PERFORMANCE OF NANOSTRUCTURED DIAMOND COMPOSITES IN WEAR TESTS Ana Lucia D. Skury 1,a , Sergio N. Monteiro 1,b , Marcia G. Azevedo 1,c , Laís B. Motta ,d , Guerold S. Bobrovnitchii 1,e 1 State University of Northern Fluminense Av. Alberto Lamego 2000 – Campos dos Goytacazes – RJ – Brazil – CEP 2801-620 a lucia@uenf.br, b s.neves@ig.com.br, c mgazevedo@uenf.br, lais.bmotta@yahoo.com.br Keywords: diamond nanocomposites, nanostructures, wear resistance Abstract. Diamond-Si nanostructured composites were obtained by cyclic high pressure and high temperature sintering with different processing conditions to examine the dominant microstructural factors and the abrasive wear resistance. The microstructure of the composites was characterized by scanning electron microscopy. The abrasive wear behavior of the composites was evaluated by weight loss in abrasion tests. It was found that improved nanostructured composite properties and denser structures were obtained for sintering performed with more than one cycle of pressure and temperature. Introduction The sintering of diamond particles to produce compacts, such as inserts for abrasive tools, is usually performed inside high pressure devices (HPD) with the application of both, high pressure and high temperature (HPHT) conditions. These HPHT conditions, where diamond sintering can be achieved, have already been determined [1-6]. However, under the conventional HPHT conditions the diamond particle displays low plasticity, which explains the difficulty in producing well consolidated compacts [3]. Actually a good consolidation of diamond compacts requires not only the elimination of existing pores formed in between adjacent particles but also convenient technical processing to avoid the graphitization of diamond particles [4]. Tomlinson et al [7] and Voronin et al [8], have shown that during the diamond sintering the existence of Si would retard the process of graphitization. Furthermore, in addition to retarding diamond graphitization, at high temperatures, molten Si penetrates the existing pores between diamond grains causing greater cohesion and hardness to the final compact. Recent studies [9] have shown that nanostructured diamond-SiC composites exhibit an even superior improvement in mechanical properties, especially the toughness. In the present study, nanostructured composites were produced in the diamond-Si and not the already investigated [3] diamond-SiC system. Cyclic application of the pressure and temperature was also a novel procedure to evaluate the wear performance of the final sintering product. Experimental Procedure For the nanostructured composite production, Si powder supplied by the firm Aldrich, with particle size of µm and diamond crystals synthesized in the authors’ laboratory with particle size of µm were used. The composition of the mixture was 70wt.% of diamond and 30wt.% of Si. In order to obtain nanopowders, a high-energy ball milling was carried out in a model 8000 SPEX equipment. After milling, the nanopowders were subjected to a uniaxial compaction in a cylindrical mold. The compacts were placed inside a graphite tube heater with ends sealed with graphite disks. The set was placed in a calcite deformable capsule and assembled in a 630 ton press. The sintering of the composites was performed by repeated application of 1 to 4 cycles of pressure and temperature (P- T) for a 1 minute time. The cyclic variation of the pressure and the temperature with processing time was conducted by alternating levels of 7GPa at 1600°C and 4GPa at 30°C. At the end of the process, the samples were extracted from the graphite matrix, cleaned, and prepared to be Materials Science Forum Vols. 727-728 (2012) pp 919-923 Online available since 2012/Aug/24 at www.scientific.net © (2012) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/MSF.727-728.919 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 186.218.138.94-29/08/12,03:23:00)