Self-lubricant coating systems able to control the release of lubricious species during operation have enormous potential to protect components working in extreme conditions combining high temperature and contact pressure.
Until now, high temperatures result in strong diffusion, leading to the rapid depletion of the lubricious agent and the inoperability of the component. On this basis, TiSiN coatings were deposited using an emergent technology (HiPIMS-high power impulse magnetron sputtering), which allows the formation, at room temperature, of nanocomposite structures consisting of a quasi-amorphous Si-N-matrix-separated TiN nanograins.
This is the key design this proposal will explore to control the outer-diffusion of the lubricious agent, in this case silver,in a new radical approach of self-lubricant coatings for high temperature applications. SI-N phase is well known to have anti- diffusion properties which,If proper tailored (thickness and distribution),can control the lubricious agent release. The low temperature deposition will allow Ag to be adequately dispersed on the nanocomposite structure either in metastable solid solution in TiN lattice or nanoparticles with different sizes in interface sites, without being continuously segregated during the deposition process. The morphology and structure of the films will be optimized for either anti-diffusion properties, by controlling the thickness of the Si-N layer,or the Ag incorporation as solid solution or as nanoparticles with different sizes and distribution. To understand the diffusion mechanisms, advanced characterization methods will be used to characterize the coatings, such as, high-resolution SEM and TEM analysis coupled to EDS, in-situ high-temperature TEM experiments and in-depth chemical composition evaluation by depth profiling XPS.
|Title||Self lubrificant coatings for high temperature applications with controlled released of the lubricious agent|
|Leading Institution||Universidade de Coimbra (UC)|
|Participating Institutions||The University of Austin at Texas (UT Austin)
Universidade do Minho (UM)
|Begin date||1st November, 2018|
|Key Words||Self-lubricant coatings, Ag control release,
Kinetics of Ag diffusion, Atomistic simulation of Ag ions release
"Based on the previous successful experiments on the achievement of nano composites structures within the Ti-Si-N system by using HiPIMS power supplies for the deposition of sputtered coatings, similar films, now alloyed with increasing Ag contents, will be produced. For testing the thermal stability of these coatings, and understanding the potential out diffusion of Ag through the nano composite structure, both experimental (HRTEM observation before and after annealing) and simulation (DFT analysis) studies will be performed. This sequential procedure will be developed in a closed loop process, where the characterisation results will determine the further deposition of coatings with optimised nano composite structures, in particular the thickness of the anti-diffusion Si-N layer enrobing Ag nanoparticles / Ti-N grains. Mechanical testing will complement this characterisation since both Ag and Si contents can influence definitely the hardness and Young's modulus of the coatings. The structure will be consider optimized when a suitable compromisse between the ability to control the out diffusion of silver and suitable mechanical properties for high temperature applications will be achieved!"