Effect of Cold-Drawn Deformation on Microstructure and Properties of Invar Alloy Wires

Invar alloy wires with different strains were prepared via cold drawing. The deformation microstructure, mechanical performance and thermal expansion properties were examined. During the drawing deformation process, the <111> and <100> fiber textures were dominantly formed in the Invar alloy wire. The <111> texture intensity monotonically increases with increased drawing strain, and the area proportion reached 85% at strain ɛ = 7.23. As the drawing strain increased, the strength and hardness of the alloy wire significantly increased, and the upward trend did not reach saturation. Owing to the formation of numerous deformation defects during the drawing deformation process, the annihilation of defects during the heating process leads to lattice shrinkage, subsequently resulting in negative thermal expansion and a decrease in the thermal expansion coefficient of the Invar alloy wire. Through large strain cold drawing deformation, a wire of 230 μm diameter was obtained with a grain size of approximately 56 nm. The tensile strength reached 1809 MPa, and the average thermal expansion coefficient of 2 × 10⁻⁶/K was obtained at 100-150 °C, showing a significant improvement in the both mechanical and thermal expansion performance.