A SURVEY OF THE DAMPING PROPERTIES OF HARD COATINGS FOR TURBINE ENGINE BLADES

摘要

The application of a thin coating of a hard material to airfoil surfaces has been proposed as a means of reducing the amplitude of resonant vibration of gas turbine components. A variety of materials and processes have been proposed. Their effectiveness, however, typically has been reported in terms of the response of coated specimens to an excitation. The use of different substrate properties and dimensions, different coating thicknesses, and different test procedures make comparative evaluations challenging. Moreover, as the damping capacity of these materials is often amplitude dependent, comparisons must be made at common values of strain.But material properties, rather than system measures, must be known if coatings are to be included in design analyses. It is the objective of this survey to compare the effectiveness of coating materials described in the open literature. Reported values of system damping and test parameters are used to estimate the loss modulus of each material. Included in comparisons are such plasma sprayed ceramics as magnesium aluminate spinel, alumina, and yttria stabilized zirconia; magnetoelastic materials, both plasma sprayed and bonded; homogeneous metals, metallic mixtures, and ceramic-metallic laminates applied by electron beam physical vapor deposition; and a ceramic infiltrated with a viscoelastic material.