On the Thermal Expansion Coefficient, and Temperature Coefficient of Young’s Modulus and Its Equilibrium Diagram of Ferromagnetic Cobalt-Manganese Alloys

Measurements of the thermal expansion, natural frequency of vibration and magnetization of ferromagnetic cobalt-manganese alloys were carried out at various temperatures, and a new equilibrium diagram was constructed. The equilibrium diagram shows that the ε-α transformation continues up to a composition range of 19.30%Mn and the magnetic transformation point in the α phase is 0°C at a concentration of 28.20%Mn. Further, the coefficient of thermal expansion and the temperature coefficient of Young’s modulus at room temperature were determined, from which it has been ascertained that a Co-23.85%Mn alloy in the ferromagnetic region of α phase shows a minimum value of 14.04×10−6 in thermal expansion coefficient and a maximum value of 2.52×10−5 in temperature coefficient of Young’s modulus. The cause of such abnormal properties of the alloy can be explained by Masumoto’s rule in regard to Invar.