激光铝热还原法制备Al2O3/Ti-Al基复合涂层

利用Al和TiO₂之间的放热化学反应, 采用激光原位合成技术在TC4钛合金基体材料表面制备了Al₂O₃/Ti-Al金属间化合物基复合涂层。对比分析了激光功率、激光束扫描速度和光斑尺寸变化对激光能量密度变化量的影响程度, 借助X射线衍射仪(XRD)、光学显微镜(OM)、能谱仪(EDS)和显微硬度计分别考察了激光束扫描速度对复合涂层表面宏观形貌、截面显微组织结构和显微硬度的影响。结果显示, 扫描速度的变化对激光能量密度变化量的影响程度最大, 光斑尺寸次之, 激光功率的变化影响最弱。随着激光束扫描速度的增大, 复合涂层表面渐趋粗糙, “鱼鳞纹”状形貌特征趋于明显, 复合涂层与基材结合区厚度减小。激光原位复合涂层主要由k-Al₂O₃和α-Al₂O₃增强相与α-Ti和α₂-Ti₃Al基体相组成。随着激光束扫描速度增大, 复合涂层内k-Al₂O₃部分转变为α-Al₂O₃, Al₂O₃增强相有由枝晶状向纤维状转变的趋势; 复合涂层截面显微硬度自基体至涂层表面过度平缓, 且涂层区显微硬度分布均匀, 明显高于基材平均显微硬度。

Microstructure of Al2O3/Ti-Al Composite Coatings Prepared by Laser Aluminum Thermal Reduction Processing

With composite powders of Al and TiO₂ systems as reactants, Al₂O₃ reinforced Ti-Al matrix intermetallic composite coatings were prepared on the TC4 alloy substrate by laser in-situ synthesis processing. The effects of laser power, laser scanning speed and laser spot size on laser energy density were analyzed, respectively. The macroscopic morphology, cross-section microstructure, and micro-hardness of Al₂O₃/Ti-Al composite coatings were characterized by optical microscope (OM), X-ray diffraction (XRD), energy dispersive spectroscope (EDS) and micro-hardness tester. The results show that scanning speed has the greatest impact on laser energy density firstly, then the laser spot size, and then the weakest is laser power. With the scanning speed increases, Al₂O₃/Ti-Al composite coatings surface become rougher, “fish-scale shape” morphology are more obvious, and the thickness of bonding-zone decreases. The reinforced phase of composite coating is composed of k-Al₂O₃ and α-Al₂O₃, while the matrix phase is composed of α-Ti and α₂-Ti₃Al. And with the increase of laser scanning speed, k-Al₂O₃ changes into α-Al₂O₃ partially. The morphology of Al₂O₃ reinforcement tends to change from dendrite shape to fiber. The micro-hardness of samples has a smooth transition tendency from the substrate to the coating surface. The micro-hardness distribution of coating cross section is uniform, and the average micro-hardness is significantly higher than that of the substrate.