Development of micro-heating elements based on bilayers PVD coatings and evaluation of their robustness under electro thermal and cavitation erosive load in nucleate boiling

在DFG项目“开发一种抑制PVD涂层中生长缺陷影响的微观结构方法”中，开发的铬基涂层满足加热元件设计的基本要求。加热器由PVD双层构成，用于加热，温度测量以及气泡形成过程的研究，这对于研究核沸腾中的传热过程是必要的[FISH 2011 FISH 2012 Slom 2013 a]。使用选择性功能化的PVD涂层，将开发微加热器，使国际空间站的核沸腾过程的分析和评价成为可能。因此，涂层必须承受电热、空蚀和腐蚀载荷。用于施加涂层的基材由诸如氟化钡或硫化钡的透明材料制成。这些加热器的几何设计必须高度适应国际空间站上的沸腾实验，例如尽量减少空间的使用。氮化铬基层的制造方式必须使其能够通过红外热成像法在沸腾区中进行温度测量（由于其高发射率）。直接沉积在氟化钡上的基层需要高电阻。特别是高于铬顶层。因此，只有铬顶层作为加热器。为了保证流体所需的加热温度，涂层必须在所需的温度范围内具有限定的电阻。

In the DFG-project "Development of a microstructural approach to suppress the effect of growth defects in PVD coatings" developed chromium-based coatings meet the basic requirements for the design of a heating element. The heaters are constructed out of a PVD bilayer that is used for heating, temperature measurement and as well for the investigation of bubble formation processes, which are necessary to study heat transfer processes in nucleate boiling [FISH 2011 FISH 2012 Slom 2013a].Using selectively functionalized PVD coatings, micro-heater will be developed, enabling the analysis and evaluation of nucleate boiling processes at the International Space Station. Therefore the coating has to withstand terms of electro-thermal, cavitation pitting and erosive loads. The substrates used for the applied coating were made out of transparent materials such as barium fluoride or barium sulfide. These heaters have to be highly adapted in their geometric design to the boiling experiments on the ISS, for example minimum usage of space. The chromium nitride base layer has to be manufactured in the way that it enables, due to its high emissivity, the temperature measurement in the boiling zone by means of infrared thermography. The base layer which is deposited directly on the barium fluoride requires high electrical resistance. In particular higher than the Chromium top layer. For this reason, only the Chromium top-layer acts as a heater. In order to guarantee the required heating temperature of the fluid, the coatings have to possess defined electrical resistance in the required temperature ranges.