Infrared Vacuum Brazing Fe3Al Intermetallics Using Au-based Filler Metals and Studies on the Development of Novel Cu-based Braze Alloys
Date Issued
2010
Date
2010
Author(s)
Li, I-Hung
Abstract
Microstructural evolution and bonding strength of infrared brazed Fe3Al and stainless steels(SS) using Au-based and CuMn-based fillers, respectively, are studied. Firstly the wetting experiments using these braze alloys are conducted to make sure the suitable brazing temperature. Al2FeNi, Fe3Al and AlAu2 intermetallics are found in the joint of AuPdNi (Au-8wt.%Pd-22wt.%Ni) braze alloy brazed at 980℃ and all specimens are fractured in brittle. For AuCu(Au-20wt.%Cu) braze alloy, the brazed joint is fractured along the central β-phase in which the fracture exhibits ductile/brittle mode(s) with different brazing conditions. The highest shear strength for AuCu filler is 327MPa for specimen brazed at 880℃×300s. Raising the brazing time or temperature will deteriorate the strength due to the fracture mode transfers to brittleness. For infrared brazed 304, 422 and 440C stainless steels using Cu-33.7%Mn filler, a continuous interfacial (γFe,γMn) phase is found in between the braze and SS which is not well bonded with (Cu,γMn) primary phase in the brazed joint. Thus some cracks are observed in between (γFe,γMn) and (Cu,γMn) due to the thermal expansion mismatch of these two phases. In addition, solidification shrinkage voids or impurities are also observed in the central region of the joint and the fracture mode along this central voids/impurities is ductile with the shear strength of 280MPa for brazing 304 and 422 SS brazed at 875oC×180s. Cu-33.7%Mn filler alloyed with Ni can improve the joint properties, but increase slightly the fillers’ melting points. The Ni alloyed CuMn fillers can effectively wet all SS at appropriate temperatures and the interfacial cracks in between (γFe,γMn) and (Cu,γMn) phase are greatly reduced with increasing the Ni addition.
Subjects
Infrared brazing
Fe3Al intermetallic
Au-based fillers
CuMn-based fillers
bonding strength
stainless steel
wetting behavior
Type
thesis
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