Changes in thermal expansion coefficients

Thermal expansion coefficients are usually given as an average value for a certain temperature range.
In reality there are non-linearities over large ranges - the range of temperature differences we're working with is definitely large enough that this is a concern.

[Source](https://www.researchgate.net/figure/Thermal-expansion-coefficient-of-Nb-Sn-bronze-and-copper-as-a-function-of-temperature_fig2_224635796)

If I can verify the expansion coefficient of alloys are not noticeably affected by the alloying elements, I'll see if I can implement polynomials for thermal expansion coefficients.