Abstract
WCCo/cBN composites have been considered as a next-generation material for use in cutting-tool edges, being characterized by an optimal combination of hardness and toughness. They can be used instead of WCCo/diamond composites in machining of iron-based materials. The major challenge in sintering these composites is to produce a well-bonded interface between the WCCo matrix and cBN particles. In this study, WCCo/cBN composites were fabricated by the pulse plasma sintering technique. The aim of this work is to obtain sintered parts with density near the theoretical value and with very good contact between the cBN particles and WCCo matrix. cBN/cemented carbide containing 30 vol.% of cBN particles was produced using a mixture of 6 and 12 wt.% Co-added WC powder, with WC grain size of 0.4 μm and cBN powder with grain size ranging from 4 to 40 μm. Scanning electron microscopy (SEM) observations of the microstructure and diffraction phase examinations did not show the presence of hBN phase. The specific heating conditions used to consolidate the material using high-current pulses hamper the transformation of cBN into hBN and ensure a strong bond between the cBN particles and the cemented carbide matrix. Fractures through the WCCo/cBN composite showed that only few cBN particles were torn out from the cemented carbide matrix, with most of them having been cleaved along the fracture plane. This provides evidence that the bond at the WCCo/cBN interface is mechanically strong. Composites sintered at temperature of 1,200 °C under pressure of 100 MPa for 5 min had density near the theoretical value. Increase of the sintering temperature to 1,200 °C resulted in an increase of the hardness to 2,330 HK1 for the WC6Co/cBN(1/3) composite and to 2,160 HK1 for the WC6Co/cBN(37/44) composite.
Highlights
Cubic boron nitride is a material next to diamond in hardness [1], but its thermal stability and chemical neutrality are superior to those of diamond
Scanning electron microscopy (SEM) observations of the microstructure and diffraction phase examinations did not show the presence of hBN phase
When the sintering process was conducted at temperature of 1,150 °C, the density of the WC6Co/cBN(37/44) composite increased to 100 % of theoretical density (TD) and that of the WC6Co/cBN(37/44) composite increased to 96.5 % of TD
Summary
Cubic boron nitride is a material next to diamond in hardness [1], but its thermal stability and chemical neutrality are superior to those of diamond. Without the use of a catalyst, cubic boron nitride is obtained at temperature between 2,300 and 3,300 °C and pressure of 6–10 GPa as a result of the phase transformation of hBN with hexagonal structure into a cBN regular structure [2] or, with the participation of a catalyst, at a temperature between 1,000 and 1,700 °C under pressure of 2–6 GPa [3]. When produced with the participation of a catalyst, cBN has the form of a powder with grain size ranging from 10 nm to 2 lm Composites sintered from this powder using high-melting materials (most often titanium and its compounds) as a binding phase are used in cutting tools [4]. To avoid the transformation of cBN into low-hardness hBN, they must be sintered under pressure of 5–6 GPa, which substantially increases their production cost
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