Al-Al_2O_3结构件钎缝处的剪切应力分布与热膨胀匹配

采用有限元数值模拟方法研究了冷却过程在Al Al2 O3 异种材料结构件钎缝处导致的剪切应力分布。计算结果表明 :最大剪切应力位于钎缝圆角处和靠近钎缝圆角的Al2 O3 陶瓷 /Cu镀层金属界面处 ,同时中间层合金的热膨胀系数与Al的热膨胀系数相匹配时 ,可以最大限度减小剪切应力     

钎缝圆角几何形状对Al-Al_2O_3钎焊件剪切应力分布的影响

异种材料连接结构中由于被连接材料的热膨胀系数不匹配 ,焊后冷却过程将在钎焊件内部导致较大的应力。同时 ,钎缝圆角几何形状对这一热应力分布有重要影响。本文采用有限元数值模拟方法研究了钎缝圆角几何形状对Al-Al2 O3 异种材料钎焊件内部剪切应力分布的影响。计算结果表明 ,钎缝圆角的最佳几何形状为钎缝伸出长度略大于钎缝高度的凹型。     

钎缝圆角几何形状对Al-Al2O3钎焊件剪切应力分布的影响

异种材料连接结构中由于被连接材料的热膨胀系数不匹配,焊后冷却过程将在钎焊件内部导致较大的应力。同时,钎缝圆角几何形状对这一热应力分布有重要影响。本文采用有限元数值模拟方法研究了钎缝圆几何形状对Al-Al2O3异种材料钎焊件内部剪切应力分布的影响。计算结果表明,钎缝圆角的最佳几何形状为钎缝伸出长度略大于钎缝高度的凹型。     

复合钎料钎焊Al_2O_3接头剪切应力场的数值模拟

对Al2O3颗粒增强复合钎料钎焊Al2O3/Al2O3接头的残余应力场进行了数值模拟,分析了Al2O3陶瓷颗粒的加入对陶瓷接头残余剪切应力的影响.模拟发现,陶瓷接头的最大应力位于陶瓷-钎缝界面,陶瓷颗粒的加入对钎焊接头应力起到了缓解作用,其缓解程度随陶瓷颗粒体积分数的增加而增大;在陶瓷颗粒百分比一定的情况下,钎缝厚度的...     

钎料对TiC陶瓷/铸铁钎缝处剪应力的影响

采用有限元数值模拟方法研究了采用不同钎料对冷却过程中TiC陶瓷／铸铁焊缝处剪应力的影响。结果表明，无论采用Ni基钎料、Ti基钎料还是他基钎料，剪应力均主要集中在TiC陶瓷／铸铁的钎缝端点上。当采用Ni基和Ag基钎料时，剪应力的最大值出现在钎料／TiC陶瓷界而；而采用Ti基钎料时，剪应力的最大值出现在铸铁／钎料界面。当采用Ni基和Ti基钉料时，冷却到室温的钎缝最大剪应力值较大，因此接头的连接强度较低；当采用Ag基钎料时，冷却到室温的钎缝最大剪应力值较小，因此接头的连接强度较高。     

利用化学镀实现Al2O3陶瓷与金属的连接

为寻求Ａｌ２Ｏ３陶疱与金属连接的新途径,本文进行了新的尝试：先在Ａｌ２Ｏ３陶瓷表面化学镀一层Ｎｉ,然后将镀镍瓷与金属在辉光炉中进行钎焊,试验结果表明,利用化学镀和辉光钎焊的方法连接Ａｌ２Ｏ３陶瓷与金属,可获得处形美观,无内在缺陷并具有足够强度的优良钎焊接头。     

Al2O3 陶瓷与Al低温连接工艺研究

采用共晶烧结工艺对Ａｌ２Ｏ３陶瓷进行表面Ｃｕ金属化,并采用乔探钎焊的办法实现了陶瓷与Ａｌ的低熳连接。实验结果表明,钎料与Ａｌ基体和金属化层之间均有良好的冶金作用,能够保证接头的强度,而且钎焊过程不会对金属化层／陶瓷界面造成不良影响。     

Ni—Ti活性钎焊高纯Al2O3界面反应微观机理

基于部分液相瞬间连接工艺，采用Ni-Ti活性钎焊技术实现了高纯Al2O3陶瓷与可伐合金（4J33－Kovar)的气密性封接，采用微观组织分析，微区优分分析和X射线衍射分析等方法，研究了封接反应的微观机理，研究结果表明，氧化铝陶瓷中的氧扩散进入焊料中，在焊料／Al2O3界面形成了Ni2Ti4O反应层，厚度1μm-2μm，起到了陶瓷晶格到金属晶格的过渡作用。     

连接温度对TiC陶瓷/铸铁钎缝处剪应力的影响

采用有限元数值模拟方法研究了冷却过程中用Ni基钎料对TiC陶瓷／铸铁进行钎焊连接钎缝处剪应力的分布情况及连接温度对钎缝处最大剪应力的影响。结果表明，在冷却过程中，剪应力均主要集中在TiC陶瓷／铸铁的钎缝端点上；连接温度越高，钎缝处的最大剪应力越大，连接接头的强度越低。     

X射线管中95Al2O3和Kovar合金的活性钎焊

通过润湿性实验，钎焊接头性能实验，系统地研究了９５Ａｌ２Ｏ３和Ｋｏｖａｒ合金在不同形态Ａｇ－Ｃｕ－Ｔｉ活性钎料作用下的润湿钎焊机制，实验发现钎焊合金与陶瓷发生了界面反应，生成了Ｔｉ３Ａｌ，ＴｉＡｌ等相，采用Ａｇ－Ｃｕ－５Ｔｉ非晶钎料时，接头四点弯曲强度可达２７０ＭＰａ。     

Ion-plated Al-Al2O3 films as diffusion barriers between NiCrAlY coating and orthorhombic-Ti2AlNb alloy

Ion-plated Al-Al₂O₃ cermet films were fabricated as diffusion barriers between NiCrAlY coating and orthhombic-Ti₂AlNb alloy. The oxidation and interdiffusion behaviour of coatings with and without diffusion barrier were investigated in isothermal and cyclic oxidation tests at 800 °C. The results indicated that substantial interdiffusion and rapid oxidation degradation occurred in the coated specimens without diffusion barrier. With Al-Al₂O₃ diffusion barriers, deferred interdiffusion and improved oxidation resistance was observed. Among them, duplex coating containing 1Al-Al₂O₃ interlayer exhibited the best performance. Coefficient of diffusion hindering and factor of reaction hindering were proposed to compare and quantify the efficiency of the diffusion barriers.     

ZrW2O8薄膜的制备及热膨胀性质

采用溶胶-凝胶技术结合退火工艺在Pt(111)/Ti/SiO2/Si(100)基片上制备ZrW2O8薄膜,并研究了退火温度、退火时间对薄膜的影响.利用X射线衍射(XRD)及扫描电镜(SEM)对薄膜的物相及表面形貌进行表征;利用变温XRD研究薄膜的热膨胀性能.薄膜的变温XRD结果表明,在室温～700℃温度范围内,随着温度的升高,(211)和(310)晶面间距变小,其热膨胀系数为负值,而(332)晶面间距随温度升高变大,显示出正膨胀性质.这表明ZrW2O8薄膜材料的热膨胀性能是各向异性的.     

Synthesis behavior of nanocrystalline Al-Al2O3 composite during low time mechanical milling process

In this work, four different volume fractions of Al₂O₃ (10, 20, 30 and 40 vol.%) were mixed with the fine Al powder and the powder blends were milled for 5 h. Scanning electron microscopy analysis, particle size analysis and bulk density measurements were used to investigate the morphological changes and achieving the steady state conditions. The results showed that increasing the Al₂O₃ content can provide the steady state particle size in 5 h milling process. It was found that increasing the volume fraction of Al₂O₃ leads to increasing the uniformity of Al₂O₃. Standard deviations of microhardness measurements confirmed this result. The XRD pattern and XRF investigations depicted that increasing the Al₂O₃ content causes an increase in the crystal defects, micro-strain and Fe contamination during 5 h milling process of nanocrystalline composite powders while the grain size is decreased. To investigate the effect of milling time, Al-30 vol.% Al₂O₃ (which achieved steady state during 5 h milling process) was milled for 1-4 h. The results depicted that the milling time lower than 5 h, do not achieve to steady state conditions.     

烧结助剂Y2O3和Pr6O11对Al2O3陶瓷相对密度和热导率的影响

采用高分子网络法制备混合纳米粉体,研究稀土氧化物Y2O3和Pr6O11加入量对Al2O3陶瓷相对密度和热导率的影响。采用阿基米德方法测定样品的体积密度,利用激光脉冲法测量试样的热扩散率并计算得出热导率。结果表明:两种添加剂都可以降低Al2O3陶瓷的烧结温度,提高Al2O3陶瓷的热导率,其中Y2O3的促进作用较强;当保温时间相同、烧结温度为1 500~1 650℃时,Al2O3陶瓷的相对密度和热导率都随烧结温度的升高而增大;当烧结温度相同、保温时间为30~120 min时,Al2O3陶瓷的相对密度和热导率也随保温时间的延长而增大。     

Thermodynamics and phase diagrams in the binary systems Na2O-SiO2, Na2O-GeO2, Na2O-B2O3, Li2O-B2O3, CaO-B2O3, SrO-B2O3, and BaO-B2O3

We applied our model to the enthalpy of mixing data of the binary systems Na₂O-SiO₂, Na₂O-GeO₂, Na₂O-B₂O₃, Li₂O-B₂O₃, CaO-B₂O₃, SrO-B₂O₃, and BaO-B₂O₃. The most stable composition in the liquid, that is where the enthalpy of mixing is most negative, is with a metal-oxygen ratio of 4 to 3, for monovalent metals (Na and Li) and 3 to 4 for divalent metals (Ba and Ca) in liquid silicates or borates. The same applies to the CaO-SiO₂, CaO-Al₂O₃, PbO-B₂O₃, PbO-SiO₂, ZnO-B₂O₃, and ZnO-SiO₂ systems. The oxygen to metal ratio, its constant value in various types of systems, reflects and describes the structure of the liquid. Using the analyzed enthalpies of mixing data and the available phase diagrams, we calculated the enthalpies of formation of the various binary compounds. The results are in excellent agreement with data in the literature that were obtained from direct solid-solid calorimetry.     

Thermal conductivity and thermal cycle life of La2O3 and HfO2 doped ZrO2-Y2O3 coatings produced by EB-PVD

The effects of La₂O₃ and HfO₂ addition on thermal conductivity and thermal cycle life of EB-PVD YSZ coatings were investigated. La₂O₃ and HfO₂ were selected as additives, because they significantly suppress the sintering of YSZ. The developed coating showed low thermal conductivity as well as high resistance to sintering. Burner rig tests confirmed that the developed coating have a superior thermal insulating effect and have a longer life than that of a coating with conventional composition.     

含B2O3钙铝基连铸保护渣剪切变稀特性

为兼顾钙铝基连铸保护渣在结晶器弯月面上下方不同剪切速率区域的冶金功能,从非牛顿流体特性角度出发,研究了CaO-Al₂O₃-Li₂O-B₂O₃保护渣的剪切变稀特性。结果表明,在剪切稀化温度区间内,随着温度的降低,保护渣剪切变稀特性逐渐增强。在钙铝基保护渣中,B₂O₃对剪切变稀特性具有明显的抑制作用,该作用与其在硅酸系保护渣中的作用明显相反。在1 300 ℃下,B₂O₃质量分数由4%提高至6%时,保护渣剪切变稀特性逐渐减弱。当B₂O₃质量分数提高至8%时,保护渣转变为牛顿流体,剪切变稀特性消失。