Studies of invar alloys sintered from powders mixtures

Abstract

In this work studies of the alloys sintered by powder metallurgy method are presented. Samples were obtained from mixtures of powders Fe and Ni (30-40 wt % Ni) after ball-mill treatment, cold pressing and sintered in a vacuum furnace. It has been shown that the face centered cubic and body centered cubic (no more than 5%) alloys are formed at sintering of powders mixture. The lattice parameter of the γ-phase depends on content of Ni and increases from 3.585×10-10 to 3.596-10 m, these lattice parameters correspond to well-known invar alloys. The hardness of sintered samples changes from 0.8 to 1.5 GPa, the Young's modulus changes from 83 to 126 GPa that correspond to values obtained for invar alloy in literature. The coefficient of thermal expansion is 1.1×10-6°-1 for interval 0-150° and is 15.8 × 10-6°-1 for interval 300-500° and this change corresponds to magnetic transformation at 225°. So, alloys obtained by sintering of powders Fe and Ni are formed as invar alloy and its properties are typical of cast alloys.