Size Change of Compacts Fabricated by Hot Pressing of Metal Powders
Metal powders are an important and versatile material used in a variety of manufacturing processes. One of these processes is hot pressing, which is utilized in the fabrication of pressed and sintered components. Hot pressing involves the consolidation of metal powders at elevated temperatures and pressures for varying lengths of time. This process produces components with a range of complex geometries that can be used in various applications. A significant characteristic of hot pressed compacts is their size changes during the pressing process, and this has been studied extensively in the literature.
Size change is an important measure of the efficacy of a pressing operation. During a hot pressing operation, the volume of the compact is reduced by a number of different mechanisms. The most significant of these are grain growth (due to recrystallization of the metal powder), and physical deformation. Grain growth occurs due to the diffusion of metal particles, while physical deformation is due to plastic deformation of the metal particles. As a result of these two mechanisms, the volume of the compact decreases, and the size of each individual grain or particle increases.
The magnitude of the size changes which occur during a hot pressing operation is strongly dependent on the type and composition of the metal powder, the pressing parameters (temperature and pressure) used, and the length of time of the pressing period. For example, the size change of a compacts fabricated with a nickel powder may be significantly different than a compacts fabricated with an steel powder, due to the differences in their physical and chemical properties. Furthermore, the magnitude of the size changes is typically greater for higher temperature and pressure, and for extended pressing times.
Size changes are generally characterized using dimensional techniques such as optical microscopy and scanning electron microscopy. Microstructural indicators such as grain size and porosity are also commonly monitored. These techniques allow for the precise measurement of the size changes occurring during the hot pressing process, and can be used to optimize the pressing parameters for a given metal powder.
In conclusion, size change is an important parameter that affects the efficacy of the hot pressing process, and is strongly dependent on the type and composition of the metal powder, along with the pressing parameters used. Various dimensional and microstructural techniques are utilized to monitor the size changes during the pressing operation, and these can be used to optimize the pressing parameters in order to achieve desired characteristics.
