| Various surface properties of boride layer formed by plasma paste boronizing were examined. A boride layer of flat structure was formed on the STS 304 stainless steel substrate by plasma paste boronizing treatment at several different temperatures from 1023K to 1223K under gas mixture of Ar/H₂: 2/1(vol.%). The paste was composed of 30wt% boron and 70wt% borax. The properties of boride layer were evaluated by micro vickers hardness tester, SEM, EPMA, and corrosion tester. Metallographic cross section of the bonded specimen was consisted of the boride layer, Ni rich layer, Cr rich layer, and matrix structure. It was found to form boride layer in a short time as compared with the pack and molten salt boronizing. In XRD analysis of boride surface, various peaks such as FeB, Ni₃B and CrB were presented. Especially, the peak of CrB was more intensive than other peaks. Activation energy for the formation of boride layer was found to be 123kJ/㏖ which is lower than the pack and molten silt boronizing. The microhardness of these boride layers were in the range of HV 1800-2000. However, from the results of anodic polarization curve in 1M H₂SO₄ solution on the bonded specimens, it is found that the corrosion resistance is improved by boronizing treatment. And primary passive current density is increased with the boronizing temperature. |
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