Superalloy Disc Heat Treatment with Insulation for Microstructure Control
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Solution Overview
Problem
Large gas turbine engine discs face challenges in achieving uniform temperature distribution during heat treatment, leading to inconsistent microstructure and reduced mechanical properties due to their greater size and thermal mass, which can result in overaging or dissolution of gamma prime precipitates.
Innovation Solution
A method involving solution heat treatment below the gamma prime solvus temperature, followed by insulation placement to create temperature gradients, and controlled ramp rates to maintain fine and coarse grain structures in specific regions of the disc, with a transitional zone angled relative to the axis, ensuring optimal microstructural properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a single stage isothermal solution heat treatment is applied to large gas turbine engine discs, then the entire disc is heated uniformly, but the hub region reaches temperatures that cause overaging or dissolution of gamma prime precipitates due to the greater thermal mass and slower heating rate
Solution Approach 1:
The patent applies different thermal treatments to different regions of the disc by positioning insulating material selectively. The hub region is covered with insulation to reduce its heating rate and prevent overaging, while the rim region is exposed to higher temperatures for coarse grain structure development. This local differentiation of thermal conditions resolves the contradiction between uniform temperature distribution and microstructure consistency.
Solution Approach 2:
The disc is effectively segmented into two thermal zones: an insulated hub region and an uninsulated rim region. This segmentation allows independent control of thermal history for each region, enabling the hub to maintain temperatures below the gamma prime solvus while the rim exceeds it, thereby achieving consistent microstructure control across the entire component.
2Manufacturing precision
If insulation is placed over the hub region to reduce heating rate, then gamma prime precipitates are maintained, but the device complexity increases due to additional insulation placement and removal steps
Solution Approach 1:
The patent uses simple, inexpensive insulating material (such as ceramic fiber or refractory brick) that is placed over the hub region, used for the duration of the heat treatment cycle, and then removed or discarded. This disposable insulation approach provides precise microstructure control without requiring complex, reusable insulation systems with multiple components and maintenance requirements.
3Strength
If the disc is heated to above the gamma prime solvus temperature, then coarse grain structure is achieved in the rim for high temperature creep resistance, but the hub region experiences dissolution of gamma prime precipitates due to excessive temperature exposure
Solution Approach 1:
The patent creates local quality differences in the disc by applying insulation selectively to the hub region. This allows the rim to be heated above the gamma prime solvus temperature for coarse grain structure and high temperature creep resistance, while the insulated hub remains below the solvus temperature to preserve gamma prime precipitates and maintain overall mechanical reliability.
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 achieves a uniform temperature distribution and microstructure optimization across larger discs, enhancing mechanical properties by maintaining gamma prime precipitates and improving high-temperature creep and low-cycle fatigue resistance.
Implementation Method 1
placing the insulated assembly of disc and insulation in a furnace at a temperature below the gamma prime solvus temperature
Implementation Method 2
placing insulation over at least one first predetermined area of the disc and leaving at least one second predetermined area of the disc without insulation
Implementation Method 3
increasing the temperature in the furnace at a predetermined ramp rate to a temperature above the gamma prime solvus temperature to maintain a fine grain structure substantially in a first region of the disc, to produce a coarse grain structure substantially in a second region of the disc
Data Source
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AI summary
A method of heat treating a superalloy component comprises solution heat treating the component at a temperature below the gamma prime solvus temperature to produce a fine grain structure in the component. Insulation is placed over a first area of the component to form an insulated assembly. The insulated assembly is placed in a furnace at a temperature below the solvus temperature and maintained at that temperature for a predetermined time to achieve a uniform temperature in the component. The temperature is increased at a predetermined rate to a temperature above the solvus temperature to maintain a fine grain structure in a first region, to produce a coarse grain structure in a second region and to produce a transitional structure in a third region between the first and second regions of the component. The insulated assembly is removed from the furnace when the second region of the component has been above the solvus temperature for a predetermined time and/or the first region of the component has reached a predetermined temperature.