Superalloy Cladding with Composite Filler Powder
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Solution Overview
Problem
Fusion welding of nickel and cobalt-based superalloys, such as Inconel 738, often results in cracking due to low ductility and residual stresses, leading to costly preheating requirements and reduced productivity, with existing methods failing to produce crack-free welds at ambient temperatures.
Innovation Solution
A method involving the use of a composite filler powder containing 5-50% brazing powder and 50-95% high-temperature welding powder, heated by a local welding source to create a heterogeneous weld bead with a continuous framework of high-temperature dendrites and an interdendritic eutectic matrix, allowing for self-healing of cracks during post-weld heat treatment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If fusion welding is used to join superalloys, then coalescence and joining occur through melting of base material, but cracking occurs due to low ductility and residual stresses
Solution Approach 1:
The invention changes the temperature parameter by implementing preheating to 1800°F-2100°F (982°C-1148°C) before welding and maintaining heat during welding. This parameter change increases ductility and reduces residual stresses, preventing cracking while achieving strong joints in low-ductility superalloys
Solution Approach 2:
The invention uses composite filler materials with specific compositions (e.g., Inconel 713 plus 5-15% boron, or Inconel 738 plus 5-15% boron) that combine the base superalloy properties with crack-inhibiting elements. The composite filler creates a weld metal with improved ductility and crack resistance while maintaining joining strength
2Reliability
If preheating is applied before welding to avoid cracking, then crack-free welds are achieved, but productivity decreases and costs increase
Solution Approach 1:
The invention performs preliminary preheating to 1800°F-2100°F (982°C-1148°C) and maintains this temperature during welding through continuous heating. This preliminary action ensures the material remains in a high-ductility state throughout the welding process, preventing cracking without requiring lengthy post-weld heat treatments or rework
Solution Approach 2:
The invention maintains continuous heating during the welding process to keep the base material and weld zone at elevated temperatures (1800°F-2100°F). This continuity prevents cooling-induced cracking and eliminates the need for separate post-weld heat treatment steps, improving productivity while ensuring crack-free joints
3Reliability
If brazing is used instead of welding to avoid cracking, then crack-free joints are produced, but mechanical properties decrease by 50-75% at high temperature
Solution Approach 1:
The invention changes the temperature parameter by welding at elevated temperatures (1800°F-2100°F preheat, maintained during welding) which is higher than conventional brazing temperatures. This allows the use of filler materials with melting points above 2000°F that can provide high-temperature mechanical properties comparable to the base material, unlike traditional brazing materials
Solution Approach 2:
The invention uses composite filler materials (e.g., Inconel 713+boron, Inconel 738+boron) that combine the base superalloy matrix with boron additions. These composite fillers create weld metals with high-temperature strength comparable to the base material, eliminating the 50-75% strength loss typical of brazed joints while still preventing cracking through the boron's crack-inhibiting effects
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach produces crack-free welds at ambient temperature, reduces costs, increases productivity, and enhances the mechanical and oxidation resistance of welds, while eliminating the need for costly rework and preheating, thereby improving the health and safety of the welding process.
Implementation Method 1
heating the base material and the composite filler powder by a local welding source. The filler powder is heated to a temperature that will fully melt the brazing powder and at least partially melt the high temperature welding powder
Implementation Method 2
subsequent solidification and cooling of a weld pool forming a heterogeneous weld bead comprising of a continuous interconnected framework of high temperature dendrites and interdendritic eutectics matrix
Implementation Method 3
post weld heat treatment at a temperature exceeding the solidus temperature of the brazing powder but below the solidus temperature of the base material that will result in at least a partial melting of the eutectic that is adapted to self healing by filling of cracks up to 0.8 mm in width and up to 20 mm in length
Implementation Method 4
self healing by filling of cracks up to 0.8 mm in width and up to 20 mm in length
Data Source
Figure 1a~1b
Figure 2a~2b
Figure 3a~3b
AI summary
The present concept is a method of cladding and fusion welding of superalloys and includes the steps of firstly application of a composite filler powder that comprises 5- 50% by weight brazing powder which includes melting point depressants, and 50-95% by weight high temperature welding powder, to a superalloy base material. Secondly there is simultaneous heating of the base material and the composite filler powder by a welding heat source that is movable relative to the base material. There is heating to a temperature that will fully melt the brazing powder and at least partially melt the high temperature welding powder and also melt a surface layer of the base material, thereby forming a weld pool. Thirdly upon solidification and cooling of the weld pool, there is coalescence between a weld bead and the base material.