Graded coatings by gradient temperature densification

Abstract

Functionally gradient materials (FGM) were prepared using layers of ZrO2-3 mol % Y2O3 ceramic and NiCrAlY powders. A fine-grained zirconia powder was chosen to lower the ceramic sintering temperature and achieve simultaneous metal and ceramic densification, Consolidation of FGM's was achieved by a short time field-assisted sintering technique. Sintering was performed either at a constant temperature or in a temperature gradient by using punches made of different materials (i.e., one graphite and one tungsten). A temperature gradient of at least 100 degrees C was required with a low value of 1200 degrees C at the metal end and exceeding 1300 degrees C at the ceramic end. Increasing the number of intermediate layers alleviates some of the cracks formed during sintering due to different coefficients of thermal expansion.