Hot Isostatic Pressing of Cubic Boron Nitride–Tungsten Carbide/Cobalt (cBN–WC/Co) Composites: Effect of cBN Particle Size and Some Processing Parameters on their Microstructure and Properties

Abstract

Cubic boron nitride (cBN)-cemented carbide composites have gained attraction over the last few years because of their potential uses as wear parts. The densification behavior of cBN-hard metal composites by glass encapsulation hot isostatic pressinghas been investigated. Composites with different cBN grades (from 0/0.5 to 6/12 lm particle sizes) and cBN content (up to 50 vol%) were selected for this study. Near-full densification was obtained at temperatures between 11001 and 12001C, and pressures between 150 and 200 MPa, respectively, while no phase transformation of cBN into the low-hardness hexagonal form has been detected by X-ray diffraction. The addition of cBN to the hard metal base material led to an increase of hardness, a significant increase of fracture toughness (K IC measured by Vickers indentation), and a moderate decrease of mechanical strength (determined by three-point bending). cBN, cubic boron nitride; Co, cobalt; WC, tungsten carbide.

Evaluation of physical phenomena occurring in turning of nodular cast iron with use of the WCCo/cBN composite cutting edges

“…Należy podkreślić, że im większa jest zawartość fazy twardej (cBN) w kompozycie, tym staje się on twardszy, bardziej wytrzymały mechanicznie oraz odporny na kruche pękanie, zmniejsza się natomiast jego odporność termiczna i chemiczna. Liczną grupę wśród wymienionych kompozytów stanowią materiały WCCo/cBN -uzyskane metodą izostatycznego prasowania na gorąco (HIP) [5], iskrowego spiekania plazmowego (SPS) [6,7] oraz impulsowego spiekania plazmowego (PPS) [8].…”

WCCo/cBN composites produced by pulse plasma sintering method

“…4) were evenly surrounded by the binding cobalt phase, providing evidence that the high-current pulse sintering proceeded with participation of a liquid cobalt phase. When the sintering process occurs without participation of the liquid phase, cobalt usually occurs in the form of agglomerates and is distributed nonuniformly in the cemented carbide matrix [5], even though the sintering process is conducted at temperature of 1,100°C, which is below the melting point of cobalt.…”

“…In addition, the cBN particles can considerably increase the fracture toughness of the material due to the crack deflection effect, wherein crack energy is absorbed [5].…”

“…Composites with cBN particles dispersed in cemented carbides, known as cubic boron dispersed carbides (CBDC), were obtained by Martinez and Eceberria [5] by sintering using the method of hot isostatic pressing (HIP) at temperature between 1,100 and 1,200°C under pressures of up to 200 MPa. The CBDC composites thus obtained were dense, and no phase transformation of cBN into hBN took place during the sintering process.…”

Densification, phase transformation and hardness of mullite-cubic BN composites prepared by spark plasma sintering

“…Martínez and Echeberria 10) reported that the densification of WC-Co-cBN composites was significantly suppressed compared with that of WC-Co. Martín et al 24) also showed that the densification of cBN-Cu-Ti composites decreased by the addition of cBN. The relative density of monolithic BN prepared at 1500-1700°C for 600 s was 50-60%, resulting in almost the same density as BN compacts before sintering.…”