采用多道搅拌摩擦焊搭接的固态加工方法, 并借助焊后表面铣削加工处理, 在TC4钛合金表面制备了厚度约为500μm的Al涂层,并对基板试样和涂层试样在700℃大气环境下进行了高温氧化实验.用扫描电镜、能谱分析和X射线衍射分析等手段研究了涂层和界面的微观组织结构,并讨论了界面中间层在高温氧化过程中的相结构演变. 结果表明, 经过搅拌摩擦焊搭接加工,涂层/基体的界面为富Ti的条带状结构, 界面中间层厚度达60μm.在表层富Al组织发生高温氧化及熔化现象的同时, 足够厚度的Al涂层可对O的内扩散起到一定阻碍作用,而中间层的Ti和Al二元扩散行为促进了Ti-Al相在界面稀氧环境下的形成, 最终起到对基体抗氧化的主要防护作用.高温氧化后表面相组成主要为Al₂O₃, Al₂Ti和Al₃Ti,而界面中间层的Ti-Al相结构呈显著的梯度分布特征.

The poor oxidation resistance of titanium and its alloys limits their use at elevated temperature. To solve this problem, a large amount of surface engineering techniques to produce anti-oxidation coatings on titanium alloys were utilized. In the present research, a solid-state processing method of friction stir lap welding (FSLW) was used to fabricate Al cladding or coating on the surface of TC4 titanium alloy, with lower cost and simpler operation which are still desirable for the coating preparation on titanium alloys. The lap joint structure was smartly transformed into an interface structure of coating. In this work, the Al coating with a thickness of 500μm was fabricated via multi-pass FSLW process using a slight plunge depth of tool-pin. The mechanical milling was used as a post-treatment for a suitable coating thickness. The oxidation testing was conducted at 700℃ under air atmosphere. The microstructure, chemical composition analysis and phase determinations were performed using SEM, EDS and XRD methods. The evolutions of interlayer under the high-temperature oxidation procedure were detailed. It was found that the Ti- rich interlayer, with a thickness of 60μm, had a typical structure of mixed layers. The sufficient Al coating thickness played an important role in preventing the inter diffusion of oxygen, while the oxidation and melting phenomenon of Al coating occurred. The abundant Al content in the Al coating upper the interlayer, with a significant thickness, also benefited to the anti-oxidation performance and forming of the beneath Ti/Al interlayer at a rare oxygen environment due to the obstacle effect of the Al layer to oxygen diffusion, which exerted a main role in oxidation prevention for titanium alloy. As a result, the phases of outer surface were mainly Al₂O₃, Al₂Ti and Al₃Ti. The gradient distribution characteristic of Ti/Al interface structure occurred after the oxidation testing.