Effect of Zinc Addition on Electrodeposition of Fe-W Alloys

Abstract

Tungsten (W) and its alloys have been applied to various industrial fields for its excellent mechanical, tribological and chemical properties. Electrodeposition process is anticipated to be a economical and cost-effective method for preparing W-based alloys since W has the highest melting point among metals (3422 ℃). In general, electrodeposition of metal W from aqueous solution is difficult because it exists as oxyanions in a wide pH range. However, electrodeposition in the co-existence of iron group metals such as iron (Fe), nickel (Ni), and cobalt (Co), enables W to be reduced to metal state, which is so called the induced co-deposition. Recently, electrodeposited W alloys have gained increased attention due to their advanced properties such as high microhardness, thermal stability, wear resistance and corrosion resistance. Among them, binary Fe-W, Ni-W alloys have been most intensively studied. These alloys are expected to be promising substitute for hard chrome (Cr) plating due to its high hardness, abrasion resistance, heat resistance and corrosion resistance without the use of hazardous hexavalent chromium (Cr6+). Meanwhile, Ni has been reported as the one of the major elements in triggering skin allergies for humans. Therefore, we focused on Fe-W-based alloys that do not use Ni. Unfortunately, Fe-W alloys are reported to have inferior mechanical properties and corrosion resistance compared to Ni-W alloys. Thus, the addition of Zinc (Zn); an element that is widely used in anti-corrosion coatings, as a third element to the Fe-W binary alloy was considered for preparation of a ternary alloy with improved properties.This study reports the first experimental results of electrodeposition of ternary Fe-W-Zn alloy by incorporation of Zn to Fe-W alloys. Ternary Fe-W-Zn plating was prepared in citrate-ammonia aqueous solution heated to 80℃ by potentiostatic elcecrolysis range from -1.1 to -1.4V (vs. Ag/AgCl). Ternary alloys with the compositions of Fe-(28.8 to 37.1 at.%) W-(1.7 to 6.5 at.%) Zn were obtained with maximum current efficiency of 42%. The corrosion properties of the prepared ternary alloys were compared with those of Ni-W and Fe-W platings by a potentiodynamic polarization test in deaerated 1M sulfuric acid solution and 3 mass% sodium chloride solution. Although Zn has lower potential than Fe, ternary Fe-W-Zn alloys with relatively low Zn contents of 1.7 to 2.6 at.% showed better anti-corrosion properties than Ni-20 at.%W and Fe-33 at.%W alloys in acidic media. Addition of a small amount of Zn was found to be effective in tuning properties of Fe-W alloys. Acknowledgement This work was partially supported by the JST-OPERA Program, Japan [grant number JPMJOP1843]