Refractory Metals: Alloy Development and Compositionally Complex Alloys
Sponsored by: TMS Structural Materials Division, TMS: Refractory Metals Committee
Program Organizers: Eric Taleff, University of Texas at Austin; Lauren Garrison, Commonwealth Fusion Systems; Alexander Knowles, University of Birmingham
Monday 2:00 PM
February 28, 2022
Room: 252B
Location: Anaheim Convention Center
Session Chair: Sandy Knowles, University of Birmingham; Lesley Cornish, University of the Witwatersrand
2:00 PM Invited
Platinum-based Superalloys: Combating High Temperatures and Aggressive Environments: Lesley Cornish1; 1University of the Witwatersrand
Platinum is fcc with a relatively high melting point, and good corrosion resistance in many aggressive environments. In the same group as nickel, it reacts similarly with other elements. Platinum’s higher melting point (1769°C) than nickel (1455°C) is advantageous. However, there are two serious disadvantages for platinum-based alloys in applications for moving parts: high densities and high costs. Partly due the improvements in recycling, the platinum price has decreased, and the densities can be slightly reduced by alloying with lighter metals.Different platinum-based alloys were designed and tested. Most alloys had aluminium to produce the strengthening precipitates, as well as corrosion resistance. Density was reduced by substituting lower density but high melting point elements: vanadium and/or niobium. Ruthenium was added for corrosion resistance and solid solution strengthening. A thermodynamic database of Pt-Al-Cr-Ru was developed to optimize compositions, which were characterized and mechanically tested.
2:20 PM
Design of BCC High-entropy Alloys with Low Neutron Absorption Cross-section: Pedro Ferreirós1; Daniel King2; Alexander Knowles1; 1University of Birmingham; 2Imperial College London
High-entropy alloys (HEAs) are promising candidates for generation IV fission & fusion energy, offering high melting points, high strength and irradiation tolerance. However, their selection & design remains a major challenge with the vast size of the composition design space & predictive capability. In this work, we explore several million of element combinations using the Alloy Search and Predict (ASAP) software, which screens for HEAs candidates with single-phase stability at high temperature. Within the ASAP HEA screening, we further select for HEAs with lower thermal neutron absorption cross section. These HEAs have refractory metals (RM) as their main constituents providing great potential for application in extreme environments. These newly identified RM-HEAs have been experimentally product, their microstructure & properties analysed by experimental techniques and compared with phase predictions of ASAP and CALPHAD.
2:40 PM
Design of MoWTaTiZr Refractory Multi-principal Element Alloys: Gaoyuan Ouyang1; Prashant Singh1; Jun Cui1; Matthew Kramer1; Duane Johnson1; 1Ames Laboratory
Refractory Multi-principal Element Alloys (RMPEA) show high strength at elevated temperatures, surpassing that of Nickel-based superalloys. Recent efforts in RMPEA focus on developing lighter alloys with a combination of strength and ductility. Under the guidance of accurate density-functional theory (DFT) theory, we have studied the phase formation and room temperature (RT) elastic constant of a set of 32 compositions in the Mo-W-Ta-Ti-Zr-(Al,Cr) system. W or Cr addition increased the RT modulus and provided the basis for down selection. Down-selected RMPEA samples show good compressive yield strength (700-900MPa) and ductility (~10% strain) at room temperature. As-casted samples demonstrated good high-temperature yield strength up to 250MPa at 1300°C by small punch testing. Our results also showed that the homogenization heat treatment at ~75% of melting point is sufficient to cause phase redistribution and significant grain growth for RMPEA, adversely affecting their mechanical properties.
3:00 PM Invited
Refractory High Entropy Alloys for Applications in Extreme Environments: Osman El-Atwani1; Hi Vo1; Matheus Tunes1; Andrew Alvarado1; Kevin Baldwin1; Koray Iroc2; Eda Aydogan2; Stuart Maloy1; Enrique Martinez3; 1Los Alamos National Laboratory; 2Middle East Technical University; 3Clemson University
In the quest of new materials that can withstand severe irradiation and mechanical extremes for advanced applications (eg. fission reactors, fusion devices, space applications, etc.), design, prediction and control of advanced materials beyond current material designs become a paramount goal. W-based refractory high entropy alloys (HEA) have been recently developed in the context of high temperature applications. Here, we present thermal stability, mechanical properties and irradiation resistance experiments on several simulation (CALPHAD, DFT and Cluster Expansion) guided compositions of W-based refractory HEAs. In-situ TEM-annealing experiments are performed on different compositions of the HEAs and the results are compared with CALPHAD simulations and the enthalpies of mixing determined through DFT and Cluster Expansion methodologies. Ductility and strength are assessed, and in-situ TEM-irradiation and implantation experiments are performed and discussed. This work constructs a timely and urgent pathway to optimize the properties of these HEAs for different current and future applications.
3:20 PM Break
3:40 PM
High-throughput Engineering of Oxidation Behavior in Complex Refectory Alloys: Daniel Sauceda1; Prashant Singh2; Raymundo Arroyave1; 1Texas A&M University; 2AMES Laboratory
High-temperature mechanical response makes refractory alloys a potential candidate for replacing existing superalloys. However, the technological application of refectories is limited by severe oxidation. We present an automated machine-learning-based framework for high-throughput assessment of oxidation behavior through the evaluation of thermodynamic stability, chemical activity, reaction products (phases), phase fractions of competing phases, as well as the survivability of the parent alloys. Two extreme examples were chosen to establish the applicability of approach (i) refractory-based ceramics (MAX phases) and (ii) refractory high-entropy alloys. The predicted oxidation behavior of Ti2AlC MAX phase shows good agreement with our experiment performed on wedge samples. The proposed approach could guide the experimental discovery and optimization of structural materials with superior high-temperature performance under oxidizing conditions.
4:00 PM
Sustainability-based Selection of Materials for Refractory High Entropy Alloys: Xinyi Wang1; Annalise Kramer1; Haoyang He1; Julie Schoenung1; 1University of California, Irvine
Refractory high entropy alloys (RHEAs) are considered candidate materials for high temperature applications beyond nickel superalloys. In addition to good mechanical behavior, sustainability-related materials selection and design should be considered at an early stage of development, which will allow the application of RHEAs to expand. In this work, we present an alloy design framework for RHEAs from three different perspectives. We evaluate resource availability based on geographic concentration for refractory elements and generate a supply risk index for each element. We then evaluate material prices and price volatility for each element. We also estimated an aggregate price of select alloys and compared them to their yield strength at room and high temperatures. A proper balance of improved performance and economics is considered. Finally, we evaluated environmental, physical, and human health hazards for refractory elements and used the Green Screen® for Safer Chemicals methodology to assign benchmark scores to each element.
4:20 PM
The Influence of Impurities on the Interfacial Chemistry of Niobium – Alumina High-temperature Refractories: Michael Eusterholz1; Torben Boll1; Alexander Kauffmann1; Reshma Sonkusare1; Tilo Zienert2; Dirk Endler2; Vincent Ott1; Anja Weidner2; Julian Gebauer1; Christos Aneziris2; Michael Stüber1; Martin Heilmaier1; Bastian Kraft1; 1Karlsruhe Institute of Technology; 2TU Bergakademie Freiberg
Composites of coarse-grained refractory metals and refractory α-Al2O3-ceramic offer an outstanding combination of thermomechanical and functional properties, e.g., low shrinkage, excellent resistance to thermal shock, and electrical conductivity. Conventionally sintered composites from technical grade raw materials of α-Al2O3 and Nb include impurity elements and carbides alongside oxides, which further develop after exposure at a typical application temperature of 1500°C to 1800°C. To understand the principles of formation of such phases we investigated α-Al2O3 substrates, which were sputter-coated with Nb as a model system beside the technical grade material. This allows to independently study the influence of various impurity elements at the interface. The chemistry was investigated on different length scales. Backscatter electron imaging and electron backscatter diffraction were used to elucidate the microstructure, while transmission electron microscopy and atom probe tomography advanced the understanding of nano-scale segregation and phase formation at the phase boundary.