The sputter etching was carried out on a W Cr tool steel specimen quenched at 1373 K using argon plasma to form conical or ring shaped carbide protrusions on the surface. Nano indentation tests were used to investigate deformation characteristics of the protrusions from load P vs. displacement h curves at maximum loads of 10, 50 and 245 mN. For the surface layer with conical protrusions, the P h curve at the maximum load of 245 mN is almost similar to that of the specimen without sputter etching. The reason is explained by a balance of two factors, i.e. the hard carbide layer decreases the deformation during the indentation, while the soft region formed by the depletion of carbide forming elements under the carbide layer increases the deformation especially after the carbide layer is cracked by the indentation. When the maximum indentation load is 10 mN, the scatter of P h curves appears reflecting different indentation positions such as the top or side of the protrusions. For a mixture of the thick block like layers with ring shaped protrusions and the matrix areas surrounded by them, the maximum displacement and recovery after unloading are both large when the maximum load is 245 mN. The reason will be that the elastic deformation of the thick block like layers supports the indentation load decreasing the plastic deformation of the soft region under the layers. When the indentation load is 10 mN, the scatter of displacement is very large depending on the indentation either to the protrusions or to the soft matrix region. Tempering after the sputter etching increases the deformation resistance of the whole layer perhaps due to the precipitation of fine carbides in the soft region under the carbide layer.
Anodic polarization testing of SUS304 stainless steel with crevice was carried out in an aqueous solution of 3.5 massNaCl at a potential increasing at a constant rate of 0.33 mV/s. When the current density reached 10, 12 or 50 A/m 2 , the potential was kept at a constant value for a constant period. When an ultrasonic wave (UW) was applied to the specimen during the holding period of the potential, the current density on the specimen surface was compared to that without the application of UW. Crevice corrosion and pitting corrosion were found on the specimen after the polarization test. The corrosion of specimen was largely decreased when UW was applied to the specimen. The current density almost synchronized with the cyclic application and stop of UW. The suppression of crevice corrosion and pitting corrosion in the specimen is attributed to the decrease in the enrichment of hydrogen ions and chloride ions in the crevice or pits by the stirring effect of UW.
Micro contaminants on SUS304 stainless steel were observed and confirmed by atomic force microscope, and micro contaminant removal was carried out by ultraviolet ozone (UV O 3 ) treatment. With an increase in the holding time in air, particle and film like micro contaminants appeared and their amount increased on the specimen surface. Then, the amount of particle like contaminants decreased and finally almost all the surface was covered by film like contaminants. The amount of micro contaminants on the specimen surface decreased with an increase in UV O 3 treatment time, with extensive removal of the organic substance in the contaminants but leaving part of the contained water in the contaminants. The micro contaminants slowly re adhered on the treated surface when the surface was re exposed to air, with a long period of more than 172 ks for the recovery to the state before the UV O 3 treatment. The surface for macro droplets after the UV O 3 treatment became hydrophilic, while no large change of the wettability for micro droplets on the same surface can be observed.
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