Hafnium-Bearing Superalloy Microstructure Control in Additive Manufacturing
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Solution Overview
Problem
Nickel-based superalloys face challenges in additive manufacturing due to rapid heating and cooling, leading to sub-optimal alloy microstructure and material properties, particularly microcracking issues, despite efforts to control carbon content, as seen in trials with RENE 108 alloy variants.
Innovation Solution
A hafnium-bearing superalloy composition with specific carbon and hafnium content ranges, combined with additive manufacturing techniques like direct metal laser melting, and subsequent heat treatments, such as hot isostatic pressing and solution aging, to control carbide formation and reduce segregation, thereby minimizing microcracking and enhancing gamma prime phase presence.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If additive manufacturing is used to fabricate nickel-based superalloy components, then design flexibility and manufacturing capability are improved, but the rapid heating and cooling rates result in sub-optimal alloy microstructure and material properties
Solution Approach 1:
The patent modifies the chemical composition parameters of the nickel-based superalloy, specifically controlling carbon content (0.015-0.06 wt%) and adding hafnium (0.02-0.2 wt%), to change the material's response to additive manufacturing thermal cycles. This compositional adjustment enables the formation of fine carbide particulates (median size <300 nm) that improve microstructure quality while maintaining design flexibility
Solution Approach 2:
The patent creates a composite microstructure within the superalloy by introducing hafnium-bearing carbide particulates as a secondary phase. These fine carbide precipitates (present at 0.003-0.05 wt%) act as reinforcement elements and nucleation sites, improving the overall microstructure quality and mechanical properties of the additively manufactured component
2Reliability
If carbon content is increased to control carbide formation, then microcracking resistance may be improved, but alloy composition complexity and processing sensitivity increase
Solution Approach 1:
The patent extracts the carbide-forming function from a high carbon content approach and concentrates it into controlled hafnium-bearing carbide particulates. By limiting total carbon to 0.015-0.06 wt% while adding 0.02-0.2 wt% hafnium, the patent achieves effective carbide formation for microcracking resistance without the complexity of high carbon alloy design
Solution Approach 2:
The patent introduces hafnium as an intermediary element that mediates between carbon and the nickel-based matrix. Hafnium has high carbide-forming affinity and creates fine, stable carbide particulates that improve microcracking resistance while keeping the overall carbon content low and the alloy composition simpler
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 approach results in articles with reduced microcracking and desirable microstructure, maintaining high strength and temperature stability, effectively addressing the limitations of conventional additive manufacturing methods for nickel-based superalloys.
Implementation Method 1
applying a direct metal laser melting (DMLM) process to form an intermediate article comprising a series of layers of solidified material from a metal powder feedstock
Implementation Method 2
hot isostatic pressing the intermediate article at a temperature and pressure effective to substantially close porosity within the intermediate article
Implementation Method 3
performing a solution heat treatment and an aging heat treatment to form a gamma prime precipitate phase within the processed article
Data Source
AI summary
Additive manufacturing methods, and articles made using additive manufacturing methods, are described herein. One embodiment is an article that comprises a hafnium-bearing superalloy. The superalloy includes at least about 50 weight percent nickel, from about 0.015 weight percent to about 0.06 weight percent carbon, and up to about 0.8 weight percent hafnium. The article further includes a plurality of primary carbide phase particulates disposed within the superalloy; the plurality has a median size less than about 1 micrometer. A method includes melting and solidifying particulates of a metal powder feedstock to build an intermediate article comprising a series of layers of solidified material. The feedstock includes the above-described superalloy composition. The method further includes heating the intermediate article to a temperature of at least about 950 degrees Celsius to form a processed article. The processed article further includes a plurality of primary carbide phase particulates disposed within the solidified material, the plurality of particulates having a median size less than about 1 micrometer.