Guided Discovery of Refractory High-Entropy Alloys for Additive Manufacturing

Next-generation aerospace systems will operate in extreme environments to remain ahead of our adversaries. Their components will experience very high temperatures (beyond 1300 °C) and a highly oxidizing environment, exceeding the operating range of the state-of-the-art superalloys. Thus, development of these propulsion systems requires materials that are capable of tolerating extreme environments. Currently, there is no additively manufacturable off-the-shelf material that performs adequately under these conditions. Due to their potential for exceptional strength at high-temperature, refractory high-entropy alloys (RHEAs) have emerged as one of the most promising materials for these applications. However, their material performance, additive manufacturability, cost-effectiveness, and supply chain availability must be improved to meet the performance targets of the Missile Defense Agency (MDA). This proposed program will be a collaborative effort led by CFD Research Corporation in collaboration with The Applied Research Laboratory at Penn State University and the University of Tennessee – Knoxville. The Phase I effort will leverage existing machine-learning-based property models developed by CFD Research for RHEAs in conjunction with additive manufacturability and cost/supply chain considerations to identify novel materials capable of meeting and exceeding all MDA requirements. Properties of interest include high-temperature specific yield strength, room-temperature ductility or plasticity, and oxidation resistance. Moreover, key thermophysical properties, such as the coefficient of thermal expansion, isobaric heat capacity, and so on, will be considered. Furthermore, powder synthesis for this work will be achieved via the Field Assisted Sintering Technology (FAST) for bulk material production followed by milling to form powder. In Phase I, we will demonstrate this approach to powder synthesis with a reference refractory alloy composition. In Phase II, using a selection of RHEA candidates computationally identified in Phase I, the validated FAST-based approach to powder synthesis will be leveraged to produce sample powders of the candidate RHEAs of interest. To serve as a baseline for comparison, we will also produce material samples of each RHEA candidate through a traditional arc-melting and casting approach. Mechanical testing and characterization at room and high temperature will be undertaken to validate model predictions and understand differences in materials processed via additive manufacturing versus traditional routes. Moreover, we will leverage our prior experience in physics-based solidification modeling in additive manufacturing to understand microstructural evolution and factors affecting the quality (e.g., build density) of RHEAs processed via additive manufacturing. Approved for Public Release | 25-MDA-12052 (27 Mar 25)