Kamaraj M

Fretting is a form of adhesive wear normally occurring at the contact points gradually leading to premature of load bearing medical implants made of titanium alloys. The aim of this work is to characterize the fretting fatigue damage features of PVD TiN coated, plasma nitrided and thermally oxidized Ti-6Al-4V and Ti-6Al-7Nb contact pairs. Fretting damage is applied with calibrated proof ring and contact pad arrangement. The results are compared with fretting damage of uncoated alloys. The damage progression during fretting process is apparently explained with friction coefficient curves. Plasma nitrided pairs performed better in terms of fretting fatigue lives with low friction coefficient of friction. PVD TiN coated pairs have experienced early failures due to third body mode of contact interaction with irregular friction coefficient pattern. Thermally oxidized pairs have experienced early failures due to high case thickness as well as irregular development of modified layer. © 2005 Elsevier B.V. All rights reserved.

Fretting wear resistance of uncoated and surface modified biomedical titanium alloys (Ti-6Al-7Nb) in air and Ringer fluid has been investigated in the present work. Laser nitrided specimen has shown superior performance with minimum surface damage and wear rate (<0.1 × 10-6 mm3/Nm) despite high friction coefficient in air (0.6) compared to uncoated and plasma nitrided (>12 × 10-6 mm3/Nm) specimens. This is due to presence of TiN dendrites (60-80%) in the laser nitrided layer. Plasma nitrided surface is relatively softer and hence wear rates and surface damage are comparable with uncoated alloys. Friction coefficient is high for uncoated (0.8) and plasma nitrided alloys (0.6) in air as well as Ringer fluid. Fretting induced electrochemical dissolution is responsible for higher wear rates in uncoated and plasma nitrided specimens. The fretting damage resistance is primarily governed by relative hardness and modified layer thickness of the mating components. © 2006 Elsevier B.V. All rights reserved.

The use of metals and materials for replacement and repair of human body parts are attracting more attention in recent times. Like any other components in service, biomaterials also undergo degradation due to fretting, wear and corrosion. Fretting wear, fretting fatigue and fretting corrosion are the three main areas of concern for the orthopedic surgeons. This paper reviews fretting fatigue along with various methodologies and mechanisms. Fretting of materials is controlled by several sets of variables working synergistically, making the process difficult to quantify. A fretting test rig for biomaterials has been developed simulating the conditions of the actual implants as close as possible. Fretting fatigue life is also controlled by contact geometries, which delay or accelerate the crack initiation. Several contact geometries have been mentioned which can influence the fretting life of the materials. Fretting conditions are also governed by normal pressure and slip amplitude regime in fretting maps. Physiological medium may aggravate or reduce the fretting failures depending on the nature of surface and the medium. Titanium alloys have been established as the most suitable materials for bio implants due to their attractive properties within the body environment. Some important aspects of the fretting damage of these alloys are mentioned in this paper. Fretting fatigue life of these alloys can be significantly improved by surface modification with specialized techniques such as plasma nitriding, ion implantation and Physical Vapour Deposited TiN coatings. The paper describes details of these methods as well.

Fretting fatigue is a form of adhesive wear damage due to small oscillatory movement between two contacting bodies under the action of uniform or non-uniform cyclic loads. Cyclic loads may be experienced due to vibration of one or both the bodies eventually leading to failure at the contact area. Fretting damage is also experienced by load bearing implants within the body environment such as hip joints, knee joints, bone plates, etc. Damage characterization is important from the view of minimizing in-vivo failures. Titanium alloys are frequently used as bioimplants due to its excellent biocompatibility and low modulus of elasticity compared to stainless steel or Co-Cr-Mo alloys. Fretting wear damage of load bearing implants can be minimized through suitable surface modification process. Ti-6Al-4V and Ti-6Al-7Nb are commonly used for biomedical applications and PVD TiN coated alloys are used for our fretting fatigue studies. Fretting fatigue life of PVD TiN coated alloys improved compared to uncoated alloys. © 2005 Elsevier B.V. All rights reserved.

Fretting fatigue is an adhesive wear mechanism caused by repetitive tangential micro-oscillation between two contacting materials pressed together under cyclic load. Bioimplants, such as hip joints and bone plates, are prone to undergo fretting fatigue failures during their service within the body. This article presents the fretting fatigue damage characterization of physical vapor deposition (PVD) TiN-coated biomedical titanium alloys (Ti-6Al-4V and Ti-6Al-7Nb) subjected to cyclic loads. The PVD TiN layer delayed the damage because of superior tribological properties compared with uncoated alloys. Delamination and abrasive wear damage of TiN at contact caused failure of the alloy. Friction coefficient curves of the PVD TiN-coated pair showed an irregular pattern caused by the influence of wear particulates and Ringer fluid at the contact. © ASM International.

Fretting fatigue is an adhesive wear damage caused by tangential micromotion under normal force at contact areas. It is observed along the contact points of hip implants and bone plates. Surface-modified biomedical titanium alloys offer better resistance against fretting damage. PVD TiN coatings and plasma nitriding have proved effective in minimizing friction and delaying the failure of materials. In the present study, attempt has been made to explain the fretting fatigue failure mechanism sequence of PVD TiN-coated and plasma-nitrided Ti-6Al-4V and Ti-6Al-4V couple through friction measurement and microscopic examination. © 2006.

Alloyed gray cast irons were made with and without misch metal inoculation (0.1%). The mechanical and wear properties were compared with conventional gray cast iron used for a typical clutch application in heavy commercial vehicles. Alloyed gray iron without misch metal showed higher volume fraction of pearlite (89%) and lower flake graphite (11%). Misch metal inoculated gray irons showed higher volume of flake graphite (15%) with 85% pearlite as matrix. Alloyed gray irons produced tensile strength from 300 to 344 MPa and hardness in the range of 221-247 VHN. Misch metal inoculation has slightly increased the graphite volume (40-60%) with corresponding decrease in strength and hardness (9-13%) in alloyed gray irons. The specific wear rates of all alloyed gray irons are significantly lower (<34%) compared to unalloyed base at two different sliding speeds (1.6 m/s and 2.5 m/s). The friction coefficient is less than 0.4 for alloyed gray irons as against 0.5-0.7 for unalloyed base gray iron at both the sliding speeds. This is attributed to the presence of alloying additives within the matrix which resists adhesive and abrasive wear loss. Among the inoculated alloyed gray irons, the alloy with lower S content (0.08%) showed higher wear rate at higher sliding speed due to lower graphite flake density compared to higher S containing iron (0.12%). This indicates that the wear rate is influenced by the amount of graphite which is released into the interface during sliding to provide lubrication and reduce wear. Inoculation with rare earth misch metal has a positive influence over graphite morphology in gray iron. © 2009 Elsevier Ltd. All rights reserved.

Fretting fatigue failures of bioimplants such as hip joints and bone plates occurs due to relative sliding motion of two bodies under contact pressure. In this experiment, fretting fatigue performance of plasma nitrided pairs is compared with unmodified pairs in Ringer solution which represents simulated body fluid. Calibrated proof ring with pads was used for applying fretting damage. Unmodified pairs have exhibited high friction and severe oxidation due to high metallurgical compatibility of the pairs. Plasma nitrided titanium alloys pairs have shown significant improvement in fretting fatigue lives over unmodified pairs with low friction between contact pairs. The oxidation at contact is similar to unmodified pairs but the lives are longer. Three body abrasive damage is also evident at the contact. The steady formation of oxides at the contact seems to play an important role in altering friction during fretting fatigue.

Fretting fatigue is a form of adhesive wear damage caused due to tangential micro motion ol two contact bodies under normal pressure and cyclic load. Biomedical implants such as hip joints and bone plates undergo fretting fatigue damage leading to premature in-vivo failure and revisior surgeries. Surface modification of implants delays the process of fretting and thereby improves the life of these medical devices. This work involves investigation of fretting fatigue damage of surface treated titanium alloys couple. The surface treatment involves PVD TiN coating, Plasma nitriding, Ion Implantation, Laser nitriding and thermal oxidation. Fretting of all surface treated alloys have shown both adhesive and abrasive mode of contact damage. Friction coefficient of all the surface treated pairs is less compared to uncoated alloys. Plasma nitrided pairs have shown the best performance in terms of fretting fatigue life and friction coefficient compared to all other coatings Ion implanted pairs have shown little improvement in fretting fatigue lives due to shallow modified layer. PVD TiN coated pairs have irregular friction pattern due to abrasive particles at contact Thermal oxidation and Laser nitriding have shown poor fretting fatigue performance due to high case thickness.