Investigating the fatigue performance of soft multilayer coatings with varying locations of an intermetallic interlayer

A multilayer coating system containing two hard intermetallic layers (IMLs) within a soft metallic system provides improved fatigue performance. To further optimise this system, various coatings with different locations of the intermediate intermetallic (IML-Top) interlayer were manufactured and experimentally investigated. Their characteristics were assessed and fatigue performances were compared, revealing the improvement of fatigue resistance by locating the IML-Top layer close to the top overlay coating surface. The mechanisms, based on post-test observations of crack morphology, are identified as (1) improved retardation of crack initiation and (2) improved crack growth resistance provided by the shielding effect of the IML-Top layer.