The manufacture and fatigue cracking resistance of grit free aluminide diffusion coatings

Abrasive blasting is an inexpensive and effective means of cleaning superalloy castings, and of roughening the surface of these castings prior to platinum electroplating or overlay coating deposition. However, during the blasting operations, some of the abrasive grit particles become embedded in the surface of the superalloy and this embedded grit can result in detrimental effects on the mechanical properties of gas turbine components. A research program was conducted to evaluate the use of molten caustic immersion to eliminate entrapped grit particles, and to determine the effects of entrapped grit removal on the Thermo-Mechanical Fatigue (TMF) crack resistance of aluminide diffusion coatings. Using aggressive TMF testing conditions, the average life of the samples increased by 47% using the molten caustic immersion to remove the embedded grit particles. The research program is described, the results are presented and discussed and all possible conclusions are summarized.