Changes in microstructure of oriented Ba₃Co₂Fe₂₄O₄₁material during sintering. I

Abstract

Samples of the ferrimagnetic material Ba3Co2Fe24O41, prealigned in a rotating magnetic field and sintered at 1260°C, have been examined for (1) preferred orientation, (2) grain growth, and (3) porosity. The quantitative orientation of the fibre texture obtained in the samples measured by means of the (0001) pole figures, increases with sintering time. The maximum in the (0001) pole figures appears to be a linear function of the average intercept line length measured on sample surfaces perpendicular to the [0001] fibre axis. The relationship of texture and average intercept line length can be explained theoretically if it is assumed that the well oriented crystallites in the samples grow at the expense of the poorly oriented ones resulting in a decrease in number of the latter crystallites, whereas their averaged size remains unchanged. The transport mechanism of the densification process of the material used could not be determined. With the sintering equations given by Johnson [J. Amer. Ceram. Soc. (1970). 53, 574–577] the two transport mechanisms, viz. grain‐boundary and volume diffusion are possible. However, from the fact that the bulk porosity and the area pore fraction of the sample surfaces seem to be approximately proportional to the averaged intercept line length the conclusion may be drawn that the densification occurs most probably by volume diffusion.

Changes in microstructure of oriented Ba3Co2Fe24O41material during sintering. II

“…Of these three types of textured material the changes in texture and density with sintering time are studied, as well as the occurrence of exaggerated grain growth and its effect on the final structure. As earlier microstructure investigations (Huijser-Gerits & Rieck, 1974b) have revealed, the densification process is not completely uniform and differences in density, as well as in texture, have been found over the height of the samples. This phenomenon had to be studied further.…”

“…The textureless samples (a) are prepared and selected according to Huijser-Gerits & Rieck (1974a, b). The samples with fibre texture (b) are made as described by Huijser-Gerits & Rieck (1974b) and those with fan texture (c) according to Huijser-Gerits, Rieck & Vogel (1970). The measuring techniques used are also described in these previous papers.…”

“…In a previous paper (Huijser-Gerits & Rieck, 1974b), the relation between grain growth, preferred orientation and porosity of the ferrimagnetic material Ba3Co2Fe240,,1, prealigned in a rotating magnetic field and sintered at 1260:C, was reported. However, in order to obtain in this material, which has technical applications, a microstructure with optimal physical properties, it is also necessary to know the relation between time and temperature of sintering and the factors which determine the microstructure, such as grain size, density and texture.…”

“…However, in order to obtain in this material, which has technical applications, a microstructure with optimal physical properties, it is also necessary to know the relation between time and temperature of sintering and the factors which determine the microstructure, such as grain size, density and texture. In a sample of this material different types of crystallographic preferred orientation (or texture) may occur, depending on the magnetic anisotropy of Ba3Co2Fe240.,1 at room temperature and the kind of magnetic field that is applied during the pressing of the powders (Huijser-Gerits & Rieck, 1974b). Investigated are:…”

“…(b) material with a fibre texture (Huijser-Gerits & Rieck, 1974b), pressed at room temperature in a rotating magnetic field;…”