Development of ceramic coatings on aluminium and plastics by laser pyrolysis of particle filled silazanes

近年来的研究表明，前驱体技术适用于炉内热解制备陶瓷涂层。然而，制备陶瓷涂层所需的高温只允许使用高熔点的衬底。最近，我们证明了激光热解也适用于在钢表面形成陶瓷涂层。作为能源的激光辐射的特定输入应该能够降低衬底的热应力，从而能够在低熔点的衬底上制备陶瓷涂层。然而，首次用激光照射在铝衬底上的涂层的测试表明，热膨胀系数(CTE)以及导热系数对该过程有很大的影响。导热系数越高，散热速度越快。此外，衬底和涂层的CTE之间的高差异增加了产生的应力。这些问题导致涂层在激光热解过程中或之后立即分层。因此，已成功应用于钢的涂层系统不容易应用于铝和镁，因此需要进行更深入的研究。由于这些原因，在本项目范围内，应专门开发用于在铝表面以及随后在镁衬底上进行激光热解的涂层。因此，有必要系统地改变涂层的组成和工艺参数，并研究它们对所得涂层性能的影响。下一个雄心勃勃的发展阶段是通过在塑料衬底上激光热解制备以前驱体为基础的陶瓷涂层。到目前为止，这些活动还没有在文献中被描述过。此外，塑料表现出更低的热稳定性，非常高的CTE和低的导热系数。此外，激光热解过程中的散热减少可能会导致基片温度的意外升高。由于预期的问题不能一蹴而就，应首先开发碳纤维增强塑料涂料，然后再开发纯塑料涂料。对于所有涂层系统，将对最重要的机械和物理性能以及耐化学性进行表征。因此，应该获得基础知识，以便能够根据涂层成分和待确定的工艺参数，系统地开发适用于不同基材的陶瓷涂层。

In the recent years it has been shown, that the precursor technology is suitable for the preparation of ceramic coatings by pyrolysis in a furnace. However, the required high temperatures for the preparation of the ceramic coatings only allow the use of substrates with high melting points. Recently, it was demonstrated by us, that laser pyrolysis is also suitable for the formation of ceramic coatings on steel substrates. The specific input of laser radiation as the source of energy should lead to a reduction of thermal stresses of the substrate, thus enabling the preparation of ceramic coatings on substrates with low melting points. However, first tests with laser irradiation on coatings applied on an aluminium substrate showed, that the coefficient of thermal expansion (CTE) as well as the thermal conductivity have a strong influence on the process. A higher thermal conductivity leads to a faster heat dissipation. Furthermore, a high difference between the CTEs of the substrate and the coating increase the stresses generated. These problems lead to the delamination of the coating during or immediately after the laser pyrolysis. Thus, coating systems, which were successfully applied onto steel are not easily applicable to aluminium and magnesium, whereby a more intense research will be needed. For these reasons, coatings should be specifically developed for the laser pyrolysis on aluminium and subsequently on magnesium substrates within the scope of this project. Therefore it is necessary to vary the composition of the coatings as well as the process parameters systematically and to investigate their influence on the properties of the resulting coating. The next ambitious stage of development concerns the preparation of precursor-based-ceramic coatings by laser pyrolysis on plastic substrates. Until now, none of such activities have been described in the literature. In addition, plastics show an even lower thermal stability, very high CTEs and low thermal conductivity. Moreover, the resulting reduced heat dissipation during the laser pyrolysis can lead to an undesired increase of the substrate temperature. As the expected problems cannot be solved at once, coatings for carbon fiber reinforced plastics shall be developed at first and afterwards for pure plastics. For all coating systems the characterization of the most important mechanical and physical properties as well as the chemical resistance will be performed. Therefore, fundamental knowledge should be obtained, to enable a systematic development of ceramic coatings for different substrates, based on the coating composition and the process parameters to be determined.