【作者】 李崇桂；

【导师】 王铀；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2007， 硕士

【摘要】 本文采用等离子喷涂在TC4钛合金基体上分别制备了常规Metco130涂层及纳米结构Al₂O₃-13wt%TiO₂涂层,并利用CO2激光器对所制备的涂层进行了激光重熔处理,研究了激光重熔对涂层组织结构及性能的影响。采用X射线衍射分析（XRD）、扫描电镜分析（SEM）、能谱分析（EDAX）、显微硬度试验等方法对激光重熔前后的Al₂O₃-13wt%TiO₂涂层进行了组织结构及性能测试与分析。试验结果表明,采用等离子喷涂方法制备的涂层与基体形成了较好的机械结合,纳米结构涂层的孔隙率低于Metco130涂层。激光重熔后,获得了表面平整,内部无明显裂纹的激光重熔层。等离子喷涂层的缺陷得以消除,重熔层孔隙率降低,致密度得到了较大提高,且重熔层与基体形成了冶金结合,结合状态良好。微观组织结构分析表明,等离子喷涂层中相成分主要包括α-Al₂O₃相、γ-Al₂O₃相、TiO₂相及一部分非晶相。激光重熔后,等离子喷涂层中亚稳的γ-Al₂O₃相全部转化成了稳定的α-Al₂O₃相。此外,在重熔过程中, Al₂O₃和TiO₂反应生成了Al2TiO5相,且基体中有部分活性元素Ti渗入到熔池中。粒径分析结果表明,等离子喷涂Al₂O₃-13wt%TiO₂涂层及激光重熔后的Al₂O₃-13wt%TiO₂涂层均处于纳米结构。等离子喷涂纳米结构涂层中主要有两种组织,即熔凝组织和三维网状组织。激光重熔后,纳米结构重熔层组织具有明显的区域特征,在不同区域发现了柱状晶,胞状晶及其混合组织,这是由不同温度条件、不同冷却速度及熔池中不均匀传质等综合因素引起的。等离子喷涂层的显微硬度约为HV700¹050,是钛合金基体材料显微硬度值的2³倍。激光重熔后,重熔层的显微硬度可达HV800¹300,其硬度值相对于等离子喷涂层又有了较大提高。在等离子喷涂及激光重熔过程中,纳米结构涂层表现出了组织结构遗传性。在纳米结构可喷涂喂料中发现了黑白相间的网状组织,等离子喷涂后,网状结构的组织保留到喷涂态的涂层中,最后,在纳米结构重熔层中,仍然可以看到球形放射状组织中包含有网状特征的组织。更多还原

【Abstract】 In this paper, conventional Metco130 ceramic coating and nanostructured Al₂O₃-13wt%TiO₂ coating have been successfully fabricated by plasma spraying on a titanium alloy （TC4） substrate. A CO2 laser has been used to remelt the plasma sprayed coatings, with the purpose of homogenizing their microstructure, eliminating their porosity and enhancing their bonding strength. The influence of laser remelting on the microstructure and properties of the ceramic coatings was investigated.The microstructure, phase constitution and microhardness of the as-sprayed and laser remelted coatings were investigated by means of X-ray diffraction （XRD）, scanning electron microscopy （SEM）, energy-dispersive analysis of X-rays （EDAX） techniques and microhardness testing, respectively.Experimental results show that the as-sprayed coatings maintained good mechanical bonding to the substrate. The porosity of the nanostructured coating is less than that of the conventional Metco130 coating. After laser remelting, the remelted coatings with smooth surface, less crack were obtained. The remelted coatings possessed a more homogeneous microstructure, less porosity, and an excellent metallurgical bonding to the substrate. The defects and porosity of the as-sprayed coatings were eliminated.The microstructure analysis shows that the plasma sprayed coatings consisted ofα-Al₂O₃,γ-Al₂O₃ and TiO₂ phases. Amorphous phases were also found in the as-sprayed coatings. After laser remelting, the metastableγ-Al₂O₃ phase in the as-sprayed coatings was transferred to stableα-Al₂O₃. In addition, the reaction of Al₂O₃ and TiO₂ led to Al2TiO5. A bit of Ti of the substrate came into the molten pool during laser remelting. The average grain size in the as-sprayed coatings and laser remelted coatings was evaluated using Scherrer Equation. The results show that the plasma sprayed Al₂O₃-13wt%TiO₂ coatings were nanostructured. After laser remelting, the remelted coatings could still keep nanostructured. Two kinds of typical microstructures were found in the as-sprayed nanostructured coatings. One is the full-fused microstructure and the other is the three-dimensional net microstructure. In the laser remelted nanostructured coatings, columnar grain, cellular grain and their mixture microstructure were found in different zone. The different kinds of microstructure were due to different laser heating temperature, different cooling rate and nonuniform mass transfer process.The microhardness of the coatings before and after laser remelting was determined. It has been found that the microhardness of the as-sprayed coatings was about HV700¹050, which was 2³ times that of the microhardness of the substrate. The microhardness obtained after laser remelting was up to HV800¹300, which was higher than that of the microhardness of the as-sprayed coatings.During plasma spraying and laser remelting, the nanostructured coatings possessed microstructure heredity. The three-dimensional net microstructure could be found in the nanostructured feedstock. After plasma spraying, the net microstructure was kept in the as-sprayed coatings. At last, in the laser remelted coatings, the net microstructure feature could be also found in the ball-like micorstructure.更多还原