Evaluation of Tribological Corrosion Co-Cr Alloy's Medical Implant - Essay Example

? Evaluation of Tribological and Corrosion Co-Cr Alloy’s Medical Implant There exists use of Co-Cr alloy in medical implants due to its high biocompatibility levels, excellent mechanical and corrosion resistant properties. The problem addressed by this paper is based on the tribocorrosive behaviours that Co-Cr alloys exhibit, given that exposure to both mechanical and chemical activities in the human body does take place. It is important to find out through research the reliability and usage of these alloys in orthopaedic implants. Introduction The problem being dealt with in the study is examination of the application of Cobalt-Chromium alloy and how suitable it is as a metal alloy in the production of orthopaedic implants like hip and knee replacements. It is important because the use of metal has been exclusively done when it comes to the manufacture of these implants. Many researches were carried out on suitability of alloys in implants but the need to control wear and corrosion resistance and thus extend the life of these implants did not receive the needed attention, yet it is extremely vital in the orthopaedic implants. Other materials have been tested in the years with the view of establishing their effectiveness in the replacement for bones. Metallic alloys are extensively used and this is attributed to their availability and success in implants. The alloys are derived from metals such as iron, cobalt, chromium, titanium, and tantalum. Clinical tests have proven the viability of using these metals in the manufacture of orthopaedic implants which are left in vivo for quite a long time. Being a metal alloy made out of cobalt and chromium, Cobalt-Chrome is commonly used in orthopaedic implants and has the ability to withstand different porous forms, which allow for biologic fixations in growth. Their characteristics make them critical in making artificial body parts for replacing bone and act as load bearing. This research is different from the others in that few studies have targeted tribocorrosion systems and this is why many areas, for instance the effects of proteins on these processes have not been well established. Objectives Much information has been presented for the literature review carried out and this was aimed at gathering important information on the background of these concepts and existing knowledge of the research area identified. It is also essential that the tribocorrosion effects and subsequent behaviour exhibited by CoCr alloys is found out; analysis and comparison of the impact that heat treatment has on CoCr alloys is studied; doing data analysis of the test results that have emanated from the experiments on tribocorrosion of CoCr alloys is to be done; and finally, these results are to be presented and evaluated based on the actual field findings rather than personal intuition. Literature Review Review of studies carried out on CoCr alloys has been done. Co-Cr alloy which is the Cobalt Chrome alloy is made from a combination of the chemical elements Cobalt and Chromium in major quantities and with traces of Molybdenum and other elements to ease the working process in the manufacturing of this alloys and come in form of CoCrMo and CoCrW alloys. Cobalt is atomic number 27 on the periodic table and does exists freely as a hard, silver grey shiny metal. Cobalt has industrial uses such as production of high strength, wear resistant and magnetic alloys and is used in so many other areas such as radio-isotope in tracer and formation of gamma rays for radio-activity and production of Vitamin B-12. Chromium is 24th on periodic table and is the first of halo elements. Has a high polish due to its steely-grey, shiny, strong metallic properties, has no smell and is found in various shapes. It has higher corrosion resistance and hardness properties. It is essential in human body and its elimination causes chromium deficiency and other disorders, however; direct intake in high quantities is dangerous and cancerous. We have established that resistance to corrosion is attributed to ion release and wear is affected by creation of wear debris from the reactions. The electrochemical characteristics of implant alloys is feared to be affected by the proteins in the human body much as no specific protein type has been singled out as the cause or reactive to alloy implants, although; means and subsequent rates of corrosion depend on the materials used, their nature, and interaction with the environment. Chromium gives wear resisting properties to the alloy and Cobalt gives it the hardness needed. Co-Cr alloys are used in surgical implants and in machine parts that are constantly subjected to high wear and corrosion amounts and come in many variations and Co-Cr alloys also find different applications in gas turbines, orthopaedic implants and dental implants. We established that Co-Cr alloys have numerous advantages making their usage in the medical field possible such as their corrosion resistance and Biocompatibility, Visibility to X-ray procedures, higher elastic modulus, and suitable mechanical properties. Correlated ion migration and reactions of fibres closer to these alloy implants are negligible hence no major damage caused when CoCr-Mo, Co-Cr-Ni-Mo and Co-Cr-Ni which are CoCr alloys are used in the animal implantations. The CoCr alloys are the best in skeletal implants when biocompatibility is considered. Combinations of CoCr alloys with stainless steel have produced inconsistent outcomes and it is advisable to avoid combining these elements. Experimental Method & Procedures We use well prepared chromium alloy samples in the experiments. Electrochemical corrosion test It is necessary to set up conditions such as those in human body, in which 0.9% salt, as liquid contained in blood, are created with a solution of Sodium Chloride (NaCl) with 0.9% concentration and 270 grams of NaCl added to 3 litres of distilled water. Electrochemical testing is then done by Cathodic and Anodic testing procedures that have been identified as being suitable for the experiment. Tribocorrosion testing at OCP It is necessary to make loads that are representative of the actual types of Cobalt-Chromium hip replacement prosthesis. The right measurements are of 0.5N, 1.0 N, 2.0 N, 5.0 N and 10.0 N, compatible to those used in orthopaedic implants. Surface Profile Testing Use of Profilometer in taking measurement is done and recordings of surface roughness through the process of calculating the wear track length are carried out. Heat treatment We treat the samples by heating. The samples are placed in the Carbolite type air furnace for some period of time to enable heat exposure to take place. An examination of the surface layers is done by a microscope in order to examine the detailed structure and formation of the surface to establish the effect that heat produces on the surface of the alloys. Results and Discussions When we test for tribocorrosion at OCP, the current density is seen to change at once and this occurs after some period of time, an outcome which confirms that there is new performance of CoCr in cases where we have combined conditions of both corrosion and wear when the coefficient of friction is improved to a higher extent. The wear track depth and the extent of wearing for the selected samples, which are not subjected to heat treatment is more than that for samples that are heat treated when exposed to same conditions for testing. The wear mechanism observed is achieved by combining both type 1 wear abrasion and micro asperity shearing which is seen from the existence of sharp ridges and the lines found within the wear track. This kind of wear is not found in the initial stages of the As-Received samples used. However, on drastic increment of the load to 10N , this wear type is found due to complete penetration of the surface layer, generating a wear track same as that seen in the As-Received samples. It safe to say the magnitude of active materials in the wear track area does increases at a bigger and higher frequency than in other areas. Conclusion It is critical that the testing of Co-Cr samples is conducted in conditions that are similar to human body to get the levels of tribocorrosion in the same chemical environment when establishing these processes. There are not yet found definite procedures for heat treatment temperature, time and speed that are needed to give the best rutile layer to combat tribo-corrosion, which calls for more research in future. The effectiveness of CoCr alloys in orthopaedic implants can however not be ignored if major scientific discoveries are to be done in this area (Dissertation, 2011). References Dissertation (2011), Tribological and Corrosion Evaluation of Medical Implant Co-Cr Alloy, Dissertation of Master’s Degree in Mechanical Engineering Read More