Surface structuring by remelting of titanium alloy Ti6Al4V
Conventional surface structuring processes often share two crucial disadvantages. First, after the structuring process itself, some kind of surface finishing is often needed, based on another technology, which means a substantial additional expense. Second, all conventional surface structuring processes are based on the removal of material, which is wasted without any further use during processing. A new approach of structuring metallic surface structuring by laser remelting (WaveShape). In this process, no material is removed but reallocated while molten. This structuring process is based on the new active principle of remelting. The surface structure and the microroughness result from a laser-controlled self-organization of the melt pool due to surface tension. Up to now, basic research has been focused on hot work steel 1.2343 (AISI: H11), and promising results have been achieved for this material. Current research and development are now seeking to expand the spectrum of processable materials. Since remelting is a thermally driven process, significant differences between metallic materials are expected due to their thermo physical properties such as thermal conductivity, absorption coefficient, viscosity, and heat capacity. The titanium alloy Ti6Al4V has a wide range of industrial applications, especially for aviation, aerospace, and medical engineering. The WaveShape process for this material will be investigated within this paper. The procedural principle of surface structuring by remelting is based upon a sinusoidal modulation of laser power while the laser beam is moved over the surface. The lower process limit of laser power is the power required to melt material and, therefore, create a melt pool. In this context, the upper process limit of laser power is the point just before substantial amounts of the molten material are evaporated. We used metallographic cross sections to measure the dimensions of melt pool depth and width as they depend on procedural parameters, such as laser beam diameter (125-500 mu m), scanning velocity (25-200 mm/s), and laser power (20-400 W). We also investigated basic interdependencies between structural characteristics (e.g., height) and procedural parameters used, such as laser beam diameter, laser power, and wavelength of modulation. The results show that the WaveShape process is well suited to process titanium alloy Ti6Al4V since structures and process velocities achieved are significantly higher than for the previously investigated hot work steel.