Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg

© 2018, The Author(s). High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing

Microstructural heterogeneity in hexagonal close-packed pure Ti processed by high-pressure torsion

Microstructural evolution was studied quantitatively by electron backscatterring diffraction in commercial purity Ti processed by high-pressure torsion (HPT) at room temperature. The results show that a heterogeneous microstructure develops during HPT processing with regions of both nanocrystalline grains (<100 nm) and coarse grains (~1-30 m). Tensile {10 2} twins were observed in the center of the disk after the first turn of HPT. The microhardness near the disk center increases with increasing HPT turns and the hardness after 5 turns is reasonably homogeneous at radial positions >1 mm. The mechanism of grain refinement is characterized by dynamic recrystallization and the continuous formation of a necklace-like array of fine grains gradually consumes the larger grains in subsequent passe