Iron-tungsten alloys electrodeposited under direct current from citrate-ammonia plating baths

Fe-W alloys containing ~23-30 at.% tungsten were electrodeposited from citrate-ammonia solutions at different cathodic current densities. A characterization of the structural properties of these coatings is reported. The 8 to 15 μm thick Fe-W coatings obtained are smooth and nano-crystalline. The structure of such aselectrodeposited coatings evolves slightly with increasing cathodic current densities. Above 5 A dm⁻², micro-cracks appear in electrodeposited Fe-W coatings, and the oxygen content in the coatings increases. A nano-crystalline structure and a high tungsten content result in nanohardness of 13 GPa. The electrodeposited Fe-W alloys remain "nanocrystalline" after annealing up to 800 °C. After heating at 1000 °C, the nano-crystalline structure transforms into a microcrystalline one, and up to three phases are formed, namely FeWO₄, Fe, and possibly Fe₂W.