Nitinol is almost always classified by its transition temperature. This is generally because temperature is quite important for a thermally active material. However, what is the transformation temperature? Many customers start with the assumption that the transformation temperature is a discrete number and the reverse transformation occurs at the same temperature. However, this is not quite the truth. For most applications, the transformation temperature is referring to the austenite finish (Af) temperature, or the temperature at which the transformation has finished. This is just one of the eleven critical temperatures that we track at KRL when designing nitinol components. For more information about critical temperatures, check out our article on critical temperatures. The reverse transformation requires a fair bit of cooling below the transformation temperature because of the phenomenon called hysteresis. To learn more, feel free to read our article about hysteresis.
What temperatures are feasible?
Since transformation temperatures are advertised as discrete values on our website (20, 35, 45, and 80℃), people often assume that they have to choose one of these predetermined values. Fortunately, we are able to tune the transformation temperature to anything in between. So, if you want to have your system actuate at 18℃, we can make parts that actuate at 18℃.
What range of temperatures is feasible?
By altering the metallurgy of the nitinol, we have produced binary nitinol (just nickel and titanium) components with transformation temperatures ranging from -100℃ to 120℃ (-150℉ to 250℉). By adding additional elements, the range of possible transformation temperatures can be expanded out to -180℃ to 300℃ (higher temperatures are feasible, but extremely expensive). So, in short, nitinol can be used across nearly all temperature profiles existing on earth.