Fe3Al介金屬利用Ag/Cu紅外線硬銲接合之研究及新型低溫銀基硬銲填料之開發

Abstract

本研究利用紅外線快速加熱，以純Ag、純Cu及BAg-8(Ag-Cu共晶)三種填料硬銲接合Fe3Al介金屬，填料熔液與基材元素於硬銲時交互擴散劇烈。以純Ag填料於980℃硬銲，銲道中僅有固溶Al之富Ag相，顯微組織及接合強度不隨持溫時間而有明顯改變，破壞形式為銲道中富Ag相之延性破斷，剪力強度可達約127MPa。以純Cu填料於1100℃硬銲，持溫時間對於顯微組織及接合強度均有很大影響，銲道基底隨持溫時間之增長，由固溶大量Al之富Cu相轉為β1’麻田散體相，因此接合強度先增後減，破壞形式也由延性逐漸增加脆性比例，其最大剪力強度可達291MPa。以BAg-8填料硬銲之顯微組織，持溫時間及溫度對其銲道組織不會有所影響，均為富Ag相及富Cu相所組成之共晶組織，持溫時間之增長可增加富Cu相中Al含量，因此接合強度亦隨之增加，破壞形式均為銲道凝固組織之延性破壞，其最大剪力強度可達181MPa。另外，本研究探討各種銀基合金填料對304、422及440C三種不銹鋼基材，藉由紅外線加熱之動態潤濕角量測瞭解其潤濕特性，並對其顯微組織進行生成相分析，發現Sn元素可降低Ag-Cu填料之熔點，但對於潤濕性幫助不大，因此再添加Mn元素使得填料可增加對不銹鋼之潤濕性，最後發現Ag-Cu-Sn-10wt.%Mn之填料合金的確可有效潤濕不銹鋼基材。顯微組織則由Ag-Cu-Sn填料有的界面抗蝕性劣化相(損失Ni及Cr之富Fe相)及填料區複雜凝固相，隨著Mn添加量的增多，除了界面相消失，填料區中複雜的富Cu之相(Cu3Sn、Cu4MnSn及富Cu相)也逐漸單一化並析出許多富Ag相於其中，最後成為沒有明顯介金屬相之富Ag及富Cu兩相混合相。

Microstructural evolution and bonding strength of infrared brazed Fe3Al using Ag, Cu, and BAg-8 braze alloys have been studied. The joint of the Ag-brazed specimen only contains Ag-rich phase alloyed with Al. The shear strength isn’t affected by the brazing time and reaches 127MPa for specimens brazed at 980oC×300s with the ductile fracture of Ag-rich phase. The microstructure and shear strength of infrared brazed Fe3Al using pure Cu at 1100oC are strongly dependent upon the brazing time in which the brazed joint changes from Cu-rich phase into β1’ (N18R) martensite phase, and causes different fracture mechanism and bonding strength. The highest shear strength reachs 291MPa for the specimen brazed at 1100℃×300s with the mixture of brittle and ductile phases in the joint. The microstructure of the Fe3Al joint brazed by BAg-8 contains Ag-rich and Cu-rich phases eutectic for all brazing conditions. The shear strength increases slightly with increasing the brazing time because the Al is alloyed in the Cu-rich matrix. The highest shear strength of 181MPa is acquired from the 800℃×600s brazed specimen. The analyses of dynamic wetting angles and microstructures of Ag-based braze alloys on 304, 422 and 440C substrates are performed. Experimental results shows that Sn added into Ag-Cu braze alloy can reduce its melting point effectively but can not improve its wettability for stainless steel. The Ag-Cu-Sn braze alloy with adding Mn can reduce the wetting angle on stainless steel. The more the Mn content , the better the wettability it has. The best wettability is the Ag-Cu-Sn-10wt.%Mn alloy and its microstructure after wetting tests consistsd of Ag-rich and copper-rich phases. Meanwhile, increasing the Mn content results in the copper-rich phases in the braze changing from complex phases (Cu3Sn, Cu4MnSn, Cu-rich phases) into single Cu-rich phase with many Ag-rich precipitates.