Electrodeposition behavior and properties of iron-group metal alloys with W from ammoniacal citrate baths

摘要

Electrodeposition behavior of iron-group metal alloys with W was studied in ammoniacal citrate baths of various compositions at 50°C under galvanostatic conditions. The wear and corrosion resistances of iron-group metal alloys with W were also investigated by sliding wear test of ring-on-plate type at 300°C and dipping test in HNO{sub}3, H{sub}2SO{sub}4 and HF solutions. The results obtained were as follows: (1) The relationship between the alloy composition and the cathode current efficiency showed the existence of two characteristic alloy compositions, i.e., the one appeared at a maximum partial current efficiency of W and the other corresponded to the limiting W content. (2) Electrodeposition behavior of iron-group metal alloys with W was explainable by the mechanism that the intermediate W4 oxide electrochemically formed was reduced by atomic hydrogen held on freshly deposited iron-group metals. (3) The wear resistance of iron-group metal alloys with W was improved with increasing W content in the deposit and showed the best performance at 30～40 mass% W. When W content in the deposit was high, hardness of the film was increased to prevent adhesive wear between the film and press ring. Hardening of the film due to the frictional heat also seemed to be contributed to the improvement of wear resistance. (4) The corrosion resistances of the films were improved with increasing W content in the deposit, especially in HNO{sub}3 solutions.