Study on the mechanical properties of electroplated iron-carbon alloy coating

Abstract

Electrodeposition of martensitic Fe-C and Fe-Ni-C alloy coatings was carried out hom sulphate based batbs at room temperature. The baths contained various amount of citric acid (0.2 to 10 gill and L-Ascorbicacid 10.2 to 10 gill and in some cases additives viz. gelatin 10.2to I gil),sodium lauryl sulphate 10.5gil) to observe their influences.on the morphology and mechanical properties of the coatings_ Chemical analysis showed the carbon content of both Fe.C and Pe-Ni-C alloy deposits to be above I% and Ni content of Fc-Ni.C alloy deposit within 4-6%. It was observed that the carbon content of the Fe-C deposits becomes less sensitive to CA and LAAcontent of the bath as higher amounts of CA and LAA are added. Structure of the deposit was examined by optical microscopy and xray diffractometry. The microstructure of as-deposited etched sample was dark and difficult to observe under a microscope,but the annealed structure showed a structure similar to annealed carbon steel. X-ray diffraction pattern of asdeposited Fe-I.1%C alloys suggests these to be rnartensitic in structure. Mechanical properties of these coatings viz. microhardness, ductility, wear resistance were investigated in relation to the prcscnce of additives like gelatin and sodium lauryl sulphate in the bath and post-deposition heat treatment. Fe-C alloy deposited from bath containing 10 gil CA and 10 gil LAAshowed hardness as high as 790 HV, whereas the deposits hom other baths showed relatively lower bardness values such as 701, 386 HV. It was found that as the percentage of CA and LAA in the bath decreases, hardness of the deposit also decreases. Tempering of the as-deposited Fe-1.1%C alloy at 2000C lor half an hour does not cause any appreciable decrease in hardness. However, gelatin was found to have a significant role on bardness; as the gelatin content in the bath increases, the corresponding hardness decreases.It was found that presence of gelatin in the baths and tempering of the deposits cause considerable improvement in ductility. FeA.3%Ni-1.1%C alloy showed better ductility than as deposited or tempered Fe-I.l %C alloy.