Refractory Metals 2020: Refractory Metal Alloys, Silicides, and Composites
Sponsored by: TMS Structural Materials Division, TMS: Refractory Metals Committee
Program Organizers: Eric Taleff, University of Texas at Austin; Gary Rozak, H.C. Starck Solutions; Todd Leonhardt, Rhenium Alloys Inc.

Monday 2:30 PM
February 24, 2020
Room: Cardiff
Location: Marriott Marquis Hotel

Session Chair: Eric Taleff, University of Texas; Todd Leonhardt, Rhenium Alloys


2:30 PM  Invited
Intermetallic Precipitate Reinforced Refractory Metal Alloys toward ‘bcc-superalloys’: Alexander Knowles1; Chris Hardie2; David Dye3; 1University of Birmingham; 2Culham Centre for Fusion Energy; 3Imperial College London
     New materials with improved high temperature performance are sought for nuclear fusion/Generation-IV fission reactors and gas turbines. Refractory metals have exceptionally high melting points >2000°C, far higher than nickel-based fcc-superalloys, <1400°C. However, they do not exploit ordered-intermetallic precipitates, which is a potent strategy in γ-γ’ fcc-superalloys for strength, creep resistance and ductility. There is great scope for the exploitation of this strategy in bcc metals, including within compositionally complex alloys (CCAs, or high entropy alloys, HEAs).Opportunities for precipitate reinforcement of refractory metal alloys will be discussed. New design strategies exploit the two-phase field bcc β (Ti) to β’ TiFe, whereby precipitates can be produced within a matrix of β (Mo,Ti) and also β (W,Ti). Such precipitation offers superalloy-like β-β’ microstructures where understanding in being developed for (1) Microstructure control, (2) Properties achieved and deformation mechanisms. Such work is critical to realise bcc-superalloys as a new materials class.

2:50 PM  
Alloying for Precipitation Hardening in Chromium: Mathias Galetz1; Anke Ulrich1; Petra Pfitzenmaier2; Uwe Glatzel2; 1DECHEMA-Forschungsinstitut; 2University Bayreuth
     Refractory alloys based on chromium have been disregarded for a long time mainly due to its strong nitridation behavior above 1000°C and its accompanying embrittlement, when it transforms into a ceramic. Another challenge of such alloy system are their ductile to brittle transition temperature (DBTT) above room temperature. On the other hand, chromium offers a lower density compared to Ni, a high oxidation resistance along with high availability and competitive pricing. Thus in this work a new class of heat treatable Cr-alloys is presented. Alloying with A15 forming elements (Ge, Si, Pt) or Mo that substitutes Cr in solid solution and A15 has a major impact on the microstructure, high temperature strength and oxidation resistance.

3:10 PM  
Development of Refractory Complex Concentrated Alloys RCCAs Using Diffusion Couple Approach: Vivek Verma1; Michael Titus2; David Johnson2; Kaustubh Kulkarni3; 1Department of Materials Science and Engineering, Indian Institute of Technology; 2School of Materials Engineering, Purdue University; 3Department of Materials Science and Engineering, Indian Institute of Technology, Kanpur
    Exceptional properties of Refractory High Entropy Alloys (RHEAs) and Refractory Complex Concentrated Alloys (RCCAs) make them promising candidate materials to replace conventional refractory alloys for high temperature applications. However, due to the enormous composition available for these alloys, novel approaches are required for development of specific alloy compositions. Being multicomponent alloys with potential high temperature applications, an in-depth understanding of diffusional interactions is important. As we move from binary to higher order systems, diffusion interactions among alloying elements become significant and in turn affect the interdiffusion behavior of the system. Recent work has shown that diffusional interactions correlate with the enthalpy of mixing, potentially enabling new alloy development strategies by predicting the enhancement or decrease of elemental activities and mobilities. In the present work, a series of AlMoNbTi alloys were fabricated for maximization of Al activities and characterized using the diffusion couple technique. Importance of diffusional interactions will be discussed.

3:30 PM  
ZrC-W Composites Prepared by Reactive Melt Infiltration of Zr2Cu Alloy into Binder-jet Printed WC Preforms: Rina Mudanyi1; Corson Cramer2; Amy Elliott2; Dhananjay Kumar1; 1North Carolina A &T State University; 2Oak Ridge National Laboratory
    Making stable materials for hypersonic and ultra-high temperature systems is challenging. High-temperature carbide/metal composites exhibit excellent properties such as desirable flexural strength at elevated temperatures, high hardness, resistance to wear, creep and corrosion, and low density. ZrC-W is studied for use in these environments because W and ZrC are mechanically, chemically, and thermally stable; i.e., they have similar thermal expansion coefficients, low solid solubility in each other at elevated temperatures, and high melting points, respectively. In this study, Zr2Cu was melt infiltrated into binder-jetted WC preforms to form ZrC-W. Zr2Cu was used for its low melting point; however, the copper precipitates out of the composite sample, leaving ZrC-W. The effects of preform sintering, amount of Zr2Cu added, and processing time on the cermet were studied. Microstructure, phase analysis, and mechanical properties of the cermets were analyzed. Applications for these materials include aerospace, automotive, energy, and defense.

3:50 PM  
Seeking Toughness in Mo-Si-B: Composites of Stable Oxides: Peter Marshall1; Sharvan Kumar2; Xiang Yu2; Alex Jackson1; 1Imaging Systems Technology; 2Brown University
    Molybdenum-silicon-boron materials with a metallic matrix are candidates for high temperature structural applications requiring oxidation resistance, strength, and toughness. Mo-Si-B itself has a high ductile to brittle transition temperature below which the brittle fracture behavior is problematic. The possibility of improved toughness at these lower temperatures is explored through the addition of thermodynamically stable oxides as a major dispersed phase. Mechanisms will be discussed including extrinsic toughening and changes in the solid solution chemistry. Utilizing powder processing for this composite allows for considerable flexibility in the overall composition and that of the individual phases. Of particular importance are the overall silicon and boron concentrations as well as their ratio in the intermetallic phases. Through this composition selection, the oxidation resistance and creep strength remain similar to other Mo-Si-B alloys. Additional results on the microstructural dependence of these properties will be presented.

4:10 PM Break

4:30 PM  
Microstructure, Microhardness and Oxidation Behavior of Mo-Si-B alloys in the Moss+Mo2B+Mo5SiB2 Three Phase Region: Longfei Liu1; John Perepezko1; 1University of Wisconsin, Madison
     A series of Mo-Si-B alloys in the Moss+T2 (Mo5SiB2)+Mo2B three phase region were designed to examine the effect of the lower Si solubility limit in the Moss phase on the microstructure, hardness and oxidation behavior. SEM images establish the microstructure evolution during the annealing. The analysis of the Vickers hardness tests demonstrate that the samples in the Moss+Mo2B+T2 three phase region have about a 50% higher fracture toughness than comparable samples in Moss+Mo3Si+T2 three phase region due to the lower Si solubility in the Moss phase . The thermogravimetric analysis results show that the oxidation resistance directly related to T2 phase fraction. Alloys with a Moss+Mo2B+T2 microstructure exhibit a similar oxidation behavior to those with a Moss+Mo3Si+T2 microstructure when the T2 phase fraction in the two alloys is similar. Mo-Si-B alloys in the Moss+Mo2B+T2 three phase region could achieve better mechanical properties and are attractive candidates for high temperature applications.

4:50 PM  Cancelled
Magnetic Field Effects on the Compression Properties of Pure Tantalum: Hitesh Adhikari1; Rajiv Mishra1; 1University of North Texas
    The effect of high magnetic field on the compression properties and micro-structure has been investigated. Tantalum alloy specimens were compressed continuously under different magnetic field (B = 0, 1 and 2T) using a servo-hydraulic material testing system (MTS) at initial strain rate of 1x10-3 s-1 . The results show that the magnetic field increases the flow stress during the compression of pure Tantalum. The observed increase of strength is related to the magneto-plasticity effect (MPE), which impacts the motion of dislocations under magnetic fields. The size and orientation of the grains seem to play a crucial role during the compression test under magnetic field. This observation is further explained using electron back scatter diffraction (EBSD) results.