Development of Low-Temperature Processes for High-Temperature Intermetallic Compounds and their microstructure control

(1) Al- si液浸镀Nb在940 ~ 1140 K温度下，将Nb浸在si饱和的Al液中，在Nb的界面处形成c40型Nb(Si_<0.9>, Al_<0.1>)_2层。金属间层由直径为亚微米的细颗粒组成，颗粒之间含有Al-Si液体。Nb(Si, Al)_2层的生长受Nb/Nb(Si, Al)_2界面的溶解-沉淀反应的速率控制。Mo浸镀过程中Nb(Si, Al)_2的生长速度比Mo(Si, Al)_2快3倍。在1025 K下将Nb浸在不饱和Al-Si液中，与Al- 23mol % Si液形成c40型Nb(Si, Al)_2。与饱和铝硅液相比，其生长速度更快。将Nb浸在含20 mol% Si左右的Al-Si液中，产物层呈现出由c40型Nb(Si, Al)_2和D0_<22>型Nb(Al, Si)_3组成的逐层结构。当Al-Si液中Si含量降低至5 mol%时，产物层由…More D0_<22>型Nb(Al, Si)_3组成。结果表明，在1025 K时，Nb-Si-Al体系中不存在c54型Nb(Si, Al)_2。(2) Al-Si液浸镀机理：将Mo浸入饱和Si的Al液中，在Mo表面形成c40型Mo(Si, Al)_2层，c40型Mo(Si, Al)_2晶粒由针状Mo(Si, Al)_2晶粒组成，晶界处为Al-Si液。c40型金属间层的生长机理是在Mo(Si, Al)_2和Mo之间的界面处通过Al-Si液的溶解-析出过程。c40型金属间层的生长机理是在Mo或Nb与产物层的界面处通过Al-Si液的溶解-析出过程。讨论了Mo(Si, Al)_2和Nb(Si, Al)_2晶粒形态的差异，以及界面中液相Al和Si的供给和消耗。在d0 <22>和C40中不同比例的Al和Si的消耗解释了Nb浸镀中逐层结构的形成。(3) Al-Si液浸镀无裂纹涂层的研制为了防止Mo(Si, Al)_2层在Mo大曲率表面形成裂纹，在Al-Si液中加入Cr、Nb、Ta和Ti。MO浸入Al-Si-Cr液中可形成无裂纹层。在Al-Si-Cr液浸渍过程中，在Mo(Si, Al)_2层上形成了（Cr, Mo） （Si, Al）_2晶粒。在铝硅液中加入Cr对Mo(Si, Al)_2的化学组成和生长速率没有影响。(4) Mo-Si-Al粉末混合物的液相反应烧结研究了Mo-Si-Al粉末混合物的液相反应烧结。在高Al含量的粉末混合物中，发生自扩散反应，形成Mo(Si, Al)_2。烧结体具有多孔结构。少

(1) DIP COATING OF Nb BY USING Al-Si LIQUIDBy 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 … More 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 LIQUIDAddition 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 MIXTURELiquid-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