IN-SITU MEASUREMENT AND SIMULATION FOR DEFORMATION AND SOLIDIFICATION PHENOMENA OF SUPER-COOLED SINGLE DROPLET UNDER PLASMA SPRAY CONDITIONS (2002)

主要研究结果如下：1.到目前为止，已有许多关于等离子喷涂条件下液滴撞击基板的变形和凝固过程的模拟工作被报道。然而，尽管已经有许多过冷效应的证据被报道，但还没有建模工作涉及过冷对变形和凝固过程的影响。在这项研究中，我们可以展示我们最近对Al_2O_3液滴所做的模拟工作的第一个结果，它清楚地表明了过冷条件对变形和凝固过程的强烈影响。例如，我们成功地预测了变形度-定义为液滴与熔滴直径的比率-显著降低到2.0时，还预测了更快的凝固前沿速度，最高可达5m/S。尽管变形度较小是由于过冷条件下粘性值较大造成的，但Rapi…过冷最终会导致更多的凝固。该模型没有预测枝晶生长，但它清楚地表明，等离子喷涂颗粒实际上可能处于过冷状态，任何建模努力都应该考虑过冷效应。2.我们开发了一套原位测量系统，通过连续采样控制气氛下的事件，精确地1：1关联等离子喷涂条件下撞击衬底过程中的裂片形貌和温度历史。为了揭示该系统的有效性，利用辐射板在水平移动的衬底上连续测量了混合等离子喷涂的氧化钇稳定氧化锆粉的变形和凝固过程。温度是通过液滴700和1000 nm的发射来测量的，液滴的大小是基于液滴的三维形态在异地精确评估的。该系统可以在10秒内连续取样约10个单颗粒，并精确地关联每个液滴的尺寸、温度和冲击速度与变形-凝固过程和碎片形貌之间的关系。最引人注目的发现是，在撞击之前，可能有一部分液滴处于过冷状态，但在变形过程中并没有发现明显的差异。此外，作为二次结果，我们可以评估YSZ的粘度和基片与基材之间的热阻。由此可见，该项目的总体目标取得了相当大的进展，到目前为止所获得的结果清楚地证明了该方法的可行性。较少

The principal findings can be summarized as follows:1.To date, many modeling efforts related to the deformation and solidification processes of a droplet impacting on the substrate under plasma spraying conditions have been reported. However, no modeling effort has dealt with the super-cooling effects on the deformation and solidification processes, though much evidence of super-cooling effects has been reported. In this research, we could show the first results derived from our recent modeling efforts for the case of Al_2O_3 droplets, which clearly show the strong effects of the super-cooling conditions on the deformation and solidification processes. For example, we successfully predicted a significant decrease in deformation degree -defined as the ratio of droplet to splat diameters -to less than 2.0, and also a faster solidification front velocity of up to 5 m/s. Although the small deformation degree is caused by the larger value of viscosity under super-cooled conditions, the rapi … More d solidification is eventually caused by the super-cooling. The model did not predict a dendritic growth, but it clearly suggested that plasma sprayed particles are not all but may be actually in super-cooled state, and any modeling efforts should include the super-cooling effects.2.We developed an in-situ measurement system for precise 1:1 correlation between splat morphology and temperature history during impinging on the substrate under plasma spraying conditions with sampling the events successively under controlled atmosphere. In order to reveal the effectiveness of the system, deformation and solidification process of yttria-stabilized zirconia powder sprayed by hybrid plasma was measured successively at a horizontally moving substrate heated up to 700 K by a radiation-plate. The temperature was measured by 700 and 1000 nm emissions from a droplet, and the droplet size was evaluated ex-situ precisely based on the three dimensional morphology of the splat. The system made it possible to sample about 10 single particles successively within 10 second, and correlate precisely the relations between the size, temperature and impacting velocity of each droplet, and deformation-solidification process and morphology of the splats. The most striking finding is that a part of the droplets may be actually in super-cooled condition before impinging, but a drastic difference was not found in deformation process. In addition, as secondary results, we could evaluate the viscosity of YSZ and the thermal resistance between the splat and the substrate.From the above, it can be seen that considerable progress was made towards the overall goal of this project, and the results obtained so far clearly demonstrate the feasibility of this approach. Less