Nonmagnetic Elinvar-Type Alloys in the Mn–Ni System

Abstract

Measurements of Young’s modulus and thermal expansion and of rigidity modulus and hardness (R.T.) have been carried out for Mn–Ni alloys subjected to a variety of heat treatment and cold working. The 10.15∼35.30% Mn–Ni alloys slowly cooled after heating at 950°C for 1hr showed a clear minimum or maximum in Young’s modulus-temperature curves. These anomalies may correspond to antiferromagnetic Néel points or fcc\ ightleftarrowsfct martensitic transformation. The value of Young’s modulus at room temperature was almost independent of cold working and heat treatment except for a large difference between the γ and the mixture phases on the Mn side. A remarkable minimum in Young’s modulus was also observed near 18.50% nickel. The temperature coefficient of Young’s modulus at room temperature depends largely on the heat treatment, cold working and alloy composition. When it is plotted as a function of composition, it exhibits a large maximum of positive sign and a minimum of negative sign. The highest positive temperature coefficient of the Young’s modulus in the annealed state is +119.50×10⁻⁵ for the alloy containing 20.30% Ni, thus exhibiting the Elinvar property. The rigidity modulus also exhibits a similar behavior. The values of hardness in the annealed, water quenched and reheated states were generally lower than that in the cold worked and reheated states.