Emerging High Temperature Materials for Potential Application to Fusion.

Transcription

1 Emerging High Temperature Materials for Potential Application to Fusion Y. Katoh 1,*, C.M. Parish 1, L. Tan 1, P. Edmondson 1, T. Koyanagi 1, L.M. Garrison 1, C. Ang 1, L.L. Snead 2, C.H. Henager 3, Jr., S.J. Zinkle 1,4 1 Oak Ridge National Laboratory 2 Stony Brook University, 3 Pacific Northwest National Laboratory, 4 University of Tennessee *katohy@ornl.gov 1. Technology to be assessed This white paper examines novel high temperature materials that have the potential to enable break-through concepts for plasma-facing, blanket, and/or structural components in fusion reactors. Such materials include 1) emerging materials of high interest in the general materials science and engineering (MSE) community [such as MAX phases, ultra-high temperature ceramics (UHTC), and high entropy alloys (HEA)], 2) novel structural materials that may be specifically developed for fusion based on recent materials science advancements [such as castable nanostructured alloys (CNA) and MAX-phase ceramic matrix composites (CMC)], and 3) tungsten (W)-based refractory multi-functional composites that potentially enable extensive use of W in fusion reactors. The US fusion energy sciences program is uniquely positioned to explore and potentially adopt new materials due to its strong connections to the broader US materials science community and the current timeline flexibility for DEMO development. These emerging materials exhibit several clear and outstanding advantages over the current reference PFC and blanket materials, presenting potential game-changing opportunities for improved fusion energy systems. 2. Application of the technology All classes of high performance, high temperature materials discussed here may be considered for applications in fusion divertor components, first walls, and blanket structures. For these applications, the developed new materials will exhibit improved performance attributes including high temperature resistance, toughness, thermal conductivity, and neutron irradiation tolerance. 3. Emerging novel high temperature materials of interest Category I Emerging materials of the MSE community There are ample examples of new unconventional materials that are of high interest and are actively studied by the MSE community for a broad spectrum of potential applications. UHTC, MAX phases, and HEA are among the widely-studied emerging high temperature materials that may be attractive for fusion thermo-structural components. UHTC includes various borides and carbides, among which transition metal diborides are recently extensively studied. ZrB2, for example, exhibits high strength ( ) up to temperatures exceeding 2,000 C with a thermal conductivity kth >80 W/m-K [1,2]. Comparison of these properties with W in Fig. 1 depicts clear advantages of UHTC in terms of the operating temperature window with the comparable thermal stress figure of merit (~ /kth) as compared to W. The operating temperature window for W is bound by the upper temperature recrystallization limit at ~1,100 C under irradiation and a lower temperature limit of ~800 C due to radiation 1

2 embrittlement. Development challenges include improvement in ductivity and fracture toughness and exploration of radiation effects. Fig. 1 Comparison of strength and thermal conductivity of selected emerging high temperature materials with tungsten in unirradiated condition. Refractory HEA s are another class of emerging materials of potential interest for PFC. There are numerous possible combinations of elements to constitute HEAs and only very limited systems have so far been explored. Among them, for example, the Nb-Mo-Ta-W system and its variants possess good strength up to >1,600 C [3]. The high configurational entropy and reduced atomic self-diffusion are considered to potentially offer exceptional radiation tolerance in HEAs; promising radiation resistance results have been recently obtained on the Fe-Ni-Mn-Cr and Ni- Co-Fe-Cr systems [4,5]. Moreover, HEAs allow access to the face-centered cubic crystal structure that generally offers enhanced ductility compared to the body-centered cubic structure of W and ferritic steels. Low thermal conductivity is considered a primary drawback for HEAs for thermo-structural applications, but it is known to approach the values for traditional low entropy structural alloys as temperature increases. MAX phase materials are another option in this category, exhibiting a combination of metallic and ceramic properties. MAX phases are materials of high potential for nuclear applications at operating temperature exceeding ~500 C, and may exhibit improved radiation resistance compared to traditional ceramics at elevated temperatures due to a high-density nanolayered structure [6]. Similar to HEAs, the atomistically layered ternary MAX phases consist of numerous possible combinations of elements [7]. To date, only a few MAX phase systems have been studied for radiation effects to reveal that each ternary system has characteristic temperature range in which the layered structure achieves dynamic recovery from radiationinduced atomic disorder. Recent unpublished work conducted in an ORNL-PNNL collaboration demonstrated lack of degradation after 20 dpa neutron irradiation at 500 C for Ti3SiC2. Properties of Ti3SiC2 are compared with other materials in Fig. 1 [8,9]. Category II Modified materials where the fusion community can lead development 2

3 Historically the US fusion materials community played leading roles in development of certain materials including reduced activation ferritic/martensitic (FM) steels based on the 9Cr-1Mo heat resistant FM steel and nuclear grade SiC/SiC composites adapted from the refractory composite development for ceramic gas turbines. In these developments, work on new materials in nonnuclear areas presented opportunities for the fusion materials community to modify and improve these materials to satisfy fusion-specific requirements such as reduced long-lived activation and enhanced tolerance against neutron irradiation. This approach is still valid today. The fusion program-developed castable nanostructured alloys (fusion CNAs) are a reducedactivation class of ferritic/martensitic steels designed with nanostructural features generated by thermo-mechanical treatments. These CNAs are manufactured using the traditional industrial steelmaking methods used for RAFM steels, instead of the powder metallurgy route required for other advanced oxide dispersion strengthened (ODS) steels. Successful development of the fusion CNAs would enable access to new, low cost, high performance industrial scale RAFM steels with significantly improved high temperature capability and radiation tolerance over the conventional RAFM steels [10]. Moreover, the US fusion program currently leads the world in this development. Several additional development opportunities are found in this category, including: reducedactivation HEAs, enhanced radiation-tolerance UHTCs, and enhanced radiation-tolerance MAXphase-matrix ceramic composites. Category III W-based refractory composites W is the leading option for plasma-facing material despite a number of outstanding challenges. The lack of a viable method to ductilize the bulk form tungsten likely mandates its use in composite forms. The fusion materials community will have to carry out the W composite development due to the general lack of leveraging opportunities with non-fusion applications. Fortunately, the MSE community has accumulated significant knowledge and experiences with a wide variety of processing techniques for refractory ceramic composites and ceramic-metal composites (cermets), and many of these may be modified and applied to explore W-based composite development. For example, continuous fiber, W-matrix composites can be produced by multiple routes including chemical vapor infiltration and powder sintering. Small diameter W fibers and SiC fibers are two prime candidate reinforcements. Distributed or semi-interconnected W particulate composites with a ductile metal matrix (often referred to as ductile phasetoughened composites) may be produced through recently developed methods like rapid sintering. Related discussions on unconventional processing techniques that may enable improved functional performance are found in other white papers discussing the topic of advanced manufacturing.[11 13] 4. Risks and uncertainties Engaging in development of new materials introduces well-known general risks including those related with uncertain ultimate properties (unirradiated and irradiated) and development timeline associated with material development and industrialization. Fusion-specific performance risk factors include neutron irradiation tolerance, plasma-interactive performances, and tritium transport. Fortunately, the US fusion materials community has accumulated experience of studying these aspects of W and other material systems. Therefore a somewhat streamlined 3

4 evaluation scheme may be formulated without difficulty, excluding materials with large amount of radiologically prohibitive elements like Ta and Co. 5. Maturity In general, the materials discussed in this document have been extensively studied for less than 10 to 20 years and therefore have relatively immature engineering property databases and limited industrial fabrication experience. However, some of these novel materials, such as UHTCs and MAX phases, are already finding niche applications and steady industrialization is expected. Transition from a science-driven curiosity matter to an engineering material requires both the industrial/technology pull (business case) and a strong materials science foundation. 6. Technology development for fusion applications Since the topic of the present discussion is emerging materials, the TRL levels for the examples mentioned are generally low at 1 to 3 regarding application in fusion reactors. The technology development required for fusion applications includes interactive material design/development/ modification/evaluation to meet fusion-specific needs. The experimental evaluations in a fission reactor to examine basic irradiation performance and using both toroidal and linear devices for plasma-interactive performances are the key stepping stones for assessing their suitability. Our recent experience with evaluation of W and novel RAFM steels sets a useful precedent toward establishing efficient procedures. For W, it is taking roughly a decade to collect a set of useful data and achieve understanding of basic nuclear performance. Time and cost required for the myriad nuclear performances evaluations depend largely on the activation properties of the material (W is relatively challenging due to high short-term radioactivity that typically requires cooling time of a few years following neutron irradiation). Acknowledgment This document was developed based partly on the ongoing collaborative research with Michel Barsoum (Drexel Univeristy), Greg Hilmas and William Fahrenholtz (Missouri University of Science and Technology). 4

5 References [1] E.W. Neuman, G.E. Hilmas, W.G. Fahrenholtz, M. Cinibulk, Ultra-high temperature mechanical properties of a zirconium diboride-zirconium carbide ceramic, J. Am. Ceram. Soc. 99 (2016) doi: /jace [2] J.M. Lonergan, W.G. Fahrenholtz, G.E. Hilmas, Zirconium diboride with high thermal conductivity, J. Am. Ceram. Soc. 97 (2014) doi: /jace [3] J.W. Yeh, Alloy design strategies and future trends in high-entropy alloys, JOM. 65 (2013) doi: /s [4] N.A.P.K. Kumar, C. Li, K.J. Leonard, H. Bei, S.J. Zinkle, Microstructural stability and mechanical behavior of FeNiMnCr high entropy alloy under ion irradiation, Acta Mater. 113 (2016) doi: /j.actamat [5] Y. Zhang, G.M. Stocks, K. Jin, C. Lu, H. Bei, B.C. Sales, L. Wang, L.K. Béland, R.E. Stoller, G.D. Samolyuk, M. Caro, A. Caro, W.J. Weber, Influence of chemical disorder on energy dissipation and defect evolution in concentrated solid solution alloys, Nat. Commun. 6 (2015) doi: /ncomms9736. [6] C. Ang, C. Silva, C. Shih, T. Koyanagi, Y. Katoh, S.J. Zinkle, Anisotropic swelling and microcracking of neutron irradiated, Scr. Mater. 114 (2016) doi: /j.scriptamat [7] M.W. Barsoum, T. El-Raghy, The MAX Phases: Unique New Carbide and Nitride Materials, Am. Sci. 89 (2001) doi: / [8] M.W. Barsoum, T. El-raghy, C.J. Rawn, W.D. Porter, H. Wang, E. a Payzant, C.R. Hubbard, Thermal properties of Ti 3 SiC 2, 60 (1999) doi: /j x. [9] M. Radovic, M.W. Barsoum, J. Seidensticker, S. Wiederhorn, TENSILE PROPERTIES OF Ti 3 SiC 2 IN THE 25 ± 13008C TEMPERATURE RANGE, Scan. Electron Microsc. 48 (2000) [10] L. Tan, L.L. Snead, Y. Katoh, Development of new generation reduced activation ferriticmartensitic steels for advanced fusion reactors, J. Nucl. Mater. 478 (2016) doi: /j.jnucmat [11] Y. Katoh, R.R. Dehoff, A.S. Sabau, L.M. Garrison, S.J. Zinkle, L.L. Snead, C.H. Henager, Jr, Advanced Manufacturing for Fusion PFC and Blanket Materials, in: FESAC Work. Transform. Enabling Capab., Chicago, IL, [12] R.E. Nygren, P.R. Schunk, D.A. Buchenauer, Development of Fusion Sub-components with Additive Manufacturing, in: FESAC Work. Transform. Enabling Capab., Chicago, IL, [13] C.H. Henager, Jr, R.J. Kurtz, G.R. Odette, Plasma-Facing Materials by Design and Rapid Prototyping via Additive Manufacturing, in: FESAC Work. Transform. Enabling Capab., Chicago, IL,