【作者】 花国然；

【导师】 黄因慧；

【作者基本信息】 南京航空航天大学 ， 机械制造及其自动化， 2003， 博士

【摘要】 纳米材料表现出许多不同于传统材料的新奇特性，世界范围内掀起了对纳米材料的研究热潮。本文总结了等离子喷涂、激光重熔、纳米材料等技术的研究与发展，提出了在等离子喷涂基础上，利用激光重熔制备纳米改性涂层的新思路；将快速成型应用于纳米材料加工，进行了纳米材料的激光烧结快速成型技术的基础试验研究，所完成的工作主要有： 1．在分析纳米材料已有烧结理论的基础上，结合激光加工中有关热传导理论，建立了纳米材料在激光作用下晶粒尺寸变化的数学模型。对不同加工参数变化下的晶粒直径尺寸进行了数值计算，提出了晶粒长大简化数学模型，对生产或实验中参数的优化或选择，晶粒大小的预测与控制具有实际意义。 2．利用等离子喷涂技术，设计了合理的涂层材料体系，制备了Al₂O₃，NiCrAl／Al₂O₃，NiCrAl／Al₂O₃+13％wt．TiO₂，NiCrAl／WC-Co四种涂层。对四种涂层的组织结构、界面结合能力进行了测试与分析。 3．提出了一种纳米改性涂层的复合工艺方案和技术路线。以纳米为填料，在激光重熔等离子涂层的同时，将纳米材料熔覆在等离子喷涂层表面或渗入等离子喷涂层内部。获得了在该工艺下的纳米改性陶瓷系列涂层，实验验证了该工艺的可行性。 4．采用X射线衍射、扫描电镜、能谱仪等，对陶瓷系列涂层的微观组织与结构进行了详细分析。结果表明，激光重熔后，含纳米的各种涂层致密化程度明显提高，晶粒得到明显细化。研究发现，在各种涂层中纳米颗粒明显填充在粗颗粒间，构成晶间型组织结构；初步测试还表明，在Al₂O₃+13％wt．TiO₂渗入纳米SiC的涂层中，存在Al₂O₃与SiC纳米构成晶内型组织结构的可能性；在Al₂O₃+13％wt．TiO₂渗入纳米Al₂O₃的涂层表面形成了一纯纳米Al₂O₃薄层，构成了纳米-纳米间的复合。同时，研究还发现，分布在粗颗粒间大间隙内的纳米颗粒也构成了微区内的纳米-纳米复合。探讨了这些组织与结构的形成机理以及对涂层性能的潜在影响。测试了纳米颗粒在涂层中的分布及渗入的深度（70μm以上）。验证了各种参数选择的合理性与数学模型的正确性与准确性。 5．对所制备的纳米复合系列陶瓷涂层进行了性能测试。与相应等离子喷涂层相比，硬度测试表明，含纳米Al₂O₃或SiC的各种复合涂层硬度提高了0.6-1.5倍左右；耐磨性测试表明，小功率下单纯的激光重熔耐磨性提高了30％，而纳米渗入后涂层的耐磨性提高了1.3-5倍左右，对耐磨性提高的机理作了进一步的探索和分析研究；耐蚀性测试表明，经激光熔覆纳米渗入后的各种涂层耐蚀性能提高了4倍以上，同时涂层厚度、表面质量对腐蚀性能有影响。 6．基于选择性激光快速成型技术，提出了纳米材料选择性激光烧结制备块体纳米结构材料的新工艺。制备了多种块体或薄层试件，并作了相关测试。研究结果表明，激光烧结在保证晶粒尺寸不致长大，快速制备块体材料上有独特的优势。基于激光扫描的纳米陶瓷涂层和纳米结构块体制备技术的基础研究 7.发现了在激光烧结过程中的SIC纳米线，并对纳米线的形成作了简要分析。 纳米技术与激光技术或快速成型技术的复合，及其在纳米涂层、块体和薄膜制备中的应用是一个新的研究领域，有很多问题需要探索和解决。本课题的研究为这些技术的进一步开发打下了基础，无疑对传统产业的提升，产品质量的改善，新的工艺方法的探索，具有十分重要的意义，并为这些技术在制造业及其它领域的早日应用奠定了理论与实验基础。更多还原

【Abstract】 Because of its magic characters different from that of general material, nano-structured material is cared enthusiastically by the world and numbers of relative researches are carried out to impulse the development of many subjects such as material science, electronics, mechanics and physics. Summarizing the development of plasma spray, laser remelting and nano technology, a new nano modification coating technology based on plasma spray, laser remelting is put forward; Introducing Rapid Prototyping into nano material processing, experimental researches on the selective sintering of nano material are carried out systematically, the main work accomplished and conclusions gotten in this dissertation are presented as follows:1. Analyzing the sintering theory of nano material and the heat conduction theory of laser machining, the mathematic model of grain size growth of nano material in laser sintering is built. The grain sizes of the production under different laser sintering parameters are calculated. Then, according to the calculation, a simplified mathematic model of nano material grain size growth in laser sintering is put forward which could be used in the optimization of sintering parameters, the forecasting of grain size and its control.2. Under the aiding of plasma spraying, series reasonable coating material systems are designed to fabricate alumina, NiCrAl/Al2O3, NiCrAl/Al2O3+13%wt.TiO2, NiCrAl/WC-Co coating. Then, the microstructure, mechanical performance and combination strength of the coating are tested and analyzed.3. A nano-structured coating technology is brought forward. Using nano structured material powder as the coating stuff, laser is employed to remelt the plasma spraying coating basis so that the nano structured powder material could be clad on the surface of the plasma spraying base or infiltrated to the plasma spraying coating. With the technology gotten above, series of nano modifying ceramic coating are fabricated to verify its feasibility.4. The microstructures of the coating series gotten are studied in detail with X ray diffraction, scanning electron microscopy. It is indicated after laser remelting, the density of the nano material infiltrated coating is improved and grain size is decreased greatly. In above researches, it is found that the nano material is distributed among general material grains to form inter-granular structure of the coating. With initial tests, it is shown that nano silicon carbide grains are embedded in the grain of general alumina to form intra-granular structure of the Al2O3+13%wt.TiO2+nano-SiC composite ceramic coating. A pure, thin nano structured alumina layer is manufactured in the surface of Al2O3+13%wtTiO2+nano-Al2O3 composite coating whose combination is nano-nano style. It is also found that the combination between the nano granules in the clearance among grains of the general material is nano-nano style. Thus, it can be concluded that several combination styles exist in the coating structure; its forming mechanism and potential effects on the coating performance are discussed. The distribution and infiltration depth(greater than 70 micron) of the nano material in the coating gotten are tested to prove the technology and the mathematic model built once more.5. Mechanical performances of the ceramic coating manufactured are tested. With the hardness tests, it is indicated the hardness of the nano alumina or nano silicon carbide coating is improved to 1.6-2.5 times as that of the plasma spraying coating. With the wearing tests, it is indicated that low laser power employed, the wearing performance of the coating without nano material increase to 1.3 times as that of the plasma coating, at the same time, the wearing performance of the coating with nano material increase 2.3-6 times as that of the plasma spraying coating, the wearing mechanism is further analyzed. With the erosion tests, it is indicated that the erosion performance of the coating with nano material increase five times as that of the plasma spra更多还原