CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 38 (2012) 6469–6480 Effect of ball milling on reactive spark plasma sintering of B 4 C–TiB 2 composites L. Nikzad a,b , R. Licheri a , T. Ebadzadeh b , R. Orr  u a,n , G. Cao a a Dipartimento di Ingegneria Meccanica, Chimica e dei Materiali, Unit  a di Ricerca del Consorzio Interuniversitario Nazionale per la Scienza e Tecnologia dei Materiali (INSTM), Unit  a di Ricerca del Consiglio Nazionale delle Ricerche (CNR), Dipartimento di Energia e Trasporti—University of Cagliari, Piazza D’Armi, 09123 Cagliari, Italy b Division of Nanotechnology and Advanced Materials, Materials and Energy Research Center, P.O. Box 14155-4777, Tehran, Iran Received 6 February 2012; received in revised form 9 May 2012; accepted 9 May 2012 Available online 17 May 2012 Abstract The influence of mechanical activation by ball milling (BM) of Ti, B and graphite powders mixture on the synthesis of dense B 4 C-41% vol. TiB 2 composite by Spark Plasma Sintering (SPS) is investigated. BM treatment produces grains size refinement (50–150 nm) in the processing powders and the formation of TiB and TiB 2 , when milling times are longer than 6 h. The synthesis process occurs through a solid-state diffusion mechanism where the first crystalline phase formed is TiB, which is gradually converted to TiB 2 , while the formation of B 4 C takes place subsequently. The complete conversion of unmilled reactants is reached at about 1500 1C, while this goal is achieved at 1100 1C when using 3 h milled powders. A near to fully dense product with fine grained microstructure (down to submicrometer level) and homogeneous phases distribution is obtained by SPS when starting from 8 h milled powders, if the applied current intensity does not overcome 1150 A. & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Milling; D. Borides; D. Carbides; Spark Plasma Sintering 1. Introduction Due to the combination of its remarkable hardness, high melting temperature, low density, wear resistance, chemical stability, neutron absorption capability, etc., boron carbide is a very attractive material in several innovative and traditional industrial fields, particularly for neutron absorption, armor, thermoelectric and cutting tools appli- cations [1]. In spite of these interesting properties, the diffusion of this ceramic is hindered due to its intrinsic brittleness and the difficulties encountered when sintering the corresponding powders for the fabrication of massive bodies. Therefore, a considerable effort has been devoted in the last two decades to the improvement of B 4 C sintering behavior and mechanical properties. In this context, the introduction of appropriate amounts of a suitable reinforcing phase, particularly TiB 2 , to the B 4 C matrix is well known to produce a useful contribution to overcome both drawbacks mentioned above [1]. Thus, several bulk ceramic composites in the B 4 C–TiB 2 system have been investigated by various researchers using different fabricating routes [2–21]. So far, the majority of the investigations took advantage of the conventional pressureless (PLS) [2,5,8,9,12,14,15] or hot-pressing (HP) [3,4,6,10,11,18] techniques, although alternative approaches, such as high-pressure sintering [7], hot-isostatic pressing (HIP) [5], crucibleless zone melting method [16], plasma pressure compaction (P 2 C) [13], and pulsed electric current sintering (PECS) [17,19– 21] have been also adopted. Regardless the sintering method utilized, the obtainment of bulk B 4 C–TiB 2 composites has been addressed either starting directly from the previously synthesized ceramic constituents in powder form [2,4–7,12–16,21] or after accomplishing the reaction synthesis and densification in a single step using appropriate reaction promoters [3,8,9,11,17–20]. www.elsevier.com/locate/ceramint 0272-8842/$36.00 & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2012.05.024 n Corresponding author. Tel.: þ 39 70 6755076; fax: þ39 70 6755057. E-mail address: orru@dicm.unica.it (R. Orr  u).