Study For Fretting Corrosion, Fretting Wear Of NiTi Shape Memory Alloy/Human Bone In Simulating Human Environment

Fretting corrosion, as one of the primary forms of damage to metallic implants, often occurs in orthopaedic implants such as contacting surfaces of implanted plates and screws, contacting points of joint stem and cement or joint stem and caput articularis. Most studies in literature focused on various factors affecting fretting corrosion of metallic implants, whereas few investigations based on the theories of simulating human environment (for example, human wound PH value) and synergy of corrosion and fretting wear have been done on fretting corrosion behaviors of metallic implants.Fretting corrosion is tested on plate-on-flat contacts of NiTi shape memory alloy/Human bone using Optimol SRV fretting test machine under different media, number of cycles, normal load and displacement amplitude level. Extensive analyses on fretting corrosion characteristics of NiTi shape momory alloy have been performed based on synergy theories with scanning electron microscopy (SEM), profilometer and optical microscope (GM). The purpose of this study is to provide experimental results and practical guide to the choice of determination and exploitation of metallic implants and their clinical applications. The present study draws the following conclusions:The friction coefficient, wear spot and wear volume of NiTi shape memory alloy depend strongly on displacement amplitude, number of cycles and experimental media. With the increase of displacement amplitude, it is found that the friction coefficient is increasing; wear spot and volume is rising in air. In comparison with that in air, the friction coefficients become more complex in Hank's solution of different pH values (The friction coefficient decreases in Hank's solution but obviously increases in acidic and alkaline Hank's solution). With the increase of number of cycles, it is found that the wear becomes more serious.Fretting wear mechanisms of NiTi shape memory alloy/human bone are mainly adhesive wear and particle damage. The fretting wear process consists of three phases: primal, oxidizing and steady phases. In air, the adhesive and particle wear aggravates with the increase of the displacementamplitude. The central part expands while the marginal part shrinks, worsening the wear.Surface roughness has greater effect on the corrosion rate of NiTi shape memory alloy at the primal phase. Surface roughness has no direct effect on the change of the corrosion rate of NiTi shape memory alloy. With the increased surface roughness (Ra), it is found that the corrosion rate increased. Similarly, steady corrosion rate is independent to the pH value of Hank's solution. The Ni releasing rate basically comes from pitting (local) corrosion hole.The fretting corrosion of NiTi shape memory alloy/human bone is a processing which fretting wear has mainly effected the total material loss, chemical corrosion, synergistic interaction of chemical corrosion and mechanical damage together effect. The fretting wear accelerated corrosion rate. The synergy of corrosion and fretting wear in Hank's solution promote the fretting wear and corrosion of NiTi shape memory alloy, and bate the resistance of corrosion and wear.Fretting results in the production of debris between contacting surfaces, and the wear debris exerts an important influence on friction coefficient and wear volume of materials. The generation, evolvement and disappearance of wear debris are sometimes promoted and sometimes restrained by aqueous media, the competitive results depending on the experimental conditions.