【作者】 陈文琳；

【导师】 刘宁；

【作者基本信息】 合肥工业大学 ， 材料加工工程， 2007， 博士

【摘要】 随着高速精密切削和数控技术的发展，对刀具切削性能的要求也日益提高。金属陶瓷具有硬度高、耐磨性好、高温力学性能好等优良特性，但因其抗塑性变形能力差、抗崩刃性能差及韧性不好等限制了应用，长期以来对金属陶瓷刀具的增韧研究一直是材料学者努力的方向。本文在课题组前期研究的基础上，制备了超细晶粒Ti（C，N）基金属陶瓷刀具，对其切削性能进行了研究，运用有限元软件建立了有限元切削仿真模型，仿真了切削过程，更加真实地揭示了刀具和工件的切削状态，计算出了刀具磨损量、切削力及温度等分布规律。本文主要做了以下工作：首先，介绍了金属切削加工在国民经济中的重要性及加工技术发展对切削刀具的要求，刀具材料及金属陶瓷的发展背景、目前面临的问题以及今后的发展趋势；Ti（C，N）基金属陶瓷的组织性能和发展过程及其在切削刀具领域的应用，纳米复合陶瓷的发展现状和趋势；概述了金属切削技术的复杂性和切削加工过程数值模拟技术的发展历史、现状和当前存在的问题。其次，详细地叙述了超细晶粒Ti（C，N）基金属陶瓷的制备过程，力学性能的测试方法以及显微组织表征的方法；重点讨论了超细晶粒Ti（C，N）基金属陶瓷成分、显微组织和宏观力学性能之间的关系；研究了原始粉末粒度，不同粒度组合，TiC／TIN添加量，Mo、Co添加量对材料组织以及力学性能的影响。研究发现：1)晶粒细化使材料的硬度上升，但抗弯强度和断裂韧性有所下降。2)原料粉末中过多的氧杂质或者过量TiN的分解都会导致组织缺碳，在这些缺碳的组织中，发现了一种化学式为(Ni₂Mo_2.5W_1.3)Cx的特殊化合物。该物相的出现有利于提高材料的硬度，但是降低了材料的强度和韧性。3)在以亚微米Ti（C，N）为硬质相为原料的试样中出现了一种新型的白芯／灰壳结构。本文认为由于原始粉末粒径微小，促进了扩散反应，因而导致了这种芯／壳结构的生成，初步研究表明这种结构对提高材料的强韧性有利。4)Mo添加量的多少显著影响材料的组织形貌，Co比Ni对Ti（C，N）的润湿性更好，以Ni+Co合金作为粘结相的材料其陶瓷相与粘结相之间的界面强度得到了增强。5)由TiC粗粉所制得的材料组织具有较多的“黑芯-灰壳”结构，有的颗粒全部呈灰色：而由TiC细粉所制得的材料组织，则呈现较多“黑芯-灰壳-白壳”Ti（C，N）基金属陶瓷的典型三层结构或白色内壳层；“黑芯—灰壳”结构中黑色芯部（core）主要为TiC或Ti（C，N），灰色的壳层为（Ti，W，Mo）（C，N），“白芯—灰壳”结构中白色芯部（core）为（W，Mo，Ti）（C，N）固溶体。此外，研究了两组刀具对45号钢切削性能的影响，考察了不同切削速度和进给量对刀具耐用度以及磨损／失效方式的影响。研究表明高速切削时刀具的磨损形式以氧化磨损和扩散磨损为主。基于刚粘塑性有限元法理论建立了金属切削过程的二维和三维热力耦合有限元模型，对建模过程中的一些关键问题如摩擦模型、切屑与工件的分离和断裂准则、磨损模型以及新刀具的复合材料模型等进行了分析和处理，提出了较为有效的方法；所建立的模型的模拟结果与实验结果吻合：结合切削理论和模拟计算得到切削过程中的应力应变分布、温度分布切削力的变化及大小，对前述物理实验中的现象进行分析，更加合理地解释了物理实验的现象，使人们更加清晰地理解切削的内部现象，更好地研究切削机理，为新材料刀具的研发提供依据；基于三维切削模拟，得到了刀具磨损量的适时变化和总磨损值的变化趋势，在此基础上，成功地对不同刀具前角进行了仿真，由此得出不同切削前角刀具的磨损、温度及等效应力的变化曲线。上述的研究表明，如果精选成分并对刀具的几何外形和切削参数进行优化，超细晶粒Ti（C，N）基金属陶瓷将是非常有希望的刀具材料；三维数值模拟技术为研究刀具磨损、优化刀具的几何参数和匹配切削对象提供了依据，为新刀具的开发降低了成本，提高了效率。最后，对全文进行总结并对未来工作提出了建议。更多还原

【Abstract】 With the development of high speed precision cutting and numeric control technique, the needfor the cutter with high performance is increasing everyday. There are some advantages in cermetcutter, such as good wear resistance and high temperature mechanical properties and so on, but itsapplication has been limited for its brittleness. Many research works have been done in order toincrease the toughness. Based on the previous studies, ultra-fine grade Ti （C,N）-based cermet cutterwas prepared and its machinability was studied. Finite element cutting models were built and thecutting progress was simulated by using finite element software. Calculating results such as the cutstatus, wear resistance as well as the distribution of cutting force and temperature between the tooland work-piece were obtained.In the first part, the importance of machining in national economy, the need for cutting-tool, thedevelop-background of cutter, problems existed, as well as the developing trend of cermet wereintroduced. The development process, microstructures and properties of Ti（C,N）-based cermet andits application in cutting-tool area, development status and trend of nano cermets was outlined,Complexity of metal-cutting technique, development history and status of simulation technique ofmachining process and problems presented are also outlined.Next, the manufacturing process, mechanical properties and microstructure of ultra-fine grainedTi（C, N）-based cermets have been discussed in detail. A special attention is paid to the relationshipbetween the composition, microstructure and macro-mechanical property, the influence of rawpowder size on the microstmcture and mechanical property of material as well as the addition of TiC,TiN, Mo, Co on materials was studied. The results denote that: 1) The hardness of cermet increaseswith the decrease of ceramic particle size while its bending strength and fracture toughness shows anopposite trend to hardness. 2) If the raw material contains too much oxygen or too much TiN, it willlead the decarbonization. A new compound appeared in cermets which can be written as(Ni₂Mo_2.5W_1.3)Cx. The presence of this phase seems to be beneficial to hardness, however, harmfulto strength and toughness. 3) A new type "white core-grayish rim" grain appeared in cermetsfabricated from sub-micron sized Ti（C,N） starting powders. It was believed that promoteddiffusional reaction caused by ultra-fine raw powders led to the formation of this new core/rim grainwhich helps to improve the strength and toughness of the material. 4) Mo addition played animportant role in determining the microstructure of the cermets. Since the wettability of Co toTi（C,N） is better than that of Ni, the interface strength between ceramic phase and binder phasecould be strengthened when binder phase is composed of Ni+Co. 5)There are lots of typical grains,i.e. "black core-grayish rim" grains in cermets which prepared with micro-sized TiC powders. Incermets prepared with sub-micron Ti（C,N） raw powders, except typical grains, some exhibit coreless grains. At the same time, a new kind of grains with white core-grayish rim was found. It was foundthat the white core mainly is （W, Mo,Ti）（C,N） solid solution.The machinability of two group experimental cutter inserts against AISI 1045 carbon steel wasstudied. Effect of cutting force and feed rate on the tool life as well as wear mechanism was alsodiscussed. Results show that in high speed turning, oxidative and diffusion wear are two main wearmechanisms.Based on rigid-plastic finite element method, thermal coupling finite element models of 2D and3D were built, the key problems existed such as friction model, separate, break criterion betweenchip and work-piece, wear model and composite model of new cutter were analyzed. The results ofsimulation correlate well with the experiment. Some dates, for example, the distribution ofstress-strain, temperature, the change and magnitude of cutting force, are obtained through analogcomputation. Based on above works, the phenomenon can be explained more reasonable. The worksprovides the basis to better understand the internal phenomenon during cutting process. Based on 3Dcutting simulation, the changes of time, the cutter wearing capacity and the total value of the weartrend were obtained. The finite element cutting model with different rake angles was simulated.The works above-mentioned shows that: ultra-fine grade Ti （C,N）-based cermet will be apromising cutter material if appropriate geometry and cutting parameters were adopted.Three-dimensional numerical simulation can provide the basis for studying cutting-tool wear,optimizing the geometry and cutting parameters, reducing the cost and improve the efficiency.Finally, the whole works were summarized and some suggestions on future works wereproposed.更多还原