Metallographic Specimen Preparation Procedures

Ceramic Coating Superalloys

To improve both the wear and temperature resistance of Superalloys, coating of zirconia or other ceramics are applied to the turbine blade. Metallographic analysis is used to determine the quality and integrity of the coating, as well as, any delamination problems. In order to get an accurate measurement on the coating, specimen preparation must focus on minimizing damage to the coating. Minimizing damage as early as the abrasive cutting operation ensures successful preparation. For cutting ceramic coated Superalloys, the MAX-H series blade is recommended. Mounting with a fine EPOCOMP epoxy helps to better protect the surface during grinding and polishing.

Grinding must also minimize damage to the coating, so initial grinding should be with the finest SiC paper which provides acceptable grinding rates (e.g. 320 grit SiC paper). Final grinding down to 1200 grit SiC paper is recommended. For rough polish on a 3 micron diamond on a GOLDPAD polishing cloth produces a moderate finish that is flat across the various materials. For the final polish the use of our newly developed ATLANTIS polishing pad, which is a woven pad on a compressible foam backing produces excellent flatness and surface finishes. This pad, works extremely well for polishing materials of significantly different hardenss (i.e. metal substrate with ceramic coating). To also aid in the polishing of ceramic and metal combination materials, the use of colloidal silica as a lubricant / abrasive produces a chemical mechanical polishing effect (CMP) which provides the best finish and flatness for ceramic coating and metal interfaces.

SECTIONING
MAXCUT Abrasive blade (Cat. No. MAX-E or MAX-I series)

MOUNTING
Compression Mounting fine EPOCOMP Epoxy compression mounting resins

POLISHING

Zirconia thermal spray coating, as polished Mag 1000x (B.F.)