Influence of Addition of Fe, Co or Ni on the Properties of Antiferromagnetic Invar Mn–Ge Alloys

Abstract

Investigations have been made on the effect of Fe, Co or Ni addition on the thermal expansion, magnetization, lattice constants, hardness and workability of Invar-type Mn-20 and 22%Ge alloys cooled to room temperature at various rates after homogenizing at 1100 K (830°C) for 10.8 ks (3 h). In the thermal expansion vs temperature curves of the ternary alloys containing 10%Fe and Co or Ni less than 5%, a bending point corresponding to the Néel temperature of the ε phase was distinctly observed. Below the Néel temperature, these alloys show very small values of thermal expansion coefficient and the Invar characteristics. The region in which the thermal expansion coefficient at room temperature becomes zero is expanded by the Fe addition, while it is rather reduced by the Ni or Co addition. Temperature dependence of the magnetization of these alloys is very analogous to that of the binary alloys. The ε phase which shows antiferromagnetism at room temperature is stabilized by the addition of Fe, Co or Ni.The Vickers hardness of the Mn-20%Ge alloy is decreased at first from 500 to about 400 by the addition of a few per cent of Fe, and then a value of about 400 persists up to 10%Fe. The performance of cutting and forging of the binary alloys has much more been facilitated by the addition of Fe, Co or Ni.