【作者】 杨发展；

【导师】 艾兴；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 高速、高效切削加工技术是先进实用的制造技术,已成为切削加工的主流,而高性能刀具材料对实现高效加工具有重要的影响。众所周知,高效加工对刀具材料的要求比普通加工更加苛刻,要求刀具材料的性能更高、可靠性更好。虽然目前已有多种多样的高效加工刀具材料,但刀具材料不可能是万能的,各有其特点和应用范围。目前,刀具材料有PCBN、PCD、陶瓷、金属陶瓷、硬质合金刀具和涂层刀具等。但加工铸铁类工件材料还缺乏一类力学性能介于硬质合金刀具材料和陶瓷刀具材料之间的非TiC（N）基金属陶瓷刀具材料。因此,本文探讨研究开发新一类适于高效加工铸铁类工件材料的高性能新型WC基纳米复合刀具材料,以扩大刀具材料的品种。本文系统研究了纳米复合刀具材料的设计、组分配比、制备工艺及其优化、力学性能与显微组织结构之间的关系、刀具材料的断裂机制、刀具材料的摩擦磨损特性以及刀具的切削性能和磨损破损机理等。提出了基于界面增强的纳米复合刀具材料设计方法,并根据界面的损坏机制,建立了基于界面脱粘和断裂的强度模型,并对纳米复合刀具材料增强相含量与界面强度之间的关系进行了分析与研究。建立了纳米复合刀具材料的设计理论框架,利用界面脱粘极限体积含量模型及内应力作用下径向裂纹不贯穿条件的极限体积含量模型,确定增强相的最大极限体积含量。利用界面断裂条件下材料承受最大载荷,设计基体相与增强相的粒径配比。此外,利用界面增强条件,建立了纳米复合刀具材料致密化模型。确定了刀具材料的基体相为WC,增强相为ZrO₂,弥散相为Al₂O₃。基于热力学原理,分析并计算了WC基纳米复合刀具材料体系内各相间的化学热力相容性。同时,将工件材料的组成元素视为纳米复合刀具材料的一种相,分析了刀具材料各相与工件材料组成元素间的化学热力相容性,确定了合适的刀工匹配关系。研究了WC基纳米复合刀具材料的制备工艺,并对纳米添加相进行了分散试验研究,探讨了纳米粉末分散的影响因素。研究了分散介质温度对分散体系的影响,并系统分析了分散温度对纳米颗粒分散的稳定机制。结果表明,在分散介质温度100℃下分散可获得良好的分散效果。研究了WC基纳米复合刀具材料的致密化机理,通过对纳米复合刀具材料烧结温度和保温时间的优化设计,确定了WZ10A纳米复合刀具材料较为合适的烧结温度为1600℃、保温时间为30min、烧结压力为32MPa～35MPa,制备的WZ10A纳米复合刀具材料的密度为12.8g/cm³,维氏硬度为19.8GPa,抗弯强度为996MPa,断裂韧性为9.2 MPa.m^1/2,导热系数为38W/（m·K）。研究了WC基纳米复合刀具材料增韧补强机理。结果表明,纳米复合刀具材料的主要增强增韧机制为纳米晶粒的细化机制,裂纹扩展中的偏转、弯曲、分支、桥连以及增强相的相变增韧作用等。此外,纳米相的多尺度效应和弥散强化效应以及纳米晶粒的钉扎作用等促进了材料裂纹的微细化并提高了材料的抗弯强度和断裂韧性。研究了WC基纳米复合刀具材料的显微组织结构,利用透射电镜和扫描电镜对纳米复合刀具材料显微结构及界面结构特征进行了分析研究。结果表明,WC基纳米复合刀具材料界面所占比例较大,材料内部主要以晶间型组织结构为主,部分存在晶内型结构。研究了WC基纳米复合刀具材料裂纹扩展形式和断裂机制,结果表明,烧结制备工艺（特别是烧结温度）对刀具材料的断裂形式和断裂机制影响较为明显。在烧结温度低于1600℃时,WC基纳米复合刀具材料主要以沿晶断裂为主,当烧结温度高于1650℃时,WC基纳米复合刀具材料以穿晶断裂方式为主。基于分形理论,建立了沿晶断裂、穿晶断裂和沿晶/穿晶混合断裂三种断裂形式下的分形模型,并依据能量耗散原理,对分形模型进行了分析与计算。结果表明,沿晶断裂的能量消耗最大,穿晶断裂的能量消耗最小,并依据该结论,结合纳米复合刀具材料的显微组织结构,验证了优化的制备工艺。研究了WC基纳米复合刀具材料WZ10A高效切削灰铸铁和球墨铸铁的切削性能,并对刀具切削加工中的切削力、切削温度与切削参数之间的关系进行了系统研究与分析。结果表明,在同等切削条件下,WZ10A纳米复合刀具产生的切削力、切削温度等均比YG8硬质合金刀具低,特别适于在200m/min～300m/min的切削速度范围内切削球墨铸铁,刀具寿命比YG8普通硬质合金提高60%～125%。通过对刀具磨损和破损区域微观形貌观察与分析,揭示了WC基纳米复合刀具材料的摩擦磨损特性和磨损机理以及刀具的破损机制。更多还原

【Abstract】 High performance machining（HPM） is one of the advanced manufacturing technologies and is going to be the mainstream due to its advantages.The tool material is indispensable and more important for high performance machining.It’s well known that the requirements of tool material for HPM are more stringent than traditional processing in mechanical properties and reliability to tool materials.Currently,there are more comprehensive types of tool materials,such as PCBN,PCD,ceramics,cermet, cemented carbide and coated tool materials,etal,each of which has different peoperties and is suitable for machining the difinite workpiece materials.However,there is no tool material that the mechanical properties is between cemented carbide tool material and ceramic tool materials,which is suitable for high performance machining cast iron. For example,the TiC（N） based cermet which is suitable for high performance machining steel.In this paper,a novel WC based nanocomposite tool material is developed that is suitable for high performance machining cast iron and expand the variety of tool material.In this paper,the design theory for nanocomposite tool materials,the composition of the tool material,the toughening and strengthing mechanisms,hot pressing technology,mechanical properties,microstructure,fracture mechanisms,tribological behaviors and the cutting performance of the tool material are investigated.A design methodology for nanocomposite tool material（NTM） is developed based on interface-enhanced theory.An intensity model is developed based on interfacial debonding and interfacial fracture mechanisms.Meanwhile,the effect of reinforcing phase content on grain boundariy strength is discussed also.Theoretical frame for the design of NTM is established.The critical volume content of reinforcing phase is determinated based on interface-enhanced theory and toughening mechanism of residual thermal stresses in nanocomposite tool material. Grain diameter rate between the matrix and reinforcing grain is determined based on the maximum loading when interface fractured Densification model is built based on the interface toughening mechanism.Based on thermo-dynamics theory,the composition system for the tool material is decided as tungsten carbide matrix,two reinforcing phases-zirconia and alumina.Chemical compatability between the phases in the tool material is considered based on chemical comparability theory when designing the tool materials.Meanwhile, the chemical compatability between the tool material and the workpiece material must be considered.An appropriate matching relation between the tool materials and the workpiece is determined.Fabrication technique of NTM is studied and a dispersion experiments is carried out to investigate the dispersivity of nano additives.The factors for influencing the dispersion processing are also explored.The dispersion experiments indicated that a good quality,re-agglomerated composite powder can be obtained by the optimization of the molecular weight and concentration of dispersant,especially the adjustment of the media temperature is the most important.Results show that 100℃is the best temperature to achieve a good dispersion mixture.The densification mechanism of the nanocomposite tool materials is studied and the sintering parameters,for example,the sintering temperature and soaking time,are optimized.The optimal results show that the best mechanical properties of WZ 10A are obtained under the condition of the sintering temperature 1600℃,soaking time 30min and pressure 32MPa～35MPa.The mechanical properties are:density 12.8g/cm³, Vicker’s hardness 19.8GPa,bending strength 996MPa,fracture toughness 9.2MPa.m^1/2 and heat conductivity coefficient 38W/（m·K）,respectively.Strengthening and toughening mechanisms for NTM were thoroughly studied. Results show that the main strengthening and toughening mechanisms of the materials include the effect of grain fining and grain boundary strengthening caused by nano-scale particles,residual stress toughening and the phase transition toughening effect caused.Additionally,the multi-scale effect,the dispersion strengthening effect and nano-grain pinning effect are emphasized on the toughening and strengthening the nanocomposite tool materials.Microstructure of WC matrix nanocomposite tool material is studied.By TEM and SEM,it reveals that grain boundaries have a large proportion in nanocmposite tool materials and inter granular microstructure is the main structure.Meanwhile,a few small intra granular structures are involved in the tool materials.In this paper,much effort is paid on the microcrack propagation and fracture mechanism of the nanocmposite tool material.Results reveal that sintering parameters have great influence on the fracture mode and fracture mechanisms.It shows that intergranular fracture is the main fracture mode when sintering temperature is lower than 1600℃while intragranular fracture appeared when sintering temperature is higher than 1650℃in WC based nanocomposite tool materials.Three fractal fracture models（including intergranular fracture,intragranular fracture and the mixture fracture of intergranular and intragranular） are proposed based on the fractal theory.Analysis and calculation is accomplished to fractal fracture models based on the principle of energy dissipation.Results show that energy consumption of intergranular fracture is the most while intragranular fracture is the least.Preparation technology can be optimized based on the combination of fracture fractal models and microstructure analysis.Cutting performance of WC based nanocomposite tool materials in machining cast irons and nodular cast iron are studied.The relationship between cutting parameters and cutting forces or cutting temperature is discussed.Results show that cutting force and cutting temperature of WZ10A nanocomposite tool materials is smaller than YG8 cemented carbide tool material.WZ10A tool material is more suitable for cutting nodular cast iron in the cutting speed of 200m/min to 300m/min and the tool life is prolonged more than 60%～125%.Wear mechanisms and failure mechanisms of the WZ1 0A tool materials are studied based on the wear morphologies of the tool.更多还原