Why Aren’t Detailed Shape Setting Instructions Posted Online?
This is one of the most common questions we get from customers who are building prototypes. Obviously, it would be greatly helpful if specific instructions could be published and followed precisely because, then more people would be using nitinol and nitinol would rapidly be adopted by just about everyone.
Unfortunately, there isn’t a detailed, standardized process to follow. This is largely due to the fact that nitinol is extremely sensitive to the heat profile. Changing the heat treatment profile by a few degrees can have rather dramatic changes in the mechanical properties of the nitinol. This means that seemingly unrelated things, like changing the fixture, can have significant changes in the properties of the part unless the heat treatment profile is customized for that part.
So, even though specific heat treatment profiles cannot be published, some guidelines can be published:
- Basic shape setting: To set the memory shape, you want the nitinol to reach a temperature of 500-550℃ (930-1020℉). If the temperature exceeds 600℃ (1,100℉), you start to lose the microstructure.
- At Kellogg’s Research Labs, we use temperatures ranging 250-750℃ (480-1,380℉).
- Short heat treatment times result in smaller grains, yielding better fatigue properties and higher stiffness.
- At Kellogg’s Research Labs, we use heat treatment times ranging from 30 seconds to 72 hours.
- Multi-step heat treatment profiles are common. At Kellogg’s Research Labs, we use up to 8 stage heat treatment profiles with quenches and ramps between each stage.
- Optimum properties are going to be tightly distributed around a particular heat treatment profile, so the profile must be closely adhered to.
While this may come as a bit of a let-down, I hope it provides some clarity about why specific heat treatment profiles are not posted online. Read our book Nitinol in Plain Language to learn more about the shape setting process. https://www.kelloggsresearchlabs.com/product/nitinol-in-plain-language/