使用MBF601填料真空硬銲鎳(鐵)基兩種合金之研究

Abstract

本研究使用MBF601箔片填料分別對鎳基Inconel 625合金及鎳鐵基Inconel 800合金進行真空硬銲。藉由調整硬銲溫度、硬銲時間等硬銲參數，以EPMA觀察銲道中心與交界處顯微組織與析出物分佈的變化。部分試片製成剪力試片以剪力試驗評估硬銲後接合強度，以研究銲後顯微組織的變化與剪力強度的關係。首先以MBF601硬銲Inconel 800中，銲道中央在冷卻過程中形成連續Cr-Fe-Ni rich之磷化物(Phosphide)及B2Cr5P，此時銲道之剪力強度不隨硬銲時間及溫度的增加而有所提升。由破壞橫截面觀察可觀察到皆從銲道中央之連續脆性化合物開始生成裂紋並快速導致脆性破壞。使用MBF601硬銲Inconel 625，在低溫且短時間持溫時進行硬銲，於銲道中央會形成零星的Ni-Cr rich phosphide，在交界處則析出零碎的化合物。隨著硬銲溫度及持溫時間的增加，銲道中央的磷化物因擴散作用增強而消失，交界處也因擴散作用增強使析出物之密度及量都明顯減少。剪力強度與溫度並無太大關係，試驗後觀察破斷面發現破裂的起始位置皆為交界處的脆性析出物，並開始成長，最後於銲道與基材交界處斷裂。由於析出物不連續使裂縫生長速度較慢。硬銲接合強度以Inconel 625表現明顯較為出色，銲點之剪力強度皆大於400 MPa，也代表著這樣的硬銲合金組合是較可以被應用於工業上。而最後對於板式熱交換器的分析也說明製程清潔度的重要以及減少硼化物、磷化物、矽化物於銲點析出的量才能確保銲後銲點的強度。

In this research, MBF601 filler metal had been applied in the vacuum brazing of two substrates, Nickel base alloy (Inconel 625) and Nickel-Iron base alloy (Inconel 800), respectively. Brazing was performed by controlling parameter such as brazing temperature and holding time. The microstructure and the distribution of precipitates at the joint were observed and analyzed by the EPMA. The relationship between the microstructural evolution and the joint strength was evaluated and discuss by conducting the shear tests of the selected braze joints. For IN-800/MBF601/IN-800 joints, continuous Cr-Fe-Ni rich phosphide and B2Cr5P formed in the centerline of the joint and the shear strength did not increase as the brazing time and temperature increased. The crack initiated and propagated quickly from the compound at the centerline of the joint and lead to the failure of the joint by the observation of the cross section of the fractured joints. As for IN-625/MBF601/IN-625 joints, Ni-Cr-rich phosphide would form in the centerline of the joint. With the increase of the brazing temperature and holding time, the compound at the centerline of joint would be eliminated and the amount of the precipitation at the interface decreased since the effect of the diffusion. The results of shear test showed that since the precipitations are discontinuous, the crack would propagate slower and lead to the higher strength than brazing with IN-800. As a result, the combination of IN-625 and MBF alloy performed better joint strength, higher than 400 MPa, and may have better potential application in the industry. After the analyze of the plate heat exchangers at the end of experiments, it turned out the importance of the process cleanliness and keep the least precipitate of boride, silicide, phosphide at the joint to ensure the strength of joint.