Laser shock peening without coating induced residual stress distribution, wettability characteristics and enhanced pitting corrosion resistance of austenitic stainless steel

Low energy laser shock peening without coating (LSPwC) was conducted on AISI 304 austenitic stainless steel specimens with varying pulse densities or overlapping. Highest magnitude of compressive residual stress (CRS) was achieved for an optimized pulse density of 2500 pulses/cm2 (75% overlapping). The 2-D and 3-D topographical analysis were indicative of the fact that controlled roughening of the surface was achieved after the LSPwC process. After the LSPwC process, the hydrophilic unpeened surface was converted into the hydrophobic surface, thus decreasing the wettability characteristics of the surface. The X-ray diffraction (XRD) results reveal that there is a beginning of the martensite transformation and the rise in the intensity value of the peaks after LSPwC indicates the presence of compressive residual stresses induced in the specimen. The optical microscope and high-resolution transmission electron microscope results provided evidence of grain refinement and deformation induced refinement features such as multidirectional mechanical twinning, dislocations lines, micro shear cells and stacking faults in the near and sub-surface areas. The average hardness value of the LSPwC specimens was found to be increased by 28% more than the untreated specimen. The potentiodynamic polarization revealed that there was a considerable amount of increase in the pitting corrosion resistance after the LSPwC process, thus, supporting to extend the fatigue life of the specimen. The electrochemical impedance spectroscopic (EIS) analysis depicts that the LSPwC process supports the formation of the strong passivation layer in 3.5% NaCl solution.Publisher Statement: NOTICE: this is the author’s version of a work that was accepted for publication in Applied Surface Science. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Applied Surface Science, [428, (2017)] DOI: 10.1016/j.apsusc.2017.09.138© 2017, Elsevier. Licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International http://creativecommons.org/licenses/by-nc-nd/4.0

4-(3-Eth­oxy-4-hydroxy­styr­yl)-1-methyl­pyridinium tosyl­ate monohydrate

In the title compound, C16H18NO2 +·C7H7O3S−·H2O, the dihedral angle between the pyridyl and benzene rings of the pyridinium cation is 0.2 (1)°. The benzene ring of the tosyl­ate anion makes a dihedral angle of 4.8 (2)° with the best mean plane of the pyridinium cation. The pyridinium cation and the tosyl­ate anion are hydrogen bonded to the water mol­ecule, and the crystal packing is further stabilized by inter­molecular C—H⋯O and π–π inter­actions [centroid–centroid separations of 3.648 (3) and 3.594 (2) Å

Laser Cleaning of Grey Cast Iron Automotive Brake Disc: Rust Removal and Improvement in Surface Integrity

There is a great need for removal of rust and surface damage from corroded engineering parts. This enables the retention of strength and increased longevity of metals and alloys in general. The use of lasers for cleaning, polishing and ablation has proven to be effective and promising overtime. This research is focused on a parametric study of laser cleaning a corroded grey cast iron brake disc. A continuous wave CO2 laser having a wavelength of 10.6μm was used for the study. A systematic approach was employed for the experiments where one parameter was changed while other parameters remained constant. Additional effects of laser cleaning were predicted by a Gaussian process regression approach. The results revealed that the best parameters which cleanly removed the rust were 60W of laser power, 900mm/s traverse speed, and a spot size of 722μm. The enhancement of surface microhardness of laser cleaned specimen was 37% compared to the rusted specimen surfaces. The roughness of the laser cleaned surface was, 1.29μm while the rusted surface comprised of 55.45μm (Ra). Microstructural analysis showed a presence of randomly distributed graphite flakes surrounded by a pearlitic matrix containing ferrite and cementite after laser cleaning. This was similar to that of the un-rusted surface. The hardness, roughness and microstructural content were in close relation with the respective properties of the unrusted automotive brake disc. This showed that the mechanical and physical properties of the brake disc were not altered negatively during the laser cleaning process. Implementation of the laser-cleaning technique in automotive and manufacturing industries should be embraced as it provides a faster, safer and cheaper way of enhancing the surface integrity of components and also paves way for other surface enhancement methodologies to be applied such as blast cleaning or laser shock cleaning for inducing extra strength, by beneficial residual stresses