ELSEVIER Diamond and Related Materials 7 t 1998 ) 422 426 DIAMOND AND RELATED TERiAL$ The influence of refractory particles (A1203, TiN) on the mechanical strength of carbonado type synthesized polycrystalline diamonds Vladimir P. Poliakov ~'*, Ana L. Skury a, Andr6 A. Ermolaev b, Marina M. Poliakova ~ "~ Stade UniversiO' of Norte Fluminense, Campos-RJ, Av. Alberto Lamego, 280!5-620 Rio d,o Janeiro, Brazil b Moscow State blstitutefor Steel and A/how, Len#tski Av. 4, Moscow, B-49, Rus'sia Received 23 June 1997; accepted 2 August 1997 Abstract Carbonado type Synthesized Polycrytalline Diamonds (CSPD) are produced under high pressure and temperature in the presence of metals and alloys, which are the promoters of the transformation graphite-diamond and, at the same time, participate in the formation of diamond polycrystalline composite with inclusions of metallic phase on the grain boundaries. In this study, experimental results are presented to show the increase in the mechanical strength of CSPD, through the addition of dispersed refractory particles (A120 3, TiN ) in the Ni- 15% Mo alloy. The experimental data of CSPD strength dependencies on the content of mI,O 3 and TiN dispersed in the alloy, were explained on the basis of the dispersal particles' influence on the strength of the non-diamond phase of CSPD. The mechanism of metallic melt with dispersed refractory particle transfer to the bulk of CSPD was also discussed. © 1998 Elsevier Science S.A. Kevwm'ds: Polycrystalline diamond: Doping: High pressure and high temperature: Strengthening 1. introduction A recent study [!] demonstrated the possibility of CSPD strengthening by addition of transition metals (Mo, Ta and Ti) to an initial alloy Ni-Cr, which is widely used for production of CSPD in industry. However, this strengthening is limited to the extent of metal-dopant solubility in the 7-solid solution based on Ni. Moreover, the presence of Cr in a 7-solid solution based on nickel of the CSPD metal phase causes the formation of chromium carbides, which considerably weaken the non-diamond component, reducing the mechanical properties of CSPD [2]. Therefore, in the present study, an :~lloy based on nickel with I5% molyb- denum was used for production of CSPD [3]. A further increase in CSPD mechanical strength is possible via the strengthening of the metallic component by dispersed refractory oxides (for example, AI,O3) [4]. Researchers also chose the 'titanium nitride (TIN) for simihtr strengthening. The stability of TiN in solution based on Ni at high pressure (P) and temperature (T) in condi- tions of diamond siogle crystals synthesis was deter- mined experimentally [5]. * Corresponding author. Tel: 0055024 7263728 or I}1)551124 7263733: fax: 0055024 7263730: e-mail: vladimir(auenf.br 0925-9635/98/$19.00 c:', 1998 Elsevier Science B.V. All rights reserved. Pll S0925-9635(97)00163.5 2. Materials and experimenta| procedure The following metal powders and compounds were used as the basic elements for CSPD synthesis: Ni with particle size 5 20 ~tm, of 98.85% purity; Mo 5 20 l.tm, of 99.65% purity; Ni dispersed with particles size 100-.200 nm, of 97.00% purity; Mo dispersed with a mean particles size 100nm, of 96.00% purity; TiN dispersed with particles size 70 nm, of 95.00% purity, and also A1203 dispersed with a mean particles size 70 nm, of 96.00% purity, and A1203 dispersed with a mean particles size 70 nm, of 96.00% purity. High purity graphite was used as the initial substance for CSPD synthesis. The initial alloys based on nickel were produced by the powder metallurgy method [6]. For a more unitbrm distribution of components, mixtures of the above- mentioned powders were exposed to ultrasound process- ing in hexane for 1 min. The advantages of such process- ing are confirmed experimentally by the study of pressings fractures of powdered mixtures in characteris- tic radiation of Ti (SEM/EDS) (Fig. 1). The higher uniformity of distribution of phase strengthener TiN was reached using the method of internal nitrogenation to obtain dispersion-strengthened