Effect of Annealing on the Structure and Hardness of Electrodeposited Ni–W Alloys

• Published in: ISIJ International 2015/05/15, Vol.55(5), pp.1083-1090
• Main Authors: Hayata, Shinichiro, Oue, Satoshi, Nakano, Hiroaki, Takahashi, Takehiro
• Format: Article
• Language: English
• Subjects: annealing; deposits; electrodeposition; hardness; morphology; Ni–W alloy; orientation; structure
• ISSN: 0915-1559; 1347-5460
• DOI: 10.2355/isijinternational.55.1083

The electrodeposition of Ni–W alloys was conducted from an unagitated sulfate solution containing citric acid at pH 5 and 60°C under coulostatic (3.44–6.22×105 C/m2) and galvanostatic (30–5000 A/m2) conditions. Before annealing, the lattice constant of Ni increased linearly with an increase in W content up to 40.7 mass% in accordance with Vegard’s law. This shows that the W formed a supersaturated solid solution in Ni. At W contents of 40.7 mass% of the solid solubility limit, the cross section of the deposits showed a layered morphology, with a smooth surface and small granular crystals. After annealing, Ni4W precipitated with deposits of W contents of 32.6 and 37.1 mass%. Fine precipitates of Ni4W and NiW formed over the entire surface with W contents of 40.7–45.3 mass%. Before annealing, the hardness of the deposits increased with W content, and the increase was particularly large at a W content of 40.7 mass%. The hardness was almost constant regardless of the current density for W contents of >40.7 mass%. The alloy composition required to change the hardness of the deposits corresponded with that required to change the deposit structures. The hardness of the deposits increased for all W contents by annealing, with the increase being particularly large for W contents of >40.7 mass%.