Interfacial reaction of infrared brazed NiAl/Al/NiAl and Ni_3Al/Al/Ni_3Al joints

摘要

The early-stage microstructural evolution of NiAl/Al/NiAl and Ni_3Al/Al/Ni_3Al in temperature ranges between 800 and 1200 deg C for 2-290 s was studied by infrared brazing. Al_3Ni phase is firstly formed in both Al-rich melt and the interface between nickel aluminide base material and Al-rich melt for specimens brazing at 800 deg C. The solid-state interdiffusion between Al3Ni and base material results in the formation of the interfacial Al_3Ni_2 phase, and further growth of Al_3Ni_2 phase at 800 deg C is impeded by the Al_3Ni interlayer due to its stoichiometry. For specimens brazing at 1000 deg C, the reaction changes from hypereutectic into peritectic reaction. The Al-rich melt dissolves more Ni atoms with the increment of brazing temperature to 1000 deg C. The Al_3Ni_2 phase is now initially formed in both the Al-rich melt and joint interface. The growth of Al_3Ni_2 interlayer at 1000 deg C is much faster than that at 800 deg C. Transport of Al atoms in forming Al_3Ni_2 phase at 1000 deg C is greatly increased due to the contact between Al_3Ni_2 and liquid Al-rich melt. The Al_3Ni shown in the joint is formed upon cooling cycle of the infrared brazing. The microstructural evolution in Ni_3Al/Al/Ni_3Al joint is similar to that in NiAl/Al/NiAl except for the formation of NiAl phase between Al_3Ni_2 and Ni_3Al. It can also be attributed to the solid-state interdiffusion between Ni_3Al and Al_3Ni_2 interlayer. However, the intermediate phase Ni_5Al_3, which is stable below 700 deg C, is not found in the experiment.