Journal of the Japan Society of Powder and Powder Metallurgy

The Fatigue Properties of Dispersion Strengthened Copper Alloys Containing a Dispersion Phase of Thoria, Alumina or Tungsten

Yasuji Fujii

1964 Volume 11 Issue 2 Pages 57-65
Published: April 25, 1964
Released on J-STAGE: May 22, 2009

DOIhttps://doi.org/10.2497/jjspm.11.57

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The fatigue behaviors of three dispersion strengthened copper alloys were experimented. The specimens were prepared by ball mill mixing of electrolytic copper powder (-325 mesh) with thoria, alumina or tungsten powder up to 3.0 volume percent, followed by compacting, sintering, hot extruding and cold drawing, and annealed at 600°C for 1 hr in vacuum before testing. For comparison two kinds of pure copper were studied, -one was of the sintered electrolytic copper powder compact and the other of the ingot of vacuum-melted cathode copper. The fatigue tests were performed on an alternating-torsion fatigue machine.
From the experimental results, it has been shown that the fatigue lives of the dispersion strengthened alloys became longer than that of pure copper with an increase in the tensile strength of the alloys. The alloy containing alumina had a little longer life than pure copper. For the alloys containing a dispersed phase of 3.0 volume percent, the microscopic change of surface was observed during fatigue testing.

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Fundamental Study on Ferrite Manufacturing Process

(Part 3) Grain Growth in Ferrite

Takashi Yamaguchi

1964 Volume 11 Issue 2 Pages 66-72
Published: April 25, 1964
Released on J-STAGE: December 04, 2009

DOIhttps://doi.org/10.2497/jjspm.11.66

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Microstructures of ferrite obtained with differently processed powders both at various temperatures and times of sintering were examined and growth sequence was observed. Grain growth process is divided into four stages with respect to microstructure and processes occurring in each stage were discussed.
Effects of calcination and ball milling on the grain growth in Mn-Zn ferrite were studied and it is shown that the wide variation obseved in growth behavior could be interpreted in terms of calcination as well as ball-milling performance. Based on these experimental results, mechanism of grain growth is presented.

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The Coagulation of Colloidal Powders

Akira Watanabe

1964 Volume 11 Issue 2 Pages 73-96
Published: April 25, 1964
Released on J-STAGE: May 22, 2009

DOIhttps://doi.org/10.2497/jjspm.11.73

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The stability of hydrophobic colloids is mainly governed by the magnitude of the potential energy of repulsion due to the superposition of electrical double layers and van der Waals attraction between approaching particles. In the absence of potential barriers, every collision between particles leads to adhesion (rapid coagulation), and in the presence of potential barriers, the probability of collision is decreased, thus leading to slow coagulation. A quantitative theory was given by Reerink and Overbeek to describe the influence of the double layer thickness at constant Stern potential on colloid stability, a situation which occurs when indifferent inorganic electrolytes are added to sols. While, Ottewill, Rastogi and the present author gave a theory which treated the case where the change in the Stern potential occurs due to adsorption. An extended theory of coagulation was also given which treated the general case of changing ionic strength and potential.
The experimental verification of the theory thus obtained was carried out by measuring the coagulation kinetics of positively charged silver iodide sols spectrophotometrically. Electrokinetic measurements were also made by using ultramicroelectrophoresis. The agreement between the theory and experiments was very good and a reasonable value of the van der Waals constant was obtained. Experiments were also shown which were carried out by employing the twin dropping mercury electrodes polarized at various potentials in electrolytic solutions. The condition of coalescence of the mercury droplets, i. e. the relation between the ionic strength and the critical potential of coalescence, was proved to be in excellent agreement with the theory of coagulation of colloid particles. Thus, the interaction between finely dispersed particles in hydrophobic colloids is essentially the same as that acting between macroscopic mercury droplets.

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