【作者】 章晓波；

【导师】 刘宁；

【作者基本信息】 合肥工业大学 ， 材料学， 2008， 博士

【摘要】 本文采用粉末冶金方法制备了不同成分及粒度的Ti（C,N）基金属陶瓷。研究了化学成分、粉末粒度及渗硼处理对Ti（C,N）基金属陶瓷显微组织和力学性能的影响。并研究了纳米改性Ti（C,N）基金属陶瓷的抗热震性能和切削性能。首先,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、抗热震性能及切削性能。重点概述了金属陶瓷的制备方法,包括陶瓷相粉末的制备方法、成形方法、烧结方法等,并对比了各种方法的优缺点。总结了Ti（C,N）基金属陶瓷的显微组织和力学性能的表征方法以及影响因素,同时指出了化学成分、制备工艺、粉末粒度对Ti（C,N）基金属陶瓷显微组织和力学性能的具体影响。分析了Ti（C,N）基金属陶瓷的应用前景及本文的研究目的和意义。其次,对不同Mo含量的超细Ti（C,N）基金属陶瓷组织和力学性能进行了研究。研究发现Mo以固溶体（Ti,Mo,W）（C,N）的形式存在于Ti（C,N）基金属陶瓷中,该固溶体与Ti（C,N）的晶体结构相同、点阵常数相近;Mo的加入可细化晶粒、提高材料的相对密度、抗弯强度和硬度,固溶强化和细晶强化为主要强化机制。研究了ZrC含量对TiC基金属陶瓷显微组织和力学性能的影响。由于金属相对陶瓷相ZrC的润湿性不理想,导致材料相对密度下降;随着ZrC含量的不断增加,在TiC基金属陶瓷中逐渐形成富Zr的碳化物固溶体,并且显微组织细化,材料的强度与硬度有不同程度的降低,但是对完全致密材料的理论抗弯强度的计算结果表明,ZrC的加入量在一定范围内可大大提高材料的强度。随着Mo、WC的相继加入,发现材料成分为10%TiC-40%ZrC-14%Mo-15%WC-20%Ni-1%C的金属陶瓷显微组织由白色和灰色球状晶粒组成,同时存在相当数量的微孔洞和微裂纹。由于无芯晶粒增韧、微裂纹增韧和微孔洞增韧的作用,该试样的断裂韧性高达16.6 MPa·m^1/2,比未加ZrC的金属陶瓷断裂韧性高出51%。此外,还研究了Zr对Ti（C,N）基金属陶瓷组织和断裂韧性的影响。结果表明Zr的加入使组织中无芯晶粒增多,晶粒细化,由于无芯晶粒增韧、裂纹偏转和分叉增韧等机制改善了Ti（C,N）基金属陶瓷的断裂韧性。再次,研究了不同金属相（20%Ni、10%Co-10%Ni、20%Co）对纳米改性Ti（C,N）基金属陶瓷显微组织、力学性能和抗热震性能的影响。发现纳米TiN的加入可明显改善金属陶瓷的力学性能,纳米改性的金属陶瓷中出现新的组织结构——灰芯结构,金属相Co有利于提高Ti（C,N）基金属陶瓷的硬度,而金属相Ni能提供更高的抗弯强度和断裂韧性。采用急冷-强度法、压痕-急冷法以及对试样端部预制缺口法分别测试了纳米TiN改性Ti（C,N）基金属陶瓷的抗热震性能。三种不同测试方法均表明,在三组不同金属相的试样中,相对于金属相为20%Co的金属陶瓷而言,金属相为10%Co-10%Ni的抗热震性能较好,20%Ni的抗热震性能最好。金属陶瓷的抗热震性能与材料的强度及断裂韧性密切相关,强度及韧性越高,抗热震性能越好。并且试验结果和理论计算吻合得很好。此外,纳米TiN改性的Ti（C,N）基金属陶瓷经过热震后,即便抗弯强度急剧降低,其硬度衰减率仍不到1%,表明材料的硬度受热震影响很小。最后,对纳米改性Ti（C,N）基金属陶瓷进行了表面渗硼处理。结果表明,渗硼处理后金属陶瓷表面组织中生成了一系列硼化物,其表面显微硬度明显升高。并且对比了渗硼前后Ti（C,N）基金属陶瓷刀具在不同速度下的切削性能,结果表明在相对较低的切削速度下,渗硼处理后的Ti（C,N）基金属陶瓷刀具的使用寿命要比未经渗硼处理的刀具寿命长。更多还原

【Abstract】 Ti（C, N） based cermets with different compositions and powder sizes were made by powder metallurgical method. The effects of chemical composition, powder size and boronizing on the microstructure and mechanical properties of Ti（C, N） based cermets were studied. Thermal shock resistance and cutting performance of nano modified Ti（C, N） based cermets were also studied.Firstly, the development history, fabricating method, microstructure, mechanical properties, thermal shock resistance and cutting performance of Ti（C, N） based cermets were introduced. The fabricating methods of cermets, including the methods of preparing ceramic phase powder, formation, sintering and so on, were outlined specially; the advantage and disadvantage of each method were also compared. The conducted methods and influenced factors on the microstructure and mechanical properties of Ti（C, N） based cermets were summarized. Simultaneously, the detailed influences of chemical composition, fabricating process, powder size on the microstructure and mechanical properties were pointed out. Furthermore, the purpose and significance of this desertation, as well as the application future of Ti（C, N） based cermets, were analyzed.Secondly, the effect of molybdenum （Mo） content on the microstructure and mechanical properties of ultra-fine grade Ti（C, N） based cermets were researched. It shows that Mo exists in Ti（C, N） based cermets as the form of （Ti, Mo, W）（C, N） solid solution, and the solid solution has the same crystal structure and similar lattice parameter as Ti（C, N）. The addition of Mo refines grains, improves the relative density, transverse rupture strength and hardness. The solid solution strengthening and refining strengthening are responsible for the strengthening mechanisms. Moreover, the effect of zirconium carbide （ZrC） content on the microstructure and mechanical properties were studied. It is found that the relative density of materials declines due to the imperfect wettability of metallic phase to ZrC. Zr-rich carbide solid solution is gradually formed in TiC based cermets with increasing ZrC content, and the microstructure gets finer, strength and hardness declines. However, the results calculated according to the full density show that transverse rupture strength can be improved significantly with proper addition of ZrC. Bright and gray spherical grains, as well as micro pores and cracks, are found in cermets with the chemical constitute of 10%TiC-40%ZrC-14%Mo-15%WC-20%Ni-1%C. The fracture toughness of the cermets is 16.6 MPa·m^1/2, which is 51% higher than those without ZrC. Coreless grain toughening, micro crack toughening and micro pore toughening are responsible for the improved toughness. Furthermore, the influence of Zr on microstructure and fracture toughness was also studied. It is found that coreless grains increase and grains get finer. Fracture toughness of Ti（C, N） based cermets is improved due to coreless grain toughening, crack deflection and branching toughening mechanisms.Thirdly, the effect of different metallic phases （20%Ni、10%Co-10%Ni、20%Co） on the microstructure, mechanical properties and thermal shock resistance of nano modified Ti（C, N） based cermets were studied. It is found that nano TiN can improve mechanical properties of cermets, and a new structure which can be named grey core structure is found in cermets. In addition, cobalt can exhibit higher hardness and nickel can offer higher transverse rupture strength and hardness. Quenching-strength test, indentation-quench test and notches pre-made in the end of samples are operated to study the thermal shock resistance of nano TiN modified Ti（C, N） based cermets. All the results obtained by these three methods show that the thermal shock resistance of cermets with 10%Co-10%Ni is better and that of cermets with 20%Ni is the best compared with cermets with 20%Co. The thermal shock resistance of cermets depends on strength and fracture toughness of materials, the higher strength and fracture toughness are, the better thermal shock resistance is. The experimental results have a good agreement with the theoretical calculated results. Moreover, the decline rate of hardness of nano modified Ti（C, N） based cermets after thermal shock is less than 1% even though the strength decreases sharply. This result shows that the effect of thermal shock on hardness of cermets is very slight.Finally, boronizing treatment was operated on the surface of nano modified Ti（C, N） based cermets. The experimental results show that a series of borides are presented on the surface of cermets and the microhardness of surface increases significantly. Furthermore, the cutting performances of Ti（C, N） based cermet cutters were compared before and after boronizing at the various cutting speeds. The results show that the tool life of boronized Ti（C, N） based cermet cutters exhibit the longer tool life than those without boronizing at lower speed.更多还原