微波烧结GPLs增韧Al₂O₃陶瓷刀具的制备及切削性能研究

【作者】 张勇；

【导师】 程寓；

【作者基本信息】 南京理工大学 ， 机械制造及其自动化， 2017， 硕士

【摘要】 本文以提高氧化铝基陶瓷刀具材料的断裂韧性为目标,以A1₂O₃/TiC陶瓷刀具为研究对象,基于微波烧结技术,通过添加石墨烯纳米片（GPLs,Graphene platelets）研制了一种新型的氧化铝基陶瓷刀具材料A1₂O₃/TiC/GPLs。系统研究了GPLs的含量对刀具材料物相组成、力学性能、微观形貌和增韧机理的影响。通过摩擦磨损试验,研究了刀具材料的摩擦磨损性能和磨损机理。通过切削试验,探究刀具的切削性能和磨损、破损机理,并与微波烧结AT刀具、热压烧结LT55陶瓷刀具和硬质合金刀具YT15进行切削性能对比。研究了 GPLs对刀具材料物相组成、力学性能、微观形貌和增韧机理的影响。由XRD和拉曼光谱分析可知,GPLs与基体材料之间具有良好的化学相容性,高温条件下GPLs的组织结构得到了保留;当GPLs的含量为0.2 wt.%时,陶瓷刀具的综合力学性能最佳,此时刀具材料的致密度、维氏硬度和断裂韧性分别为97.70±0.20,18.47±0.45 GPa和8.73 ±0.35 MPa m^1/2,GPLs的添加使得维氏硬度下降了 12.88%,但是断裂韧性提高了 68.53%;GPLs均匀的分散于陶瓷基体中,材料的平均晶粒尺寸可由1.71μm下降到1.40μm,相比于AT刀具材料晶粒尺寸下降了 18.13%;刀具材料的增韧机理主要是裂纹的偏转、桥接、分支以及GPLs的片拔出,GPLs可通过拔出效应显著提高材料的断裂韧性,但是过量的GPLs会发生团聚,在材料的晶界处产生气孔降低材料的综合力学性能。研究ATG刀具材料的摩擦磨损性能,并与微波烧结AT刀具材料作对比。结果表明,刀具材料的摩擦系数和磨损率变化趋势相似,均随着法向载荷的升高而升高,随摩擦速度的升高而降低,ATG刀具材料的摩擦系数和磨损率均低于AT。材料的磨损机理主要是磨粒磨损和粘结磨损,GPLs可覆盖在磨损表面降低ATG的摩擦系数和磨损率。研究了 ATG陶瓷刀具连续干式切削淬硬钢40Cr（50±2HRC）的切削性能。在v=173m/min,f=0.1mm/r 时,低的切削深度下（a_p=0.5mm 和 0.6mm）,ATG 刀具的失效形式是磨损,主要的磨损机理是磨粒磨损、粘结磨损、微崩刃以及月牙洼磨损,而AT刀具在a_p=0.5mm时发生了破损失效,高的切削深度下（ap=0.7mm）,ATG刀具的失效形式是破损,破损形式是崩刃和碎断,微波烧结的ATG陶瓷刀具具有较好的抗破损能力。在 a_p=0.1mm,f=0.15mm/r 时,不同的切削速度下（v=173 m/min、240 m/min 和310m/min）,ATG刀具的使用寿命约是LT55刀具的1.04-1.33倍,但是ATG刀具加工工件的表面质量要低于LT55和YT15。刀具主要的磨损机理是磨粒磨损和粘结磨损,GPLs增加了 ATG刀具抗粘结磨损能力。更多还原

【Abstract】 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.更多还原