Processing of CP-Ti by high-pressure torsion and the effect of surface modification using a post-HPT laser treatment

Commercial purity titanium (CP-Ti) was processed by high-pressure torsion (HPT) with various numbers of turns (N = 1, 10 and 20). The hardness of the CP-Ti increased with an increasing number of HPT turns due to grain refinement. Tensile testing showed that the HPT-processed 10 turns sample had low ductility and high strength but the ductility may be improved through post-HPT short-term annealing at carefully selected temperatures. Some HPT-processed samples were laser surface-treated with different laser powers and scanning speeds. The surface roughness of the laser-textured samples increased with increasing laser power and led to a lower contact angle which signifies an increased hydrophilicity. After a holding time of 13 days, the samples underwent a hydrophilic-to-hydrophobic transformation as the contact angle increased to as much as 129 degree. It is concluded that laser surface texture processes are capable of controlling the hydrophilic / hydrophobic properties of ultra-fine grained CP-Ti

Fabrication and characterization of nanostructured immiscible Cu-Ta alloys processed by high-pressure torsion.

Nanostructured Cu–Ta alloys show great potential as high strength nanocrystalline materials due to their excellent mechanical properties and limited grain growth at high temperatures. This report describes the fabrication of nanostructured immiscible Cu-Ta alloys in bulk by high-pressure torsion (HPT) using a stack of Cu/Ta/Cu discs at room temperature. A microstructural study after HPT processing showed that the internal Ta layer breaks into small individual flakes which distribute uniformly over the Cu matrix through increases in the numbers of HPT turns. There is solid-state diffusion between the Cu and Ta when the HPT processing increases to 100 turns due to microstructural refinement and increasing crystalline defects. After processing through 150 turns, a composite microstructure of two phases is formed including supersaturated Cu-Ta solid solutions (Cu81Ta19 and Ta78Cu22 alloys) with a crystallite size of ~35-45 nm. This fine microstructure produces exceptional mechanical properties including a high hardness of over 350 Hv corresponding to ~3.43 GPa, a tensile strength of ~1300 MPa and a tensile elongation of about 40%

The fabrication of graphene-reinforced Al-based nanocomposites using high-pressure torsion

Metal matrix nanocomposites were fabricated by high-pressure torsion (HPT) using 5% graphene nanoplates as a reinforcement contained within an Al matrix. Powders were mixed and compacted at room temperature and then processed by HPT at three different temperatures of 298, 373 and 473 K. After processing, microstructural observations were undertaken to reveal the distributions of graphene in the matrix, the grain refinement in the aluminium and the nature of the graphene-aluminium interfaces. Tests were performed to measure the microhardness, the tensile stress-strain curves and the electrical conductivity. The results show that processing by HPT is advantageous because it avoids the sintering and high temperature deformation associated with other processing routes