Research of compaction and creep processes during sintering of aluminum oxide ceramics

Non-uniform densification of green compacts, sample warping, and deformation during sintering influence the final shrinkage of specimens, potentially leading to erroneous interpretation of sintering outcomes. The objective of this study was to investigate densification and creep behavior during the sintering of ceramics fabricated from submicron α-Al₂O₃ powder admixed with 0.25 wt. % MgO. Dilatometric techniques were employed to evaluate the development of shrinkage anisotropy in specimens subjected to increasing applied loads during sintering. Results demonstrate that, under low applied stresses (below the sintering stress), specimen densification remains independent of the imposed load. Creep rates increase with elevated applied stress, reduced initial green density, and extended isothermal holding times. Analysis of dilatometric shrinkage data for aluminum oxide specimens enables the decoupling of densification and creep contributions, thereby elucidating the effects of initial green density and sintering parameters. No grain growth was observed in the examined specimens at relative densities below 90% of theoretical. The observed exponential decline in average creep rate with increasing density is attributable to the pronounced grain size dependence of diffusional creep. The analogous response of densification and creep rates to variations in specimen density suggests that both processes are governed by identical mass transport mechanisms. The ratio of densification rate to creep rate was found to be proportional to the sintering stress and only weakly dependent on temperature. This ratio increases with specimen density. The findings offer valuable insights for refining sintering protocols and accurately assessing ceramic densification under constant heating rate regimes and isothermal holds.

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