Development of Thick Nanocomposite Coatings for Erosion Protection Applications, 18-9448

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Principal Investigator
Ronghua Wei

Inclusive Dates:  01/01/04 – 06/30/05

Background - Solid particle erosion and abrasion often occur to key components of modern machinery in various fields, including compressor blades and vanes of turbine engines, rotor blades of advanced aircraft, impellers of fluid pumps, and piston rings of heavy-duty diesel engines. To increase the erosion and abrasion resistance of the components, better materials such as superalloys are being developed and adopted. In addition, hard coatings are increasingly considered for use in minimizing wear to these components. However, with the increasing demand for higher loads and speeds, damage becomes more and more severe. In some cases, failure of these components leads to severe or even fatal disasters. Superalloys are expensive and heavy, while conventional coatings using present commercial technologies are too thin to meet the increasing demand. Therefore, the objective of this project is to develop a novel deposition technology to meet the challenges. The methodology here is to deposit thick, extremely hard and tough, nanocomposite coatings on light alloys such as Ti-6Al-4V or commercial steels for the above-mentioned applications.

Approach - During this project, a plasma-enhanced magnetron sputtering (PEMS) system has been developed. The technique utilizes magnetrons to sputter metallic materials such as titanium (Ti) onto tools and components. During the deposition, a reactive gas such as nitrogen is fed into the system to form hard nanocrystalline coatings such as titanium nitride (TiN). Deposition of TiN or the like using PVD processes is routinely practiced in tooling and component industry. However, the uniqueness of this approach lies in the use of intensive ion bombardment. Together with the introduction of Si and C in an N2 environment, the coatings thus formed contain nano-sized TiN particles embedded in an amorphous matrix of SiCN. This nanocomposite has a very high hardness and toughness, hence, a very high erosion resistance is obtained. Another unique aspect of our technology is that it can be used to deposit thick coatings. Using conventional coating technologies, the typical coating thickness is limited to approximately 10 to 15 micrometers because of the stress buildup and the increase in defects. In contrast, because of the intensive ion bombardment of the PEMS technology, thick nanocomposite coatings up to 80 micrometers thick can still adhere well to the substrate.

Accomplishments - Figure 1 is a photograph showing the PEMS system. To date, we have prepared thick single-layered hard coatings including TiN, ZrN, CrN and their nanocomposites on Ti-6Al-4V and stainless steels. Shown in Figure 2 are cross-sectional scanning electron micrographs of various coatings. The coating nanohardness and the thickness are listed in Table 1. These are the thickest single-layered nitride coatings ever made to our knowledge. Certainly, thinner coatings or multilayered coatings, often needed for other applications, can be made easily. Shown in Figure 3 is a photograph of a small number of turbine blades that have been coated with the PEMS technology. To verify the coating quality, we conducted a number of erosion tests, in which a stream of white sand is directed at high speeds and grazing angles onto the coated surface for a predetermined period after which the coating mass loss is measured. Shown in Figure 4 is the erosion resistance of various coatings. It is clear that all nitride coatings perform better than the uncoated steel, while the nanocomposite coatings outperformed the nitrides. The best nanocomposite outperforms the uncoated steel by a factor of about 20 times. We also sent our samples to a well-recognized research organization in Canada to perform the standard erosion evaluation. They compared the erosion data of our nanocomposites with those of commercial TiN that is used currently for protecting the blades of jet engines. It is clear our the SwRI nanocomposite coating outperformed the commercial TiN by seven to ten times. If this technology is implemented into the present hard coating systems, the benefit can be realized quickly.

Table 1. Thick single-layered nitride and nancomposite coatings

  Thickness (µm) Nanohardness (GPa)
CrN 35 24.5
ZrN 78 33.5
ZrSiCN 29 29.6
TiN 43 31.7-27.7
TiSiCN 18 42.4

Figure 1. A sample being prepared using the PEMS technique

Figure 2. Cross-sectional scanning electron micrographs of thick single-layered nitride coatings and nanocomposite coatings

Figure 3. Nanocomposite-deposited turbine blades

Figure 4. Erosion resistance of various coatings

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