【作者】 袁训亮；

【导师】 赵军；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2008， 硕士

【摘要】 本文在微米级Al₂O₃基体中添加纳米TiC和微米WC作为增强相，通过调整复合陶瓷材料中基体和增强相的含量、优化烧结工艺参数，成功制备出性能良好的Al₂O₃／TiC／WC纳米复合陶瓷刀具材料，并对其力学性能、微观结构、压痕裂纹扩展形态进行了研究。将新研制的纳米复合陶瓷刀具材料制成刀片进行切削实验，研究了刀具的切削性能和失效机理。通过合理选择分散剂及其用量、采用合适的分散工艺，较好的解决了纳米TiC颗粒团聚的问题。确定了纳米复合粉体的制备工艺，制备出了混合均匀、分散效果良好的纳米复合粉体。当基体Al₂O₃的体积含量为59％、增强相TiC和WC的体积含量分别为24％和16％时，在烧结温度1700℃、烧结压力30MPa、保温时间10min的工艺条件下烧结，可获得综合力学性能良好的复合陶瓷刀具材料，抗弯强度为840MPa、硬度为20GPa、断裂韧度为5．32 MPa·m^1／2。微观结构观察发现，Al₂O₃／TiC／WC纳米复合陶瓷刀具材料为晶内型和晶间型的混合结构，Al₂O₃基体以部分粒径较小的纳米TiC颗粒为核生长形成晶内型结构，其余粒径较大的TiC颗粒和所有WC颗粒镶嵌在Al₂O₃基体晶粒之间形成晶间型结构。在Al₂O₃和TiC晶粒中观察到的位错以及在Al₂O₃晶粒中观察到的微裂纹说明，在复合陶瓷刀具材料内部存在较大的残余应力场，残余应力增韧是该复合陶瓷刀具材料的一种增韧机制。在Al₂O₃／TiC／WC纳米复合陶瓷刀具材料压痕裂纹扩展路径上观察到大量的裂纹偏转、桥联和裂纹分叉现象，上述裂纹扩展方式有助于提高材料的断裂韧性。连续切削淬火45钢时，在不同速度下，LWT刀具的寿命都明显高于SG-4刀具。LWT刀具的磨损形态为前刀面的月牙洼磨损、后刀面磨损和边界磨损。磨损机理为磨粒磨损和粘结磨损。连续切削淬火T10A时，在较低的速度（v=100m／min）下，LWT刀具的寿命高于SG-4；速度较高（v=160m／min）时，LWT刀具的寿命不如SG-4。较低速度下，LWT刀具的磨损形态以前刀面的月牙洼磨损、后刀面磨损和边界磨损为主，并伴随有轻微的微崩刃；随着切削速度的提高，崩刃、碎断等破损成为刀具的主要失效形式。机械疲劳和热疲劳是造成刀具破损的原因。断续切削淬火45钢时，在较低的切削速度下，LWT刀具的抗冲击能力低于SG-4；当切削速度提高时，LWT刀具的抗冲击能力优于SG-4刀具。两种刀具的破损形态都是前刀面的剥落和切削刃上的碎断。更多还原

【Abstract】 Nano-scale TiC and micron-scale WC particles were added into Al₂O₃ matrix. By adjusting the contents of TiC, WC and Al₂O₃ and optimizing the sintering parameters, an Al₂O₃/TiC/WC nano-composite ceramic cutting tool material with good mechanical properties was fabricated successfully. The mechanical properties, microstructure and fracture extension pattern of the ceramics were consequently studied. The cutting performance and failure modes and mechanisms of the newly developed ceramic tool were investigated via a series of cutting experiments.The problem of agglomeration of the nano particles was solved satisfactorily by selecting the appropriate dispersing medium and the right dispersion procedure. The preparation procedure of the nano-composite powders was established and well-dispersed powders were prepared.When the volume contents of Al₂O₃, TiC and WC are 59%, 24% and 16%, a ceramic with strength of 840MPa, hardness of 20GPa and toughness of 5.32MPa·m^1/2 can be obtained by hot-press sintering under the temperature of 1700℃, pressure of 30MPa and holding time of 10 minutes.The microstructure of the Al₂O₃/TiC/WC nano-composite ceramic is characterized by a mixture of intragranular and intergranular structure. Some of the TiC particles in small scale are enwrapped by Al₂O₃ matrix and then intragranular structure is formed. Other TiC particles and all the WC particles embed between the Al₂O₃ boundaries to form intergranular structure. The dislocations in Al₂O₃ and TiC grains and the micro cracks in Al₂O₃ were observed, which indicate the existence of residual stresses in the Al₂O₃/TiC/WC nano-composite ceramic. Residual stress plays a role of toughening in the ceramic.The crack deflection, crack bridging and crack branching in the crack extension path also contribute to improving the toughness of the ceramic.The tool life of LWT tool was superior to that of SG-4 tool in different cutting speeds when machining hardened 45 steel. The failure modes of LWT tool are rake wear, flake wear and notch wear caused by abrasive and adhesive wear.As for the machining of hardened T10A steel, the tool life of LWT is longer than that of SG-4 under lower speed （v=100m/min）,but shorter than that of SG-4 under higher speed. The failure modes of LWT tool are rake wear, flake wear and notch wear with chipping in the cutting edge in lower speed, but fracture becomes the main failure mode when speed is high. Mechanical and thermal fatigue is the main mechanisms for the tool failure.The tool life of LWT is shorter at lower speed but longer at high speed than that of SG-4 when intermittent machining hardened 45 steel. The failure modes of both tools are flaking in rake face and fracture in cutting edge.更多还原