Effects of chemical inhomogeneities on grain growth and microstructure in Al2O3

Effects of chemical inhomogeneities and single-crystal seeds on normal and discontinuous grain growth were investigated in both undoped and MgO-doped Al2O3. The chemical impurities in the samples were exsolved at a lower temperature than the sintering temperature and measured by SEM/EDS to determine the correlation between the distribution of impurities and the microstructure in Al2O3. A feature of this study was the use of clean-room processing and firing procedures to maintain sample composition at the levels initially present in the starting powders. As the local concentrations of chemical impurities (i.e., Si, Ca) increased, the grain boundary–grain boundary dihedral angle distribution widened, with many angles at 180°, the grain-size distribution widened, and pore–boundary separation was enhanced. Discontinuous grain growth was observed in regions of undoped Al2O3 containing the largest Ca and Si concentrations. It is suggested that doping with MgO solute reduces the effects of impurities on grain growth by increasing the bulk solubility and decreasing interfacial segregation of impurities, especially Si, and by narrowing the distribution of grain boundary–grain boundary dihedral angles.

[1]  D. Beasley,et al.  The influence of layer and bond strengths on the ductility of an all beryllium laminate , 1975 .

[2]  M. Kinoshita.  Boundary Migration of Single Crystal in Polycrystalline Alumina , 1974 .

[3]  M. Yan.  Microstructural control in the processing of electronic ceramics , 1981 .

[4]  J. Halloran,et al.  Single‐Crystal Boundary Migration in Hot‐Pressed Aluminum Oxide , 1979 .

[5]  Michael P. Anderson,et al.  Computer simulation of grain growth—IV. Anisotropic grain boundary energies , 1985 .

[6]  M. Harmer,et al.  Grain‐Growth Kinetics for Alumina in the Absence of a Liquid Phase , 1985 .

[7]  C. Handwerker,et al.  Effect of chemical composition on sintering of ceramics , 1986 .

[8]  S. Roy,et al.  Solubilities of Magnesia, Titania, and Magnesium Titanate in Aluminum Oxide , 1968 .

[9]  C. Handwerker,et al.  Effect of a Liquid Phase on the Morphology of Grain Growth in Alumina , 1987 .

[10]  M. Harmer,et al.  Swelling of Hot-Pressed A12O3 , 1985 .

[11]  R. Coble.  Sintering Crystalline Solids. II. Experimental Test of Diffusion Models in Powder Compacts , 1961 .

[12]  M. Harmer,et al.  Effect of MgO Solute on the Kinetics of Grain Growth in A12O3 , 1983 .

[13]  C. Thompson,et al.  The relative rates of secondary and normal grain growth , 1987 .

[14]  David J. Srolovitz,et al.  Computer simulation of grain growth—V. Abnormal grain growth , 1985 .

[15]  W. C. Johnson,et al.  A Test of the Second‐Phase and Impurity‐Segregation Models for MgO‐Enhanced Densification of Sintered Alumina , 1978 .

[16]  Robert L. Coble.  Effects of Particle-Size Distribution in Initial-Stage Sintering , 1973 .

[17]  A. M. Glaeser,et al.  Technique for Measuring Grain‐Boundary Mobility: Application to MgO‐Doped Al2O3 , 1982 .

[18]  I. Cutler,et al.  Grain Growth in Sintered Alumina , 1965 .