Secondary Microstructure and Its Effect on the Functional Properties of Ferrites in the Mg–Mn–Zn–Ca–Fe–O System

Abstract

The paper examines the evolution of secondary microstructure and electromagnetic parameters under different thermal treatment conditions of ferrite elements in the Mg–Mn–Zn–Ca–Fe–O system used in commutators and logical units. An optical microscope revealed two types of secondary microstructure—point and lattice. The point structure is found in the samples sintered at 1603 K, hardened at 1273 K, and additionally annealed at 823 K. It is shown that annealing up to 3 h results in grow of the coercivity H_c, without worsening other parameters. This permitted an increase in the percentage of valid elements by 1.5 times due to transition of rejected elements (for low H_c) into valid ones by annealing. We developed a technique to provide equal temperature–time conditions for all the annealed samples and to control the output of valid elements via periodic adjustment of annealing duration according to quality inspection of reference batches of the samples.