Defects in Ultra-Fine Grained Mg and Mg-Based Alloys Prepared by High Pressure Torsion Studied by Positron Annihilation
J. Čížeka, I. Procházkaa, B. Smolaa, I. Stulíkováa, R. Kužela, Z. Matěja, V. Cherkaskaa, R.K. Islamgalievb and O. Kulyasovab
aFaculty of Mathematics and Physics, Charles University in Prague, V Holešovičkách 2, 180 00 Praha 8, Czech Republic
bInstitute of Physics of Advanced Materials, Ufa State Aviation Technical University, Ufa 450000, Russia
Full Text PDF
Received: 20 09 2004;
Despite the favourable strength and thermal stability, a disadvantage of the Mg-based alloys consists in a low ductility. Recently it has been demonstrated that ultra fine grained metals with grain size around 100 nm can be produced by high pressure torsion. A number of ultra fine grained metals exhibit favourable mechanical properties consisting in a combination of a very high strength and a significant ductility. For this reason, it is highly interesting to examine microstructure and physical properties of ultra fine grained Mg-based light alloys. Following this purpose, microstructure investigations and defect studies of ultra fine grained pure Mg and ultra fine grained Mg-10%Gd alloy prepared by high pressure torsion were performed in the present work using positron annihilation spectroscopy combined with X-ray diffraction, TEM observations, and microhardness measurements. Positrons are trapped at dislocations in Mg and Mg-10%Gd alloy deformed by high pressure torsion. A number of dislocations increases with the radial distance r from the centre to the margin of the sample. No microvoids (small vacancy clusters) were detected. Mg-10%Gd alloy deformed by high pressure torsion exhibits a homogeneous ultra fine grained structure with a grain size around 100 nm and high dislocations density. On the other hand, pure Mg deformed by high pressure torsion exhibits a binomial type of structure which consists of "deformed regions" with ultra fine grained structure and a high dislocation density and dislocation-free "recovered regions" with large grains. It indicates a dynamic recovery of microstructure during high pressure torsion processing.
DOI: 10.12693/APhysPolA.107.738
PACS numbers:78.70.Bj, 79.60.Jv, 61.72.-y