The primary goal of sintering research is the controlled manipulation of microstructure. Out of the entire range of microstructures which are theoretically possible, each material system will be able to achieve only a subset of them, depending on the intrinsic material properties. Within these material constraints, the aim is to produce microstructures which enhance specific properties. Our understanding of the relationships among materials processing, microstructure, and properties is just beginning to emerge, and is producing unexpected results. For example, in a recent study of toughness in Al2O3 by Bennison and Lawn, microstructures with platy grains and a bimodal grain size distribution in undoped Al2O3 exhibited a greater resistance to crack propagation than did the more uniform microstructures in MgO-doped Al2O3 [1]. As a result of this emerging understanding, the focus of sintering science is changing from the modification of microstructures in incremental ways for correspondingly incremental improvement in properties to more effectual manipulation of microstructures to optimize properties. However, the production of the optimum microstructure will be dependent on both the material and the application and may require radically different processing routes for different materials. In this review paper, we have examined the research in sintering science over the past five years which has advanced the goal of microstructure manipulation.

Sintering of Ceramics

High-density alumina was produced by fast firing (5 min, temperatures ≤1550°C). Most of densification occurred under nonisothermal conditions. High densification rates observed are related to a change in the internal structure of the compact. The formation of a dense outer alumina layer controlled the heat flux to the interior of the compact, and increased the amount of energy available for sintering. Sintering in fast firing occurred as a densification front moving from the outer surface toward the sample center. As long as the rate of heat transfer is enough to sustain its advance, no differential densification occurs.

Building a Sintering Front through Fast Firing

Macroscopic simulation of consolidation during hot isostatic pressing

Models for analysing shape changes during the hipping of powder compacts enclosed in preshaped containers are presented. Two limiting mechanisms are considered: homogeneous densification and the mo ...

Modelling Shape Change of Parts Produced by Hot Isostatic Pressing of Powders

Densification in a HIP cycle is non-uniform because of the temperature gradient in the powder body. This gradient gives rise to a densification front, which moves from the surface inward. The densi ...

Eric Navara

Papers

Modelling Shape Change of Parts Produced by Hot Isostatic Pressing of Powders

Modelling the shape change of parts produced by hot iostatic pressing of powders