Electrochemical properties of electroless Ni plated super duplex stainless in 3.5% NaCl solution

Abstract

Si wafers used in semiconductors require precise machining; therefore, they are processed using an STS304 saw wire, which is made of an austenitic stainless steel with excellent strength and corrosion resistance. However, the recently developed super duplex stainless steel (SDSS) exhibits superior performance compared to STS304 and is suitable for use as a saw wire. SDSS is a stainless steel composed of austenite and ferrite, with the ratio varying depending on the temperature during heat-treatment. Ferrite has better wear resistance than austenite; therefore, Ni plating was applied to ferritized SDSSs to improve the saw wire performance, and the electrochemical properties were analyzed. The nickel layer increased with time, forming a non-uniform coating until 180 s, followed by uniform plating. This was confirmed by the changes in the surface roughness and surface images. With the formation of a uniform nickel-plating layer, the distinction between austenite and ferrite became visible, resulting in decreased surface roughness. When the time exceeded 240 s, the difference in roughness increased owing to the difference between in the reactivities of austenite and ferrite. This difference in the surface roughness influenced the electrochemical behavior. The uneven nickel-plating layer exhibited a potential change of over 200 mV during the initial open-circuit potential (OCP) stage (prior to 800 s). In a potentiodynamic polarization test, plating for more than 300 s resulted in a reduced corrosion resistance owing to overplating. Increasing the thickness of the Ni layer altered the electrochemical behavior from SDSS to nickel. By analyzing the surface conditions and electrochemical properties, a uniform nickel-plating layer, exhibiting the characteristics of SDSS, was observed at 240 s. Therefore, the optimal duration for electrolytic nickel plating of ferritized SDSS was 240 s