Lokesh Choudhary

Magnesium alloys as body implants: fracture mechanism under dynamic and static loadings in a physiological environment.

It is essential that a metallic implant material possesses adequate resistance to cracking/fracture under the synergistic action of a corrosive physiological environment and mechanical loading (i.e. stress corrosion cracking (SCC)), before the implant can be put to actual use. This paper presents a critique of the fundamental issues with an assessment of SCC of a rapidly corroding material such as magnesium alloys, and describes an investigation into the mechanism of SCC of a magnesium alloy in a physiological environment. The SCC susceptibility of the alloy in a simulated human body fluid was established by slow strain rate tensile (SSRT) testing using smooth specimens under different electrochemical conditions for understanding the mechanism of SCC. However, to assess the life of the implant devices that often possess fine micro-cracks, SCC susceptibility of notched specimens was investigated by circumferential notch tensile (CNT) testing. CNT tests also produced important design data, i.e. threshold stress intensity for SCC (KISCC) and SCC crack growth rate. Fractographic features of SCC were examined using scanning electron microscopy. The SSRT and CNT results, together with fractographic evidence, confirmed the SCC susceptibility of both smooth and notched specimens of a magnesium alloy in the physiological environment.

In-vitro characterization of stress corrosion cracking of aluminium-free magnesium alloys for temporary bio-implant applications

The complex interaction between physiological stresses and corrosive human body fluid may cause premature failure of metallic biomaterials due to the phenomenon of stress corrosion cracking. In this study, the susceptibility to stress corrosion cracking of biodegradable and aluminium-free magnesium alloys ZX50, WZ21 and WE43 was investigated by slow strain rate tensile testing in a simulated human body fluid. Slow strain rate tensile testing results indicated that each alloy was susceptible to stress corrosion cracking, and this was confirmed by fractographic features of transgranular and/or intergranular cracking. However, the variation in alloy susceptibility to stress corrosion cracking is explained on the basis of their electrochemical and microstructural characteristics.

Mechanical integrity of magnesium alloys for biomedical applications

Abstract The concept of using magnesium and its alloys as biodegradable temporary implants has triggered increasing research interest. Such implants will provide mechanical support during the healing process and then harmlessly degrade away. However, the mechanical and chemical stabilities of implant materials during the service period in the human body will still be critically important. Implants often experience considerable loadings while they are simultaneously exposed to human body fluid and, thus, may undergo environmentally assisted cracking (stress corrosion cracking (SCC) and corrosion fatigue). This chapter summarizes the current research on SCC of magnesium alloys and then presents a review on their SCC in simulated human body environments.

Threshold Stress Intensity for Stress Corrosion Cracking (KISCC) of a Magnesium Alloy in Physiological Environment

Threshold stress intensity factor for stress corrosion cracking (KISCC) of AZ91D magnesium alloy in a simulated physiological environment has been determined using circumferential notch tensile (CNT) technique. Fracture surfaces of the tested specimens were analysed using scanning electron microscopy (SEM) in order to examine the features for SCC.