Transformation stability and mechanical properties of infiltrated functionally graded mullite/yttria-stabilized tetragonal zirconia polycrystal/alumina composites

A novel infiltration method for processing mullite/yttria-stabilized tetragonal zirconia polycrystal/alumina (mullite/3Y-TZP/Al2O3) composite with graded transformation stability is described. This process involves infiltrating porous 3Y-TZP/Al2O3 composite preforms with a solution of ethyl silicate, followed by sintering at 1600degreesC and 1700degreesC for 2.5 hours. The resultant material has a homogeneous 3Y-TZP/Al2O3 core encased with a graded and heterogeneous layer of mullite/3Y-TZP/Al2O3. Analysis by X-ray diffraction and energy-dispersive spectrometry has revealed the existence of a concentration gradient of mullite, with the concentration decreasing with increasing depth into the sample. The graded composite displays a gradual change in thermal expansion values due to the presence of mullite. The partial loss of the Y-TZP/Al2O3 composite's mechanical strength and fracture toughness due to the introduction of Al2O3, can be prevented.