【作者】 周咏辉；

【导师】 艾兴； 赵军；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2009， 博士

【摘要】 纳米复合陶瓷刀具材料的计算设计是当前国际上该领域内的重大研究方向之一。本文提出了基于Mori-Tanaka方法的纳米复合陶瓷刀具材料设计方法,研究纳米复合陶瓷刀具材料的微观结构与宏观力学性能的关系,预测纳米复合陶瓷刀具材料的强度、断裂韧度及硬度,优化纳米复合陶瓷刀具材料的制备工艺参数,并对纳米复合陶瓷刀具材料的力学性能与微观组织结构之间的关系、材料断裂机制、刀具的切削性能和磨损破损机理等进行了分析与研究。提出了基于Mori-Tanaka方法的纳米复合陶瓷刀具材料设计方法,详细讨论了刀具材料中的组分设计、物化相容性分析以及微观结构设计。为获得具有较高致密度的陶瓷素坯,应用多组元双尺度球形颗粒堆积模型,计算求得纳米复合陶瓷刀具材料体系中最佳的纳米颗粒与微米颗粒的粒度比及纳米颗粒体积分数。根据自洽理论,应用Mori-Tanaka方法建立了二相胞元的刚度预报模型,预测了Al₂O₃/（W,Ti）C（简称AWT）纳米复合陶瓷刀具材料的有效弹性模量。复合陶瓷刀具材料的有效弹性模量随增强相体积含量的增大而增大,增强相颗粒大小对有效弹性模量的影响不是很明显。在纳米复合陶瓷刀具材料三相模型的基础上,应用Mori-Tanaka方法和微裂纹能量释放理论,推导出包含随机分布微裂纹的材料强度预测公式;结合已有的材料断裂韧度预测公式,建立了纳米复合陶瓷刀具材料断裂韧度预测公式。结果表明,增强相粒径对AWT纳米复合陶瓷刀具材料预测强度的影响很明显,粒径越小材料强度越高,增强相体积分数对强度的影响不算大;粒度对材料的韧性影响也很大,粒度越小材料的断裂韧度越大;材料的断裂韧度随增强相体积含量的增大先增大后减小,增强相体积含量为25%～50%时,材料的断裂韧度相对较高。从纳米复合陶瓷材料组分的原子硬度、离子硬度和键硬度这三个微观层次上研究材料硬度的本质,根据键硬度理论,应用混合法则,建立了纳米复合陶瓷刀具材料的硬度预测公式。结果表明,AWT材料的硬度随增强相体积分数的增大而提高。优化了AWT纳米复合陶瓷刀具材料的热压烧结工艺参数。在宏观力学性能理论预测的指导下,通过对纳米复合陶瓷刀具材料烧结温度和保温时间的优化设计,确定了AWT10纳米复合陶瓷刀具材料较为适合的烧结温度为1700℃、保温时间为10min、烧结压力为30MPa。制备的AWT10纳米复合陶瓷刀具材料的综合力学性能最好,其抗弯强度为930MPa,维氏硬度为23.5.GPa,断裂韧度为7.55MPa·m^1/2、导热系数为12.6W/（m·K）。研究了AWT10纳米复合陶瓷刀具材料的显微组织结构、裂纹扩展形式和断裂机制。结果表明,材料微观结构主要为晶内/晶间混合型,材料的断裂模式为穿晶断裂和沿晶断裂的混合,裂纹的弯曲、偏转、桥联、分叉等使裂纹在扩展过程中消耗更多的能量,从而促进了材料强度和断裂韧度的提高研究了纳米复合陶瓷刀具材料的强韧化机理。建立了AWT纳米复合陶瓷刀具材料内晶/晶间型结构残余热应力分析模型,计算了材料内部的残余热应力。纳米复合陶瓷刀具材料中拉、压应力区的结构形式与纳米基体颗粒及增强相颗粒的分布方式密切相关。在残余热应力场中,裂纹易于偏转或钉扎。在残余压应力作用下,晶界结合强度得到增强,在晶界处易于出现位错。这些特征的存在致使裂纹在扩展过程中需要消耗更多的能量,因此促进了材料强度和断裂韧度的提高。此外,纳米颗粒的引入,进一步细化晶粒,从而强化材料。研究了AWT10纳米复合陶瓷刀具连续车削淬硬45钢和淬硬工具钢T10A时的刀具寿命、切削力及切削温度,深入研究了刀具磨损破损特征、机理及其与微观组织结构的关系。结果表明,AWT10的刀具寿命比同组分的微米级SG-4刀具大幅提高,且适于淬火钢的高速精加工。AWT10刀具连续车削淬硬45钢时刀具的磨损机理主要是磨粒磨损和粘结磨损。AWT10刀具连续车淬硬工具钢T10A时随着切削速度的提高,刀具的失效形式从磨损转变为破损。研究了AWT10纳米复合陶瓷刀具断续车削淬硬45钢时的切削性能及刀具破损形态和机理。AWT10的刀具寿命在低速和高速下均优于SG-4刀具,其刀具寿命约为SG-4的1.2倍左右。低速断续车削淬硬45钢时,机械冲击是AWT10刀具破损的主要原因,刀具除发生破损外还具有明显的磨损特征,磨损机理主要为粘结磨损和磨粒磨损;而高速断续切削淬硬45钢时,机械应力和热应力共同作用是AWT刀具破损的主要原因。更多还原

【Abstract】 The compution design of nanocomposite ceramic cutting tool materials is one of the important research direction currently throughout of the world.The methods of the design based on Mori-Tanaka theory of nanocomposite ceramic cutting materials have been proposed in this dissertation.The relationships between micro-structure and mechanical properties have been investigated and the strength,fracture toughness and hardness have been predicted.The fabrication processing parameters is optimized according to the results of predication.The crack extension mechanism of cutting tool materials,cutting performance,abrasion and fracture mechanism of nanocomposite ceramic cutting tool materials also have been analyzed and researched.A theoretical frame for the design of nanocomposite ceramic cutting tool materials is established firstly.Composition design,physical compatibility,chemical compatibility and microstructure design of nanocomposite ceramic cutting tool materials are investigated.Granular-metric composition between nano-particle and micro-particle and volume fraction of nano-particle have been calculated by using multi-component double scaling equation of powder particles packing to attain high relative density of ceramic.biscuit.The predication model of rigidity of two phase cell has been established applying Mori-Tanaka method based on self-consistent theory.The effective Young’s modulus of Al₂O₃/（W,Ti）C（Abbreviation:AWT） nanocomposite ceramic cutting tool is predicted and the effective modulus of elasticity would increased with the increase in volume fraction of reinforced phase,the particle size of reinforced phase didn’t obviously affect the effective modulus of elasticity.By using the Mori-Tanaka method,a group of equations to predict strengthen and fracture toughness of nanocomposite ceramic cutting tool materials which include random distribution micro-crack.Results show that the strength was obviously influenced by reinforced phase particle size of nanocomposite,the Strength increased with decreasing grain size,and the volume fraction of reinforced phase didn’t obviously affect the strength.Grain size obviously influenced the fracture toughness of cutting tool materials,the fracture toughness increases with decreasing grain size and the fracture toughness is higher when volume fraction of reinforced phase is 25-50vol%.Intrinsic behavior of hardness of nanocomposite ceramic cutting tool materials has been studied for atom hardness,ion hardness and chemical bond hardness.The prediction equation based on chemical bond hardness theory has been derived.It is shown from the results that hardness of AWT cutting tool material increased with increasing volume fraction of reinforced phase.Processing parameters of hot pressing sintering were optimized according to predication of mechanical properties of AWT.The optimum results show that the best mechanical properties of AWT10 are obtained under the condition of the sintering temperature 1700℃,soaking time 10min and pressure 30MPa.The mechanical properties are:flexural strength 930MPa,Vickers’ hardness 23GPa,fracture toughness 7.55MPa.m^1/2 and thermal conductivity 12.6 W/（m.K）.Micro-structure,mode of crack propagation and fracture mechanisms of AWT10 nanocomposite ceramic cutting tool material were thoroughly studied.Results show that the microstructure is mainly intragranular/intergranular structure,the fracture characteristics are mixed by intergranular fracture and transgranular fracture.Crack bending,deflection,bridging,and branching et.al consume much more energy in crack extension and so bending strength and fracture toughness of tool materials can be improved.Strengthening and toughening mechanisms in nanocomposite ceramic cutting tool material were researched.Thermal residual stress field has been researched.The analysis model for thermal residual stress of intra/inter structure of AWT nanocomposite ceramic cutting tool material was established and thermal residual stress was calculated.Results reveal that the structural configuration of tension stress section and compressive stress section in nano-composite ceramic cutting tool material closely related to distribution of nano-scale matrix and reinforced phase grain. Crack deflection,branching and bridging easily carried out in thermal residual stress field.Bonding strength of crystal boundary is strengthened and dislocations easily carry out on crystal boundary under residual compressive stress and crack extensions consume much more energy,and therefore the bending strength and fracture toughness can be improved.Moreover nanopartcles refine grain size,and so the strength of materials can be incresased.Results show that the main strengthening and toughening mechanisms of the material include the effect of grain refining and grain boundary strengthening caused by nano-scale particles,thermal residual stress of intra/inter structure and dislocation toughening.Cutting performance of AWT10 nanocomposite ceramic cutting tool material in turning hardened 0.45%C steel and hardened tool steel T10A are studied.Wear and fracture mechanism of AWT10 cutting tool are investigated.The relationship between cutting parameters and cutting force or cutting temperature is discussed.Results show that the tool life of AWT10 is higher than SG-4 and AWT10 cutting tool material is more suitable for high speed finish machining hardened carbon steel.Wear mechanisms are abrasive wear and adhesion abrasive in turning hardened carbon steel. Failure mode of AWT10 is changed from abrasive failure to dilapidation failure with increasing cutting speed in machining hardened tool steel T10A.Cutting performance of AWT10 nanocomposite ceramic cutting tool material in intermittent turning hardened 0.45%C steel is studied.Tool life of AWT10 is higher than that of SG-4 at both higher and lower speed.Tool life of AWT10 is about 1.2 times than that of SG-4.The fracture mechanisms is mainly mechanical impact when intermittent cutting hardened carbon steel at lower speed,wear patterns can be seen obviously from inserts and wear mechanisms are abrasive wear and adhesion abrasive. The fracture mechanisms are interaction of mechanical impact stress and thermal shock stress when intermittent cutting hardened carbon steel at higher speed.This dissertation is supported by the Foundation for the Author of National Excellent Doctoral Dissertation of P.R.China（200231） and National Basic Research Program of China（2009CB724402）.更多还原