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Fretting wear and fretting fatigue studies of surface modified biomedical titanium alloys
Published in Nova Science Publishers, Inc.
Pages: 143 - 233
Load bearing implants such as hip joints, knee joints and bone plates etc. are prone to failure from the synergistic effect of fretting wear and fatigue during physical bodily movement. Fretting wear or fretting fatigue is a form of adhesive wear phenomenon wherein a small tangential oscillatory motion under high contact pressure gradually erodes the surface and initiates crack within the contact leading to ultimate failure of the material under fatigue loading condition. Modular junctions of hip implants consist of ball on a tapered shaft experiencing fretting wear during body movements. Titanium alloys, Stainless steels and Co-Cr-Mo alloys are the most commonly used alloys for medical grade devices. Titanium alloys has high strength to weight ratio, superior biocompatibility and corrosion resistance compare to other materials. Surface modified titanium alloys have better tribological properties. In this work, the substrate materials used are Ti-6Al-4V and Ti-6Al-7Nb. PVD TiN coating, plasma nitriding, nitrogen ion implantation, laser nitriding favors formation of TiN and Ti2N of different thickness according to the process. Thermal oxidation process favors formation of hard and brittle oxide layer. Fretting wear tests were conducted to study the quality of the coatings and modified layers. Laser nitriding and PVD TiN coating has shown better performance than other coatings due to high hardness of the layers. Friction coefficient for PVD TiN coating is around 0.2 throughout the test. Wear volume for PVD TiN coated and laser nitrided samples were almost 10 and 50 times lesser than other coatings respectively. Fretting fatigue life of surface modified titanium alloys has considerably improved compared to unmodified materials. Plasma nitrided pairs have shown the best performance over all the coatings. The average fretting fatigue lives of unmodified pairs were 15 to 18% of plasma nitrided pairs, 45 to 50% of the PVD TiN coated pairs and about 60% of ion implanted pairs. Fretting of unmodified alloy pairs have shown high friction and oxidation at the contact due to metallurgical compatibility of the pairs. Fretting of PVD TiN pairs have shown delamination and subsequent oxidation. The damage and friction generated within the contact is a complex interaction between third body particulates, oxide debris and ringer solution. Fretting fatigue life is more for plasma nitride pairs compared to all other modification processes. The damage of ion implanted pairs is similar to unmodified alloys with little improvement in fretting fatigue life. Laser nitrided pairs and thermally oxidation pairs have shown poor fretting fatigue life due to high case thickness and inhomogenities of the layers formed. Friction generated is low compared to al other process, but the specimens experienced premature failure at higher loads. © 2010 Nova Science Publishers, Inc. All rights reserved.
About the journal
JournalTitanium Alloys: Preparation, Properties and Applications
PublisherNova Science Publishers, Inc.
Open AccessNo