Effect of microstructure on the strength of nanostructured Invar 36 alloy

Invar 36 (containing 64% iron and 36% nickel) is a precision alloy with a specific coefficient of thermal expansion. Because of this, it is used in many special devices from simple radio to lasers or tankers carrying liquefied natural gas. However, the alloy does not have high enough strength and hardness, which limits its applications. In this work, Invar alloy with an increased strength is obtained using deformation nanostructuring by high pressure torsion. After nanostructuring, the microstructure of the alloy is fragmented with an average fragment size of about 100 nm. The results show that the deformation nanostructuring leads to an increase in the microhardness and tensile strength of Invar 36 by factors of 2 and 3.7, respectively, compared to the coarse-grained alloy. Subsequent annealing of the nanostructured alloy results in a decrease in the tensile strength and microhardness, which correlates with an increase in the average grain size during heat treatment. Nevertheless, the strength properties of the nanostructured Invar 36 after annealing at 500 degrees C remain significantly higher than those of the coarse grained alloy.