Multi-element Ni-Cr-Mo-Cu surface alloyed layer on steel using a double glow plasma process

Ni-Cr-Mo-Cu multi-element surface alloying has been carried out by means of the double glow plasma surface alloying technique on low carbon steel and AISI 304 stainless steel substrate materials. The results showed that highly alloyed nickel-based surface alloying layers were formed on the surface of the two kinds of steel. The alloy content of the alloyed layer showed gradually tapering from surface to the inside of substrate, the ideal profile which is beneficial to the cohesion of the surface alloying layer with substrate materials. The alloying layer is continuous and compact. Precipitated alloy phases formed on the low carbon steel consisted of the M6C and mu phases, but the precipitated phase of alloying layer formed on stainless steel is mu phase and the amount R phase is very low. The electrochemical tests were conducted in 3.5%NaCl solution, and 200-h immersion tests in a 20%H2SO4, and 20%HCl solution. The corrosion resistance of surface alloying layer formed on AISI 304 stainless steel substrate is better than that of the nickel-base alloy Hastelloy C-2000 and 304 stainless steel, and the corrosion resistance of the alloying layer formed on the low carbon steel is lower than that of Hastelloy C-2000 alloy but slightly higher than that of AISI 304 stainless steel. After the anodic polarization tests, the chemical states of Ni, Cr, Mo elements in the passive film of alloyed layer formed on the two kinds of substrate were investigated using X-ray photoelectron spectroscopy. The experiments indicate that this is an effective way to obtain a high quality corrosion resisting surface alloyed layer on the surfaces of steels using the double glow plasma surface alloying technique. (C) 2003 Elsevier Science B.V. All rights reserved.