Intermetallics growth behavior and microstructure-mechanical properties relationship of Mo/BNi-2/FeCrAl brazed joint

Abstract

The pure Mo metal was brazed to FeCrAl alloy by using the BNi-2 filler alloy. The wetting process, interfacial microstructure, reaction layer growth kinetics and joint mechanical properties were investigated. It's found that the reactive wetting involves a transition from Mo-Ni-Si reaction layer at liquid front to MoNi reaction layer in wetting area. The growth kinetics of MoNi reaction layer is controlled by MoNi short-circuit diffusion. Based on the diffusion-reaction model and experimental data, the time exponent n is calculated as 2.98 and the activation energy Q is 353.9 kJ·mol⁻¹. At higher brazing temperature or prolonging the brazing time, a Si-rich layer composed of Mo₂Ni₃Si and MoNi₄ preferentially grows between Mo and MoNi layer. The mutual diffusion between filler alloy and FeCrAl promotes the formation of (Ni, Fe)Al, strip-shape σ(Fe,Cr) and (Fe,Ni)₃Al nanophases in FeCrAl. The highest shear strength of 258 ± 41 MPa was obtained for the joint brazed at 990 °C for 10 min. The fracture morphology demonstrates that the thick MoNi layer degrades the joint performance.