide specimen and the tension direction is vertical. You could actually see light through this crack when it was loaded. Image taken at 40C, thus the microstructure present is mostly stress induced.

Specimen T3a

We tried another polycrystalline specimen with fewer grains across it. It still fractured. Here is an animation of the crack loaded and then unloaded. The fracture is clearly very brittle.

Here is the stress-strain curve for this test with the fracture above. You can see the dissipation.