【作者】 邱利霞；

【导师】 郑伟涛；

【作者基本信息】 吉林大学 ， 材料物理与化学， 2008， 博士

【摘要】 本论文对TiN_x基、ZrN_x基和HfN_x基纳米复合陶瓷材料的形成规律、制备工艺、微观结构、力学、热学和电学性能进行了系统研究与分析。以过渡金属（Ti,Zr,Hf）原粉和六方氮化硼（h-BN）粉为原料,通过机械合金化方法制备出纳米晶TiN_x、ZrN_x和HfN_x粉末。研究了纳米晶TiN_x与ZrN_x和HfN_x的不同形成机制。结合机械球磨和高温高压合成技术,原位固态反应制备出致密的TiN-TiB₂、ZrN-ZrB₂和HfN-HfB₂等几种纳米复合陶瓷材料。研究结果表明,本研究合成的几种纳米复合材料的硬度、热膨胀系数、高温导电性等物理性能与单一相的常规粗晶材料相比明显不同,这是由于纳米材料的特性所引起。对纳米复合陶瓷的高压合成机制、材料微观结构对其力学、热学、电学和光学等性能的影响规律进行了深入研究。更多还原

【Abstract】 The need for new materials becomes more demanding with the developing of modern science and technology. The design and manufacture of advanced materials for applications at high stress and high temperature are one of the most challenging tasks of modern engineering. The primary purpose of researching on ceramics matrix composites is tone up the tenacity and dependability of composite materials.Nanocomposite ceramics are usually used as reinforced and functional nanocomposite. The reinforced nanocomposites are usually prepared by dropping particles or fibers with nanometer scale in matrix and then sintering under vacuum or by precipitating nanophase from matrix. The decrease in grain size will improve the mechanical properties for nanocomposite dramatically. Meanwhile, large number of grain boundaries obvious reduce the second phase capacity which may distribute at grain boundary, and hence the negative influence caused by boundary materials can be minimized. Furthermore, small grain size for composite is useful to improve fracture toughness of nanomaterials, grain boundary sliding is in favor of improving the plasticity of materials. As a result, the intensity, toughness and super plasticity of nanocomposite will greatly improved.Refractory materials such as borides, nitrides, carbides, and silicides are natural candidates for applications due to their exceptional hardness and stability at very high temperatures. Transition metals boride and nitride ceramics have received increasing attention in recent years because of their unique chemical and physical properties. Among such materials, titanium nitride （TiN） is one of particular interest, due to its high hardness, good chemical and thermal stability, excellent corrosion resistance, and relatively high electrical conductivity. Another refractory material, diboride （TiB₂）, also possesses attractive properties such as high melting point, high hardness, good electrical conductivity, and excellent wear and corrosion resistance, which are superior to those of TiC and TiN. In addition, TiB₂ also demonstrates good impact performance. Therefore, the addition of TiB₂ to form TiN-TiB₂ composites has the potential of improving the hardness and toughness of TiN. TiN-TiB₂ composite has useful in the applications such as cutting tools, electrodes, and wear resistance materials.Titanium nitride and diboride can be synthesized using different techniques. For example, TiN is often prprepared by the chemical or physical vapor deposition （CVD or PVD）, while TiB₂ is obtained usually using sintering method by hot isostatic pressing （HIP） or hot pressing （HP）. Therefore, it is difficult to prepare composite featuring both ceramics by conventional techniques. In contrast, some new techniques such as combustion synthesis or self-propagating high-temperature synthesis （SHS） has been employed to produce a variety of advanced materials, including borides, carbides, nitrides, silicides, carbonitrides, intermetallics, etc..In recent years, h-BN has been used to prepareδ-TiN_x or its composites. It has been reported thatδ-TiN_x /TiB₂ composite was prepared by hot pressure reaction between TiH2 and h-BN at high temperature of 1600 oC and self-propagating reaction between Ti and h-BN at high temperature of 1200oC. Theses reports show that the composite of theδ-TiN_x and TiB₂ can be realized using different experimental conditions. However, the mechanisms of formingδ-TiN_x/TiB₂ composite by solid reaction between Ti and BN are still not clear, and need further investigation.In this thesis, the morphological and structural evolution and reaction products after milling or isothermal annealing Ti and BN powders are investigated, and mechanisms of formation ofδ-TiN_x and TiB₂ are discussed based on thermodynamics and kinetics.In this thesis, nanocrystallineδ-TiN_x is prepared using mechanical milling of the mixture of Ti and BN powders or annealing of the milled mixture. Theδ-TiN_x is formed by diffuse reaction between Ti and a-BN, rather than self-propagating reaction during milling process, in which Ti firstly reacts with N in a-BN to form amorphous Ti-N alloy, and then a-Ti-N is crystallized, formingδ-TiN_x. This process is driven by local pressure and local temperature induced by collisions between balls or ball and vial.During annealing,δ-TiN_x can be obtained by two steps: 1. below 600℃, a small amount ofδ-TiN_x is formed through crystallization of a-Ti-N in a milled mixture. 2. above 600℃, Ti（N） solid solutions with higher N content than solubility limit, 23 at. % N, will decompose into Ti （N） solid solution with the solubility limit 23 at. % N andδ-TiN_x. No TiB₂ is observed during both milling and annealing. This can be ascribed to that the heat of formating TiN is more negative than that of TiB₂ based on thermodynamics, and the solubility limit is zero for B in Ti, but N can be solved into Ti based on reaction dynamics.TiN/TiB₂ composite materials have been obtained using mechanical milling and subsequent high-pressure （4-5GPa） and high temperature （1200-1300℃） treatment. It is found that pressure promotes the formation of TiB₂ in TiN/TiB₂ composite. At ambient pressure,δ-TiN_x is only formed by sintering Ti and a-BN at 900℃, while TiB₂ are obtained at 5 GPa and 1300℃. It is found that an increase in pressure or temperature may reduce pores in composite, increases the density of composite, and makes the grains uniform. An increase in temperature or sintering time can increase the grain size in composite.The obtained TiN/TiB₂ nanocomposite exhibits good mechanical and electrical properties, whose HV hardness is 20 GPa, and temperature coefficient resistivity （TCR） is 1×10^-4℃^-1, which is smaller than that of either TiN or TiB₂ (6×10^-4℃^-1 ). Nanocrystallineγ-ZrN_x is prepared by mechanical milling the mixture of Zr and BN powder or sintering the mixture milled for 20 h.γ-ZrN_x is formed by diffuse reaction between Zr and a-BN, rather than self-propagating reaction, during milling. Zr reacts with N in a-BN to form Zr （N） solid solution, and then Zr （N） decomposes intoγ-ZrN_x, driven by local pressure and local temperature induced by collisions between balls or ball and vial. At sintering at 1050 oC, Zr （N） solid solutions with higher N content than solubility limit （21 at. %） decompose into Zr （N） solid solution with the solubility limit andγ-ZrN_x. No ZrB₂ is observed during both milling and annealing. This can be attributed to that more heat of forming ZrN is released than that of ZrB₂ based on thermodynamics, and the solubility limit is zero for B atoms in Zr matrix. However, N atoms can be solved into in Zr matrix based reaction dynamics.In this thesis, nanocrystalline HfN_x is also synthesized using mechanical milling a mixture of Hf and h-BN powders, and the synthesis process is controlled by diffuse reaction, rather than self-propagating reaction. Nanocrystalline Hf reacts with N to formα-Hf（N） solid solution, and thenα-Hf（N） decomposes into HfN_x, driven by local pressure and local temperature induced by collisions between balls or ball and vial.更多还原