Date of Award
Master of Science (MS)
This study used grain size control and ductile phase reinforcement to improve fracture toughness of ����� ceramics. Alpha alumina particles of 100 nm, 0.5-1 micrometers, and 10 micrometers were coated with 1-5 nm nickel by electroless nickel plating (ENP). The coated powders were consolidated at 1200℃-1500℃ by spark plasma sintering (SPS). The sintered samples were annealed at 1100 oC for 1.5 hours and 10 hours to determine the effect of post sintering annealing on hardness and fracture toughness. Density of the samples were measured by the standard Archimedes method using a 5 mL pycnometer. Hardness values were determined by Vickers micro hardness indentations and the fracture toughness values were calculated from indentation dimensions and indentation-tip crack length measurements. Uncoated powders, coated powders, consolidated samples and post SPS annealed samples were characterized by Scanning Electron Microscopy (SEM). The fracture toughness of alumina increased by more than 100% (9.19 MPa.Öm for coated alumina in comparison to about 3.98 MPa.Öm for uncoated alumina) for certain particle size-coating-sintering conditions. Results were analyzed in terms of crack bridging mechanisms.
Shankar Sastry, Kathy Flores, Peng Bai