Microstructure and temperature dependence of the microhardness of W–4V–1La 2 O 3 and W–4Ti–1La 2 O 3 B. Savoini ⇑ , J. Martínez, A. Muñoz, M.A. Monge, R. Pareja Departamento de Física, Universidad Carlos III de Madrid, 28911 Leganés, Spain article info Article history: Available online xxxx abstract W–4V–1La 2 O 3 and W–4Ti–1La 2 O 3 (wt.%) alloys have been produced by mechanical alloying and subse- quent hot isostatic pressing. Electron microscopy observations revealed that these alloys exhibit a submi- cron grain structure with a dispersion of La oxide nanoparticles. Large V or Ti pools with martensitic characteristics are found segregated in the interstices between the W particles of the respective alloys. Microhardness tests were carried out over the temperature range 300–1073 K in vacuum. The microhard- ness–temperature curve for W–4V–1La 2 O 3 exhibited the expected decreasing trend with increasing tem- perature although the microhardness stayed constant between 473 and 773 K. The W–4Ti–1La 2 O 3 presented quite different temperature dependence with an anomalous microhardness increase for tem- peratures above 473 K. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction The current He-cooled divertor concepts for the future demon- stration fusion reactor (DEMO) are based on the use of pure W and W alloys because some of these materials could exhibit a more favourable combination of properties required for armour or struc- tural material in plasma facing components (PFCSs) [1,2]. Favour- able properties include high melting temperature, good thermal conductivity and creep strength, thermal shock resistance, minimal tritium retention, low sputtering and erosion rates, and resistance to damage from fusion neutrons. Nevertheless, W and W alloys are inherently brittle at low temperatures. According to the existing literature data, the reliable operating temperature window (OTW) for W materials in a PFC is between 1073 and 1500 K [2]. The low- er and upper bounds of this OTW are respectively defined by the ductile–brittle transition temperature (DBTT) and recrystallization temperature (RCT) of the material. The safety and efficiency of a fu- sion reactor will depend on the OTW-range. In particular, it would be compulsory to use W materials having a DBTT as low as possible and a suitable toughness and ductility at low temperatures, for pre- venting accidental brittle fracture when the PFCs are at tempera- tures below the lower bound of the OTW. Oxide reinforcement, or Al–K–Si doping, can enhance the mechanical strength of W and in- crease its recrystallization temperature, although without lowering the DBTT [3,4]. Recently, W–Ti and W–V alloys, reinforced or oxide dispersion strengthened (ODS) with Y 2 O 3 or La 2 O 3 , have been produced by mechanical alloying and subsequent consolidation by hot isostatic pressing (HIP) [5–7]. It has been reported that the addition of Ti by itself, or combined with Y 2 O 3 , can moderately en- hance the strength and fracture toughness of W in the temperature range below 873 or 1073 K, and noticeably enhance microhard- ness [8,9]. However, these results did not show an apparent de- crease of the DBTT. In the case of W–Ti alloys, the formation of some metastable Ti phase (a 0 , a 00 or x) could impair the mechanical behavior of W–Ti alloys. However, because W–V alloys have an iso- morphous phase diagram with a continuous range of solid solution, similar impairment is not expected to occur. Further, the potential of W–V composites as a wide OTW material for high-temperature applications has been investigated by numerical simulation. Simu- lation results, and preliminary toughness and creep measurements performed on a trial W–V composite, suggest a plausible capability of V to improve the mechanical characteristics of W at low temper- atures [10]. Also, it is noteworthy that Y 2 O 3 addition to W–V alloys appears to inhibit the growth of grains having sizes larger of 1 lm [11]. This paper reports the results of the microstructural studies and microhardness tests at elevated temperature performed on W–4V– 1La 2 O 3 and W–4Ti–1La 2 O 3 (wt.%) alloys in an attempt to explore the potential of this type of ODS W alloys for fusion applications. Hereafter the alloys will be referred to as W–4VLa and W–4TiLa. 2. Experimental procedure The alloys were prepared from W, V, Ti, and La 2 O 3 powders with purity and particle sizes of 99.9% and <5, 99.5% and 41, 99.9% and 110 lm and 99.5% and <50 nm, respectively. The powders were 0022-3115/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jnucmat.2013.03.039 ⇑ Corresponding author. Address: Departamento de Física, Universidad Carlos III de Madrid, Avda. Universidad Carlos III de Madrid 30, 28911 Leganés, Spain. Tel.: +34 916249413; fax: +34 916248749. E-mail address: begona.savoini@uc3m.es (B. Savoini). Journal of Nuclear Materials xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Journal of Nuclear Materials journal homepage: www.elsevier.com/locate/jnucmat Please cite this article in press as: B. Savoini et al., J. Nucl. Mater. (2013), http://dx.doi.org/10.1016/j.jnucmat.2013.03.039