Severe Plastic Deformation of Aluminium Alloy : Scholars' Press : 9786138827993 : 6138827996 : 09 Oct 2019 : It is usually impossible to completely eliminate porosity, even in materials consolidated under very high pressure and temperature. In addition, nanopowders are very susceptible to oxidation and absorb large quantities of impurities such as O2, H2 and N2, making it difficult to obtain clean bulk materials. The porosity as well as impurities significantly affects the mechanical properties of the bulk materials, often making them brittle. These problems prevent us from studying the intrinsic properties of bulk nanomaterials. As a consequence of these difficulties, much attention has been paid to alternative procedures of introducing ultrafine grains in materials by severe plastic deformation.