Investigation into the laser polishing of an austenitic stainless steel

Surface Morphology Evolution Mechanisms of Laser Polishing in Ambient Gas

During the crystal growth process using the floating zone method, the uneven distribution of impurities on the surface of the melt can trigger a coupling mechanism between solutocapillary convection driven by the concentration gradient and thermocapillary convection driven by the temperature gradient, resulting in the Marangoni convection at the free surface. When the temperature and concentration gradients reach certain values, the crystal surface and interior exhibit time-dependent, periodic oscillations, leading to the formation of micrometer-scale impurity stripes within the crystal. This study focuses on the effects of temperature difference and heat loss in a liquid bridge under microgravity on the structure and interface oscillation characteristics of thermo-solutocapillary convection, aiming to explore the coupling phenomenon of this oscillation and provide valuable information for crystal growth processes. An improved level set method is employed to accurately track every displacement of the interface, while the surface tension is addressed using the CSF model. In addition, the area compensation method is used to maintain simulation quality balance. A comprehensive analysis is performed on the oscillation characteristics of thermo-solutocapillary convection at the free surface, ranging from the temperature, concentration, deformation, and velocity distributions at the upper and middle heights of the liquid bridge. The results indicate that under small temperature differences (ΔT = 1 − 3), the transverse velocity at the upper end exhibits a single-periodic oscillation, while the longitudinal velocity presents a double-periodic oscillation. At the intermediate height, both the transverse and longitudinal velocities display a single-periodic oscillation. Under a large temperature difference (ΔT = 6), the oscillation of velocities at the upper end and the middle position become multi-periodic. In addition, heat loss has certain regular effects on the oscillatory flow of thermo-solutocapillary convection within a certain range. The velocity, amplitude, and frequency of the upper end and the middle position at the free surface decrease gradually, and the oscillation intensity also weakens with the increase in heat loss (Bi = 0.2 − 0.6). These new discoveries can provide a valuable reference for optimizing the crystal growth process, thereby enhancing the quality and performance of crystal materials.

/pdf/effects-of-temperature-difference-and-heat-loss-on-3fk19wcn.pdf

Effects of Temperature Difference and Heat Loss on Oscillation Characteristics of Thermo-Solutocapillary Convection in Toluene/N-Hexane Mixed Solution

Tungsten carbide is currently the most widely used tool material for machining difficult-to-machine materials, such as titanium alloys and nickel-based super alloys. In order to improve the performance of tungsten carbide tools, surface microtexturing, a novel technology that can effectively reduce cutting forces and cutting temperatures and improve wear resistance, has been applied in metalworking processes. However, when fabricating the micro-textures such as micro-grooves or micro-holes on tool surfaces, the significant decrease in material removal rate is a major obstacle. In this study, a straight-groove-array microtexture was fabricated on the surface of tungsten carbide tools via a femtosecond laser with different machining parameters including laser power, laser frequency, and scanning speed. The material removal rate, surface roughness, and the laser-induced periodic surface structure were analyzed. It was found that the increase in the scanning speed decreased the material removal rate, whereas increasing the laser power and laser frequency had the opposite effects on the material removal rate. The laser-induced periodic surface structure was found to have a significant influence on the material removal rate, and the destruction of the laser-induced periodic surface structure was the reason for the reduction in the material removal rate. The results of the study revealed the fundamental mechanisms of the efficient machining method for the fabrication of microtextures on ultrahard materials with an ultrashort laser.

/pdf/surface-quality-and-material-removal-rate-in-fabricating-3nfqvv2w.pdf

Surface Quality and Material Removal Rate in Fabricating Microtexture on Tungsten Carbide via Femtosecond Laser

A new method of surface structuring by laser remelting with the help of surface tension (mainly thermocapillary force and solutocapillary force) and volume expansion was proposed. A multiphysics coupled numerical model was proposed for this surface structuring method, in which the calculation of surface tension and solutocapillary force is improved. Using the established numerical model, the formation mechanism of the surface structure was explored from the aspects of surface tension, fluid flow, volume expansion, and surface profile evolution. The reason why the surface structure changes from a “W” shape to an “A” shape was explained, and the contributions of thermocapillary force, solutocapillary force, and volume expansion to the surface structure were investigated. The effects of laser power, scanning speed, and beam diameter on the surface profile of the surface structure were studied by experiments, which indicates that the desired surface structure can be obtained by adjusting the process parameters. All the experimental results were simulated by the established numerical model, and the simulation results are in good agreement with the experimental results, indicating that the numerical model is effective and available. 

Investigation on the mechanism of a new laser surface structuring by laser remelting

The machinability of stainless steel 316L fabricated by selective laser melting: typical cutting responses, white layer and evolution of chip morphology

Lu Liu

Papers

Investigation on the mechanism of a new laser surface structuring by laser remelting

The machinability of stainless steel 316L fabricated by selective laser melting: typical cutting responses, white layer and evolution of chip morphology

Investigation into the laser polishing of an austenitic stainless steel