Thermal Stability of NiCrAlY/PSZ FGM by Plasma Twin Torches Method

Abstract

Fundamental researches were carried out to improve thermal stability of NiCrAlY/PSZ FGM in uniform and gradient temperature fields. NiCrAlY/PSZ NFGMs, NiCrAlY/PSZ FGMs and NiCr/PSZ FGMs were prepared on SUS310S substrates by plasma twin torches method under atmospheric or low pressure. Designed compositional gradient of FGMs could be sprayed. Porosity in NiCrAlY/PSZ FGMs was increased with volume fraction on PSZ. When the FGMs were heat treated in a uniform temperature field of 1473 K, PSZ part was sintered and vertical cracks were formed by shrinkage. At the same time, metal which contained a number of Fe atoms went into the cracks, and climbed up to the surface. The Fe atoms were migrated from the substrate through NiCrAlY part. Therefore, it is most important to decrease porosity in PSZ area as well as to control the distribution of pore to restrain crack formation. Coating metal with the same composition as the substrate is desirable for the thermally stable FGM.
When the FGM was heat treated in a gradient temperature field of 1473-873 K, there was little change in the FGM structure. The FGM showed a high potential for protection coatings of turbine blades.