Executive Summary : | Magnesium alloys got increased attention in the field of temporary orthopedic implant application for the osteosynthesis (fixation of a bone fracture) process because these materials possess excellent biocompatibility, biodegradability and relative bone stiffness. Compared to the traditional implant materials in the osteosynthesis process, these properties of magnesium alloys avoid the stress shielding effect and eliminate the need for revision of surgery to remove the fixed implants. However, a high corrosion rate and low wear resistance in the physiological environment impede their application. Hence, the surface modifications should be carried out to overcome these limitations as both corrosion and wear are the surface phenomenon. Accordingly, the project's main aim is to modify the surface parameters of the magnesium-based alloys using laser shock peening and to study its effect on in-vitro degradability and synergetic effect on wear and corrosion, i.e., Tribocorrosion. Laser shock peening is a non-contacting surface modification technique that uses a high-intensity laser beam to cause plastic deformation on the target material surface. This results in inducing the microstructural change and compressive residual stresses on the surface of the specimen, which are the major influencing factors of degradation rate and wear resistance. The magnitude of compressive residual stresses induced in the implant can be precisely controlled by controlling the laser shock parameters such as laser power density (wavelength, frequency and number of pulses) and overlap percentage. These parameters will be changed, and their effect will be studied by measuring the peened sample's grain size, residual stress, and hardness. The microstructural changes will be analyzed using Electron Backscatter Diffraction (EBsD). The residual stress on the surface of the peened specimen will be studied using an X-ray residual stress analyzer. The hardness of the material will be tested using a Vickers microhardness tester. Experimental tests will be conducted to evaluate the effect of the residual stresses on the in-vitro degradation behavior of the peened samples through detailed immersion corrosion and electrochemical corrosion method in a simulated body fluid environment. In addition, experimental studies will be carried out to evaluate the effect of the residual stresses on the tribocorrosion behavior of the peened samples using modified friction and wear test rig. This research develops a systematic approach for improving corrosion and wear resistance of magnesium-based materials for bio-implant applications. |