Manufacturing of tungsten and tungsten composites for fusion application via different routes

Tungsten Tungsten (2019) 1:80–90 https://doi.org/10.1007/s42864-019-00011-y www.springer.com/42864 REVIEW PAPER Manufacturing of tungsten and tungsten composites for fusion application via different routes Yucheng Wu1,2,3 Received: 24 January 2019 / Revised: 22 March 2019 / Accepted: 22 March 2019 / Published online: 26 April 2019 © The Nonferrous Metals Society of China 2019 Abstract Tungsten is a refractory metal with the highest melting point of all metals, which is considered as a promising candidate material for plasma-facing materials in the future fusion reactor. However, tungsten faces several challenges from intrinsic embrittlement, irradiation embrittlement and recrystallization embrittlement during the operation of the fusion reactor. To satisfy the fusion engineering application, an advanced tungsten material with the fine grain and dense microstructure is required and developed. This paper briefly introduces the application background of the tungsten materials and mainly illustrates a series of common techniques for manufacturing advance tungsten materials, such as powder preparation technologies, bulk densification techniques, continuous processing technologies and the coating and additive manufacturing technologies. Furthermore, the development prospects for manufacturing techniques of tungsten materials are also presented in the end. Considering the tungsten materials employed in the fusion engineering application, combining these scalable techniques of the wet-chemical method, pressureless sintering and continuous deformation processing techniques would be the possible research and development routes to realize the manufacture of the advanced tungsten materials. Keywords Tungsten · Future fusion reactor · Mechanical alloying · Wet-chemical method · Deformation processing 1 Introduction In the fusion reactor, the research and development of plasma-facing materials (PFMs) have become one critical issue for realizing controlled nuclear fusion energy, because the PFMs have to face an extremely harsh operating environment. For the case of deuterium (D)-tritium (T) nuclear fusion reaction, PFMs undergo a high-energy particle irradiation from the helium ion (3.5 MeV) and neutron (14.1 MeV), and particle irradiation-induced thermal effects in PFMs [1]. Furthermore, PFMs are inevitably subjected to the thermal shock from edge-localized modes (ELMs), * Yucheng Wu 1 School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China 2 National‑Local Joint Engineering Research Centre of Nonferrous Metals and Processing Technology, Hefei University of Technology, Hefei 230009, China 3 Key Laboratory of Interface Science and Engineering of New Materials, Ministry of Education, Taiyuan University of Technology, Taiyuan 030024, China 13 Vol:.(1234567890) plasma disruption, vertical displacement events, etc. [2–6]. This means that PFMs are required to possess at least a good resistance to particle sputtering, good thermal conductivity and high melting point. Tungsten (W) with decision advantages of the highest melting point (approximately 3410 °C) in all metals, high density, excellent thermal conductivity (approximately 173 W m−1 K−1 at room temperature), high sputtering threshold and low tritium retention is considered as one main promising candidate material for PFMs in the future fusion reactor [the demonstration reactor or China fusion engineering testing reactor (CFTER)] [7, 8]. Under such a harsh operational environment in the fusion reactor, intrinsic brittleness of W materials [9, 10] may be easier to exhibit a series of brittle behaviors due to fusion particle bombardment [11–13], recrystallization at high temperature [14, 15] or thermal shock loading [16]. To eliminate or alleviate the brittle behaviors and satisfy the fusion engineering application, an advanced W material is required and developed. Many researchers claimed that grain boundaries can act as traps to annihilate point defects (interstitial atoms or vacancies) from irradiation [12, 17–20]. Klimenkov et al. [12] and Fukuda et al. [17] performed a neutron irradiation test on W materials and found that the neutron Manufacturing of tungsten and tungsten composites for fusion application via different routes irradiation-induced defects were likely to gather or be annihilated at grain boundaries. EI-Atwani et al. [18–20] reported the effects of grain sizes on the irradiation resistance of pure W materials that the grain refinement could enhance its irradiation resistance. Tan et al. [21] performed an ELM-like thermal shock test on the second-phase-doped W materials with a report that the addition of the second phase would improve the resistance by strengthening grain boundaries. Recently, Wu [10] concluded several toughening routes from intrinsic or extrinsic toughening mechanism perspectives, which might help to point out a possible route to obtain the advanced W materials. The main toughening routes were composed by the intrinsic toughening approaches of the addition of alloying elements and deformation processing, and the extrinsic toughening approaches including the addition of second-phase particles or tungsten fibers, etc. Grain refinement is not only an intrinsic toughening approach but also an extrinsic toughening approach, because it is beneficial to the formation of grains with preferred deforming orientation and improved crack propagation paths. In addition, several studies claimed that impurity (C, N, O, P, S, etc.) introduction would result in the W materials developing brittle fracture along the grain boundary [22–26]. Therefore, the fine grain and high purity are the necessary factors for an advanced W material from the PFM manufacture perspective. Naturally, the high density is also an essential factor for PFMs, especially functioning as the shielding material and heat-transfer material. Traditionally, the manufacture of W materials always follows the powder metallurgy route because of the highest melting point of W. This paper illustrates the manufacturing processes of W materials including powder preparation techniques, bulk densification techniques and continuous processing technologies. In addition, some other special manufacturing techniques are also briefly introduced in the end. 2 Powder preparation techniques The powder preparation stage is a basic and key step to obtain an advanced W material. The fine grain, composition homogeneity and the second-phase distribution uniformity of the W matrix materials rely strongly on the stage of the powder preparation. To achieve a fine grain microstructure, it is better to get ultra-fine even nano-sized powders. At present, the common preparation methods of W powders include the mechanical milling (a top-down approach, also named as mechanical alloying) and wet-chemical method (a bottom-up approach, also called the liquid-phase method). During the mechanical milling process, plastic deform (...truncated)