Development of wear resistant and dry self-lubricating coatings on sintered steels from polymer-derived ceramics (PDCs)

点击翻译按钮获取中文摘要

The main objective of the proposal is the development of coatings with high wear resistance and hardness, self-lubricating properties and low friction coefficient. As substrates, sintered metal substrates specifically developed by the project partner UFSC in Florianopolis are used. As described in our report we demonstrated for the first time that the novel process of plasma assisted pyrolysis (PAP) is a suitable technology for the development of dense ceramic composites based on a polyorganosilazane (HTTS) as ceramic forming binder and TiSi2 as active filler. In contrast to conventional pyrolysis and using the sample as anode in the PAP the placing in cathode configuration leads to a dense ceramic material, due to the more reactive conditions which result in an increased conversion of the active filler to the related nitrides and to a densification. Aim of the still running 2. period is to transfer this knowledge to generate dense and hard coatings on the metal substrates from the project partner UFSC. For the 3rd project phase it is planned to apply the plasma process to modify the surfaces of the metal substrates by depositing iron nitride layer or refractory metals like molybdenum to improve the hardness of the metal substrates and the adhesion of the silazane coatings. It is also planned to use TiB2 and Ti5Si3 as active fillers. By using TiB2 it is expected that the filler conversion follows the same reaction path like TiSi2 during treatment in the nitrogen containing plasma atmosphere. The reaction of TiB2 with nitrogen ions should lead to the formation of hBN which is suitable as dry-lubricating agent, whereas titanium forms hard nitrides and carbonitrides because of the reaction with the amorphous SiCN phase resulting from precursor pyrolysis. By employing TiSi2 as active filler a remarkable amount of unreacted elemental Si was formed after PAP treatment which could influence the mechanical properties and the wear resistance of the coatings adversely. By using Ti5Si3 as active filler we expect an increased formation of hard Ti(C,N) phases while the amount of unreacted Si is reduced. Additionally it is necessary to vary the PAP parameters to improve the conversion of the active fillers, and finally to enable the sintering of the metallic substrates and the ceramization of the coatings in one cycle simultaneously. The methodology should lead to a reduction in the processing steps and time. In this cooperation project, not only materials with different natures like metals, ceramics and polymers are going to be combined, but also the expertise of the partners in different knowledge fields. The realization of such project by each of the partners individually is not possible. The joint research should quickly enable the manufacturing of new products, which are able to increase the lifetime of mechanical parts and their energy efficiency through the reduction of friction.