Investigation of Temperature-Dependent Magnetic Properties and Coefficient of Thermal Expansion in Invar Alloys.

Lin Huang,Yu Gu,Feng Pan,Tingwen Guo,Yongjian Zhou,Cheng Song,Dong Han

doi:10.3390/ma15041504

Abstract

Invar Fe–Ni alloy is a prominent Ni steel alloy with a low coefficient of thermal expansion around room temperature. We investigate the correlation between magnetic properties and thermal expansion in cold-drawn Fe–36Ni wires with different heat treatment conditions, where the annealing parameters with furnace cooling (cooling from the annealing temperature of 300, 400, 500, 600, 700, 800, 900, and 1000 °C) are used. The variation trend of magnetic properties is consistent with that of thermal expansion for all samples, where the maximum appears at 600 °C -treated sample and 400 °C shows the minimum. The domain size and the area of domain walls determine the total energy of the domain wall, and the total energy directly determines the size of magnetostriction, which is closely related to the coefficient of thermal expansion. Also, the differential thermal analysis (DTA) shows endothermic and exothermic reactions represent crystalline transitions, which could possibly cause the abrupt change of magnetic properties and thermal expansion coefficient of materials. The results indicate that there is a certain relation between thermal expansion and magnetic properties. Besides the fundamental significance, our work provides an Invar alloy with a low coefficient of thermal expansion for practical use.

Highlights

In 1897, Guillaume found a very low coefficient of expansion (0.877 × 10−6/◦C) in36% Ni–Fe alloys, which did not completely conform to the normal thermal expansion law
It has been reported that the internal defects of Ni–Fe alloys increase and the density decreases due to cold machining, which destroys the degree of short-range atomic ordering and affects the spontaneous magnetization and magnetostriction system of the alloys
We found that the trend of thermal expansion is consistent with that of saturation magnetization and energy density of magnetic domain determines the size of magnetostriction with different heat treatment conditions

Summary

Introduction

In 1897, Guillaume found a very low coefficient of expansion (0.877 × 10−6/◦C) in. 36% Ni–Fe alloys, which did not completely conform to the normal thermal expansion law. 36% Ni–Fe alloys, which did not completely conform to the normal thermal expansion law It was an abnormal thermal expansion phenomenon and was called Invar alloy [1,2]. The low coefficient of thermal expansion of Invar alloys may be caused by the fact that the normal lattice variation is compensated by the robust spontaneous volume magnetostriction in a wide temperature range [9,19,20]. How these magnetic properties systematically affect α is still unknown. The differential thermal analysis (DTA) shows endothermic and exothermic reactions represent crystalline transitions, which indicates the abrupt change of magnetic properties and thermal expansion coefficient of materials

Experimental Section

VSM Studies

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