When using ultra-short pulsed laser sources in combination with direct laser interference patterning (DLIP) technology, two different type of periodic surface structures can be produced, including a primary structure based on the DLIP features as well as a second type of structural elements having feature sizes about 2 to 10 times smaller. Such multi-scaled structures surfaces (also called hierarchical patterns) are ideal to provide metallic surfaces with unique functions. On the other hand, for increasing the process throughput it is necessary to apply higher average laser powers, what can cause heat accumulation effects and thus having a negative impact on the quality and characteristics of the produced surface topography. Consequently, the effect of substrate temperature on the topography of fabricated features requires detailed investigations.
This study presents the use of a 532 nm laser source in combination with DLIP method for fabricating hierarchical surface structures on steels. A two-beam configuration is applied in order to create line-like structures with feature sizes in the micrometer range. To investigate the influence of substrate temperature on the resulting topography, the temperature of the irradiated stainless steel substrates was varied, from room temperature to 250°C. When the substrates were heated at 250°C, a significant reduction of the produced structure depth was observed. In addition, depending on the grain orientation at the irradiated material, different LIPSS type structures were observed, which could explain the observed reduction of the structure depth. This study revealed a strong effect of substrate temperature, which is also to be expected when heat accumulation effects arise from processing surfaces at high average laser power.