Mechanical energy-induced deposition on NiTi shape memory alloys (SMAs) is difficult to accomplish due to the pseudoelasticity of NiTi SMAs. In this study, a high-frequency ball-bombardment method called ultrasonic mechanical coating and armouring (UMCA) is introduced to synthesize a hydroxyapatite (HA)-containing coating on a NiTi SMA. The effects of treatment duration, Ti addition, and ball-to-powder ratio on the HA content of the coating are investigated. Results show that the HA content of the coating largely increased during the initial 10 s and decreased with further ball-bombardment. The addition of Ti powder into the chamber assisted HA anchoring on the NiTi SMA surface. Using a ball-to-powder ratio of 1:1 induced the highest HA content on the NiTi SMA as compared to the 1:2 and 2:1 ratios. Coating consisting of 10–50 nm nanoparticles of HA and Ti formed under localized compressive forces were induced through shot collisions. The bombardment also created a local amorphous structure of the NiTi SMA near the coating/NiTi SMA interface. Laser annealing induced oxidation of the coating, which improved the coating adhesion and corrosion resistance of the NiTi SMA in Hank's balanced salt solution.
ASJC Scopus subject areas
- 化學 (全部)