【作者】 郑光明；

【导师】 赵军；

【作者基本信息】 山东大学 ， 机械制造及其自动化， 2012， 博士

【摘要】 镍基合金具有优良的力学性能,广泛应用于航空、航天及核工业等领域,但高速切削镍基合金时具有切削力大、切削温度高、刀具寿命低等特点,高性能刀具是镍基合金高效高质量加工的关键技术之一。本文借鉴梯度功能材料(FGM)和纳米复合材料的研究方法,将梯度功能复合的热应力缓解及表面压应力特性和纳米复合的强韧化机制进行有机结合,建立了梯度纳米复合陶瓷刀具材料的宏微观结构模型,系统研究了梯度纳米复合陶瓷刀具材料的制备工艺、力学性能及微观结构、抗摩擦磨损性能、抗热冲击及热疲劳性能等,并对刀具的高速切削性能及其失效机理进行了分析与研究。建立了高速切削过程的非均匀热—力—化学多场耦合模型,明确梯度纳米复合刀具组分及结构的设计目标及要求。提出了梯度纳米复合陶瓷刀具材料的设计基本原则,对刀具材料“宏观”性能进行分解,以适应和抵抗非均匀多场作用,再进行各局部“微观”结构及性能设计,建立了适于高速切削的梯度纳米复合陶瓷刀具材料的宏微观结构模型。采用粉末铺填—热压烧结工艺,制备了Sialon-Si3N4梯度纳米复合陶瓷刀具材料。以刀具材料的综合力学性能最优为目标,优化了结构参数和工艺参数：GSS1力学性能在层厚比e=0.3、烧结温度T=1700℃、保温时间t=60min、压力P=35MPa时取得最优值,其最优的综合力学性能为：抗弯强度σf=980MPa、断裂韧度(表层)KIC=9.54MPa-m1/2、维氏硬度(表层)HV=16.91GPa; GSS2力学性能在e=0.3、T=1750℃, t=60min、P=35MPa时取得最优值,其最优的综合力学性能为：σf=810MPa、KIC=9.33MPa·m1/2、HV=16.98GPa。研究了Sialon-Si3N4梯度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,材料断口处有明显的柱状β-Sialon晶粒和β-Si3N4晶粒的断裂、桥接及拔出等,材料的断裂机制为穿晶断裂和沿晶断裂的混合型。不同尺寸的Si3N4晶粒形成双峰结构,使裂纹扩展时易发生晶粒的桥接和偏转。TEM分析表明,材料的微观结构是晶内/晶间混合型,存在孪晶、位错等特征。这些特征的存在使裂纹扩展时需消耗更多的能量,从而促进了材料强度和断裂韧度的提高。研究了Sialon-Si3N4梯度纳米复合陶瓷刀具材料的抗摩擦磨损性能。结果表明,在相同条件下,梯度陶瓷材料的摩擦系数和磨损率低于均质陶瓷材料的摩擦系数和磨损率。主要的滑动磨损机理是剥落、粘结磨损及磨粒磨损。梯度材料表层存在残余压应力,能够抵抗部分摩擦过程中产生拉应力,从而减小了摩擦力,提高了材料的抗摩擦磨损性能。研究了Sialon-Si3N4梯度纳米复合陶瓷刀具材料的抗热冲击及热疲劳性能。结果表明,梯度纳米复合陶瓷材料的抗热冲击及热疲劳性能均优于对应的均质陶瓷材料。梯度纳米复合陶瓷材料和均质纳米复合陶瓷材料都表现为原始短裂纹的扩展特征,GSS1的临界热震温差为600℃,而GSS2、ST10及SAAT10的临界热震温差为400℃。研究了Sialon-Si3N4梯度纳米复合陶瓷刀具高速切削Inconel718时的刀具寿命、刀具的磨损破损特征及其失效机理等。结果表明,高速车削Inconel718时,刀具耐磨性及寿命在vc=120m/min时较好,此时GSS1的切削性能优于进口刀具KY1540；梯度陶瓷刀具GSS1和GSS2的切削性能优于均质陶瓷刀具ST10和SAAT10的切削性能；刀具主要的失效机理有磨粒磨损、粘结磨损、沟槽磨损及崩刃等。高速铣削Inconel718时,最优速度范围vc=700～900m/min;梯度陶瓷刀具表现出极好的自砺性,崩刃后仍能进行正常切削,其抗沟槽磨损能力高于进口刀具KY4300；梯度陶瓷刀具主要的失效形式是剥落、崩刃及沟槽磨损；机械应力和热应力共同作用是梯度纳米复合陶瓷刀具破损的主要原因；刀具除发生破损外还有明显的磨损特征,磨损机理主要是粘结磨损和磨粒磨损。更多还原

【Abstract】 Nickel-based super alloys have excellent mechanical properties, which have been widely employed in aerospace and nuclear industry. However, they are some characteristics in high speed cutting Nickel-based super alloys process, such as high cutting force, high cutting temperature and low tool life. Therefore, high performance cutting tool is one of the key technologies for high efficiency and high quality machining of Nickel-based super alloys. In this dissertation, the research methods of functionally graded materials (FGMs) and nano-composite materials were borrowed. The macro-micro design model of the graded nano-composite ceramic tool materials was constructed by the combination of the characteristics of thermal stress relief and surface compressive stress of the FGMs and the strengthening and toughening mechanisms of nano-composites. The preparation process, mechanical properties and microstructure, tribologiccal properties and antifriction mechanism, thermal shock and thermal fatigue resistance of the graded nano-composite ceramic tool materials were investigated in the dessertation. And the cutting performance and failure mechanism of the cutting tools were also analyzed and researched.A non-homogeneous thermal-mechanical-chemical multi-field coupling model in high speed cutting process was established. The design objectives and requirements of the tool composite and structure were identified. The basic design principles of the tool materials have been proposed. In order to adapt and resist the action of the non-homogeneous multi-field, at first, the macro properties of the tool materials were tailored. And then the micro structure and properties of each local were designed. Thus the macro-micro design model of the graded nano-composite ceramic tool materials was constructed.According to the basic design principles, two kinds of graded nano-composite ceramic tool materials were fabricated by using layered powder filling and hot pressing technique. The optimum mechanical properties were taken as the objective to optimize the structural parameters and sintering parameters. GSS1material with optimum mechanical properties was sintered under a pressure of35MPa at1700℃for60min, while the thickness ratio being e=0.3. The optimum mechanical properties are a flexural strength σf=980MPa, a fracture toughness (surface layer) KIC=9.54MPa·m1/2and a Vicker’s hardness (surface layer) HV=16.91GPa. GSS2material with optimum mechanical properties was sintered under a pressure of35MPa at1750℃for60min, while the thickness ratio being e=03. The optimum mechanical properties are σf=810MPa, KIC=9.33MPa·m1/2and HV=16.98GPa.Microstructure, crack propagation patterns and fracture mechanisms of Sialon-Si3N4graded nano-composite ceramic tool materials were thoroughly investigated. The results showed that the fracture surfaces were characterized by a mix mode of intergranular and transgranular fracture. A large amount of fracture and pull-out of rod-like β-Si3N4grains and β-Sialon grains were observed on the fracture surface. The difference in Si3N4grain size led to the formation of the interlocked duplex microstructure of β-Si3N4grains and β-Sialon grains. The interlocked duplex microstructure contributed much to the improvement of flexural strength and fracture toughness. Crack deflection and crack bridging were also observed, which can absorb additional amounts of fracture energy. According to the TEM micrographs analysis, a mix of intergranular and transgranular TiC0.7N0.3particles, stress interference stripes and twin structure acted simultaneously in the surface layer of Sialon-Si3N4graded ceramic materials.The tribological properties and antifriction mechanism of Sialon-Si3N4graded nano-composite ceramic tool materials were researched. The results showed that the friction coefficient and the wear rate of the homogeneous reference material were higher than those of the graded material. The wear mechanisms of the graded nano-composites were adhesion, chipping and abrasion. The compressive residual stresses at the surface layer of the graded specimens can counteract partially the tensile stress during sliding wear process, which cause the decrease friction force. Therefore, the graded specimen exhibits improved antifriction performance than that of the homogeneous reference one.The thermal shock and thermal fatigue resistance of Sialon-Si3N4graded nano-composite ceramic materials were also investigated. The results showed that the graded ceramics exhibited higher thermal shock and thermal fatigue resistance. Both the graded ceramics and homogeneous ceramics exhibited the propagation characteristics of short-cracks. The highest critical temperature difference of GSS1was600℃, while the critical temperature difference of GSS2, ST10ans SAAT10was400℃.Tool life, failure patterns and mechanisms of Sialon-Si3N4graded nano-composite ceramic tools were investigated via high speed cutting of Inconel718. The results showed that the highest tool life was obtained at vc=120m/min in turning. GSS1and GSS2showed higher performance than that of ST10and SAAT10respectively. The main failure mechanisms of the graded tools identified in the turning tests involved adhesive wear, abrasive wear, notch wear and chipping. The optimum cutting speed range was700-900m/min in the face milling tests. The graded tool was possessed of a self-sharpening characteristic and showed better cutting performance compared to the homogeneous ones. The resistance to notch wear of GSS1was higher than that of KY4300. The main failure types of the tools in ultra high speed cutting were flaking, chipping and notch wear. The main cause of tool fracture was the combined effect of the mechanical impact stress and thermal stress. Tool wear accompanied with tool fracture took place, with its mechanisms being abrasive wear and adhesive wear.更多还原