The wear studies of boron suboxide based cutting tool materials in machining applications

摘要

The wear characteristics of the first generation of boron suboxide (B6O) basedudcutting tool materials fabricated from spark plasma sintered B6O/Y2O3/Al2O3udmaterial have been investigated in terms of chemical and abrasive wear whenudmachining compacted graphite cast iron (CGI).udStatic interaction diffusion couple experiments were conducted atudtemperatures ranging from 700°C to 1300°C in order to simulate the chemicaludinteraction between the tool material (B6O) and the workpiece material (CGI).udThe samples were studied using optical microscopy, scanning electronudmicroscopy (SEM) and energy dispersive x-ray spectrometry (EDS) as well asudx-ray diffraction (XRD) in order to identify the microstructural andudcompositional changes as well as determine resulting phases. Interactionsudobserved below 900°C were found to be minimal, with significant chemicaludinteractions occurring at 1100°C and above. Iron boride phases were seen toudevolve at the interface of the tool and workpiece materials. Silicon diffusionudhas been identified as a rapidly diffusing constituent with a tendency to diffuseudtowards the interface. Due to the formation of various chemical productsudduring the experiments, chemical wear is expected to affect B6O tools atudexpected machining temperatures.udResistance to oxidation of B6O based materials was examined at 1000°C,udrevealing a tendency for formation of boric acids on the surface of the materialudin response to B2O3 formation and reaction with atmospheric moisture.udEvaporation of boric acids has been observed to result in a mass loss of theudmaterial along with boric acid product crystal formation upon cooling.udTurning tests have revealed that the first generation of B6O based cutting toolsudperform comparably with PcBN at very low cutting speeds, but suffer severeudabrasive wear as the cutting speed is increased, due to the need forudimprovements in tool fabrication and the reduction of material damage and audheat affected zone resulting from laser cutting.udUltrahigh pressure sintered B6O based material was produced but was found toudpossess a poor microstructure.udComputational thermodynamics and phase diagram generation has beenudsuccessfully compared to experimental results in predicting reaction productsudand chemical behaviour of the tool materials at machining temperatures.