报告主题：激光维持的等离子体及在金属表面处理中的作用（LASER-SUSTAINED PLASMA AND ITS ROLE IN METAL SURFACE PROCESSING）
报 告 人：Prof. Judith Todd（美国宾州州立大学)
时 间：2016年3月9日（周三)10:00
地 点：校本部G309
主办部门：理学院物理系
邀 请 人：马国宏教授
报告摘要：Hard, wear-resistant, cutting tools are conventionally coated with titanium nitride (TiN) films, 2.5 to 12 μm in thickness, by physical vapor deposition processes at low pressures and a typical deposition rate of 5 μm per hour. This research investigates the potential for producing low-cost, high deposition rate, functionally graded, TiN coatings on commercially pure titanium using laser-sustained, nitrogen plasma at ambient pressure. Laser nitriding introduces nitrogen into a laser melt pool in a matter of seconds. In this presentation, we will discuss the role of laser plasma by comparing nitriding without plasma, with surface-struck laser plasma, and with laser-sustained plasma. Strategies for control and optimization of melt trail microstructures and morphologies will be discussed. It will be shown how dilution of the nitrogen with argon (1) reduced Marangoni convection in the melt pool, (2) changed nitrogen transport in the melt pool from convection-dominated to diffusion-dominated, (3) reduced nitrogen incorporation into the melt pool, and (4) reduced surface roughness, surface oxidation, and the presence of surface cracks. The implications for depositing multiple overlapping nitride trails to form wide-area titanium nitride surface layers will be discussed.
