On the Stability of c-BN-Reinforcing Particles in Ceramic Matrix Materials

Abstract

Cubic boron nitride (c-BN) composites produced at high pressures and temperatures are widely used as cutting tool materials. The advent of new, effective pressure-assisted densification methods, such as spark plasma sintering (SPS), has stimulated attempts to produce these composites at low pressures. Under low-pressure conditions, however, transformation of c-BN to the soft hexagonal BN (h-BN) phase can occur, with a strong deterioration in hardness and wear. In the present work, the influence of secondary phases (B2O3, Si3N4, and oxide glasses) on the transformation of c-BN was studied in the temperature range between 1100 °C and 1575 °C. The different heat treated c-BN particles and c-BN composites were analyzed by SEM, X-ray diffraction, and Raman spectroscopy. The transformation mechanism was found to be kinetically controlled solution–diffusion–precipitation. Given a sufficiently low liquid phase viscosity, the transformation could be observed at temperatures as low as 1200 °C for the c-BN–glass composites. In contrast, no transformation was found at temperatures up to 1575 °C when no liquid oxide phase is present in the composite. The results were compared with previous studies concerning the c-BN stability and the c-BN phase diagram.

Failure Evaluation of a SiC/SiC Ceramic Matrix Composite During In-Situ Loading Using Micro X-ray Computed Tomography

“…In the Bale et al observations the phase change could have occurred without the presence of oxide as the test temperature was much higher, 1,750°C. The phase transformation could produce the proposed change in the BN shear properties (Bale et al, 2013), but it would not be restricted to high temperatures as previously suggested, as the hexagonal phase is stable throughout the temperature range covered (Wolfrum et al, 2018).…”

“…A possible explanation that might account for both the observations of Bale et al (2013) and those reported here is that heating at high temperatures (1,300°C, here and 1,750°C, in the previous work) enabled much of the BN to change phase. If the BN was initially in its cubic form then heating can transform it to the softer hexagonal phase (Wolfrum et al, 2018). The hexagonal BN formed could then have reduced friction by acting as a lubricant.…”

“…The hexagonal BN formed could then have reduced friction by acting as a lubricant. Importantly, the phase transformation was shown to occur at low temperatures (1,200°C) when a liquid oxide phase was present (Wolfrum et al, 2018). This condition can be met here with the formation of boro-silicate glass (Jacobson et al, 1999).…”

Cross-sectional transmission electron microscopy studies of boron ion implantation in hexagonal boron nitride

“…Diamondand its composites have been widely used over the years for most of the above mentioned applications. Unfortunately, these materials are not appropriate forsome applications such as machining tools made of ferrous alloys, due to the high chemical reactivity of C to Fe at elevated temperature temperatures [1][2][3][4][5]. As such, the possibility of synthesizing materials…”

Effects of V and Co Element Addition on Microstructures and the Mechanical Properties of In Situ Biphasic Hybrid (TiCxNy–TiB2)/Ni Cermets

“…Ni has excellent plasticity, ductility and impact resistance and high temperature and corrosion resistance, and the wettability between Ni and ceramic phase is good [ 21 ]. Therefore, Ni as a binder with biphasic ceramics as the matrix of cermets has better strength, hardness, wear resistance, oxidation resistance and adhesion resistance [ 22 , 23 , 24 ]. At present, many studies and reports have considered Ni-based composites with TiC x , TiB 2 and TiC x N y as single-phase reinforcements [ 25 ].…”