Effects of process parameters on the transient liquid phase bonding of dissimilar materials: in 738 superalloy and cobalt
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Date
2018
Authors
Aina, Oluyemi
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Abstract
Transient liquid phase (TLP) bonding has become a very attractive method of joining similar and dissimilar difficult-to-weld advanced materials. The effects of process parameters on the joint microstructure of TLP bonded nickel-based superalloy IN738 and cobalt metal using Nicrobraz 150 interlayer are investigated in this research. It is discovered that adequate processing time (tf) is required to prevent formation of deleterious eutectic that is known to degrade the mechanical properties of the joint. Increase in temperature to a certain point reduces the size of the eutectic in the joint due to increase in diffusivity with increase in temperature. However, a further increase in temperature above this temperature produced a larger width of the eutectic at the joint because of the overriding effect of solubility on diffusivity at higher temperatures. The eutectic in dissimilar IN 738/Co is asymmetrically distributed within the joint and this is caused by liquid-state diffusion, which has been generally ignored in the discussion of TLP bonding of dissimilar materials in the literature. In contrast to the expectation that rapid atomic diffusion in the liquid would reduce the processing time (tf) required to completely eliminate the eutectic from the joint region through diffusional solidification, the occurrence of liquid-state diffusion significantly prolonged the processing time. This requires adequate consideration in the use of TLP bonding for joining dissimilar materials.
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Keywords
TLP Bonding ,Diffusion,Liquid-state Diffusion