【作者】 林锋；

【导师】 蒋显亮；

【作者基本信息】 中南大学 ， 材料加工工程， 2004， 硕士

【摘要】 ZrO₂具有低的热导率和与高温合金相近的热膨胀系数，是制备高温下使用的热障涂层的理想材料。Y₂O₃用来稳定ZrO₂中的四方相，减少ZrO₂高低温使用时相转变产生的大的体积变化，从而降低裂纹产生的可能性。热等离子体喷涂是制备热障涂层的最主要办法。常规微米级陶瓷涂层脆性大，而纳米陶瓷脆性降低。液相法制备出来的ZrO₂／Y₂O₃纳米粉末由于单个粒子质量太小，不能直接用来进行热喷涂。 本项研究的目的就是制备ZrO₂-8％Y₂O₃大颗粒球形纳米粉末和热障涂层，且使其可以保持原始粉末的纳米结构。首先采用喷雾干燥和热处理的办法对原始ZrO₂-8％Y₂O₃纳米粉末进行再处理，然后将经过再处理的纳米粉末在不同的等离子体喷涂条件下喷涂制备成纳米结构热障涂层。利用光学显微镜和扫描电镜分析粉末粒径大小、颗粒形貌、涂层显微组织，用X-ray衍射分析原始粉末、再处理粉末和涂层的相组成，用热重-差热分析仪对纳米团聚体粉末进行热分析，并测量粉末的松装密度、振实密度及流动性。结果表明：ZrO₂-8％Y₂O₃原始纳米粉末经过再处理后近似球形，粒径在10-100μm之间，仍为纳米结构。粉末流动性好、振实密度高，可以用来热喷涂制备纳米结构热障涂层。采用再处理的纳米粉末进行等离子体喷涂制备的涂层厚度均匀，没有明显的层状结构。等离子体喷涂制备涂层的过程中发生了单斜相向四方相的转变，涂层中只有四方相和立方相存在。这种热障涂层是一种纳米-微米结构复合涂层。更多还原

【Abstract】 Zirconia has low thermal conductivity and high thermal expansion coefficient close to nickel-based superalloy substrate. It is an ideal material used as thermal barrier coatings applicable to high temperatures. Plasma spraying is the most often used method for depositing thermal barrier coatings. Conventional ceramic coatings, consisted of micro-lamellae, are brittle. However, nanostructured ceramic materials have low brittleness and improved toughness. ZrO2/Y2O3 nanocrystalline powder, prepared by the method of solution precipitation, can not be directly used as thermal spray feed stock, because of its low mass of individual nanocrystalline particle.This study was to prepare ZrO2-8%Y2O3 agglomerated nanocrystalline particles and to form nanostructured thermal barrier coatings by plasma spraying under varied conditions. Spray drying and heat treatment were used to reprocess the nanocrystalline ZrO2-8%Y2O3 powder purchased from market. Optical microscopy and scanning electron microscopy were used to observe the morphology and particle size of the starting nanocrystalline powder and the agglomerated powder as well as to examine the microstructure of the thermal barrier coatings. X-ray diffraction was used to analyze the crystal structure of the powders and the coatings. Thermal gravimetric analysis and diffraction thermal analysis were also conducted. In addition, free holding density, tap density, and flow ability of the powders were measured. Experimental results show that the large agglomerated particles are spheric, have the size of 10-100um, and remain original nanostructure. Such powders with good flow ability and high tap density are suitable for thermal spray used in the deposition of nanostructured thermal barrier coatings. Experimental results of the thermal barrier coatings deposited from the agglomerated nanocrystalline powders with different particle size distributions (<45um and 45~75um) demonstrate that the thickness of the as-sprayed coatings is uniform, and the lamellae always found in conventional microstructured coatings are not obvious in these nanostructured coatings. The porosity of the best coating sample is approximately 7%. TheHImonoclinic zirconia phase existed in the starting powder has been transformed into tetragonal phase after the plasma spraying. The nanostructured coatings are composed of tetragonal and cubic phases. It is revealed that these coatings consist of a large fraction of nanostructure transformed from unmelted agglomerates and a mall fraction of microstructure formed from melted agglomerates in plasma.更多还原