Mn-Ge系反強磁性インバー型合金“VOLCOLOY”について

Abstract

The thermal expansion, magnetic properties, electrical resistivity, lattice constant and hardness of Mn-Ge alloys cooled at various rates after homogenizing at 50 K below the melting point for 1.8-86.4 ks were investigated. It has been found that the alloys containing about 15-25 at%Ge consist of the mixture of a paramagnetic fcc γ-phase and a ferrimagnetic fct ε1-phase at room temperature.The ε-phase is stable for all heat-treatments except the cooling rate less than 0.19×10−3 K/s, showing antiferromagnetism at room temperature. The Mn-Ge alloys consisting of ε-phase exhibit the Invar characteristics below the Néel temperature, and a representative linear thermal expansion coefficient at room temperature is 0.3×10−6 K−1 in the Mn-23.2 at%Ge alloy. The magnetization of the ε-phase alloys is 0.6×10−6 Wb·m/kg at the maximum, and their electrical resistivity shows a minimum at the Néel temperature.The machinability of the ε-phase alloys is fairly good, but the hot-forging and swaging are not so easy because the hardness is remarkably high.