Laser Cladding of HTW Turbine Buckets Without Weld Cracking
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Solution Overview
Problem
Hard-to-weld alloys, due to their gamma prime and geometric constraints, are susceptible to gamma prime strain aging, liquation, and hot cracking, making them difficult to join, especially when the gamma prime phase is present in volume fractions greater than about 30%, which inhibits the formation of continuous cladding layers in turbine buckets.
Innovation Solution
A method involving laser welding of a powder of a hard-to-weld alloy to form a cladding layer on turbine buckets, where the weld path oscillates nonparallel to a reference line, creating a continuous and crack-free cladding layer, allowing for increased thickness and repeatability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard welding techniques are used to apply HTW alloy cladding layers, then the cladding layer can be formed, but cracks occur in the cladding layer due to contact between weld beads
Solution Approach 1:
The patent replaces conventional arc welding with laser welding technology. The laser beam provides precise thermal energy concentration, enabling controlled melting and solidification of HTW alloy powder deposited on the substrate. This substitution of welding mechanism eliminates the crack formation issue inherent in conventional welding of gamma prime-containing alloys.
Solution Approach 2:
The patent modifies critical welding parameters including laser power, welding speed, and powder feed rate to optimize the cladding process. By controlling the laser energy density and thermal input, the process achieves complete fusion without excessive heat accumulation that causes cracking. The oscillating weld path further distributes thermal energy to prevent localized overheating.
2Area of stationary object
If multiple concentric weld beads are applied to form continuous cladding layers, then coverage is improved, but crack occurrence increases due to contact between successive weld beads
Solution Approach 1:
The patent implements an oscillating weld path where the laser beam moves in a controlled pattern (e.g., sinusoidal, triangular, or circular oscillation) perpendicular to the travel direction. This dynamic motion distributes the heat input over a wider area, prevents excessive heat accumulation at any single point, and eliminates the contact between successive weld beads that causes cracking, while still achieving continuous cladding coverage.
3Strength
If HTW alloy content (aluminum or titanium) exceeds 3%, then superior operational properties are achieved, but gamma prime phase volume fraction increases making welding difficult
Solution Approach 1:
The patent replaces conventional arc welding with laser welding technology. The laser beam provides precise thermal energy concentration, enabling controlled melting and solidification of HTW alloy powder deposited on the substrate. This substitution of welding mechanism eliminates the crack formation issue inherent in conventional welding of gamma prime-containing alloys.
Solution Approach 2:
The patent modifies critical welding parameters including laser power, welding speed, and powder feed rate to optimize the cladding process. By controlling the laser energy density and thermal input, the process achieves complete fusion without excessive heat accumulation that causes cracking.
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 method decreases costs, increases process control and efficiency, and eliminates crack occurrence, enabling the formation of thicker, more reliable cladding layers on turbine buckets.
Implementation Method 1
laser welding a powder of a metal alloy to a surface of a substrate along a weld path, forming a weld bead of the metal alloy
Data Source
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AI summary
A method for forming an article (200) is disclosed, including laser welding a powder (104) of an HTW alloy to a surface (102) of a substrate (100) along a weld path (400), forming a weld bead (106) of the HTW alloy. The weld path (400) is propagated along a weld direction (112), forming a cladding layer (202) of the HTW alloy on the surface (102). The laser welding includes a laser energy density of at least 11 kJ/cm2, and laser welding the powder (104) to the surface (102) includes a welding speed of 5-20 ipm. The weld path (400) oscillates essentially nonparallel to a reference line (122), establishing a cladding width (114) wider than the weld bead width (108). The weld bead (106) contacts itself along each oscillation such that the cladding layer (202) is continuous. A turbine bucket (118) is disclosed including a squealer tip (206) having the cladding layer (202) with a cladding layer thickness (204) of at least 0.2 inches.