Investigation of the feasibility to characterize the properties of critical brazing joints by means of non-destructive ultrasonic testing

在钎焊过程中，避免脆性相的形成通常是很重要的。然而，为了在早期阶段识别潜在的危险，需要可靠的非破坏性质量保证方法，特别是与安全相关的部件。虽然超声波检测偶尔被用于焊接焊缝的无损分析，但其潜力尚未得到充分利用。目前，由于材料/空气的过渡，接缝中的裂纹或气孔等显著缺陷的显示率较高，这是超声检测的重点。然而，我们自己的准备工作已经揭示了超声波检测的其他未使用的可能性，可以用来检测材料性能的微小变化。因此，这一建议的目的是围绕两个决定性的科学问题。该研究项目的重点是寻找这些问题的答案：对于工业用户来说，检测降低电阻的脆性阶段尤为重要，因为这些阶段会影响接头的使用寿命，并可能导致灾难性的损坏，特别是当它们发生在安全部件中时。因此，该研究项目将研究在不同的焊料中可靠地识别这种脆性相的可能性。此外，必须从技术角度考虑基材中延长的声延迟线的几何影响，直到到达焊接缝为止，因为这可能会降低测试方法的分辨率。为了可靠地检测脆性相，待钎焊材料中脆性结构成分的声学特性必须与待钎焊的其余部分明显不同。初步研究证实了这一点。通过基础研究，确定了构件几何形状的影响以及脆性相对声学特性值的影响。基于多频测试，超声波测试提供了一种非破坏性地确定焊料间隙宽度的可能性。与焊接相比，钎焊缝由两个界面组成，有时仅相隔几微米。这可能导致严重的超声检查干扰，这取决于测试频率。一方面，这些干扰使钎焊接头的精确检查变得困难，并要求在选择测试频率时更加勤奋。另一方面，这些干扰可能提供了在焊接后非破坏性地控制元件中的焊接间隙的机会。

It is generally important for the brazing process to avoid the formation of brittle phases in a joining process. However, in order to identify potential hazards at an early stage, reliable methods for non-destructive quality assurance, especially for safety-related components, are needed. Although ultrasonic testing is sporadically used for a non-destructive analysis of soldered seams, their potential is not yet fully exploited. Currently, the detection of striking flaws such as cracks in the joint or porosity, which show a high display due to the transition from material/air, are in the focus when using ultrasonic testing. Our own preparations, however, have revealed other unused possibilities of ultrasonic testing that can be used to detect even small changes in material properties. Thus, the aim of this proposal is structured along two decisive scientific questions. The focus of this research project is to find answers to these questions:The detection of resistance-reducing brittle phases is especially important for industrial users, as these phases affect the lifetime of the joint and can lead to catastrophic damages, especially when they occur in safety components. Therefore, the research project will examine the possibility of reliably identifying such brittle phases in different solders. Additionally, the geometric influence in the form of prolonged acoustic delay lines in the base material until the soldered seam is reached, has to be considered from a technical point of view, as this can reduce the resolution of the test method. For a reliable detection of brittle phases, the acoustic properties of the brittle structural constituents in the material to be brazed have to be distinctly different from the remaining part to be brazed. This was confirmed preliminary studies. The influences of the geometry of the component as well as the change of the acoustic characteristic values by brittle phases are determined through fundamental investigations.Based on multi-frequency testing, ultrasonic testing offers the potential to determine the gap width of a solder non-destructively. Compared to a weld, the brazed seam is composed of two interfaces, which are sometimes only a few microns apart. This can lead to severe interferences during ultrasonic examinations, which depend on the test frequency. One the one hand, these interferences make a precise examination of the brazed joints difficult and request a heightened diligence when selecting the test frequencies. On the other hand, these interferences might provide an opportunity to control the solder gap in the component non-destructively after soldering.