In situ investigation of the pore development during reactive air brazing of aluminium oxide ceramics

该研究项目的目的是对RAB钎焊过程进行基础研究，这会导致钎焊接头中的多孔缺陷。利用所获得的知识，旨在降低RAB钎焊部件的孔隙率。为此，高速X射线辐射技术首次被用作高温钎焊应用中材料流动的原位分析的检查方法。为此目的，现有的X射线辐射系统适于高温钎焊的要求。这种新的检查方法能够识别发生的温度依赖性的过程中的运动在钎焊间隙与非破坏性的原位观察方法，而没有光学光检查过程的限制。高速X射线辐射还允许分析在钎焊过程期间在不同时间润湿的边界层。被确定的不同区域进行了选择性的金相分析和强度检查进行，从而不同的局部孔隙结构，反应层，结构，和由此产生的强度之间的关系可以与钎焊过程中的材料动力学。除了现场检查钎焊间隙中的材料运动外，高速X射线辐射还可以以前所未有的质量分析润湿尝试。开放式润湿样品内部视图的时间高分辨率观察允许在任何温度和停留时间下精确确定润湿角。从光学热台显微镜已知的景深问题不会发生。在开放润湿尝试中、在具有不同宽度的钎焊间隙中以及在不同温度下的传播速度的组合检查将确定润湿性、钎焊温度和差距宽度对传播速度、孔径和孔密度的影响。这些认识有助于我们更好地理解RAB钎焊陶瓷复合材料中多孔缺陷的形成过程，通过对多孔缺陷形成过程的原位观察，我们有望了解多孔缺陷与影响因素之间的关系。到目前为止，在钎焊过程中进行原位分析在技术上是不可能的。即使是在其他钎焊工艺和材料组的知识转移也有助于提高RAB钎焊部件的密封性和使用寿命。

The aim of the research project is the fundamental investigation of RAB brazing processes, which lead to porous defects in the brazing joints. With the gained knowledge, a reduction of the porosity of RAB brazed components is aimed. For this, the high speed X-ray radiation technique is used for the first time as an examination method for in situ analyses of the material flow in high temperature brazing applications. The existing X-ray radiation system is adapted for this purpose to the requirements of high temperature brazing. This new examination method enables to identify the occurring temperature-dependent processes of the movements in the brazing gap with non-destructive in situ observation methods without the limitations of optical light examination processes. The high speed X-ray radiation further allows to analyze the boundary layers that were wetted at different times during the brazing process. The different areas that were identified are selectively analyzed metallographically and strength examinations are conducted, whereby the relations between different local pore structures, reaction layers, structures, and resulting strengths can be correlated with the material dynamics during the brazing process. In addition to the in situ examination of the material movements in the brazing gap, high-speed X-ray radiation offers the possibility to analyze the wetting attempts in an unprecedented quality. The temporal high-resolution observation of open wetting samples inside view allows an exact determination of the wetting angle at any temperature and dwell time. Problems of the depth of field, as known from optical hot-stage-microscopy, do not occur. A combined examination of the propagation velocity in open wetting attempts, in brazing gaps with different width, and at different temperatures will determine the influence of the wettability, the brazing temperature, and the gap width on the propagation velocity, pore size, and pore density. These cognitions lead to an improved understanding of the development of porous defects in RAB brazed ceramic composites.By in situ observation of the pore formation fundamental knowledge about their behavior in dependence of the influencing factors is expected. So far, it was technically not possible to conduct in situ analyzes during the brazing process. A transfer of the gained knowledge even on other brazing processes and material groups can contribute to an increase in the tightness and service life of RAB brazed components.