Wear and Corrosion Resistance Improvement of CoCrMo alloy by Tantalum Based Coatings
Date
2022-05-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0002-5847-1468
Type
Thesis
Degree Level
Doctoral
Abstract
Patients with hip joint implants face a serious problem due to the relatively short lifetime of the prosthesis. Medical grade CoCrMo alloy is one of the most common materials used for femoral head fabrication. Unfortunately, the implant fails usually after 15 years of service due to the excessive wear of the polyethylene liner and corrosion of the metallic ball which causes osteolysis, inflammation, and loosening of the implant components. Coating the metallic femoral head is one of the most promising techniques to reduce the wear of the polyethylene liner and improve the corrosion resistance of the femoral head, which leads to an increase in the lifetime of the implants. Tantalum (Ta) has attracted much interest as a coating material for the femoral head due to its unique properties. Ta is biocompatible, highly corrosion-resistant, and mechanically strong and hard which make it suitable for wear resistance applications. The main objective of this research is to fabricate Ta based coatings to reduce the wear of the polyethylene liner and improve the corrosion resistance of the CoCrMo alloys for hip joint implant applications. Firstly, the wear and corrosion resistance of Ta coatings deposited on CoCrMo alloy were investigated. Ta coatings were fabricated by magnetron sputtering by varying the deposition pressure from 0.3 Pa to 1.9 Pa. The results show that the Ta coating deposited at 0.8 Pa consists of a single-phase β-Ta while the α-Ta phase is observed on the other deposition conditions. Based on the adhesive and mechanical testing results, a gradient multilayered Ta film was synthesized by continuously changing the deposition pressure from 1.9 Pa to 0.3 Pa and it showed excellent wear and corrosion resistance. Secondly, the tribological and corrosive properties of Tantalum nitride (TaN) coatings deposited directly on biomedical grade CoCrMo alloy by Plasma Enhanced Chemical Vapor Deposition (PECVD) under deposition temperature of 350oC to 500oC were investigated. The results show that the TaN coating deposited at 500oC exhibits much higher hardness and lower wear rate of polyethylene balls during ball-on-disk wear testing but lower polarization resistance than CoCrMo alloy. Finally, the wear and corrosion resistance of TaZrN coatings synthesized directly on biomedical grade CoCrMo by magnetron co-sputtering were investigated. The results indicate that the TaZrN coatings are highly adhesive and have a nanocrystalline structure with a Hardness and Young’s modulus of 19 GPa and 297 GPa, respectively. The TaZrN coatings show a 3% lower wear rate of the polyethylene balls and an icorr value 274 times lower than the uncoated CoCrMo alloy. The excellent wear and corrosion resistance of the TaZrN coating suggest that it is a promising coating material for CoCrMo alloy to improve the lifetime of hip joint implants.
Description
Keywords
Wear, Corrosion, Tantalum, Zirconium, Nitrides, Coatings, CoCrMo, Hip joint, implant
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Mechanical Engineering
Program
Mechanical Engineering