Catalytic Decomposition of Cubic Boron Nitride

: Studies for Present and Future Applications

Abstract

Cubic boron nitride (CBN) materials are a mainstay in the tooling industry, concerned primarily with advanced machining of ferrous-containing metal alloys. Combining both conventional and real-time X-ray photoelectron spectroscopy, the surface chemistry of both a commercial standard AMB90 and a high-quality binder-free polycrystalline CBN compact (provided by Element Six Ltd.) was observed in the presence of a high-purity Fe thin film, raised to temperatures over 900°C. Breakdown of binder constituents due to the workpiece analogue film is explored for AMB90. For the pure CBN, presence of a π plasmon loss feature centred ΔE = 8.8 eV for both B 1s and N 1s core levels indicated the decomposition of sp3 CBN to sp2 in the temperature region 820 – 900 °C, having implications for tool degradation at those temperatures. Boron nitride material was shown to crystallise at the metal/vacuum interface, and this thesis therefore presents a novel growth mechanism for hexagonal boron nitride (HBN) via catalytic decomposition of the cubic phase. Phase composition was confirmed with synchrotron study of near-edge X-ray absorption fine structure, and growth domains up to 10 × 10 μm were observed with photoemission microscopy. Confocal Raman spectroscopy mapping of characteristic HBN E2g peak shift suggested some domains had thickness of three monolayers or fewer. The potential for patterned growth, and HBN/graphitic heterostructures, were explored. Cubic boron nitride also shows promise as a high transparency optical window, and spectroscopic transmittance and reflection measurements on the binderfree PCBN between 350-2500 nm are presented, with wavelength dependent refractive indices reported. Complimentary real-time Raman spectroscopy studies characterised the peak shift and broadening of the CBN νTO and νLO for temperatures up to 1000 °C, determining a predictive expression which can be used as a basis for Raman thermometry.

Date of Award	2023
Original language	English
Awarding Institution	Aberystwyth University
Supervisor	Andrew Evans (Supervisor) & Rachel Cross (Supervisor)