Abstract
A new numerical model is developed using a Cellular Automata (CA) method to study the liquid-phase dissolution behavior of gap-filler powder particles in interlayer powder mixture during transient liquid phase (TLP) bonding process. The model prediction of microstructural evolution in TLP joint between single crystal substrates show that formation of misoriented stray-grains results from incomplete liquation of the gap-filler powder particles. In contrast to what is generally assumed and reported, numerical calculations coupled with experimental verification show that under properly selected process parameters, complete melting of the gap-filler powder particles is possible. This is imperative to prevent the formation of misoriented stray-grains and maintain single crystallinity during TLP bonding of single crystal materials. The dependence of complete melting of the gap-filler particles on salient TLP bonding parameters are analyzed and discussed.
Highlights
Introduction and BackgroundSingle crystal nickel-base superalloys are new generation heat resistant materials used in the manufacture of section components in aircraft and land-based power-generation turbine engines due to their remarkable mechanical properties at elevated temperatures [1]
Since initial liquid and solid concentrations near the liquidsolid interfaces are different than the local equilibrium concentrations at the bonding temperature, there exists a driving force to reach this equilibrium which results in dissolution of the solid particle to reduce solute concentration in liquid
The simulation confirms experimental observations reported in the literature that incomplete dissolution of gap-filler powder particles produces formation of stray grains during transient liquid phase (TLP) bonding of single crystal substrates [3,4]
Summary
Single crystal nickel-base superalloys are new generation heat resistant materials used in the manufacture of section components in aircraft and land-based power-generation turbine engines due to their remarkable mechanical properties at elevated temperatures [1]. The filler alloy melts and rapidly attains equilibrium at the liquid-solid interfaces through base-alloy melt-back dissolution process. Huang et al [7], investigated the diffusion bonding of Al-based dissimilar composites by using Al-Si, Al-Cu and Al-Si-SiC powders as fillers They reported that the segregation of SiC particles and formation of porous zones at the joint lead to a reduction of the joint shear strength. The understanding of the dissolution behaviour of gapfiller powder particles by molten filler alloy, which could influence formation of the stray-grains, is limited due to the large number of process and material parameters that affect the final joint microstructure and performance. A powder particle-liquid interface may break up, or join with neighboring interfaces This poses severe difficulties when conventional interface-tracking methods are used. The mathematical formulation and implementation will be discussed followed by the results and discussion
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