KOBAYASHI Kurima SHIZUOKA INSTITUTE OF TECHNOLOGY,Faculty of Materials Science, Associate Profess, 物質科学科, 助教授 (40288402)
NANKO Makoto Tokyo Institute of Technology, Faculty of Engineering, Assistant Professor, 工学部, 助手 (90272666)
SUSA Masahiro Tokyo Institute of Technology, Faculty of Engineering, Associate Professor, 工学部, 助教授 (90187691)
|Budget Amount *help
¥6,100,000 (Direct Cost : ¥6,100,000)
Fiscal Year 1997 : ¥2,600,000 (Direct Cost : ¥2,600,000)
Fiscal Year 1996 : ¥3,500,000 (Direct Cost : ¥3,500,000)
|Keywords||Mo(Si, Al)_2 / Nb(Si, Al)_2 / Nb(Al, Si)_3 / intermetallic compounds / hot dipping / self-propagation / liquid-phase reactive sintering / Mo(Si,Al)_2 / Nb(Si,Al)_2 / Nb(Al,Si)_3 / 金属間化合物 / ディップコーティング / 自己燃焼 / 液相反応焼結 / 低温合成 / 高温酸化 / 表面コーティング|
(1) DIP COATING OF Nb BY USING Al-Si LIQUID
By dipping of Nb in Si-saturated Al liquid at temperatures from 940 K to 1140 K,C40-type Nb(Si_<0.9>, Al_<0.1>)_2 layr formed at the interface on Nb. The intermetallic layr consisted of fine particles with submicrons in diameter and included Al-Si liquid between particles. The growth of Nb(Si, Al)_2 layr was rate-controlled by the dissolution-precipitation reaction at the Nb/Nb(Si, Al)_2 interface. The growth rate of Nb(Si, Al)_2 was 3 times faster than that of Mo(Si, Al)_2 in the Mo dipping.
In the dipping of Nb in non-saturated Al-Si liquid at 1025 K,C40-type Nb(Si, Al)_2 formed with Al-23 mol% Si liquid. The growth rate was faster than that in the case of the saturated Al-Si liquid. Product layr by dipping Nb in Al-Si liquid with around 20 mol% Si exhibited the layr-by-layr structure consisting of C40-type Nb(Si, Al)_2 and D0_<22>-type Nb(Al, Si)_3. With decreasing Si content down to 5 mol% in Al-Si liquid, the product layr consisted of the
D0_<22>-type Nb(Al, Si)_3. Their results imply that C54-type Nb(Si, Al)_2 does not exist in the Nb-Si-Al system at 1025 K.
(2) MECHANISM OF DIP COATING USING Al-Si LIQUID :
By dipping Mo in Si-saturated Al liquid, C40-type Mo(Si, Al)_2 layr formed on Mo. The C40-type intermetallic layr was comprised of needle-like Mo(Si, Al)_2 grains with Al-Si liquid at grain boundary. The needle-like grains grow by dissolution-precipitation process through Al-Si liquid at the interface between Mo(Si, Al)_2 and Mo.
The mechanism of the growth of C40-type intermetallic layr is the dissolution-precipitation process through Al-Si liquid at the interface between Mo or Nb and the product layr. The difference of grain shape on Mo(Si, Al)_2 and Nb(Si, Al)_2 is discussed with the phase relation and supply and consumption of Al and Si from the liquid phase in the interface. The formation of the layr-by-layr structure in the Nb dipping was explained by the consumption of Al and Si with different ratios for D0_<22> and C40.
(3) DEVELOPMENT OF CRACK=FREE COATING BY DIPPING USING Al-Si LIQUID
Addition of Cr, Nb, Ta and Ti in Al-Si liquid was carried out in order to prevent the formation of cracks of Mo(Si, Al)_2 layr on Mo surface with large curvature. The dipping of MO into Al-Si-Cr liquid leads to the formation of the crack-free layr. In the dipping with Al-Si-Cr liquid, (Cr, Mo) (Si, Al)_2 grains formed on the Mo(Si, Al)_2 layr. There is no change ofthe chemical composition and the growth rate of Mo(Si, Al)_2 by addition of Cr in Al-Si liquid.
(4) LIQUID-PHASE REACTIVE SINTERING OF Mo-Si-Al POWDER MIXTURE
Liquid-phase reactive sintering of Mo-Si-Al powdr mixture were investigated. In the powder mixture with high Al content, self-propagation reaction occurred and Mo(Si, Al)_2 formed. The sintered bodies have porous structure. Less