ALM Superalloy Processing via Segmented Powder Mixture
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Solution Overview
Problem
Nickel-based superalloys used in high-temperature applications are difficult to process through conventional methods due to high internal stresses, which can lead to cracking during Additive Layer Manufacturing (ALM) and subsequent heat treatments, especially those to the right of the 'weldability' line, where heating is either impractical or commercially disadvantageous.
Innovation Solution
A method involving a mixture of two distinct metal powders, where one powder forms the bulk matrix and the other is a minor constituent with higher concentrations of gamma prime forming elements, allowing local fusion without diffusion during ALM to build the part, followed by a heat treatment to form a gamma prime phase containing superalloy, thereby reducing stress and preventing cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If conventional ALM processing is applied to nickel-based superalloys with gamma prime forming elements, then the desired alloy composition is achieved, but internal stresses cause cracking during processing and heat treatment
Solution Approach 1:
The alloy is segmented into two separate metal powders: a bulk matrix powder and a gamma prime forming powder. This segmentation allows each component to be optimized independently - the bulk matrix can be processed without cracking while the gamma prime elements are introduced separately, avoiding the cracking problem of conventional homogeneous superalloy processing.
Solution Approach 2:
The bulk matrix powder is prepared and processed first to form the part structure without gamma prime elements. Only after successful crack-free processing is the gamma prime forming powder introduced through selective deposition. This preliminary action ensures the base structure is stable before adding elements that would cause cracking if present from the start.
2Manufacturing precision
If bulk heating is applied to reduce internal stresses, then dimensional accuracy is improved, but processing time and energy consumption increase significantly
Solution Approach 1:
Instead of bulk heating the entire part, the gamma prime forming powder is selectively deposited only in specific regions where it is needed. This localized approach allows the bulk matrix to remain at lower temperatures, maintaining dimensional accuracy without requiring extensive bulk heat treatment time and energy.
Solution Approach 2:
The processing parameters are changed by introducing a two-powder system with different thermal and mechanical properties. The bulk matrix powder enables crack-free processing at lower temperatures, while the gamma prime powder is added in controlled amounts. This parameter change eliminates the need for prolonged bulk heating while maintaining dimensional accuracy.
3Strength
If gamma prime forming elements are added to achieve desired alloy properties, then mechanical strength is improved, but internal stresses increase causing cracking
Solution Approach 1:
The gamma prime forming elements are segmented from the bulk matrix and introduced as a separate powder. This allows the bulk matrix to provide the primary structural support with low internal stress, while the gamma prime elements are added in controlled quantities to specific regions, providing strength enhancement without proportionally increasing overall internal stress.
Solution Approach 2:
Gamma prime forming elements are not uniformly distributed throughout the part but are selectively deposited in regions where they are most needed for mechanical strength. This local quality approach ensures strength is enhanced where required while minimizing the total amount of gamma prime elements, thereby reducing overall internal stress and cracking risk.
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 approach enables the formation of crack-free superalloy parts by maintaining low internal stresses during both the ALM process and heat treatment, achieving full density and desired mechanical properties without the need for porosity reduction or melt point depressants, and allows for the processing of previously unweldable alloys.
Implementation Method 1
selective application of an energy source (typically a laser or electron beam) and then solidifies in order to produce, layer by layer, a fully dense metal part
Implementation Method 2
the powder is fully melted where desired by the selective application of an energy source
Implementation Method 3
heat treating the metal mix to form a gamma prime phase containing superalloy
Implementation Method 4
these gamma prime precipitates frequently include titanium and aluminium
Implementation Method 5
subsequent heat treatments that then form a superalloy
Implementation Method 6
many metals go through a phase change as they cool from liquid adding further stresses
Implementation Method 7
as the powder is fully melted and many metals and alloys have a high coefficient of thermal expansion the as-built part typically has considerable internal stresses
Data Source
AI summary
A method of forming an article includes forming a layer of a mixture of at least two distinct metal powders selected such that when combined they are chemically in the proportions of a superalloy containing a gamma prime phase, and fusing the powders locally without diffusion to define the shape of a part of the article such that the materials of the distinct metal powders remain substantially chemically segregated forming regions of different chemical composition. The method further includes repeating the forming and fusing until the derived article is formed, and heat treating the finished article such that at least one of the distinct separate materials diffuses to form a gamma prime phase containing superalloy with the other.