N242-089 TITLE: Alternative Fabrication Pathways for Complex Alloys

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials; Hypersonics;Sustainment

OBJECTIVE: Develop a solid state processing pathway to fabricate refractory high entropy alloys that avoids partitioning (in multi-phase Alloys) seen in melting/solidification processes.

DESCRIPTION: Refractory high-entropy alloys (RHEAs) are considered a new kind of high-temperature materials with great application prospects due to their excellent mechanical properties and have the potential to replace nickel-based superalloy as the next generation of high-temperature materials for gas turbine and hypersonic applications. Currently, the majority of methods for processing of Cantor (3d transition) HEAs and metallic RHEAs are melt derived. This process can be challenging due to the disparate and extremely high melting points of the constituent metals. Moreover, elemental segregation often occurs during the solidification process, resulting in compositional inhomogeneity. In multi-phase alloys, portioning of elements into different phases occurs. This elemental partitioning promotes diverse properties in the different phases of the alloys such differing passivity properties. This SBIR topic seeks to develop a method for Cantor and RHEA production based on the reduction of a mixture of metal oxides, or a mixture of oxides and metallic powders. Processes utilizing non-flammable gas mixtures would be advantageous. The process could be aimed at obtaining (1) RHEA metallic powders (for subsequent solid-state processing) or (2) RHEA bodies (via additive processing of ceramic powders and subsequent reduction heat-treatment). Examples of target RHEAs compositions include MoNbTaW and HfNbTaTiZr.

PHASE I: Explore the literature to determine the relationship of processing versus complex alloy properties. Among the properties, what processes avoid partitioning of elements in multi-phase alloys. In addition, the offeror needs to utilize computational methods to ascertain non-additive manufacturing (AM) processes that minimize the energies to process these complex alloys. Develop model/algorithms that link alloy properties to the fabricating process and resulting microstructure and subsequent mechanical properties. The processes selected need to avoid elemental partitioning among multi-phase alloys. Determine the temperature at which elemental partitioning initiates. Focus on Cantor (3d transition) high entropy alloys. Analysis of defects and inhomogeneities is suggested to be done by non-destructive characterization methods. ICME (integrated computational materials engineering) should link the fabrication process with materials chemistry to prove the extent of feasibility of the selected process to avoid partitioning.

PHASE II: Apply ICME tolls to optimize processing to predict materials chemistry and processing parameter limits for complex alloys. Focus on employing lessons learned on RHEAs during Phase I. (Example: How do the thermodynamics and kinetics for producing RHEAs compare to the processing of Cantor HEAs?) Develop and/or modify model/algorithms that link alloy properties to the fabricating process and resulting microstructure and subsequent mechanical properties. (Note: As in Phase I, the process needs to avoid elemental partitioning among multi-phase alloys and needs to determine the temperature at which diffusional activities initiates elemental partitioning.) Analysis of defects and inhomogeneities is also suggested to be done by non-destructive characterization methods. With computational and experimental research for both Cantor and RHEAs, comprehensive models and algorithms should link optimized processing parameters with alloy chemistries that avoid elemental segregation often occurs during the solidification process after alloy melting, resulting in compositional inhomogeneities.

PHASE III DUAL USE APPLICATIONS: Continue to use the comprehensive models and algorithms to link optimized processing parameters with alloy chemistries that avoid elemental segregation and compositional inhomogeneities.

The developed process offers the opportunity of more uniform properties among phases. For instance, avoiding elemental partitioning will simplify strategies to form passive films on complex alloys due to more consistent materials chemistries among phases. Proven process optimization leading to a minimization of process - and materials - derived defects and inhomogeneities would improve acceptance of this process for producing components for the Navy and for private industry. Processing of components that are qualified for Navy use could also be applied to commercial use. Processing of components that are qualified for Navy use could also be applied to commercial use more quickly and less costly with parts are needed.

REFERENCES:

1. Ren, Xiqiang; Li, Yungang; YQi, anfei and Wang, Bo. "Review on Preparation Technology and Properties of Refractory High Entropy Alloys." Materials, 2022 Apr; 15(8): 2931. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9030642/
2. Wei, Shaolou; Kim, Sang Jun; Kang, Jiyun; Zhang, Yong; Zhang, Yongjie; Furuhara, Tadashi; Park, Eun Soo and Tasan, Cemal Cem. "Natural-mixing guided design of refractory high-entropy alloys with as-cast tensile ductility.", Nature Materials, 19, pages1175–1181 (2020)
3. Senkov, Oleg N.; Miracle, Daniel B. and Chaput, Kevin J. "Development and exploration of refractory high entropy alloys." Journal of Materials Research, 33(19), 01 October 2018, pp. 3092–3128. https://link.springer.com/article/10.1557/jmr.2018.153

KEYWORDS: Processing; RHEAs; refractory high entropy alloys; RMPEAs; arc-melting; partitioning; microstructure; Segregation; multi-phase

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