Abstract
Effect of heat treatment in the temperature range from 200 to 550°C on sliding wear resistance of Ni-P electroplated Ti-6Al-4V has been investigated. The wear mechanism has also been discussed in terms of the film structure and the variations of hardness, toughness and internal stress of the plating films by the heat treatment.
The wear resistance was influenced by the heat treatment. When the plating film was hardened from Hv700 (as plated) to approximately Hv1100 by the heat treatment at 350°C for 1h, the wear resistance slightly deteriorated. On the other hand, when the plating films were softened to below Hv800 by the heat treatment over 450°C, the wear resistance significantly improved. These behaviors were not in good agreement with the variations of the hardness nor internal stress of the films but with the number of the cracks which were microscopically observed on the wear tracks of the plating surfaces after the sliding wear test. As the number of the cracks decreased, the wear resistance increased. It is thought that the susceptibility to cracking relates to the toughness of the plating film, and that the film with good toughness obtained at temperature over 450°C is derived from the formation of soft Ni matrix due to the precipitation and growth of Ni3P phase by heat treatment. In conclusion, the sliding wear resistance of the Ni-P electroplated Ti-6Al-4V is considered to be largely governed by the mechanical property related to toughness of the plating films.
