Role of plastic deformation in sintering powders
|Yuly V. Milman 2, Alexander Slipenyuk 1|
1. Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, Krzizanovsky, Kyiv 38(044), Ukraine
The development of physical concepts and analysis of experimental results have shown that intensive densification of powders in sintering is determined not only by diffusion processes, but by shape changing due to plastic deformation as well. In the absence of external stresses, plastic deformation is caused by the forces of capillary interaction, which are essential for the assembly of sintering particles. The elaborated classification of temperature ranges of plastic deformation includes three types: hot deformation (at temperature T>Tr, where Tr is the recrystallization temperature), warm deformation (at T*<T<Tr, where T* is the characteristic deformation temperature) and cold deformation at T<T*. The sintering without loading is possible in the temperature ranges of hot and warm deformation only, i.e., at T>T*. For metals as a rule T*<TD, where TD is the temperature at which the velocity of diffusion is sufficient for the process of sintering. Therefore the minimum sintering temperature for metals is determined by the value of TD . But in covalent crystals and ceramics T*>TD usually. Therefore the temperature of intensive densification for these materials is determined by the value of T* even for nano-size powders. Severe plastic deformation intensively accelerates the sintering process in the range of warm deformation. Increasing dislocation density during severe plastic deformation leads to the accelerated mass transfer due to growth of the vacancies density and due to the accelerated diffusion along the dislocations lines. In some cases the severe plastic deformation makes possible the consolidation of metastable powders: nanostructured, amorphous and quasicrystalline in which compacting must be carried out at relatively low temperatures. The examples of successful application of a severe plastic deformation for sintering of rapidly solidificated powders are given.
Presentation: invited oral at E-MRS Fall Meeting 2005, Symposium I, by Yuly V. Milman
See On-line Journal of E-MRS Fall Meeting 2005
Submitted: 2005-05-04 07:59 Revised: 2009-06-07 00:44