Effects of Trace Additions of Magnesium on Microstructure and Properties of Fe-36Ni Invar Alloy

Low-thermal-expansion alloys play a crucial role in high-precision instruments and devices. Simultaneously improving mechanical performance and keeping or even decreasing low thermal expansion behavior are urgently required for their industrial application. Herein, a new attempt to treat Fe-36Ni Invar alloy by adding trace magnesium (Mg) in a concentration ranging from 0 wt% to 0.0030 wt% (similarly hereinafter) is conducted. The introduction of Mg results in grain refinement and an increase in the volume fraction of the annealing twins. Compared with the Mg-free sample, the coefficient of thermal expansion (CTE) of 0.0030% Mg alloy is significantly decreased by more than 20%, which is mainly related to lattice distortion and matrix purification. The yield strength of 0.0030% Mg alloy improves by 10% with respect to Mg-free alloy, because of grain boundary strengthening and solid-solution strengthening. The study may lay the basis for a better understanding of the application of Mg in low-thermal-expansion alloys.

Automated summary

The addition of trace magnesium (Mg) improves the thermal expansion and mechanical performance of Fe-36Ni Invar alloy, making it suitable for industrial application in high-precision instruments and devices.