Miloš Janeček; Peter Minárik; Tomáš Krajňák; Kristína Bartha; Josef Straskuy; Jakub Cizek
Abstract
Mg22Gd alloy was processed by high pressure torsion (HPT) at room temperature and the pressure of 2 GPa. A series of specimens with different number of rotations N (N = 0-15) was prepared from the initial coarse grained as cast material. Mechanical properties were investigated by microhardness mapping. ...
Read More
Mg22Gd alloy was processed by high pressure torsion (HPT) at room temperature and the pressure of 2 GPa. A series of specimens with different number of rotations N (N = 0-15) was prepared from the initial coarse grained as cast material. Mechanical properties were investigated by microhardness mapping. The microhardness was found to increase with increasing strain imposed by HPT and tend to saturate at about HV = 145. The microstructure (phase morphology and composition, etc.) evolution with strain was investigated by scanning electron microscopy and EDS. High Gd content in the alloy resulted in the precipitation of stable Mg5Gd phase. This phase exhibited apparently higher hardness than the magnesium matrix. During straining the phase was continuously fragmented and only tiny particles were found in heavily strained material. Electron back scatter diffraction (EBSD) and automated crystallographic orientation mapping in transmission electron (ACOM-TEM) were employed to characterize the fragmentation of the grain structure. HPT was found to result in strong grain refinement by the factor of approximately 1000. The dislocation density was determined by positron annihilation spectroscopy. Significant twinning was found in the initial stages of HPT straining. At high strains twin formation was suppressed and only dislocation storage in the material occurs.
Waleed H. El-Garaihy; Ayman M. Alaskari; Eisa A. Ameshaiei; Samy E. Oraby
Abstract
A loading combination of hot compaction (HC) together with high-pressure torsion (HTP) was used to consolidate discs of AA6061 considering rotations up to 4 revolutions and loading pressure values of 1 and 3 GPa. Mathematical models were established to grasp the true functional interrelationships and ...
Read More
A loading combination of hot compaction (HC) together with high-pressure torsion (HTP) was used to consolidate discs of AA6061 considering rotations up to 4 revolutions and loading pressure values of 1 and 3 GPa. Mathematical models were established to grasp the true functional interrelationships and variations in the resulting relative densities, mechanical properties, and micro-structural evolutions as affected by the HPT processing pressure and the imposed strain. Sequential iterative nonlinear regression procedures were employed to get the most suitable mathematical relationships that express the relationship between the variables under study. The developed models were examined for its adequacy and significance by using ANOVA analysis as well as many other statistical criteria. Response surface and contour graphs were established for a better understanding of the true functional dependence and, for a quantitative assessment of the intended relationships. It was observed that uniformity of hardness distribution increased with increasing each of the equivalent strain (εef) and the imposed pressure. A remarkable increase in the compressive strength of deformed discs has been observed. HPT processing produced a tri-model structure with micron scale grains and subgrains, and nano-scale substructure.
