Refractory Metals 2020: Refractory Metals Production and Processing
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.
Tuesday 8:30 AM
February 25, 2020
Room: Cardiff
Location: Marriott Marquis Hotel
Session Chair: Gary Rozak, H.C. Starck; Todd Leonhardt, Rhenium Alloys
8:30 AM
Pressureless Sintering and Microstructure Evolution of Ultrafine-grained Tungsten: Yanhao Dong1; Xingyu Li2; Lin Zhang2; Ju Li1; 1Massachusetts Institute of Technology; 2University of Science and Technology, Beijing
Pressureless sintering of refractory metals is a cost-effective way to produce large parts with complex geometry, yet it is not easy especially when ultrafine grain sizes are preferred. Here we report interesting low-temperature pressureless sintering data of pure tungsten (99.9%) in flowing hydrogen, ending with 99% theoretical density, 700 nm grain size and uniform microstructure. No texture, abnormal grain growth, second-phase impurities or grain-boundary liquids were observed. We found parabolic grain growth in dense samples and calculated grain boundary mobility deviates from Arrhenius-type relationship showing apparent transition at 1400 oC. As a result, sintering below 1400 oC is more favored with respect to grain growth, which provides phenomenological explanation for our low-temperature sintering data. Lastly, Vickers hardness and its Weibull modulus of low-temperature sintered samples are greatly improved, due to finer and more uniform microstructure. Parallel studies are in progress for other refractory metals and shall be discussed as well.
8:50 AM Cancelled
Direct Production of Ta Powders: Jawad Haidar1; 1Kinaltek Pty Ltd.
Powders of Ta and Ta alloys have been produced using direct aluminothermic reduction of tantalum precursors. The approach is based on controlled exothermic reduction of tantalum chlorides with aluminium using tantalum-based powder as a control agent to regulate reaction rates and prevent excessive rise in the temperature of the reactants and the reaction products. Particle size depends on composition and processing parameters and can range from less than 1 microns to coarse dimensions of more than 100 microns. Results are presented for direct production of pure Ta powder and a number of Ta alloys.
9:10 AM
Modifying Grain Boundary Cohesion in Ultra-fine Grained Tungsten and Tungsten-based Nanocomposites through Systematic Doping: Michael Wurmshuber1; Simon Doppermann1; Stefan Wurster2; Reinhard Pippan2; Daniel Kiener1; 1Department of Materials Science, Montanuniversität Leoben; 2Erich Schmid Institute, Austrian Academy of Sciences
The inherent brittleness and low ductility of tungsten often impedes its applicability in high-performance installations. A promising approach to improve mechanical strength is refining the microstructure to the ultra-fine grained regime. However, the large amount of interfaces within such materials promotes intergranular crack paths with comparably low crack growth resistance, hindering a severe improvement in toughness and ductility. Therefore, strengthening grain boundary cohesion by doping with certain elements is expected to enhance the performance. In this work, a powdermetallurgical fabrication route in conjunction with severe plastic deformation was applied to produce ultra-fine grained W, commercially pure as well as doped with potentially interface-strengthening elements. Additionally, nanocrystalline W-Cu composites with tailored interface chemistry were fabricated, adding a ductile phase for increased plasticity. Mechanical properties of all materials were thoroughly characterized applying small-scale testing techniques and the effectiveness of grain boundary chemistry tuning on the ductility of tungsten based materials is discussed.
9:30 AM
Mechanical Testing of Tungsten-Steel Laminate Composites for use in Fusion Applications: Sara Wonner1; Lauren Garrison2; 1University of Tennessee, Knoxville; 2Oak Ridge National Laboratory
The implementation of fusion energy faces fundamental materials issues, especially with respect to the interface between plasma facing materials (PFM) and structural materials. Tungsten is a commonly chosen PFM, whereas steel is desirable for the structural component of fusion reactors. The interface between tungsten and steel can host severe internal stresses, due to their inherent differences in thermal and mechanical properties. Thus, this work investigates the mechanical properties of laminate composites comprised of thin foil layers of tungsten and Grade 92 steel. These laminate composites were fabricated via forging and hot rolling at 1000˚C with 20% total reduction. Two different versions of these composites were investigated, with varying foil thicknesses. One was comprised of alternating layers of 100 μm tungsten and 100 μm steel, and the other with layers of 25 μm tungsten and 100 μm steel. For evaluation, tensile testing and elemental analysis were performed on both laminate composites.
9:50 AM
Refractory Alloys 3D Printing for Missile and Space Applications: Youping Gao1; John Porter1; Noah Philips2; Omar Mireles3; 1Castheon Inc.; 2ATI Specialty Alloys and Components ; 3NASA Marshall Space Flight Center
Refractory alloys have extraordinary resistance to heat, wear, and, with superior durability, are often the desired material for extreme environment applications on space craft, missiles, and hypersonic vehicles. Due to the difficulty and high cost of manufacturing complex shapes using refractory metals, utilization has been hampered in the most demanding applications. 3D printing has exhibited a superior shape producing capability. In this presentation, successful 3D printing of high quality Niobium C103 alloy components has been demonstrated. The properties of 3D printed Nb C103 were compared to equivalent wrought parts, including the effect of heat treatments. 3D “as-printed” microstructures were extremely stable and largely intact even after 2-hrs at 2900°F. Superior properties of 3D printed Nb C103 were observed from room temperature to elevated temperature. A hypothesis for such stable microstructures is proposed. A case study of performance gain in sophisticated Nb C103 engineered hardware will also be presented.
10:10 AM Break
10:30 AM
Hot Isostatic Pressing of WC-3009 Niobium-Based Refractory Alloy: Calvin Mikler1; Benjamin Georgin1; Brian Welk1; Gopal Viswanathan1; Kevin Chaput2; Hamish Fraser1; 1The Ohio State University; 2Air Force Research Laboratory
Niobium-based WC-3009 (Nb-30Hf-9W wt%) is a single-phase bcc refractory alloy designed as a candidate replacement for the still commonly utilized C-103 (Nb-10Hf-1Ti wt%) alloy. While WC-3009 exhibits superior high-temperature mechanical properties compared with C-103, fabrication is economically prohibitive, and the alloy was not employed in any capacity. In this study, aliquots of pre-alloyed hydride-dehydride WC-3009 powder were canned and subsequently consolidated via hot isostatic pressing (HIP). This effort was performed to identify key alloy attributes that drive processability through HIP such that higher strength Nb-based refractory alloys can be utilized. Backscattered electron (BSE) imaging and electron backscattered diffraction (EBSD) analysis revealed the degree of recrystallization and recovery substructure formation. Transmission electron microscopy (TEM) coupled with x-ray energy dispersive spectroscopy (XEDS) were employed to analyze second phase precipitation behavior and dislocation substructures. The results indicated that hot isostatic pressing is a viable method of processing high performance Nb-based refractory alloys.
10:50 AM
Performance of Niobium and Molybdenum Alloys for High Temperature Sensing Applications: Scott Riley1; Beck Perrine1; Ember Sikorski1; Lan Li1; Richard Skifton2; Brian Jaques1; 1Boise State University; 2Idaho National Laboratory
Niobium, molybdenum, and their alloys are often considered for applications in extreme environments where corrosion resistance and high temperatures are required. The Idaho National Laboratory has developed thermocouples comprised of phosphorous-doped niobium and lanthana-doped molybdenum thermoelements, an alumina insulation, and a niobium sheath. Prior to operation, the thermocouples undergo a preliminary heat treatment (above the maximum service temperature) in order to stabilize the emf signal. Herein, a study was conducted to evaluate the effects of the stabilization heat treatment (time, temperature, and process gas) on the mechanical properties, microstructure, and chemical stability of the system. A design of experiments was performed to determine the impact of the process variables on thermocouple performance. The grain size of the sheath increased with increasing temperature and time while the ductility decreased with increasing oxygen concentration in the process gas. The chemical stability of each component was studied and will be discussed in detail.
11:10 AM
Dislocation Multiplication from a Frank-Read Source in Six Body-centered Cubic Refractory Metals: Shuozhi Xu1; Yanqing Su1; Irene Beyerlein1; 1University of California, Santa Barbara
Understanding plastic deformation in metallic materials necessitates modeling of dislocation multiplication. A well-known intragranular dislocation source, the Frank-Read (FR) source, plays an important role in size-dependent plasticity in metals. Despite numerous studies in this topic, a systematic investigation of multiple aspects of the FR source in refractory metals is lacking. In this work, we simulate dislocation multiplication from an FR source in six refractory metals with body-centered cubic structure –– Cr, Mo, Nb, Ta, V, and W –– via a phase-field dislocation dynamics (PFDD) method. Two main characteristics of the FR source, including the critical shear stress and critical dislocation configuration, are investigated. For the same metal and same initial dislocation segment, selected PFDD results are benchmarked against atomistic simulations. Our results shed light on developing more accurate continuum models for FR source activation.