Effect of Coating on the TMF Lives of Single Crystal and Columnar Grained CM186 Blade Alloy

Abstract

CM186, a Hf containing nickel-base superalloy is an attractive alloy, in terms of castability and thus manufacturing costs, for aero engine and land based gas turbine applications. Mechanical property and coating characterisation studies of this alloy are sparse, whilst thermo-mechanical fatigue (TMF) data do not exist in the literature.In service however, engine components experience severe cyclic thermal gradients and mechanical loads and as a consequence, TMF is a major lifing factor. This study investigates the TMF behaviour of single crystal and directionally solidified CM186 alloy and the effect of a silicon modified al&de coating, Sermalloy 15 15, on the TMF lives. Strain controlled TMF tests on coated and uncoated samples are carried out with an out-of-phase 180' difference between mechanical strain and temperature at 3 different strain ranges. In-situ monitoring of microcrack initiation and propagation and post-mortem fiactographic analysis are implemented to understand the damage mechanisms and coating performance.

A review of thermo-mechanical fatigue behaviour in polycrystalline nickel superalloys for turbine disc applications

“…Most of the work available has focussed on turbine blade alloys (polycrystalline and single crystal), examples of which can be found in the referenced papers [1, 22,30,[43][44][45][46][47][48][49][50][51][52][53], due to the high temperature requirements of turbine blades operating within the gas stream, and the rapid temperature cycles that develop in blades. These alloys can be required to operate at gas temperatures in excess of 1600 °C, far in excess of the melting point of the alloy.…”