【作者】 詹斌；

【导师】 刘宁；

【作者基本信息】 合肥工业大学 ， 材料学， 2013， 博士

【摘要】 本文采用粉末冶金法制备了不同成分及粒度的Ti（C, N）基金属陶瓷材料和刀具。研究了粉末粒度、球磨工艺、晶粒生长抑制剂、渗硼处理对Ti（C, N）基金属陶瓷显微组织和性能的影响。并研究了几何角度对Ti（C, N）基金属陶瓷刀具切削性能的影响。介绍了Ti（C, N）基金属陶瓷的发展过程、制备方法、显微组织、力学性能、抗热震性能和切削性能。其中，重点概述了金属陶瓷的制备方法，包括混料、成形和烧结方法，总结了Ti（C,N）基金属陶瓷的显微组织特征、力学性能的测试方法，并指出了化学成分、粉末粒度和制备工艺对Ti（C, N）基金属陶瓷显微组织和力学性能的具体影响。介绍了渗硼技术的发展过程、方法及工艺和渗硼层的组织特点。其中，对几种常见的渗硼方法及其优缺点和各类材料的渗硼层组织特点进行了重点概述。另外，还介绍了金属切削有限元模拟技术的发展概况和应用价值。分析和总结了本文的研究目的和意义。研究了硬质相粉末粒度对Ti（C, N）基金属陶瓷组织和力学性能的影响。结果表明，与采用微米TiC制备的金属陶瓷材料相比，用纳米TiC制备的材料晶粒更细小，硬质相与粘结相的分布更均匀；以“纳米TiC+微米TiN”为硬质相粉末制备的材料中形成一种粗大的“灰芯-灰壳”结构晶粒，这种晶粒的形成是由微米TiN与纳米TiC颗粒在液相中的饱和溶解度存在巨大差异所引起；以“微米TiC+纳米TiN”和“纳米TiC+纳米TiN”制备的金属陶瓷分别具有最好的综合力学性能和最高的硬度。研究了球磨工艺对Ti（C, N）基金属陶瓷组织和性能的影响。研究发现在球料比较小、球磨时间较短或球磨转速较低的条件下，金属陶瓷材料中形成一种灰芯结构晶粒；球料比的增大使硬质相晶粒逐渐细化，组织趋于均匀，而材料的相对密度降低。适当增大球料比有利于提高材料的抗弯强度和硬度，改变球料比对断裂韧性影响不大；球磨时间的增加使组织趋于均匀，硬质相晶粒细化。随着球磨时间的增加，相对密度和硬度呈先增大后减小趋势，并都在球磨时间为11h时达最大值。增加球磨时间使抗弯强度和断裂韧性升高；增大球磨转速使组织的均匀程度提高，但不能细化硬质相晶粒。随球磨转速的增大，相对密度和硬度先增大后减小，断裂韧性逐渐升高。研究了晶粒生长抑制剂对Ti（C, N）基金属陶瓷组织和性能的影响。发现添加VC、Cr₃C₂以及复合添加VC/Cr₃C₂都使金属陶瓷的晶粒细化，但也导致材料的相对密度降低。VC添加量为1.5%时，硬质相晶粒最细。随着VC添加量的增加，抗弯强度和断裂韧性先升高后降低，并且都在VC添加量为1%时达到最大值。硬度随VC添加量的增加而先降低后升高，在VC添加量为1%时达到最小值；添加1.5%Cr₃C₂时，金属陶瓷的晶粒最细。添加金属陶瓷的抗弯强度、硬度和断裂韧性都随Cr₃C₂添加量的增大而呈现先升高后降低的趋势，抗弯强度和断裂韧性都在Cr₃C₂添加量为1%时达到最大值，硬度在Cr₃C₂添加量为1.5%时达到最大值；添加0.75VC-0.25Cr₃C₂时，金属陶瓷的晶粒最细。添加0.25VC-0.75Cr₃C₂时，材料的抗弯强度和硬度达到最大值，添加0.5VC-0.5Cr₃C₂时，断裂韧性达到最大值。研究了渗硼处理对Ti（C, N）基金属陶瓷显微组织、力学性能、抗热震性能以及切削性能的影响。研究发现经渗硼后，Ti（C, N）基金属陶瓷表层形成由硼化物层、扩散层和基体区组成的渗硼层组织，厚度约为100¹40μm；渗硼处理使金属陶瓷的抗弯强度降低39.8%，表面硬度升高48.7%；渗硼处理使金属陶瓷的热震残留强度降低，使金属陶瓷表面的热震裂纹扩展速率增大。在热震温差较小的条件下，渗硼金属陶瓷缺口裂纹的孕育期长于未渗硼金属陶瓷；渗硼金属陶瓷刀具在较低切削速度（vc=200m/min）下的使用寿命明显长于未渗硼刀具，而在较高切削速度（vc=300、400m/min）下的使用寿命比未渗硼刀具短。利用有限元模拟和切削实验的方法研究了几何角度对纳米TiN改性和超细晶Ti（C, N）基金属陶瓷刀具切削性能的影响。结果表明，增大前角使主切削力、前刀面及后刀面的最大等效应力、最高温度值和磨损程度减小，并且，前角为-5°时的前、后刀面最高温度值和磨损程度最小；增大后角使主切削力、前刀面及后刀面的最高温度值和磨损程度减小，后角的变化对前、后刀面的最大等效应力影响不大；两种金属陶瓷刀具的最佳前角和后角都分别为：-5°和11°，超细晶Ti（C, N）基金属陶瓷刀具的使用寿命明显比纳米TiN改性Ti（C, N）基金属陶瓷刀具长。切削实验与有限元模拟方法得出的结果吻合较好，从而验证了有限元模型的正确性。更多还原

【Abstract】 Ti（C, N）-based cermets with different compositions and grain sizes were prepared by powdermetallurgy method. The effects of powder size, ball milling parameter, grain growth inhibitor andboronizing on the microstructure and properties of Ti（C, N）-based cermets were researched. Theeffects of geometric angles on cutting performance of Ti（C, N）-based cermet tools were also studied.The development history, fabricating methods, microstructure, mechanical properties, thermalshock resistance and cutting performance of Ti（C, N）-based cermets were introduced. Thefabricating methods of cermets, including the methods of mixing, formation and sintering wereoutlined specially. The characteristics of microstructure and test methods of mechanical propertieswere summarized, and the detailed influences of chemical composition, powder size and fabricatingprocess on the microstructure and mechanical properties were pointed out. The development historyand technology methods of boronizing as well as microstructure of boronizing layer were introduced.Some common boronizing methods and their merits and demerits as well as the characteristics ofboronizing layer microstructure were outlined specially. Furthermore, the development situation andapplication value of finite element simulation technique of metal cutting were introduced. Thepurpose and significance of this desertation were also analyzed and summarized.The effect of hard particle size on microstructure and mechanical properties of Ti（C, N）-basedcermets were studied. The results show that compared with the cermets made from micron TiC, thecermets made from nano TiC possess finer grains and more homogeneous distribution of hard phaseand binder phase. There are coarse grains with the structure of “grey core-grey rim” in the cermetsmade from “nano TiC+micron TiN”, which is due to the great difference between the saturatedsolubility of micron TiN and nano TiC. The cermet made from “micron TiC+nano TiN” and “nanoTiC+nano TiN” possesses the best comprehensive property and the highest hardness respectively.The effect of ball milling parameter on microstructure and mechanical properties of Ti（C,N）-based cermets was researched. The research shows that under the condition of smallerball-to-powder weigth ratio, shorter milling time or lower milling rate, the grain with grey coreforms in cermets. The increase of ball-to-powder weigth ratio leads to the refinement of grains andhomogenization of microstructure, but results in the decrease of relative density. Appropriatelyincreasing ball-to-powder weigth ratio is helpful to promote the TRS and hardness, and the change of ball-to-powder weigth ratio does not influence fracture toughness hardly. The increase of millingtime makes the distribution of microstructure more homogeneous and the grains finer. With theincrease of milling time, the relative density and hardness increase at first and then decrease, andthey both reach the maximum when the milling time is11h. The increase of milling time results inthe increase of TRS and fracture toughness. The increase of milling rate makes the microstructuremore homogeneous, but is not useful to refine grains. With the increase of milling rate, the relativedensity and hardness increase at first and then decline, meanwhile, the fracture toughness increases.The effect of grain growth inhibitor on microstructure and mechanical properties of Ti（C,N）-based cermets was studied. It shows that the addition of VC, Cr₃C₂and VC/Cr₃C₂not only causethe refinement of grains, but also induce the decrease of relative density. The grain sizes of cermetadded1.5%VC are the finest. The TRS and fracture toughness increase at first and then decreasewith the increase of VC addition, and both reach the maximum when1%VC is added. With theincrease of VC addition, the hardness of cermet decrease at first and then increase, and the minimumis caused by1%VC. When1.5%Cr₃C₂is added, the grains of cermet are the finest. The TRS,hardness and fracture toughness all increase at first and then decrease with the increase of Cr₃C₂addition. The TRS and fracture toughness both reach the maximum for the addition of1%Cr₃C₂,and the hardness increases to the maximum because of the1.5%Cr₃C₂being added. The addition of0.75VC-0.25Cr₃C₂results in the TRS and hardness both increasing to the maximum, and theaddition of0.5VC-0.5Cr₃C₂causes the the maximum of fracture toughness.The effect of boronizing on microstructure, mechanical properties, thermal shock resistance andcutting performance of Ti（C, N）-based cermets was studied. The research shows that a boronizinglayer composed of boride layer, diffusion layer and substrate zone has formed in the surface layer ofTi（C, N）-based cermets boronized, which is about100¹40μm thick. Boronizing decreases the TRSby39.8%and increases the hardness by48.7%. The residual strength of thermal shocked cermetdecreases because of boronizing. The thermal shock crack propagation rate of boronized cermet ishigher than that of the unboronized cermet. When thermal shock temperature difference is small, theinduction period of surface crack at the notch of boronized cermet is longer than that of theunboronized cermet. The life of boronized cermet tool is longer than that of unboronized cermet toolused in the lower speed（vc=200m/min） cutting, while the life of boronized cermet tool is shorterthan that of unboronized cermet tool used in the higher speed（vc=300、400m/min） cutting.The effect of geometric angles on the cutting performance of nano TiN modified Ti（C, N）-basedcermet tools and ultra-fine Ti（C, N）-based cermet tools was researched by the method of FEMsimulation and cutting experiment. The results show that the increase of rake angle cause thedecrease of main cutting force as well as max effective stress, the highest temperature and wear degree of rake face and flank face. When the rake angle is-5°, the highest temperature and weardegree of rake face and flank face are the lowest. The main cutting force as well as the highesttemperature and wear degree of rake face and flank face decrease because of the increase ofclearance angle, while the max effective stress is not obviously influenced by the change ofclearance angle. The most appropriate rake angle and clearance angle of the two cermets both are-5°and11°respectively. The life of ultra-fine Ti（C, N）-based cermet tools are remarkably longer thanthat of the nano TiN modified Ti（C, N）-based cermet tools. The cutting experiment resultscorrespond with the FEM simulation results, which indicates that the validity of finite elementmodels is verified.更多还原