Superalloy Property Recovery via Segmented Heat Treatment
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Solution Overview
Problem
Existing methods for recovering the properties of single crystal and directionally solidified nickel-based superalloy components after high-temperature exposure lead to recrystallization, which is not desirable, as they fail to maintain the original microstructure and mechanical properties.
Innovation Solution
A regenerative heat treatment process involving stress relief, γ′ rejuvenation at a temperature below the γ′-solvus temperature, precipitation, and aging heat treatments, specifically tailored to avoid recrystallization, with precise temperature control and duration to restore the γ/γ′ microstructure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional solutioning heat treatment at high temperature is applied to recover properties of single crystal superalloy components, then degraded γ′ phase is dissolved and reprecipitated in fine form, but recrystallization occurs during the highest temperature portion of the heat treatment
Solution Approach 1:
The heat treatment process is divided into multiple distinct steps with different temperature ranges and durations: stress relief treatment (850-1100°C), γ′ rejuvenation treatment (below γ′-solvus temperature), precipitation treatment (1050-1150°C), and aging heat treatment (800-980°C). This segmentation allows each step to address specific microstructural issues without causing recrystallization
Solution Approach 2:
The invention changes the temperature parameters of the heat treatment process, specifically controlling the γ′ rejuvenation treatment to occur below the γ′-solvus temperature and using precise temperature ranges for each step. This parameter control enables property recovery while preventing the recrystallization that occurs in conventional high-temperature solutioning
2Duration of action of stationary object
If high temperature heat treatment is used to dissolve degraded γ′ phase, then microstructure is restored, but original microstructure and mechanical properties cannot be maintained due to recrystallization
Solution Approach 1:
The stress relief treatment is performed first at 850-1100°C to eliminate residual stresses before proceeding to the γ′ rejuvenation treatment. This preliminary action prevents stress-induced recrystallization during subsequent high-temperature steps
Solution Approach 2:
The γ′ rejuvenation treatment is conducted at a controlled temperature below the γ′-solvus temperature for a specific duration, allowing microstructure restoration without reaching the temperature threshold that would cause recrystallization and loss of manufacturing precision
3Ease of repair
If conventional recovery methods are applied to single crystal articles, then property recovery is achieved in conventionally cast materials, but recrystallization occurs in single crystal articles during high temperature treatment
Solution Approach 1:
The invention changes the temperature parameters from conventional high-temperature solutioning to a multi-step process with controlled temperature ranges, particularly keeping the γ′ rejuvenation treatment below the γ′-solvus temperature to prevent recrystallization while still achieving property recovery
Solution Approach 2:
The heat treatment process combines multiple treatments with different functions (stress relief, γ′ rejuvenation, precipitation, aging) into a composite process sequence, where each treatment addresses specific aspects of property recovery without causing harmful recrystallization
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
The method effectively rejuvenates the microstructure and mechanical properties of nickel-based superalloy components, preventing recrystallization and maintaining the original condition, as demonstrated by Vickers hardness testing and microstructure analysis.
Implementation Method 1
a stress relief treatment at 850° C.-1100° C.
Implementation Method 2
a γ′ rejuvenation treatment at a temperature between 20° C. and 80° C. below γ′-solvus temperature (Tsolvus, γ′) of the Nickel based superalloy
Implementation Method 3
a precipitation treatment at 1050° C.-1150° C.
Implementation Method 4
an aging heat treatment at 800°-980° C.
Data Source
AI summary
A method is disclosed for recovering the properties of single crystal and directionally solidified Nickel based superalloys and articles made thereof, after use in a high temperature environment. The method comprises the steps of a stress relief treatment, a γ′ rejuvenation heat treatment at a temperature below the γ′-solvus temperature (Tsolvus, γ′) of the superalloy, a precipitation heat treatment and an aging heat treatment.