Strengthening and toughening of additively manufactured Ti-6Al-4V alloy by hybrid deposition and synchronous micro-rolling

To overcome the disadvantages of inhomogeneous microstructures and poor mechanical properties of additively manufactured Ti-6Al-4V alloys,a novel technique of hybrid deposition and synchronous micro-rolling is proposed.The micro-rolling leads to equiaxed prior β grains,thin discontinuous intergranular α,and equiaxed primary α,in contrast to the coarse columnar prior β grains without the application of micro-rolling.The recrystallization by micro-rolling results in discontinuous intergranular α via the mechanism of strain and interface-induced grain boundary migration.The evolution of α globularization,driven by a solute concentration gradient,starts from the sub-boundary until the formation of equiaxed primary α.Simultaneous strengthening and toughening are achieved,which means an increase in yield strength,ultimate tensile strength,fracture elongation,and work hardening rate.The formation of α recrystallization leads to more fine grain boundaries to strengthen the yield strength,and the improvement of ductility is due to the better-coordinated deformation ability of discontinuous intergranular α and equiaxed primary α.As a result,the fracture mode in micro-rolling changes from intergranular type to transgranular type.

Preparation of Hydrophobic Surface on Titanium by Micro-Rolling and Laser Diffusion Carbonitriding

The application of rolling for fabricating grate on titanium stripe has been explored in this paper. Then the mechanically robust Ti（C,N） diffusion layer was synthetized directly on the grates by laser carbonitriding in the mixture gas of nitrogen and methane. The results shows that the carbonitriding process is accelerated by temperature enhancement with decreasing scanning speed, The Ti（C,N） diffusion layer is kept at 2 ~nn in thickness, when the scanning speed is smaller than 4 mm/s. The contact angle increases from 20~ to 143.6~ by designing an appropriate grate size and surface roughness. Meanwhile, the relationship between hydrophobicity, hardness performance and scanning speed is also discussed. The hardness of diffusion layer increases with decreasing laser scanning speed, and is up to 11.2 GPa. The surface structure and hydrophobic state are maintained after three cycles of sandpaper abrasion, which has improved the robustness of surface grate.

Effects of microrolling parameters on the microstructure and deformation behavior of pure copper

Microrolling experiments and uniaxial tensile tests of pure copper under different annealing conditions were carried out in this paper. The effects of grain size and reduction on non-uniform deformation, edge cracking, and microstructure were studied. The experimen- tal results showed that the side deformation became more non-uniform, resulting in substantial edge bulge, and the uneven spread increased with increasing grain size and reduction level. When the reduction level reached 80% and the grain size was 65 μm, slight edge cracks occurred. When the grain size was 200 μm, the edge cracks became wider and deeper. No edge cracks occurred when the grain size was 200 μm and the reduction level was less than 60%; edge cracks occurred when the reduction level was increased to 80%. As the reduction level increased, the grains were gradually elongated and appeared as a sheet-like structure along the rolling direction; a fine lamellar structure was obtained when the grain size was 20 lam and the reduction level was less than 60%.