Brazing with nickel-based filler metals under vacuum is frequently applied for joining metals in applications that require high resistance to mechanical loads, corrosive environments and elevated temperatures. However, melting-point depressant elements in the filler can lead to brittle phases in the brazing seam, affecting crack initiation and propagation. This study investigated cylindrical butt joints of metastable austenitic AISI 304L, brazed with NiCrSiB–based fillers containing iron and molybdenum. Tensile, fatigue and corrosion tests were applied to identify the most promising filler for subsequent corrosion fatigue experiments in a self-developed test chamber. Results in air showed that fatigue performance close to AISI 304L can be achieved, when problematic Kirkendall voids and athermal brittle phases are avoided. Corrosion fatigue tests in aqueous environments with varying sodium chloride concentrations and elevated temperatures revealed that cracked chromium-rich borides in the diffusion-affected zone act as microgalvanic elements, accelerating corrosion fatigue via hydrogen embrittlement. At 80 °C, these mechanisms became widespread, leading to multiple crack initiations across the steel surface and not just in the brazing seam. Hence, this study highlights the complex interplay of microstructure, cyclic loading, and environmental effects, offering key insights into the failure mechanisms of vacuum-brazed joints under combined mechanical and corrosive stresses.

中文翻译：

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实验镍基填充金属真空钎焊 AISI 304L 接头在空气和腐蚀性环境中的疲劳性能及失效机制

在真空下使用镍基填充金属进行钎焊，通常用于在需要对机械负载、腐蚀性环境和高温具有高抵抗力的应用中连接金属。然而，填料中的熔点抑制元素会导致钎焊缝中出现脆性阶段，从而影响裂纹的萌生和扩展。本研究调查了亚稳态奥氏体 AISI 304L 的圆柱形对接接头，该接头采用含铁和钼的 NiCrSiB 基填料钎焊。在自主开发的测试室中，应用拉伸、疲劳和腐蚀测试，以确定最有前途的填料，用于后续的腐蚀疲劳实验。在空气中的结果表明，当避免有问题的 Kirkendall 空隙和无热脆性阶段时，可以实现接近 AISI 304L 的疲劳性能。在氯化钠浓度和高温不同的水环境中进行的腐蚀疲劳测试表明，扩散影响区中开裂的富铬硼化物充当微原电池元件，通过氢脆加速腐蚀疲劳。在 80 °C 时，这些机制变得普遍，导致钢表面出现多处裂纹，而不仅仅是钎焊缝。因此，本研究强调了微观结构、循环载荷和环境效应之间的复杂相互作用，为真空钎焊接头在机械和腐蚀联合应力下的失效机制提供了关键见解。