Microstructure, Hardness and Corrosion Resistance of Surface Modified Ni - Hard 4 Cast Iron with Nitrogen using Gas Tungsten Arc

Abstract

The change in microstructure, hardness and corrosion rate of Ni-Hard 4 cast iron were studied after surface modification with Nitrogen mixed the Argon shielding environment. The microstructure of the modified layer was grains with the presence of nitrogen, observed under the optical microscope. An average of 1.37wt% of Nitrogen was observed in the modified layer during EDAX analysis. The presence of Nitrogen in the modified layer has formed FeN, Ni3N and Cr2N phases. The formation of nitride phases were confirmed during XRD spectral analysis. The hardness of the modified layer was taken along the depth direction. The hardness of the modified layer was improved from 578HV of the substrate to 1735HV of the modified layer. The electrochemical polarization test was conducted at a 3.5wt. % saline (NaCl) solution in both the substrate and the modified layer. The modified layer forms a protective layer over the surface and reduced the corrosion rate than the substrate