Processing of mullite–molybdenum graded hollow cylinders by centrifugal molding technique

Continuous microstructural graded hollow cylinders were processed and characterized using a developed technique named centrifugal molding technique. Alcohol based slurries containing mullite and molybdenum (Mo) powders were tested in this work. Hollow cylinders with ceramic rich in inner surface and metal rich in outer surface were fabricated with the smooth increase of Mo content toward outer direction. Sintering condition was optimized and graded hollow cylinders were sintered at 1600 °C for 3 h in the reducing atmosphere. No new phases were observed after sintering. Microstructural observation and EDX analysis performed showed linear gradation of Mo content along the radial direction of cylinders. The methodology of mixing process of starting materials in the form of slurry immensely influenced the microstructural pattern across the thickness of graded specimens. Measured Vickers hardness values proved the continuous compositional change from inner to outer surface of graded cylinders and the hardness became constant in outer surface of graded specimens due to formation of interconnected Mo structures.