N. Parvini Ahmadi - Materials Engineering Faculty, Sahand University, Tabriz, Iran
R. Khosroshahi - Materials Engineering Faculty, Sahand University, Tabriz, Iran
M. Abdeli - Materials Engineering Faculty, Sahand University, Tabriz, Iran

Despite having some useful properties, stainless steels suffer from lack of suitable surface hardness. In this research electroless Ni-B-Tl coating was used with the aim to increase their surface hardness. The effects of Nickel chloride, Sodium borohydride, Thallium nitrate and Ethylendiamin on the chemical composition of coating were studied. To achieve an increase in hardness, the effects of heat treatment on the hardness of the deposited layer at various temperatures, were also studied. The results showed that the deposition rate and surface hardness of the deposited layer were affected by the variation in concentration of bath components. The micro structure of the electroless Ni-B-Tl coating consists of nickel and super saturated solid solutions. It was also found that the hardness of the coating was increased due to the formation of Ni۲B and Ni۳B phases during heat treatment.

Electroless deposition, Ni-B-Tl coating, Bath composition, Heat treatment