Hardness and wear resistance of B 4 C ceramics prepared with several additives J.E. Zorzi a,b, * , C.A. Perottoni b,c , J.A.H. da Jornada b,d a Universidade de Caxias do Sul, CCET/DENQ, CEP 95070-560, Caxias do Sul-RS, Brazil b Universidade Federal do Rio Grande do Sul, Instituto de Fı ´sica, CEP 91501-970, Porto Alegre-RS, Brazil c Universidade de Caxias do Sul, CCET/DEFQ, CEP 95070-560, Caxias do Sul-RS, Brazil d Inmetro-Instituto Nacional de Metrologia, Normalizac ¸a ˜o e Qualidade Industrial, Campus de Xere ´m, Duque de Caxias, RJ, Brazil Received 25 November 2004; accepted 30 April 2005 Available online 25 May 2005 Abstract Boron carbide-based ceramics were obtained by pressureless sintering at 2250 -C in the presence of several additives (C, B, TiB 2 and SiC). All the samples were prepared under the same conditions, thus improving uniformity and comparability for method-dependent properties such as microhardness and abrasive wear resistance. While the addition of carbon improved relative density, samples with TiB 2 showed best overall performance, with an increase in microhardness and wear resistance (as compared to pure B 4 C). The improvement in mechanical properties with the addition of TiB 2 suggests it could be considered as a low-cost alternative to improve hardness and wear resistance of B 4 C-based ceramics. D 2005 Elsevier B.V. All rights reserved. Keywords: Wear resistance; Hardness; Boron carbide 1. Introduction Boron carbide ceramics and composites are important high-tech materials thanks mainly to their high hardness and low density [1]. Covalently bonded solids based on boron comprise some of the hardest materials presently known. In particular, B 4 C is the third hardest material, after diamond and c-BN [1–3]. Boron rich solids exhibit geometric and electronic structures which are rather unique [2]. Owing to its open structure and light atoms, B 4 C has a low density (2.52 g/ cm 3 ). It also exhibits a high melting point (2427 -C), and high neutron absorption cross section [4–7]. One of the major industrial uses of B 4 C is as an abrasive grit or powder. Particles with diameters in the range from 1 Am to 10 Am are used as polishing, lapping and grinding media for hard materials (cemented carbides, technical ceramics, etc). For these applications, boron carbide is far less expensive than diamond. Components made of boron carbide are also very often used in wear resistant applica- tions, (e. g., as blast nozzles, wheel dressing tools, and light weight armor plates) [1,8]. However, despite the technological interest in B 4 C based ceramics, the sintering of pure B 4 C components has proved quite difficult, mainly due to the strong covalent bonding, which is responsible for the intrinsically low diffusion mobility [9]. For ‘‘near net shape’’ mass production of parts without the need for expensive high pressure equipment and/or diamond machining, some strategies for pressureless sinter- ing have been developed, using sintering aids such as C, Al 2 O 3 and TiB 2 [6,7]. According to Lee and Speyer, the best known additive for pressureless sintering of B 4 C is carbon [7]. Schwetz and Vogt [10] first used phenolic resin as a carbon source. They observed that the addition of carbon makes it possible to attain 98% of the theoretical density 0167-577X/$ - see front matter D 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.04.047 * Corresponding author. Universidade de Caxias do Sul, CCET/DENQ, CEP 95070-560, Caxias do Sul-RS, Brazil. Tel.: +55 54 218 2100x2159; fax: +55 54 218 2100x2253. E-mail address: jezorzi@ucs.br (J.E. Zorzi). Materials Letters 59 (2005) 2932 – 2935 www.elsevier.com/locate/matlet