Comparing the Effect of Heat Treatment and Plasma-Nitriding on Corrosion Resistance of Ni-B-CNT Electroless Coating with Different CNT Concentration on Aisi 4340 Steel

The aims of the work to study the resistance of corrosion and the hardness of plasma-nitrating and heat treatment of coatings with electroless Ni-B-CNT. Various concentration of CNT range, (0, 0.35 and 0.7)g/L in Ni-B-CNT composite was deposit on 4340 steel in electroless immersion. Following the procedure of plating, every samples were plasma-nitrating in atmosphere consist of 50% N2 -50% H2 , about (400°C), at (2.5h) were compared with those of annealed one. The electrodes Ni-B-CNT coatings were prepared by using nickel chloride as source for nickel, borohydride act as reducing agent and used (MWCNT). Results of micro hardness was show that the higher hardness of (1250HV) was achieved for Ni-B-0.35g/L CNT plasmanitrating formula whereas the greatest hardness of (1010HV)was become for sample of Ni-B-0.35g/L CNT heat treated. Resistance of corrosion of Ni-B-CNT composite coating are better, and they become much better with the increase of the CNT concentration. Increase too much CNT deposited on the substrate, leading to a high region of CNT and agglomeration that occur is very unfavorable to coating, lead resistance of the corrosion of the composite coating becomes worse. Also, compared between heat treatment and plasma-nitride, results of that resistance of the corrosion with plasma-nitriding is better