【作者】 胡利方；

【导师】 孟庆森；

【作者基本信息】 太原理工大学 ， 材料科学与工程， 2013， 博士

【摘要】 本文将机械合金化和自蔓延高温合成技术相结合提出了电场激活压力辅助燃烧合成技术(Field activated pressure assisted synthesis, FAPAS)。通过FAPAS工艺分别制备了(TiC-TiB2)/Ni-TiAl-Metal复合材料和(AlMgB14-TiB2)-Metal复合材料。复合材料的界面结构是决定合成材料力学性能的关键因素,为了研究异种材料的界面扩散情况,进行了异种金属材料Ti-Ni和镁合金AZ31B-Cu的扩散连接实验。通过OM(光学显微镜),SEM(扫描电子显微镜),TEM(投射电子显微镜),XRD(X射线衍射仪),维氏硬度计和万能材料试验机重点研究了在多物理场作用下(温度场、电场和应力场)复合材料的界面微观结构和扩散动力学问题,并分析了不同物理场参数对复合材料界面微观组织结构和力学性能的影响。利用B4C粉、Ti粉和Ni粉原位合成了(TiC-TiB2)/Ni复合陶瓷,合成的陶瓷层结构均匀细密,TiB2与TiC细小颗粒均匀地分布在Ni基体中。通过Al、Ti粉体反应形成金属间化合物放热的同时实现了复合陶瓷(TiC-TiB2)/Ni与Ti、Ta金属基板的连接,结合界面扩散充分,组织致密。研究发现电流和压力是影响(TiC-TiB2)/Ni复合陶瓷晶粒大小的主要物理参数。电流能够提高复合陶瓷烧结过程中的形核率,机械压力能够促进陶瓷颗粒在烧结过程中的破碎和重排,因此随电流和辅助压力的增大,复合陶瓷的晶粒变得均匀致密。对(TiC-TiB2)/Ni复合陶瓷的摩擦学行为进行了系统研究,分析了陶瓷相含量、摩擦载荷、摩擦温度和摩擦速度对复合陶瓷摩擦学行为的影响,研究结果表明摩擦系数随温度,载荷和速度的增加而变小,磨损率随温度的升高而降低,随载荷和速度的提高而增大。在高温摩擦过程中摩擦表面形成了TiO2、B2O3和Fe2O3润滑薄膜,薄膜量随摩擦温度,载荷和速度的增大而增多,在高温环境中(TiC-TiB2)/Ni复合陶瓷的摩擦机制主要由界面氧化反应所决定。磨损实验表明含陶瓷相(TiC-TiB2)为80%的复合陶瓷具有较好的摩擦磨损性能。采用上述实验方法,通过FAPAS技术利用B、Mg、Al和TiB2粉体合成了超硬材料AlMgB14-TiB2并同步实现了与金属基板Mo和Nb的连接。研究发现B元素在材料合成和连接过程中有比较显著的扩散特点,形成了界面硬度从金属基体到AlMgB14-TiB2层呈递增的特征。AlMgB14-TiB2表层的硬度最高达到了3801HV1.0,连接界面硬度在2000HV1.0左右。FAPAS实验条件下连接界面金属间化合物的形成机制和力学性能的研究对提高陶瓷-金属异质材料连接和复合材料制备工艺具有理论意义。FAPAS条件下Ti-Ni的扩散界面按时间依次生成了TiNi3、Ti2Ni和TiNi。 TiNi3、Ti2Ni和TiNi金属间化合物的厚度随实验温度的升高和扩散时间的增长而增加,厚度随时间的增长符合抛物线规律,其中温度场对TiNi形成的影响较大。剪切实验表明所形成金属间化合物的抗剪切强度排序为TiNi>Ti2Ni>TiNi3,断裂形式为脆性沿晶断裂,断裂位置与中间生成物的厚度存在一定的对应关系。FAPAS条件下镁合金AZ31B-Cu的扩散连接表明界面扩散层主要由Cu2Mg和Mg2Cu组成。温度是影响AZ31B-Cu扩散的主要参数,元素Al在高温下具有较高的扩散能力,进而能够影响界面生成相的种类和宽度。元素Al主要通过形成MgAlCu化合物的形式影响界面的微观组织结构。总之,异种金属的扩散实验研究表明,电流可以显著降低扩散激活能,促进界面反应。通过异种金属电场激活扩散连接实验,提出了“微区界面扩散相图”的概念。界面扩散相图是两种材料在界面微区发生局部扩散反应时界面新相的生成规律,微区界面扩散相图的提出有助于深入了解和揭示外加物理场条件下异种材料的连接冶金学规律。更多还原

【Abstract】 In this paper, the Field activated pressure assisted synthesis (FAPAS) was developed based on the Metal Alloy (MA) and Self-propagating-High-temperature Synthesis (SHS). The composite materials of (TiC-TiB2)/Ni-TiAl-Metal and (AlMgB14-TiB2)-Metal was fabricated by FAPAS. The interfacial structure was the key factor to determine the mechanical properties of the composite materials. In order to invertigate the diffusion process of the dissimilar materials, the Ti and Ni, Mg and Cu were also bonded together by FAPAS. The OM, SEM, TEM, XRD, hardness tester and materials testing machine was used to investigated the diffusion process and the interfacial microstructure. The effect of the testing parameters on the mechanical propertied of the composite materials was also analyzed.(TiC-TiB2)/Ni composite ceramic, the top layer of the composite materials, was prepared in-situ by the combustion synthesis process using Ni, Ti and B4C powders as raw materials. The intermetallic of TiAl was synthesized using Ti and Al as raw materials and at the same time, the composite ceramic of (TiC-TiB2)/Ni was bonded with metal substrate of Ti or Ta. The bonding interface was well and no defects were found at the interface. Fine grained particles are distributed homogeneously in the Ni matrix, with grain size ranging from0.2to1.0μm, which indicates that the full reaction has been completed during the experiments. It had been found that the current and pressure affected the microstructure of the composite ceramics substantially. TiB2and TiC particles comminuted to be broken up and rearranged due to the applied pressure and the current can increase the nucleation rate during the synthesis process. The friction and wear properties of the (TiC-TiB2)/Ni ceramic were evaluated by sliding against a GCr15disk at temperatures from ambient up to400℃. The experimental results showed that the friction coefficient of the (TiC-TiB2)/Ni ceramic decreased with increasing testing temperature, load, and sliding speed. However, the loss rate decreased at higher temperature and increased at higher load and higher sliding speed. The oxide films of Fe2O3, TiO2, and B2O3formed during the friction process played an important role in lubrication, which results in a smaller friction coefficient. The wear resistance of composites containing80%(TiC-TiB2) compared to70%(TiC-TiB2) shows a mild enhancement due to the high strength and high hardness of TiC and TiB2.Using powders of B, Mg, Al and TiB2as raw materials, the ultra hard material AlMgB14-TiB2was fabricated and bonded with Mo and Nb metal substrate at one step. It was indicated that the B diffused into the metal substrate more easily. There was a gradual increase in hardness from the metal substrate to AlMgB14-TiB2. The hardness increased from about2000HV1.0at the bonding interface to about3801HV1.0at AlMgB14-TiB2.Three intermetallic compounds were formed at the interface of Ti-Ni diffusion couples, i.e. Ti2Ni、 TiNi and TiNi3. The thickness of the three compounds increased as the diffusion temperature increased. Testing results showed a parabolic growth for all the three phases with the increase of the diffusion time. Compared with Ti2Ni and TiNi3, the TiNi compound was more easily affected by the diffusion temperature. The shear experiments showed that the fractures were mostly brittle, i.e. inter-crystalline. The fracture occurred at TiNi3when the Ti2Ni was thin, but it occurred at Ti2Ni when some TiNi3was consumed by Ti atom to form TiNi. The order of the mechanical properties of the three intermetallic compounds can be list as follows:TiNi>Ti2Ni>TiNi3. Two intermetallic compounds were formed at the interface of magnesium alloy-Cu diffusion couples, i.e. Cu2Mg and Mg2Cu. Just as the Ti-Ni experimental results, magnesium alloy-Cu interfacial testing results also show a parabolic growth for all two phases with the increase of the diffusion time. The diffusion rate of the Al was affected by the temperature substantially. Almost no MgAlCu formed at the interface at450℃, but it would formed at475℃, and the thickness of the MgAlCu compound would increase as the diffusion time increased. Eutectic layers was formed at500℃, and the distribution of the eutectic layer increased as the diffusion time increased.Compared with the traditional diffusion bonding, electric current can decrease the diffusion energy and promote the reaction dramatically. The diffusion energy of Ti2Ni, TiNi and TiNi3reduced by60%,48%and45%respectively. As for magnesium alloy-Cu couples, compared the diffusion energy of700A and750A respectively, the diffusion energy reduced by36.1%.Based on the experimental result, the interfacial diffusion phase diagram was depicted. The interfacial diffusion phase diagram is quite different form the equilibrium phase diagram. It was formulated to show the formation order of the phases of the diffusion couples. And it’s of great importance to explore the mechanism of the diffusion process.更多还原