Research On The Ultrasonic Characterization Of The Bonding Strength Of The Six Element Coating

Six element coating prepared by low pressure plasma coating is one kind of high temperature protective coating. Coating contains Ni, Co, Cr, Al, Y, Ta six elements, it has the role of anti-high temperature oxidation, preventing the oxidation of the turbine blade to reduce the use of life. In coating preparation or use will appear with bad or decreased the binding strength, which can lead to the coating peeling off or the turbine blade damaging, when the blade is working, it may even lead to plane crash. Therefore, the bonding strength of the quality detection has become particularly important. Conventional detection method for the bonding strength is a damage detection of coating, and only the coating for sampling, can’t achieve all testing, but ultrasonic detection with low cost, high efficiency and can achieve the advantages of all products online detection.This paper studies the Six element coating thickness in the range of 60 M-130. First, based on the thermal shock method to manufacture different bonding strength of specimen, this method is using six element coating and substrate thermal expansion and contraction coefficient of different, in the temperature of the blast will generate thermal shock stresses in the six element coating, so that the six element coating bonding strength decrease. Secondly, through the metallography to measure the thickness of coating and observation of the change of the strength of the six element coating. Finally, the ultrasonic immersion focusing method was used to inspect the six element coating. The acoustic pressure reflection coefficient amplitude spectrum, the sound velocity in the six element coating and the nonlinear coefficient are used to characterize the six element coating. And then the stability and sensitivity of the three kinds of ultrasonic parameters were compared and analyzed.Research results show that: after 50 thermal shock, the six element coating and the substrate bonding interface appeared oxide layer and even fall off, micro cracks appear inside the six element coating, Which leads to the low bonding strength between the six element coating and the substrate. With the increase of the number of thermal shock, the relationship between the amplitude spectrum of sound pressure reflection coefficient and the number of thermal shock is 1y₁=224.85x₁+28482.49, the correction coefficient is 0.45; The relationship between the sound velocity of the six element coating and the number of thermal shock is y₂=-2.83x₂+2760.5, the correction coefficient is 0.72; The relationship between the nonlinear coefficient of the six element coating sample and the number of thermal shock is y₃=0.03x₃-0.055, the correction coefficient is 0.87. Compared with the other two kinds of ultrasonic parameters, using the nonlinear coefficient to characterize the bonding strength of six element coating has Better stability and higher sensitivity. The results obtained from this study provide a theoretical and experimental basis for the combination of ultrasonic testing of the coating, and lay the foundation for the establishment of the evaluation of the combined strength of the coating.