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Volume 17, Issue 5
Displaying 1-5 of 5 articles from this issue
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Yasumasa Goto, Katsuaki Takahashi1971 Volume 17 Issue 5 Pages 193-197
Published: January 25, 1971
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSPhase diagram of the quasi-binary SrO-Fe2O3 system has been determined by X-ray diffraction, DTA measurement and microscopic method in the composition range of 100-33 mole% Fe2O3 above 750°C in air. The existence of the four compounds, SrFeO3-x, 3SrO⋅2Fe2O3, SrO⋅6Fe2O3 and SrFe18O27 has been confirmed under the present experimental conditions. Crystal structure of 3SrO⋅2Fe2O3 seems to be hardly influenced by the oxygen partial pressure of the atmosphere. The temperature of eutectic reaction between SrO⋅6Fe2O3 and 3SrO⋅2Fe2O3 is 1195°±10°C, and the latter compound melts incongruently at 1225°±10°C. SrO⋅6Fe2O3 melts also incongruently at 1390°±10°C to form SrFe18O27 and liquid. Single crystals of SrO⋅6Fe2O3 have been grown from the melt containing an excess amount of SrO.View full abstractDownload PDF (1893K) -
Hiroshi Yamamoto1971 Volume 17 Issue 5 Pages 198-205
Published: January 25, 1971
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe effects of particle size on the void volume of green and sintered compacts have been studied with tungsten powders from 2.9 to 0.022μ in average diameter.
The void volume of green compacts increased with decreasing particle size down to 0.3μ, but it remained essentially constant with further decrease in particle size.
The sintering process of 0.022μ-powder consists of three stages. The first stage is characterized by an activation energy of 79 Kcal/mole and the surface diffusion mechanism would be operative. The activation energies of the second and the third stage are 102 and 124 Kcal/ mole respectively, the latter is comparable to that expected in volume diffusion. In the sintering of 0.022-powder, the first stage is important and 50-60% reduction in void volume was recorded. On the other hand, for coarser powders 60-80% reduction in void volume was observed after the second stage.View full abstractDownload PDF (539K) -
Akio Hara, Masaya Miyake1971 Volume 17 Issue 5 Pages 206-213
Published: January 25, 1971
Released on J-STAGE: December 04, 2009
JOURNAL OPEN ACCESSThe mechanism of formation of (W⋅Ti)C powder, one of the most important raw materials for cemented carbides, has been studied by microscopy, X ray and XMA analyses. Various combinations of starting powders, i.e., W, WC, TiO2, TiC and carbon black, were used. Coarse powders were used for optical microscopic observations.
The results obtained were as follows.
(1) For all combinations of starting powders, the dissolution of W and Ti began after W had almost changed to WC. When Ti02 was used as a starting powder, the formation of solid solution was assumed to begin at the temperature where TiC was formed from TiO2.
(2) With an increase in the heating temperature, (W⋅Ti)C was formed at the surface of WC particles, and the carbide particles showed shell structure of (W⋅Ti)C as observed in the cross sections.
(3) The mechanism of formation of (W⋅Ti)C in the solid state reaction was considered as follows; Ti (TiC) diffuses on the surface of the WC particle very rapidly and reacts with WC on the particle surface.
The reason for such rapid diffusion of Ti (TiC) on the carbide surface was discussed.
(4) When the carbide particle with WC in the core was heated with cobalt above the eutectic temperature, WC which remained as a result of insufficient diffusion in the solid solution reaction, dissolved into the liquid eutectic and W diffused into TiC from the surface. As a result, (W⋅Ti)C phase formed in the shape of ring around TiC particle.View full abstractDownload PDF (5295K) -
Yoshimichi Masuda, Yoshinari Amano1971 Volume 17 Issue 5 Pages 214-219
Published: January 25, 1971
Released on J-STAGE: May 22, 2009
JOURNAL OPEN ACCESSThe influence of the presence of highly dispersed oxide phase on the sintering behavior of internally oxidized alloys of aluminium-containing copper was investigated by means of wiremodel experiment. Measurement of neck-growth rate and microscopic observation of structural and cofigurational changes in the neck regions of the sintered wire specimen were carried out for the two alloys of different composition and of different configuration in dispersion of aluminium oxide particles.
In the case of the alloy of uniform dispersion, the neck-growth rate was rather promoted by the presence of dispersed oxide particles. The observed rate of neck-growth in this case can be explained by a volume diffusion mechanism.
In contrast, in the case of the alloy of non-uniform dispersion, mass transfer for the neck-growth was interrupted by the formation of a neck with convex curvature, caused by the presence of agglomerated zones of aluminium oxide under the surface of wire specimen.View full abstractDownload PDF (4689K) -
Tooru Takeda, Kiyoshi Tamura1971 Volume 17 Issue 5 Pages 220-228
Published: January 25, 1971
Released on J-STAGE: July 12, 2010
JOURNAL OPEN ACCESSDensification characteristics of stainless steel compacts having various compositions in α, γ and γ+ε phases were examined by dilatometry. Results obtained are summerized as follows:
1) The linear shrinkage (ΔL/L0) at the initial stage of the isothermal densification is given as a function of porosity (ε), particle size (r) and sintering time (t):
ΔL/L0≅K0-m⋅(ε/ε0)⋅tn,
where ε0 is the maximum porosity, and K0 a constant, m and n depend on the phase during sintering, e.g. m=1.5, n=0.5 in α and γ+δ phase region, and m=1.2, n=0.4 in γ phase.
2) Activation energy for α phase of 410L was 53, 500 cal/mol, and for γ phase of 347, 53, 600 cal/mol and 96, 000 cal/mol below and above 1300°C respectively.
3) Sintering of austenitic stainless steel powder is promoted by the presence of δ-phase in γ matrix. Activation energy calculated from the dimensional change was 70, 600-76, 500 cal/mol.View full abstractDownload PDF (6998K)
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