Chapter 31 - Sintering Processes

Abstract

Modern applications of sintering in materials technology are widespread: (1) powder-technological production of structural steel parts, (2) self-lubricating bearings, porous metals for filtering, (3) tungsten wires for lamp filaments, (4) soft and hard magnetic materials, (5) electrical contacts, (6) composite packages for highly integrated electronic devices, (7) oxide-dispersion strengthened superalloys for high temperature motors, (8) amalgams for dental applications, (9) metallic and ceramic materials for medical applications, and (10) cemented carbides for cutting tools, along with a large variety of ceramic components. All these are only a few of the many technical production processes involving sintering as an important step. The technology of sintering and hot-pressing has been thoroughly developed down to minute details. Physicists, chemists, metallurgists, and ceramists have worked together to establish the theoretical basis for understanding the complex interaction of geometrical and thermodynamic factors and the effects of a number of mechanisms that occur simultaneously or in sequence. In the majority of technical applications, powders are compacted into shaped parts, which then are heat-treated to give them the required mechanical and physical properties. The essential difference between a powder and a dense solid body of exactly the same material and identical mass is from the energetic point of view—that is, the excess free energy due to the broken atomic bonds at the surface. Stressing this fundamental aspect, pressureless sintering as material transport driven by surface energy or, in other words, by capillary forces can be defined.