Cu interlayers with thicknesses of 1, 1.5, and 2 mm were used to join niobium and AISI 304 steel. Fractures occurred in the weld, the Nb base metal, and the unmelted Cu interlayer when the Cu interlayer thickness was 1, 1.5, and 2 mm, respectively. When the thickness of the Cu interlayer was 1 mm, the weld microstructure consisted of austenite with Cu-rich particles along the austenitic grain boundaries and within the austenitic grains, a composite-like structure (the Fe₂Nb lamellae and particles in a γ matrix) embedded with coarse Cu globules, and a mixture of bulk Fe₇Nb₆, Nb-rich dendrites, and Cu matrix. The bulk brittle Fe₇Nb₆ phase embrittled the joint. However, when the thickness of the Cu interlayer was 1.5 mm, the weld microstructure consisted of austenite with Cu-rich precipitates along the austenitic grain boundaries and a Cu-rich phase embedded with Nb-rich particles and dendrites. Solid-solution strengthening of Cu by Fe was responsible for the improved mechanical properties of the joint. The mixture of Nb-rich particles and dendrites in the Cu matrix was also helpful in enhancing the joint strength. Furthermore, when the thickness of the Cu interlayer was 2 mm, the weld microstructure consisted of austenite with Cu-rich precipitates along the austenitic grain boundaries and within the austenitic grains, an unmelted Cu interlayer, and Nb-rich particles and dendrites embedded in a Cu matrix. The unmelted Cu interlayer reduced the joint strength.

厚度为1、1.5和2 mm的Cu中间层用于连接铌和AISI 304钢。当Cu中间层的厚度分别为1、1.5和2mm时，在焊缝，Nb基体金属和未熔化的Cu中间层中发生断裂。当Cu中间层的厚度为1 mm时，焊缝组织由沿奥氏体晶界和在奥氏体晶粒内具有富Cu颗粒的奥氏体组成，呈复合状结构（Fe ₂ Nb薄片和γ基体中的颗粒）。 ）内嵌有粗糙的铜球，以及大量的Fe ₇ Nb ₆，富Nb的树枝状晶体和Cu基体的混合物。散装脆性Fe ₇ Nb ₆相使关节变脆。但是，当Cu中间层的厚度为1.5mm时，焊缝组织由沿着奥氏体晶界具有富Cu析出物的奥氏体和由富Nb的粒子和树枝状晶体埋藏的富Cu相组成。Fe对Cu的固溶强化是改善接头机械性能的原因。Cu基体中富含Nb的颗粒和树枝状晶体的混合物也有助于增强接头强度。此外，当Cu中间层的厚度为2 mm时，焊缝组织由奥氏体组成，该奥氏体具有沿奥氏体晶界和在奥氏体晶粒内的富Cu析出物，未熔化的Cu中间层以及富Nb的颗粒和枝晶，其嵌入铜基体。未熔融的Cu中间层降低了接合强度。