2007 Volume 48 Issue 12 Pages 3066-3069
Functionally graded materials (FGMs) were prepared by spark plasma sintering using coal fly ash and NiCr alloy powder. The coal fly ash was produced by Misumi coal thermal power station (Chugoku Electric Power Co., Inc.), and 80 mass% nickel and 20 mass% chromium (Fukuda Metal Foil & Powder Co., Ltd) were used as source materials. The sintering was done at 1000°C in a graphite die. X-ray diffraction patterns of the sintered coal fly ash materials indicated that the mullite (3Al2O3·2SiO2) and silica (SiO2) phases were predominant. Direct joining of coal fly ash and NiCr causes a fracture at the interface due to a mismatch of thermal expansion. Cracks in the FGMs were observed between the two layers when the difference of linear thermal expansion coefficient (α) was over 4.2×10−6 K−1, while no cracks were detected in stable FGMs when the difference was less than 4.0×10−6 K−1.
