电子束表面合金化制备Ti_5Si_3/TiAl复相合金改性层

Electron beam surface alloying of γ-TiAl intermetallic alloy for Ti_5Si_3/TiAl composite coatings

通过使用高能量密度的电子束高速扫描预先涂有Si粉的TiAl合金表面,"原位"制得了以高硬度金属间化合物Ti5Si3为增强相、以TiAl、Ti3Al为基体的复相合金表面改性层。利用光学显微镜、电子探针、能谱仪及X射线衍射仪分析和研究了电子束表面改性层的显微组织结构;同时测试了沿改性层深度方向的硬度分布。结果表明:表面改性层由TiAl、Ti3Al、Ti5Si3相组成,Ti5Si3相的形态及分布沿层深方向呈现梯度变化,在表层为粗大的六棱柱状结构,沿改性层向内,其中、下部由于冷却速度相对较快,硬质相的形态及分布趋于细小、密集;改性层与基体间没有明显的界面,为完全的冶金结合;改性层具有较高的硬度,显微硬度最高达到895,约为基体的3倍。

In-situ Ti_5Si_3/ Ti_3Al/TiAl composite coatings reinforced by high hardness Ti_5Si_3 intermetallic phase were fabricated on γ-TiAl substrates precoated with silicon powders by means of electron beam surface alloying. The microstructure characteristics of the composite coatings were investigated using optical microscope, electron probe microanalysis, energy spectrometer and X-ray diffraction. Micro-hardness was measured from the surface down to the substrate by a Vickers hardness tester. The results show that composite coatings are composed of TiAl, Ti_3Al and Ti_5Si_3 phases. More specifically, the morphology and distribution of Ti_5Si_3 phase change with gradient transition along the depth of the coatings. In the upper level of the coatings, a considerable amount of large hexagonal-pillar-shaped Ti_5Si_3 phases were observed, while in the middle and lower level of the coatings, the particles get smaller and denser because of faster cooling speed. The bond zone between the substrate and the coatings is wholly metallurgical bonding with no apparent interface. As for the hardness of the composite coatings, it is higher than that of the substrate, its maximum value reaches 895, nearly triple the value of the matrix one.