Development of Improved Fatigue Resistant Nanocomposite Coatings for Rotary Machinery Components, 18-R9622

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Principal Investigators
Ronghua Wei
Sastry Cheruvu

Inclusive Dates:  04/01/06 – 10/01/07

Background - Solid particle erosion often occurs to key components of modern machinery in various fields, including compressor blades and vanes of turbine engines, rotor blades of advanced aircraft, and impellers of fluid pumps. Hard coatings are increasingly being considered for minimizing the damage to these components. In this way the conventional materials can still be used while a hard ceramic coating can withstand the harsh environment.

SwRI has developed a plasma enhanced magnetron sputtering (PEMS) technology, by which the thickest nanocomposite coatings ever reported were produced. Evaluations conducted at SwRI and outside institutions have shown that the coatings exhibit superior performance against solid particle erosion and heavy load wear over the "state-of-the-art" coatings (approximately an order of magnitude). However, the earlier high-cycle fatigue (HCF) test indicated a significant reduction of the fatigue life because of the coatings. The objective of this project is to optimize the deposition parameters so that the PEMS process induces minimal reduction in fatigue life while the nanocomposite coatings produced retain high hardness, high wear and erosion resistance.

Approach - Using the SwRI-patented PEMS technology and the Ti-Si-C-N nanocomposite coatings as the baseline, a design of experiment method was used to design the test matrix. Seven processing parameters and two to three levels for each parameter were considered. Using the design of experiment, a matrix of 18 tests was generated. By studying the coating microstructure, adhesion and erosion resistance, the deposition parameters that generated the best-performing coatings were identified and used for the deposition of a few sets of HCF specimens. Then the HCF tests were conducted, and the coated specimens were analyzed after the HCF tests to identify the failure modes.

Accomplishments - After the successful execution of the project, a few sets of deposition conditions that generated the best performing coatings have been identified. The coatings have very dense microstructure with few defects and inclusions, are very hard (approximately 40GPa), have excellent adhesion and are extremely erosion resistant (about 100 times reduction from the base materials). Then 12 HCF specimens were deposited using three deposition conditions. They were then tested at the Boeing Phantom Works. The result shows that the HCF life has been significantly increased from the previous hard coatings (about 40 times) and the HCF life of the coated specimens, though slightly lower than the uncoated samples, is satisfactory for many applications in several industries including aerospace, defense and energy production and transportation.

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