SHAPING OF MASSIVE BILLETS FROM THE NANO-PARTICLES

摘要

There is a known method of production of the highly dense billets from the powders with the initial size of particles within less than 200 nanometers that is based on the severe shear deformations at the pressures 5 to 10 GPa. However, such conditions are provided only in the relatively thin layer of the powder, which constrains the practical and technological use of this method. In this paper we give the results of cold isostatic and non- isostatic pressing. Billets possessing high level of mechanical properties have been obtained at the certain conditions from the powders with the average size of particles 30 nanometers. This method allows forming the billets whose height is bigger than the diameter. The majority of methods dealing with the production of massive ultrafine-grained nanostructured materials include compaction of initial ultrafine-dispersed powders. Until now, there are problems connected with development of practical methods to produce massive samples. One of the most effective methods is the powder torsion under a high pressure (fig. 1). The high density of a material in the samples is reached as a result of severe plastic deformation (SPD) of a powder by torsion under pressures 5... 10 GPa. However, such conditions are provided only in rather thin layer of a powder that limits this method applicability. Equal channel angular pressing (ECAP) method is known to be an effective way for the compaction of powders of plastic metals and alloys (fig. 2). To create the favorable compaction conditions and to maintain the technological plasticity of a material, the processing is carried out at the raised temperatures. For example, compaction of copper-silver powders' mixes was carried out at 300°N . At nano-size powders compaction, the temperature conditions of deformation should be controlled in view of their possible negative influence on the structure and properties of a material. In connection with the aforesaid, the opportunities to apply ECAP for the nano-size powders' compaction are also limited, especially for low-ductile and hard materials.