Superalloy Heat Treatment Prevents Cracking
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Solution Overview
Problem
Additively manufactured gamma-prime strengthened superalloy components, such as those produced by selective laser melting (SLM), often experience significant cracking due to rapid cooling and subsequent gamma-prime precipitation during conventional heat treatments, leading to rejection of parts.
Innovation Solution
A post-built heat treatment method involving rapid heating rates (at least 25°C/min) from room temperature to 850°C to minimize gamma-prime precipitation, followed by isothermal dwells to reduce residual stresses, ensuring crack-free components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional heat treatment is applied to additively manufactured gamma-prime strengthened superalloy components, then residual stresses are reduced and microstructure is adjusted, but significant cracking occurs due to gamma-prime precipitation during heat treatment
Solution Approach 1:
The patent applies a fast heating rate of at least 25°C/min during the first heat-up to rapidly pass through the temperature range where gamma-prime precipitation occurs (below 850°C). This rushing through the critical temperature zone prevents significant gamma-prime precipitation and the associated volume changes that cause strain age cracking, while still achieving the necessary microstructure adjustment and residual stress reduction at higher temperatures.
2Reliability
If fast heating rate is applied to avoid gamma-prime precipitation, then cracking is prevented, but energy consumption increases
Solution Approach 1:
The heat treatment process is segmented into distinct phases: a first fast heating phase at ≥25°C/min to reach 850°C and avoid gamma-prime precipitation, followed by a second phase with different heating rate for microstructure adjustment. This segmentation allows the high energy input to be concentrated only where necessary (during the critical first heat-up) rather than throughout the entire heat treatment process.
3Reliability
If multiple pre-weld and post-weld heat treatment steps are applied, then crack avoidance is achieved, but process time and cost increase significantly
Solution Approach 1:
The patent merges the functions of avoiding gamma-prime precipitation and adjusting microstructure into a single integrated heat treatment process. The fast heating rate of at least 25°C/min serves dual purposes: preventing harmful precipitation during the initial heat-up and subsequently enabling microstructure adjustment at higher temperatures, thereby eliminating the need for separate pre-weld and post-weld heat treatment steps.
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 prevents cracking in additively manufactured superalloy components, improving their structural integrity and reducing the risk of strain age cracking, compared to conventional heat treatments.
Implementation Method 1
heating the component from room temperature (RT) up to a temperature T1, wherein T1 is 50 to 100 °C less than a temperature Ts, at which a drop of the thermal expansion coefficient starts
Implementation Method 2
heating the component by applying a fast heating with a heating rate v2 of at least 25°C/min from T1 to a temperature T2 ≥ 850 °C to avoid or at least to reduce precipitation of the gamma-prime phase
Implementation Method 3
holding the component for a time t1 at T1 to achieve a uniform component temperature
Data Source
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AI summary
The invention relates to a method of post-built up heat treatment of an additively manufactured high strength component made of a gamma-prime (y') strengthened superalloy based on Ni or Co or Fe or combinations thereof. An application of a rapid heating-up rate of 25 to 60 °C/min in a specific temperature range during the first post-built heat treatment after additive manufacturing avoids or at least minimizes the gamma-prime precipitation in the component during heat-up. This results in crack-free components/articles compared to significant cracking present in conventionally heat treated components.