Additively Manufacturable Oxidation Resistant Refractory High Entropy Alloys for Extreme Environment

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, thus exceeding the operating range of the state-of-the-art superalloys. áThus, development of these propulsion systems requires materials that are capable of tolerating extreme environments. áCurrently, 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 have emerged as one of the most promising materials for these applications. However, their oxidation resistance and additive manufacturability must be improved to meet the performance targets of the Air Force. In this SBIR Phase II, CFD Research has teamed up with University of California, Santa Barbara and University of Tennessee, Knoxville to address these challenges. áWe propose to use an Integrated Computational Materials Science and Engineering (ICME) approach that combines various modeling and simulation tools at different length and time scales, coupled with experimental techniques to systematically develop oxidation-resistant refractory high-entropy alloy compositions that can also be additively manufactured. áCFD Research has performed extensive Phase I-like feasibility demonstration and will use machine learning-based property prediction and rapid high-throughput protocol for alloy screening, microstructural continuum mechanics simulations for oxidation and coating-substrate compatibility, and thermodynamics and phase field-based process modeling to guide experimental efforts. Experimental validation will include initial processing of select alloy compositions in an arc melter, characterization of microstructures, and determination of high-temperature oxidation resistance and mechanical properties. The two alloys which possess the best combination of high-temperature strength, oxidation resistance, and room-temperature ductility will be selected for additive manufacturing. áThe Phase II effort will also include fabrication of refractory high-entropy alloy powders via ultrasonic atomization, followed by microstructural characterization of the powder. áAdditively manufactured samples will be built via laser powder bed fusion. The microstructure of the samples will be analyzed using various imaging techniques before and after oxidation tests at temperature up to 1400 ░C. To maximize the potential operating range, the as-built samples will also be tested with an off-the-shelf coating and its performance compared to the uncoated samples. Finally, the samples will be tested at realistic flight conditions in CFD Researchĺs High Enthalpy Test Rig which can reach Mach 7 speed and a temperature of 1400 ░C. áThe microstructure and weight gain of the samples will be analyzed following exposure to these flight conditions.