THE EFFECT OF WEAR MECHANISM FOR PLASMA OXIDISED CP TI AND ITS ALLOYS ON TRIBOCORROSION PERFORMANCE

THE EFFECT OF WEAR MECHANISM FOR PLASMA OXIDISED CP TI AND ITS ALLOYS ON TRIBOCORROSION PERFORMANCEAbstract Commercially pure titanium (cp-Ti) and its alloys (Ti6Al4V, Ti45Nb, Ti6Al7Nb etc.) have an important use among biometallic materials. Recently developed alloying techniques and production methods have enabled many different titanium alloys to be used as biomaterials. Although harder and higher corrosion resistance than iron and its alloys, it is used as an invasive implant by applying various surface modifications to improve biodegradability performance. One of these processes is plasma oxidation process. With this process, corrosion resistance can be improved by obtaining more passive surfaces. There are many studies on these performance measurements in the literature. In this study, the effects of wear and corrosion mechanisms on the material in one cycle were investigated. Cp-Ti, Ti6Al4V and Ti45Nb were chosen as base materials. Samples were subjected to plasma oxidation for 600˚C-3 hours. Within the scope of this investigation, the adhesive wear mechanism on oxidized surfaces was compared with different types of abrasives, and its effect on corrosion performance was measured with the tribocorrosion test apparatus. Abrasion tests were carried out with two abrasive balls: tungsten carbide (WC) and silicon nitride (SiN) under 3 N load. Processes were carried out in two different media, dry and simulated body fluid (SBF). Potentiodynamic polarization scans were carried out using the scanning range of -0.28 V - 2 V in the presence of wear tests for tribocorrosion measurements. While abrasive wear mechanism is dominant in untreated samples, adhesive wear is at the forefront in coated samples. The effects that increase the corrosion resistance positively affected the performance of tribocorrosion. The high oxidation resistance of Ti and its alloys increased adhesive wear performance, and because of the higher corrosion resistance of Ti6Al4V and Ti45Nb, which were alloyed from these three material groups, their corrosion performance was higher than Cp-Ti.Keywords: Cp-Ti, Ti6Al4V, Ti45Nb, Plasma oxidation, Tribocorrosion

THE BIOMECHANICAL ANALYSIS FOR BIODEGRADABLE PURE MAGNESIUM BONE SCREWS UNDER THREE POINT BENDING AND TORSIONAL TEST

THE BIOMECHANICAL ANALYSIS FOR BIODEGRADABLE PURE MAGNESIUM BONE SCREWS UNDER THREE POINT BENDING AND TORSIONAL TESTAbstractRecently, magnesium and its alloys have been used as the raw material of degradable implants. In the orthopedic implant group, it is used in the production of medical tools due to its close modulus of elasticity and mechanical behavior suitable for bone tissue. In addition, magnesium is completely biodegradable both in biocompatible and living organisms. The purpose of using a degradable implant within the living organism is both to perform biomedical functions. It has become even more attractive to use the biodegradable magnesium screws due to the use of the temporary (non-biodegradable) implant in the living organism, the need for a secondary surgical operation to remove it from the body, and the increased risk of complications for the patient. However, the degradation times of magnesium screws; It is difficult to control the biological environment, the age and gender of the patients and the implant geometry Determination of the degradation stage is important for mechanical performance due to loss of mass and volume in the implant. Furthermore, loss of adhesion performance due to deterioration of bone screws weakens the mechanical properties of the implant system. Considering this feature of magnesium screws, pure magnesium screws of different origin were kept in phosphate buffer solution (pH = 7.4) for 1 day, 1,4,12 and 26 weeks. Then, three-point bending and torsion tests were performed according to ASTM F2502-11 standard to examine the mechanical properties of the screws. In the mechanical tests applied for both groups, when the three-point bending test and force-displacement curves were examined, it was observed that the mechanical properties of the 26th week decreased by about half compared to the 1st day. In the same way, when the torsion-torsion angle curves were examined in the torsion test, it was observed that the mechanical properties of the 26th week decreased for both groups.Keywords: Pure Magnesium, Biodegradation, Bone Screws, Three-Point Bending Test, Torsion Test