Investigations on the Influence of Annealing on Microstructure and Mechanical Properties of Electrodeposited Ni-Mo and Ni-Mo-W Alloy Coatings

Ni-Mo and Ni-Mo-W coatings were electrodeposited on a stainless steel sheet, and then were annealed at 200, 400, and 600 & DEG;C. The effect of annealing heat treatment on the microstructure of Ni-Mo and Ni-Mo-W electrodepositions, their nano-hardness, and tribological properties were investigated. It was revealed that the average crystalline are refined and phase separation are promoted with formation of Mo-W related intermetallic precipitates at temperature exceed 400 & DEG;C on account of the co-existence of Mo-W elements within Ni-Mo-W coatings. Annealing heat treatment leads to hardening, and the hardness and elastic module increase significantly. The grain boundary (GB) relaxation and hard precipitated intermetallic particles are responsible for the annealing-induced hardening for & LE;400 & DEG;C annealed and 600 & DEG;C annealed Ni-Mo-W coatings, respectively. In addition, both adhesive wear and abrasive wear are observed for coatings, and abrasive wear becomes predominant when annealing temperature up to 600 & DEG;C. The wear resistance of coatings is improved eventually by formation of a mixture of lubricated oxides upon annealing at 600 & DEG;C and the enhancement of H/E ratio for & LE;400 & DEG;C annealed Ni-Mo-W coatings.

Automated summary

Annealing heat treatment resulted in refinement of crystalline structure and phase separation in Ni-Mo and Ni-Mo-W coatings, with the formation of Mo-W intermetallic precipitates. The coatings showed increased hardness and elastic modulus, with different mechanisms responsible for hardening at different annealing temperatures. Wear resistance was improved by the formation of lubricated oxides and enhanced H/E ratio in the coatings annealed at lower temperatures.