【作者】 卢文壮；

【导师】 王珉； 左敦稳；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2008， 博士

【摘要】 CVD金刚石涂层刀具在汽车、航空和航天工业等领域具有巨大的应用前景,但要实现CVD金刚石涂层刀具的工业应用仍有许多基础性问题需要解决。如何改善CVD金刚石涂层与刀具基体之间结合性能,提高硬质合金基体上CVD金刚石涂层的使用性能,一直是人们关注的焦点。本文采用理论与试验相结合的研究方法,选用硬质合金基体作为研究对象,探讨各种因素对刀具上CVD金刚石涂层使用性能的影响,研究高性能CVD金刚石涂层刀具的制备工艺,为CVD金刚石涂层刀具的基础研究及实现CVD金刚石涂层刀具的工业应用奠定了重要基础。本文的主要工作包括:1.根据断裂力学理论,建立了初始裂纹状态的金刚石涂层与基体的微孔洞界面模型,得到了界面裂纹应力强度因子。研究了金刚石涂层的剥离过程,界面裂纹扩展、涂层裂纹萌生、断裂的机制。针对硬质合金基体上CVD金刚石涂层剥落的机制,提出提高膜/基结合性能的措施。2.分析了反应气体流场对CVD金刚石涂层的影响,建立了HFCVD系统中反应气体流场的模型,对HFCVD系统的反应气体流场进行了有限元仿真研究。研究了系统的结构参数对刀具衬底周围反应气体流场的影响,对采用镂空结构衬底工作台的反应气体流场进行了有限元仿真和试验研究。3.研究了基体温度场对刀具上CVD金刚石涂层的影响,设计了一套升温迅速、降温缓慢的高热阻镂空衬底工作台,该镂空衬底工作台适合于CVD金刚石涂层刀具的高效制备。建立了HFCVD系统的刀具基体温度场模型,研究了热丝数量、灯丝与刀具基体距离、热丝半径等参数对刀具基体温度的影响。获得了采用镂空衬底工作台时刀具基体前、后刀面都适合CVD金刚石涂层生长的优化参数。4.研究了界面材料、界面状态、植晶等因素对膜/基界面结合性能的影响。研究了不同的刻蚀WC和脱Co工艺对膜/基界面的影响,开发了梯度法膜/基界面预处理工艺,通过膜/基结合界面设计,获得有利于CVD金刚石膜的成核和生长,有利于提高膜/基结合性能的膜/基结合界面。梯度法是一种高效、简单、低成本的预处理工艺。5.利用纳米压痕仪测试了硬质合金基体上CVD金刚石涂层的弹性模量,采用X射线衍射仪和Raman光谱仪测量了硬质合金基体上CVD金刚石涂层的残余应力。研究了循环水强冷的衬底工作台和镂空衬底工作台上沉积的CVD金刚石涂层的残余应力,利用压痕法评价了硬质合金基体上CVD金刚石涂层的膜/基结合性能。6.进行CVD金刚石涂层刀具的切削试验,通过切削试验评价了CVD金刚石涂层刀具的使用性能。结果表明制备的CVD金刚石涂层刀具具有良好的抗粘着性,较低的切削力,刀具耐用度大大提高,CVD金刚石涂层刀具适合高硅铝合金活塞的加工。更多还原

【Abstract】 CVD diamond coated cutting tool is an outstanding candidate for machining difficult-to-machine material due to its unique properties such as low coefficient of friction, high thermal conductivity, high-temperature hardness and chemical stability. A wide spread application in the case of CVD diamond cutting tools is used for machining abrasive and hard materials, such as MMC’s, aluminum silicon alloys and tungsten carbide. It will find its wider and wider application in the field of automobile, aeronautics and astronautics. However poor adhesion of diamond coating is the main technical barrier for commercialization of diamond-coated tools. The thesis aims at some key technological issues regarding on improving the adhesion strength of diamond coated cutting tool and its application in machining. Those key technological issues include decreasing the negative effect of cracks in the diamond coating, improving the adhesive strength between the diamond film and the substrate, and evaluating the cutting performance.The main research contents of the thesis are as following:1. A theoretical model which describes the microstructural aspects of short original cracks was developed firstly based on fracture mechanics to provide a rational explanation for the phenomenon of interface strength between CVD diamond coating and its substrate. The expression of stress field, displacement field and stress intensity factor (SIF) k at interface crack tip were obtained. The interface crack extension, the coating crack growth and the coating fracture process were studied using the original crack model. The coalescence conditions were carried out to develop the adhesion between the CVD diamond coating and its substrate.2. A gas flow field model of HFCVD system was set up. Relationship between the gas flow and CVD diamond coating on the rake face and flank of cutting tool was studied. Finite element analysis method was used to investigate the gas flow field around the cutting tool substrate. Parameters such as distance between cutting tool substrates dt-t, distance between hot-filament and cutting tool substrate df-t, distance between gas inlet and substrate upper surface din-t and gas inlet number nin, which affect on the system gas flow field was discussed in detail. Experiments have been done to prove the simulation results. Excellent agreement between simulation and experiment was obtained by depositing of CVD diamond coated cutting tools using a hollow substrate holder.3. Relationship between the substrate temperature and the quality of CVD diamond coating was studied. A hollow substrate worktable on which the substrate temperature increases rapidly during the heating period and reduces slowly during the cooling period was designed based on the HFCVD system energy transfer. The hollow substrate worktable can be used for large area diamond coating deposition, which can get high efficient productivity. Parameters such as hot-filament number nf, distance between hot-filament and cutting tool substrate df-t and hot-filament radius rf, which affect on the system substrate temperature field was studied using a substrate temperature field finite element analysis model. Optimized parameters to deposite high quality CVD diamond coatings using a hollow substrate holder were obtained.4. Relationship between the substrate/diamond-coating adhesion strength and interface properties such as substrate material, substrate surface state, and substrate diamond seed implanting was discussed. The substrate pretreatment process of etching WC and etching Co was studied. A gradient substrate etching pretreatment process (GSEPP) was developed firstly. The substrate treated by GSEPP shows good properties for CVD diamond nucleation and growth, and which appears to result good substrate/diamond-coating adhesion strength. GSEPP is a high efficient, easy-to-operate and low cost substrate pretreatment for WC-Co cemented carbide substrate to deposite CVD diamond coated tools.5. The elastic modulus and hardness of CVD diamond coatings on WC- 6wt%Co cemented carbide were measured by a nano-indenter system. Stress in diamond coatings was evaluated by XRD and Raman spectroscopy. Relationship between deposition parameters and stress in diamond coatings deposited on both water-cooled substrate holder and hollow substrate holder was studied. Indentation method was developed to evaluate the substrate/diamond-coating adhesion strength.6. Cemented carbide cutting tools with and without CVD diamond coatings were used in continuous and dry turning operations of Al-20wt%Si. Comparing with diamond coated inserts, the uncoated inserts tend adhere at the tool tip and cutting edge which leads to built up edges. The analys is of frank wear and tool tip wear revealed that the tool life of diamond coated inserts is longer than that of the uncoated inserts. The diamond coated inserts are fit for aluminum silicon alloy engine piston operation.更多还原