Evolution of surface topography of 304L stainless steel irradiated by long pulse laser

Abstract

The evolution of surface topography of 304L stainless steel, induced by long pulse laser with a wavelength of 1070 nm and a pulse width of 10 μs and a pulse number of 400 in air, was investigated in the fluence range between around 3 J/cm2 and 210 J/cm2. Three-dimensional (3D) morphologies and two-dimensional (2D) cross-sectional profiles of microstructures at different laser fluences were compared. Furthermore, surface profiles of the microstructures were quantified by using the inner diameter, the outer diameter, the elevation of central area and the rim height thereof. The trends of the above four geometrical parameters and surface profiles suggest five laser fluence ranges, where the corresponding topographies change from bump to crater. Energy dispersive spectrometer (EDS) was used to analyze surface elements of different microstructures, and the results showed that the content of oxygen had a great influence on surface tension and surface topography. In this study, a complex picture was drawn where melting, vaporization, solidification, melt displacement, melt expulsion and plasma shielding take place at different laser fluences.

Experimental study on bumps formation textured by nanosecond laser on Ti6Al4V alloy

“…This shows that the nanosecond laser cannot remove the recast layer. The result of Li [28] confirms this experimental phenomenon. According to the results, the roughness parameters can be optimised to improve the surface properties.…”

“…There are some explanations to expound the causes of forming the bump in stainless steel on this basis of numerical simulation. Li [27] believed that the oxygen concentration affected the surface tension gradient, and the bump was formed by the accumulation of oxidised substances [28]. In addition, some studies suggest that sulphur is the leading forming cause of the bumps because sulphur acts as the surfactant, which has shown that laser ablation affects the sulphur concentration on the surface, affecting the surface tension gradient [23,26].…”

Metal surface wettability modification by nanosecond laser surface texturing: A review

“…Li hypothesised that the oxygen content was the essential contributor that affects the surface tension. A study further supported Li's hypothesis, in which the surface tension was proposed to be a function of the oxygen content and temperature [122]. The bump consisted of the oxide layer.…”

“…[122] √[124] √ F I G U R E 1 1 Formation of bumps. (a) Marangoni convection caused radial inward flow of a molten pool.…”

A Technological Understanding of Biofilm Detection Techniques: A Review

“…This is caused by the protection of cells from removal, thus providing a more stable environment for biofilm growth [ 139 ]. However, according to Li et al (2018), the STC of SS can be drastically changed by heating, melting, plasma formation, and vaporization [ 140 ]. Therefore, no general conclusion can be made regarding the STC properties of SS.…”