Cavitation Erosion of 6061 Aluminum Alloy Coated with TiAlN Thin Film

Abstract

Cavitation erosion is one of the major problems to be solved in hydraulic machinery. Propellers of high speed boats require a light weight metallic material for their improved high performance. This example tells us that solutions are the developments of way for the improvement of cavitation erosion resistance of light weight metallic material. Coatings on aluminum alloy can enhance the cavitation erosion resistance. This study discussed the cavitation erosion behavior of 6061 aluminum alloy coated with TiAlN thin film. TiAlN coatings were deposited by DC magnetron sputtering method at various nitrogen partial pressures of the coating process using Ti based alloy cathode. The composition of target material was 90wt%Ti, 6wt%Al and 4wt%V. Using the TiAlN coated 6061 aluminum alloy specimen, cavitation erosion tests were carried out to investigate its resistance to the ultrasonic cavitation erosion. Prior to and after the tests, the specimen surfaces were analyzed by using the surface analysis techniques such as micro-hardness test, AFM, SEM, GXRD and scratch test to measure the microstructure of thin film and bonding properties of the applied TiAlN coatings to the substrate material. An improvement in cavitation erosion resistance could be seen with TiAlN coating on 6061 aluminum alloy. Especially, the coating at a nitrogen flow rate of 0.85 sccm or more were very effective in reducing the surface cavitation erosion from the ultrasonic cavitation. In the observation of surface damages during the cavitation erosion tests, the surface cracks in TiAlN were created by the bending of TiAlN coating which were resulted from the plastic deformation of the soft substrate material of aluminum alloy. Once the cracks initiate, drastic delaminations of TiAlN from the substrate material occured. The mean depth erosion rate (MDER) could be evaluated by critical and delamination loads measured by scratch test.