Preparation And Cutting Performance Of Microwave Sintered GPLs Toughened Al 2 O 3 Ceramic Tool

In this paper,in order to improve the fracture toughness of Al₂O₃-based composite ceramic tool material,a type of Al₂O₃/TiC composites reinforced with graphene platelets（GPLs）was fabricated by microwave sintering.The effect of GPLs content on the phase composition,mechanical properties,microstructure and toughness mechanisms of Al₂O₃/TiC/GPLs wear composite ceramic tool materials were studied.The wear behavior and cutting performance of the new Al₂O₃-based composite ceramic tool were also investigated,in comparison with those of an Al₂O₃/TiC ceramic tool（LT55）produced by hot-pressing technology,a WC/Co cemented carbide tool（YT15）and AT ceramic tools.The effect of GPLs on the phase composition,mechanical properties,microstructure and toughness mechanisms of Al₂O₃/TiC/GPLs wear composite ceramic tool materials were studied.The experimental results showed that no other second phases have generated with different GPLs contents from the XRD,which indicates the excellent chemical compatibility between GPLs and ceramic particles after the composites sintered at 1700℃ for 10 min in microwave field.The structure of the GPLs has been preserved on the high temperature from Raman analysis.The optimal mechanical properties were achieved with 0.2 wt.%GPLs.The relative density,Vickers hardness and fracture toughness were 97.7±0.2,18.5±0.5 GPa and 8.7±0.4 MPa ml/2,respectively.Compared to Al₂O₃/TiC composites,the Vickers hardness decreased by 12.7%,but the fracture toughness increased by 67.3%.GPLs were well dispersed in the ceramic matrix,resulting in a refinement of microstructure.For At to ATG,the average grain size from 1.71μm to 1.40μm,decreased by 18.13%.The toughening mechanisms were crack deflection,crack bridging,crack branching and pull-out of GPLs.Also,agglomerated GPLs and pores were observed in the new composite ceramic tool materials,which caused degradation of the mechanical properties.The effect of normal load and friction velocity on the wear behavior for ATG and AT composite were thoroughly investigated.The results showed that friction coefficient and wear rate were increased with the increase of the normal load and decreased with the increase of the friction velocity.Compared to AT,the friction coefficient and wear rate of ATG were lower.Wear mechanisms of ATG ceramic tool material were mainly abrasion and adhesion,GPLscan cove on the surface of ATG material and reduce friction coefficient and wear rate.The cutting performance and wear mechanisms were investigated via high speed dry cutting of hardened steel 40Cr（50±2HRC）.When the cutting speed v=173m/min and feeding rate f=0.1mm/r,the failure form of the ATG is wear with the cutting depth is 0.5mm or 0.6mm,the wear mechanisms were abrasive,adhesion and micro tripping.However,the failure form of the AT was breakage with the cutting depth is 0.5mm.When the cutting depth is 0.7mm,tipping and cataclasm has been observed.So the ATG ceramic tools were hard to be failure.The tool life of ATG was about 104～133%higher than LT55,and increased with the decrease of cutting speed from 173 m/min to 310m/min,when the cutting depth a_p=0.1mm and feeding rate f=0.15mm/r,but the roughness is higher than LT55 and YT15.The wear mechanisms of ATG were mainly abrasive and adhesion,and the adhesion wear resistance of the tool can be improved with the incorporated of GPLs.