Journal of the Japan Society of Powder and Powder Metallurgy
Online ISSN : 1880-9014
Print ISSN : 0532-8799
ISSN-L : 0532-8799
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Volume 57, Issue 8
August
Displaying 1-9 of 9 articles from this issue
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Special Issue: Progress of Fabrication Process and Material Technology toward High Performance of Hard Materials
Summarization
Memorial Lecture of JSPM Award
  • The Development and Practical Applications of High Hardness High Toughness Si3N4 Ceramics
    Mitsuyoshi Nagano, Norimitsu Mukae, Yasuhide Mori
    2010 Volume 57 Issue 8 Pages 553-559
    Published: 2010
    Released on J-STAGE: September 30, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.553
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    In this study, with a view to improve the mechanical properties, the influence of the change in the micro-structure, crystal phase and mechanical properties were evaluated, by changing the amount of one of the sintering additives, Al2O3 and the HIP sintering conditions, from the viewpoint of the micro-structure consisting of α-Si3N4, β-Si3N4 and glassy grain boundary phase. The experimental results showed that 1) the combination of the sintering additives makes a various sorts of crystals and glassy phase formed which promotes the densification, 2) the addition of Al2O3 was effective in the densification, further, 3) as for the HIP sintering condition, N2 gas pressure higher than 60MPa greatly influences the transformation from α-Si3N4 to β-Si3N4 with densification.
    Finally, Si3N4 ceramics consist of both α-Si3N4 and β-Si3N4 crystal phase has been applied for various industrial wear parts, for example, cutting tool, crasher parts, bonding tool for FPD and semiconductor with heating, etc. In these applications, it was recognized that this materials shows the excellent performance comparing with conventional materials.
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Paper
  • Characteristics of Ti(C, N)-30%WC-5%Mo2C-20%Co Sintered Body Prepared via Mechanical Milling
    Keizo Kobayashi, Kimihiro Ozaki, Hiroyuki Nakayama
    2010 Volume 57 Issue 8 Pages 560-564
    Published: 2010
    Released on J-STAGE: September 30, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.560
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    Ti(C, N)-30mass%WC-5mass%Mo2C-20mass%Co was synthesized by a mechanical milling of Ti(C, N) powder, WC powder, Mo2C powder and Co powder for 1.8 ks in a dry process. The mechanical milling used a planetary ball milling. Various powders were prepared by changing a rotational speed of main disk, rotational speed of grinding bowl and the size of crushing ball. The obtained powders were sintered at 1693 K in a vacuum after the press forming. The effects of the absolute acceleration and the ball size in the mechanical milling on the mechanical properties of the sintered bodies were examined by the microstructural observation, the transverse rupture strength test and the Rockwell hardness A-scale test.
    The homogenous powder mixture was accomplished by using the small size ball even in a dry milling. The large absolute acceleration promoted the formation of a brittle phase in the sintered body because of the adhesion improvement between hard particle and metal powder during the milling. In our experimental condition, it was suitable for the preparation of a homogeneous powder mixture to apply the absolute acceleration of 2.5-10 G using cemented carbide balls with 2 mm in diameter. Additionally, the compact prepared using the homogeneous mixture with high carbon content at 1653 K showed 1313 MPa in transverse rupture strength.
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  • Near-net-shaping of Rod Compact of WC-FeAl Alloy by Traveling Zone Sintering
    Kimihiro Ozaki, Shuji Tada, Keizo Kobayashi, Mitsuhiro Mabari, Ken Sas ...
    2010 Volume 57 Issue 8 Pages 565-569
    Published: 2010
    Released on J-STAGE: September 30, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.565
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    Rod shape compacts and cylindrical shape compacts of WC-FeAl were prepared by TZS (Traveling Zone Sintering). The TZS method is a kind of electrical current sintering. Electrodes slide on graphite outer die at a constant speed, and a long object is sintered by a heated region moving. Using WC-40vol%FeAl powder, a rod sintered compact was produced by the TZS at 1280-1350 degree C at a moving speed of electrodes of 0.7 mm/min. At 1280 degree C, the rod shaped compact included with 38vol%FeAl was homogenously produced. The hardness of center axis region of the rod was HRA 87 except the sintering start region of the rod. In the sintering start position of the rod, a region of FeAl-rich phase exists and the length of the region was about 10 mm. However, at 1300 degree C, the region of FeAl-rich phase was 15 mm in length. Higher sintering temperature leads to wider FeAl-rich phase. Additionally, a cylindrical compact was produced by using graphite rod as a core.
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  • Effect of Fe Distribution on Microstructure of TiB2-(Fe-Al) Cermets Prepared by Pulse Current Sintering
    Hiroyuki Nakayama, Keizo Kobayashi, Kimihiro Ozaki, Shuji Tada
    2010 Volume 57 Issue 8 Pages 570-573
    Published: 2010
    Released on J-STAGE: September 30, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.570
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    The 70TiB2-30Fe3Al mass% cermets were fabricated from a mixture of TiB2, Fe and Al powders utilizing a diffusive reaction between Fe and Al. The mechanical milling of TiB2 and Fe were carried out for 0.3-2.4 ks to obtain the milled powder with different distribution state of Fe. The coercive force of the milled powder increased, when the milling duration over 1.2 ks. The cross sectional microstructure of the powder milled for 2.4 ks showed that the Fe was finely distributed and those shapes were deformed to flat. The Al was subsequently added to the TiB2 and Fe milled powder, and then the mixture was consolidated at 1473 K for 120 s using a plus current sintering method. In the sintered compact made from the powder milled for 0.3 ks, the Fe was inhomogeneously distributed and un-reacted pure Fe was observed. In contrast, the Fe was uniformly distributed and Fe3Al formed in the sintered compact prepared from the powder milled for 2.4 ks.
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  • Effect of Mo2C Content on the Microstructure and Mechanical Properties of TiC/TiB2 Base Cermets
    Wataru Koike, Tomoki Seo, Yuya Imai, Takuya Fujima, Ken-ichi Takagi
    2010 Volume 57 Issue 8 Pages 574-578
    Published: 2010
    Released on J-STAGE: September 30, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.574
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    Effect of Mo2C content on the microstructure and mechanical properties of TiC/TiB2 base cermets was studied by using model cermets with the compositions of TiC/TiB2-(11-17)Mo2C-24Ni (mass%). TiC/TiB2 ratio is set to molar ratio of 57/43 that is quasi-eutectic composition. As a result, maximum transverse rupture strength of 680 MPa was obtained for 13 mass% Mo2C content sintered at 1693 K. These cermets achieved remarkable microstructural refinement and still maintained characteristic core-rim structure of the TiC base cermets. These cermets have strong possibility to be an alternative material to cemented carbides by tailoring the composition and elimination of large defects.
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  • Clarification of Cause for Sintering Crack in Ti(C, N)-Base Cermet and Development of Its Prevention Method
    Takayuki Shoji, Tsutomu Ogura, Akira Sasaki, Osamu Terada, Koji Hayash ...
    2010 Volume 57 Issue 8 Pages 579-586
    Published: 2010
    Released on J-STAGE: September 30, 2010
    DOIhttps://doi.org/10.2497/jjspm.57.579
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    In the commercial production of thick compact for Ti(C, N)-base cermet and WC-base cemented carbide, it is said that sintering crack tends to occur in the former, compared with in the latter. This and the inferior toughness, etc., are main reasons for the minor application of cermet to wear resistant parts that are usually thicker than cutting tools.
    In this study, the cause for the sintering crack was firstly investigated from various viewpoints. The sintering crack was shown to occur during de-waxing process of the compact. The main cause was suggested to be the presence of a large amount of fine particles generated by ball-milling particularly in Ti(C, N)-base mixed powders: (1) Under the presence, molten wax makes the pores among particles closed and/or their sizes further smaller, leading to strongly restrict the smooth escape of included gases through pores, and (2) the sintering crack occurs when the gas pressure (the maximum: the equilibrium evaporation pressure) increased by the restriction exceeds the fracture strength of the compact. Based on this suggestion, it was clarified that the sintering crack could be avoided by using hard-to-pulverize Ti(C,N) special-type raw powder with more uniform grain size.
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