表面鍍有Cr/Ni薄層之17-4PH不銹鋼與Ti-6Al-4V合金紅外線硬銲接合之研究

Abstract

本研究分別使用銀基填料BAg-8、Ag-Cu-1.75Ti，和鈦基填料Ti-20Zr-20Cu-20Ni，對Ti-6Al-4V合金及具有不同表面鍍層之17-4PH不鏽鋼進行紅外線硬銲接合，期望藉由鍍層做為擴散阻隔層，阻擋填料與基材間的交互擴散以避免硬脆之介金屬相形成，得到最佳的剪力強度。實驗結果顯示，使用BAg-8填料與表面鍍鉻及鍍鎳之17-4PH不鏽鋼之接點可得到最佳的剪力強度；而使用Ag-Cu-1.75Ti填料與表面鍍鉻者剪力強度較前者低，但仍不錯。比較其顯微組織，發現均破斷於具脆性之Ti-Cu介金屬相，但前者之Ti-Cu相層較薄，破斷容易延伸進入較韌之富銀相。此外，Ti-20Zr-20Cu-20Ni填料對Ti-6Al-4V的動態潤濕性極佳，而對表面具有不同鍍層之17-4PH不鏽鋼之潤濕性以鍍鉻及鍍鎳者較佳，無鍍層者次之，鍍鉻者最差。比對17-4PH S.S./Ti-20Zr-20Cu-20Ni/Ti-6Al-4V紅外線硬銲接合所得之剪力測試數據與界面顯微組織，發現銲道中分佈著許多不同的相，並於界面處生成極脆之Ti-Fe介金屬相。且不鏽鋼上之鍍膜作為保護仍無法避免Ti-Fe相的生成，故其剪力強度不佳。

In this study, Ti-6Al-4V and 17-4PH stainless steel (S.S.) are joined by infrared vacuum brazing using three different filler alloys. Those filler alloys are BAg-8, Ag-Cu-1.75Ti, and Ti-20Zr-20Cu-20Ni (wt%). Prior to infrared brazing, thin films of Cr/Ni (10μm/1μm) or Cr (10μm) are coated on the 17-4PH S.S. as diffusion barriers. The aim of introducing the diffusion barrier(s) is to prevent interdiffusion between two dissimilar alloys from forming intermetallics, so better bonding strength can be expected. Experimental results show that the best shear strength can be obtained from the Cr/Ni film coated on 17-4PH S.S. By SEM observation of crack propagation in shear-tested specimens, for both Cr/Ni and Cr surface coatings on 17-4PH S.S., they are mostly fractured at Ti-Cu intermetallics. The former ones have thinner Ti-Cu intermetallics layer, so that the crack can easier extend to the Ag-rich phase, which is tougher than the Ti-Cu phase. Dynamic wetting angle test of Ti-20Zr-20Cu-20Ni on different substrates shows that Ti-6Al-4V is completely wetted, and Cr/Ni surface coating on 17-4PH S.S. has better wettability than bald on 17-4PH S.S. By the shear test and SEM observation for the joints of Ti-6Al-4V/Ti-20Zr-20Cu-20Ni/17-4PH S.S., the bonding strength is quite low due to the formation of Ti-Fe intermetallics, even if there is Cr/Ni thin film coated on 17-4PH S.S. as a diffusion barrier.