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1 2011

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Cubic boron nitride based composites for cutting applications

Klimczyk P., Figiel P., Petrusha I, Olszyna A.

Journal of Achievements in Materials and Manufacturing Engineering

2011

Vol. 44, nr 2

198--204

Purpose: The aim of our work was to obtain durable fined-grained cBN-Si3N4 composite with high values of hardness and fracture toughness, which can be successfully used as a cutting tool. Little quantity of the Si3N4 nanopowder fills up the porous between cBN grains thus result in resistance to crack propagation by means so called “crack deflection” mechanism. Design/methodology/approach: Two variants of the cBN-Si3N4 composites („I” - with micropowder cBN and „II” - with mixture of micro- and nanopowdes cBN) contained 3% of nanodispersed Si3N4 powder, have been sintered at High Pressure - High Temperature (HPHT) conditions. Basic physical-mechanical properties, phase composition and microstructure of sintered materials have been investigated. Findings: The comparison of the mechanical properties of cBN-Si3N4 (I) and cBN-3N4 (II) composites showed that the addition of 10% cBN nanopowder to mixture caused small increase in hardness from 4750 up to 4855 HV10 and decrease in Young’s modulus from 842 to 812 GPa. Fracture toughness of both type of composites is on the same level above 10 MPa-m1/2. Research limitations/implications High hardness of cBN-Si3N4 composites present a technical challenge in shaping of them. Commercial application of presented materials, e.g. cutting tools production, needs to develop a high efficient cutting, lapping and grinding techniques. Practical implications: The material obtained could be successfully applied for different cutting applications due to its favourable combination of hardness and fracture toughness. Originality/value: Commercial superhard materials, so called “high content cBN composites”, have usually 10-20 vol% of binding phase, often in the form of Ti or/and Al compounds. In the presented work only 3% of Si3N4 phase was used as a sintering aid. The high content of cBN phase allows to keep Young’s modulus and hardness values close to the theoretical ones for pure PcBN.