Erosion Resistant Nano Technology Coatings for Gas Turbine Components

Abstract

Solid particle and liquid particle erosion in the compressor section of gas turbines and steam turbine vanes and blades lead to significant reduction in turbine efficiency over time. This results in increased downtime and operating cost of the power plants. Some of the conventional coatings and erosion protection shields used by the currently available commercial processes have limitations in their temperature and erosion protection capabilities. Under a project funded by the Electric Power Research Institute (EPRI), nano coatings with thickness within 40 microns (about 1.5 mils) have been produced on test samples using a state-of-the-art Plasma Enhanced Magnetron Sputtering (PEMS) technique. Five coatings were selected for the initial screening tests. Titanium silicon carbonitride nano-composite (TiSiCN), stellite and modified stellite, chromium carbide and Ti-TiN nano layered coatings are being studies in this project. The substrate selection is based on some of the alloys currently used in aeroderivative engine compressor blades, land based gas turbine compressor blades and steam turbine blades and vanes. They include titanium alloys and stainless steels. The PEMS coating technique differs significantly from the conventional techniques such as air plasma spray (APS), low-pressure plasma spray (LPPS), diffusion coatings, chemical or physical vapor deposition (CVD or PVD) used on blades and vanes. PEMS method involves a magnetron sputtering process using a vacuum chamber with an independently generated plasma source from which high current density can be obtained. This method used heavy ion bombardment prior to and during deposition to increase the coating adhesion and limit columnar growth in the coatings. Single-layered thick nitrides coatings up to about 80μm and thick carbonitride coatings of TiSiCN about 30μm have been obtained by this process. A novel method using trimethylsilane gas instead of solid targets was successful in producing this nanocomposite. Initial tests conducted on some of the coated titanium alloy samples produced thus far show significant improvement in the erosion resistance in laboratory sand erosion tests. It was observed that TiSiCN exhibited the best low-angle erosion resistance — nearly 25 times higher than the uncoated Ti-6Al-4V and about 5–10 times higher than all other nitrides. This paper covers a brief description of the deposition technology and the properties of the coatings. Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy (EDS), and X-Ray diffraction (XRD) analysis were used to study the microstructure and morphology of these coatings. Nanoindentation was conducted to determine the hardness and Young’s modulus, while sand erosion tests were conducted to rank the erosion resistance of the coatings produced using several processing variables.