Formation of titanium nitride, titanium carbide, and silicon carbide surfaces by high power femtosecond laser treatment

Coatings based on titanium nitrides, titanium carbides and silicon carbides can optimize the surface properties of titanium or silicon for various applications ranging from biocompatibility to chemical stability and durability. Here, we investigated a high power (100 W) high pulse repetition rate femtosecond laser process (λ=1030 nm, τ=750 fs, f=1 MHz) for the treatment of titanium and silicon in atmospheres of argon, nitrogen, methane, ethene and acetylene. In a nitrogen atmosphere, a homogeneous coating of TiON is formed on titanium. In an ethene/argon atmosphere coatings of TiOC and SiC are formed on Ti and Si, respectively. The process allows a fast surface transformation with a process rate of 0.33 cm2 s−1 and a high spatial resolution below 0.5 mm with a minimal heat affected zone at the same time. In contrast to low repetition rate femtosecond laser processed samples, the surfaces are more robust against mechanical impact. At the same time, the surfaces reveal a distinct microstructure in comparison to coatings obtained by vapor deposition techniques

From femtosecond to nanosecond laser microstructuring of conical aluminum surfaces by reactive gas assisted laser ablation

A conical microstructure is one of the most versatile surface textures obtained by ultrashort laser micromachining. Besides an increased surface area, unique surface properties such as superhydrophilicity, increased absorptivity; and thermal emissivity can be tailored. On metals, usually ultrashort laser pulses in the femtosecond to low picosecond range are used to obtain these surface structures, whereas nanosecond laser pulses favor melting processes. Herein, we report on an investigation of reactive gas atmospheres such as oxygen, steam, and halogens during laser micromachining of aluminum with 6 ns laser pulses. At a reduced pressure of 20 hPa (air) with additional iodine vapor as reactive species, we found a perfectly microconical structured surface to be formed with nanosecond laser pulses. The resulting surface structures were proven to be free of residual halogens. The application of nanosecond instead of femtosecond laser pulses for the surface structuring process allows to apply significantly less complex laser sources

Microconical surface structuring of aluminium tubes by femtosecond laser processing

Femtosecond laser microstructuring is a convenient technology for the targeted surface functionalization of various materials. Commonly, the structuring process is performed on planar surfaces. Here, we investigated femtosecond laser structuring of aluminium tubes. Process parameters, i.e. the number of pulses per spot on the surface and the line distance, have been transformed from a line-by-line process on planar samples towards a helical process. The process is based on laser treating the rotating tube while the laser beam is moved along the axis of the tube. A significant difference of the surface structure obtained on a cylinder in comparison to the planar geometry is revealed. With exactly matching process parameters, a strong increase of the dimensions of the surface structures on aluminium tubes has been observed. With a typical parameter set to achieve microconically structured aluminium, the cone height increases from 5 to 24 µm and the cone-to-cone distance from 13 to 59 µm. The structure sizes were found to be unaffected from the diameter of the tube within a range from 12 to 40 mm. A possible explanation for the increased structure size is given by altered particle redeposition. Two different parameter sets have been transformed from a planar geometry to the cylindrical geometry. Deep black aluminium tubes providing hydrophobicity with a water contact angle up to 148° and a thermal emissivity up to 87 % are demonstrated

Conical microstructuring of titanium by reactive gas assisted laser texturing

Femtosecond laser micromachining is an important and flexible method to generate precisely targeted surfaces on various materials. On titanium, the laser structuring process strongly depends on the laser parameters. For example, an increasement of the pulse length and repetition rate favors melting processes instead of ablation and microstructuring. We report on an investigation of reactive halogens (iodine, bromine, chlorine) and halocarbons as additives to the laser structuring process of pure titanium and the common alloy Ti-6Al-4V with 0.75 ps laser pulses. The choice of the halogen allows control of whether solely the chemical composition or the surface microstructure should be altered. Bromine was found to be an efficient additive to generate homogeneous microstructures based on micropillars at convenient conditions (air, atmospheric pressure). The resulting surfaces have been characterised by scanning electron microscopy, energy dispersive X-ray spectroscopy, thermal emission infrared photography, reflective UV/Vis spectroscopy and contact angle measurements. The bromine/air processed titanium surfaces revealed superhydrophilicity, strongly increased thermal emissivity and a high absorptivity (“black metal”)