All issues
Volume 34, Issue 6
Displaying 1-7 of 7 articles from this issue
- |<
- <
- 1
- >
- >|
-
Petzow Günter1987 Volume 34 Issue 6 Pages 235-247
Published: August 25, 1987
Released on J-STAGE: May 22, 2009
JOURNAL FREE ACCESSShrinkage, grain growth, dimensional changes and homogenization during liquid phase sintering of ceramics or metallic systems, are influenced by the presence of additives. Additives are intentionally added to control the microstructural and dimensional development during sintering. Additives may be present in solid state only or may form liquid phases. In this paper the effect of additives on sintering will be described using examples which cover some of the essential basic principles of interactions of additives with the host material.
The addition of Ni to the refractory metals W and Mo is used to describe all three stages of solid state sintering as well as postdensification by hot isostatic pressing. It is shown that the densification phenomena during solid state sintering are changed by the presence of additives via simultaneous increase of the grain boundary diffusivity and of the surface diffusivity in this system. From experiments with W-Ni, Mo-Ni and Fe-Cu it is concluded, that in the presence of liquid additives the densification phenomena, rearrangement and center to center approach occur by elementary mechanisms as particle disintegration, coarsening and directional grain growth.
The influence of driving forces provided by chemical reaction on the kinetics of mass transfer is discussed for diffusion induced grain boundary migration and for liquid film migration. These types of interface migration were found to be caused by the interdiffusion of the additives with the host metal. Liquid film migration is thought to be of great importance for the homogenization of Fe-Cu and Fe-Cu-C alloys during liquid phase sintering.View full abstractDownload PDF (11794K) -
Masaru Yokota, Taiji Ueda, Tadashi Asakura, Keiichiro Shoji1987 Volume 34 Issue 6 Pages 248-253
Published: August 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSBy using flame spraying gun, Al alloy powders containing 8 wt%Fe were solidified rapidly by collision onto the stainless steel vessel out of which was cooled by ice water.
Characterization of these powders were carried out by referring to X-ray diffraction analysis, secondary electron microscopic observation and electron probe X-ray micro analysis. Results obtAlned were as follows:
(1) At higher cooling rate, i.e., -105K/s, fine spherical primary AlmFe (m=4.4) metastable phase was observed to form in large part of powders, and rest parts were composed of typical cellular dendrite. At medium or lower cooling rate, asicular or angular shaped primary Al3Fe stable phase plus Al3Fe-Al eutectics were observed to form in a small part of as-flamed powders.
(2) Cooling rates of powders were estimated from the lamellar type eutectics of AlmFe-Al and the arm spacing of secondary dendrite of a-Al; the effective cooling rate was approximately 1×105K/s.
(3) According to the point analysis of EPMA in the field of a-Al, Fe concentration was about 1.5 wt% (0.7 at%). On the contrary, the lattice constant of a-Al in Al-8 wt%Fe alloy powder was exactly the same as that of pure Al within experimental error. In addition, fine spherical precipitates in a-Al were observed in SEM images. Then we concluded that the solubility of Fe in a-Al was very small or nearly equal to the equilibrium state at the cooling rate -105 K/s.
(4) The mAln phases formed in rapidly solidified Al-8 wt%Fe alloy powders by flame spraying method were composed of a-Al, stable Al3Fe and metastable AlmFe phases. And metastable Al6Fe phase was observed to form slightly in powders at a relatively lower cooling rates.View full abstractDownload PDF (3498K) -
Masaru Yokota, Taiji Ueda, Hayao Kuroda, Keiichiro Shoji1987 Volume 34 Issue 6 Pages 254-258
Published: August 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSRapidly solidified Al-8 wt%Fe alloy powders were produced by flame spraying method. The powders were cold pressed to billet and then hot-extruded at the temperature 573 K and the extrusion ratio of 41 to rod of 5 mm diameter. The influence of annealing of mechanical properties of extruded materials was investigated. Results obtAlned were as follows:
(1) Mechanical properties of as-extruded materials were as follows: tensile strength; 37kgf/mm2, elongation; 9.5%, proof strength (0.2%); 27 kgf/mm2 and hardness; 100 kgf/mm2. These mechanical properties measured at room temperature were mAlntAlned up to 773 K of annealing for 1 hour. Beyond that, opposite to the increase of elongation, the other mechanical properties decreased with the annealing temperature.
(2) At the annealing temperature 773 K, hardness was decreased rapidly with the prolong of annealing time. The same tendency against annealing time was observed in the X-ray diffraction experiment; the X-ray intensity of AlmFe (m=4.4) metastable phase was increased rapidly with the prolong of annealing time.
The mechanism of strengthening of rapidly solidified Al-Fe alloys is thought to be the dispersion strengthening, and fine AlmFe particles formed during solidification might play a role of dispersoids.View full abstractDownload PDF (4106K) -
Koji Hayashi, Hiroshi Kihara, Masao Itabashi1987 Volume 34 Issue 6 Pages 259-263
Published: August 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe relative density and average Cu grain size of the sintered compact which was prepared from Cu ultrafine powder (0.03 μm, 6.3 mass% oxygen) and Al2O3 powders (0.02 or 0.5μm) were investigated in relation to the relative density (Dg) of green compact and the amount and particle size of Al2O3 powder. The compacts were sintered mainly at 1273 K for 3.6 ks in hydrogen.
The fully dense sintered Cu-Al2O3 compacts were obtained in the range of a small amount of Al2O3 (the limiting value was about 4 vol% for Al2O3 of 0.02 um, and 10 vol% for Al2O3 of 0.5 μm), when Dg was below a critical value (Dgc) in the same way as in the case of the pure Cu compact. The Dgc increased with increasing amount of A12O3 powder. When the amount of Al2O3 was lager than the above limiting value, the sintered compact became porous, irrespective of Dg. The grain growth of Cu matrix became more surpressed in general as the Al2O3 powder became larger in the amount and finer in the size; the minimum average grain size in the dense Cu-Al2O3 compact was about 2 μm, compared with 9 um in the pure Cu compact.View full abstractDownload PDF (2996K) -
Yoshiro Arami, Hiroshi Korekawa, Osamu Iwatsu1987 Volume 34 Issue 6 Pages 264-268
Published: August 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSCu-Al2O3 powders were prepared by the process, where the electrolytic fine copper powders were mechanically alloyed with Al-propoxide in the atmosphere of air, argon or others, then heated in hydrogen. The properties of the powders obtained were studied. The results obtained were as follows:
1) The mass-transfer of copper to the surface of each Cu-Al2O3 powder particle occurred at the considerably lower temperature of about 873 K.
2) By the effect of the above phenomenon, the sinterability of these Cu-Al2O3 powder was improved. Especially the powder processed in the air was remarkably superior in the sinterability and in the mechanical properties of this sintered body.View full abstractDownload PDF (4198K) -
Hiroshi Yamamoto, Mitsuru Nagakura, Hideaki Ono, Yoshiaki Takahashi1987 Volume 34 Issue 6 Pages 269-276
Published: August 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSExperiments were carried out to investigate the effects of A1203 and La203 substitution on magnetic properties of isotropic BaO⋅2ZnO⋅8Fe2O3 magnets. The compositions were chosen according to the formula {(BaO)0.091(ZnO)0.182(Fe2O3)0.727}100-X-Y(A12O3)X(La2O3)Y where X was varied between 0 and 5, and Y between 0 and 4. The raw materials used in this experiment were α-Fe203, BaCO3, ZnO, A12O3 and La2O3 powders. Mixed powders of the raw materials prepared by the wet-mixing method were semisintered at 1200-1400°C in air for 1 h. The resulting products were finely ground by a vibration-mill crusher, compacted into cylindrical specimens, and then sintered at 1225-1350°C in air for 0.5 h. The magnetic properties of {(BaO)0.091(ZnO)0.182(Fe2O3)0.727}100-X-Y(Al2O3)X(La2O3)Y magnets were apparently improved by the substitution of A1203 and La203 for BaO⋅2ZnO⋅8Fe2O3 compound. Some properties of a typical specimen are as follows. The preparation condition: composition {(Ba0)0.091(ZnO)0.182(Fe203)0.727}94(A1203)4(La2O3)2, semisintering condition 1300°C×1 h in air, sintering condition 1300°C×0.5h in air. Magnetic and physical properties: Jm=0.373 T, Jr=0.250 T, Hcj=104.8kA/m, HCB-90.4 kA/m, (BH)max=8.42 kJ/m3, Tc=346°C, D=4.68 Mg/m3, a=5.883×10-10 m, c=32.84×l0-10 m, c/a=5.582.View full abstractDownload PDF (1807K) -
Nobujiro Tsuchiya, Hisashi Suzuki, Osamu Terada1987 Volume 34 Issue 6 Pages 277-282
Published: August 25, 1987
Released on J-STAGE: December 04, 2009
JOURNAL FREE ACCESSThe cause of uneven surface of titanium carbide (named TiC) layer often observed, when TiC was deposited by CVD process on iron base tool materials such as SUS440C, SKH9, SKD61, etc. (according to JIS), has been studied. It was assumed that, when CVD atmosphere having considerably high carbon potential was applied, iron atoms diffused from substrates in the layer during treatment to realize (TiC+Fe) two phase or (TiC+Fe+Fe2Ti) three phase equilibrium. However, the diffusion of iron atoms across the interface was not always uniform, Large Fe rich-region locally formed in the layer acted as a source of radiated columnar structure of TiC, resulting in the uneven surface. Detailed discussion concerning the phenomena was given.View full abstractDownload PDF (6953K)
- |<
- <
- 1
- >
- >|