Influence of thermal and mechanical surface modifications induced by laser shock processing on the initiation of corrosion pits in 316L stainless steel

Pure mechanical and thermo-mechanical laser shock processing treatments have been carried out on an AISI 316L stainless steel. Surface properties, mostly mechanical and metallurgical modifications, were analysed at different scales: a local scale using the nano-indentation technique and AFM analysis, and a more macroscopic scale, using microhardness, optical microscopy and residual stress determinations. After a pure mechanical laser-peening treatment, a significant improvement in the pitting corrosion resistance (+0.1 V) was observed in 0.05 M NaCl. This improvement was attributed to the combined effects of compressive residual stresses and work-hardening, and, in turn, to a mechano-electrochemical phenomenon by which a modification of cathodic reactions occurs during electrochemical tests. For the surface treated by thermo-mechanical laser peening (combination of a surface ablation and shock waves), a tendency for decreasing resistance against pitting corrosion was shown, and attributed to the processing-specific surface texture (ablation craters), which made the material susceptible for the creation of occluded cells.

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EVALUATION OF THE INFRAALYZER 400 FOR THE ANALYSIS OF BARLEY AND MALT

A collaborative study is described of the use of infra-red reflectance for the evaluation of the analytical characteristics of barley and malt. Transfer of centrally-prepared calibrations to other reflectance machines was found to be possible for moisture content and protein content in barley and malt but not for malt extract or malt modification. The examination of infra-red reflectance results, obtained at different wavelengths, by step-wise ascending regression rather than step-wise descending regression showed that the former was more satisfactory, especially in being more rapid in execution.