Biocorrosion and biodegradation behavior of ultralight Mg–4Li–1Ca (LC41) alloy in simulated body fluid for degradable implant applications S. S. Nene • B. P. Kashyap • N. Prabhu • Y. Estrin • T. Al-Samman Received: 24 November 2014 / Accepted: 30 December 2014 / Published online: 30 January 2015 Ó Springer Science+Business Media New York 2015 Abstract Biocorrosion and biodegradation behavior of Mg–4Li–1Ca alloy were investigated for industrially impor- tant end product conditions, namely the homogenized, rolled, and rolled ? annealed ones. Among the three, homogenized material showed the highest corrosion rate (27.2 mm/year) in a simulated body fluid (SBF) owing to its coarse grain struc- ture containing long dumbbell-shaped eutectic phase. Roll- ed ? annealed material exhibited the lowest corrosion rate (0.94 mm/year) corresponding to the highest corrosion resis- tance (1.854 kX cm 2 ) in SBF. This higher corrosion resis- tance is associated with a uniform distribution of corrosion sites and a lower occurrence of twins in the microstructure. However, the rolled material showed a greater corrosion rate due to an appreciable volume fraction of {10  11} compression twins, {10  12} tension twins, and {10  11}–{10  12} double twins, which form galvanic couples with the adjacent grains that enhances localized corrosion. A mechanism of biodeg- radation at the alloy/SBF interface is proposed. It involves the formation of bone-like hydroxyapatite and metastable octa calcium phosphate, along with other degradation products, such as magnesium hydroxide and lithium hydroxide. Introduction Magnesium is considered to be a very promising bio- degradable material for orthopedic implants and vascular stents, owing to its solubility in physiological environment of the human body. Pure Mg has some limitations, such as low strength, poor room temperature formability, exces- sively high degradation rate, and poor ignition resistance. For this reason, developing new degradable Mg alloys for implantology, based on binary (e.g., Mg–Al, Mg–rare earths (RE), and Mg–Ca alloys), ternary (e.g., Mg–Al–Ca and Mg–Zn–Ca alloys), or other more complex Mg-based systems, is becoming a subject of great interest [1–3]. It was reported that among these alloy candidates, Mg–Ca alloys have the greatest potential as far as good biocom- patibility and strength are concerned, in spite of their limited formability [3]. Alloying of magnesium with lithium reduces its already low density and at the same time improves its formability at ambient temperature. However, the use of Li as an alloying element in Mg may cause toxicity issues. According to Timmer and Sands [4], the maximum level of Li in human blood plasma needs to be limited to *75 ppm, above which it may cause toxicity. The authors also pointed out that Li is almost completely excreted from kidneys, since it is not bound to serum proteins [4]. From a metallurgical perspective, Li addition below 5 wt% in Mg S. S. Nene  B. P. Kashyap (&)  N. Prabhu  Y. Estrin IITB-Monash Research Academy, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India e-mail: bpk@iitb.ac.in S. S. Nene  B. P. Kashyap  N. Prabhu Department of Metallurgical Engineering and Materials Science, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India S. S. Nene  Y. Estrin Department of Materials Engineering, Centre for Advanced Hybrid Materials, Monash University, Clayton, VIC 3800, Australia Y. Estrin Laboratory of Hybrid Nanostructured Materials, Moscow Institute of Steel and Alloys, Leninsky prosp. 4, Moscow 119049, Russia T. Al-Samman Institut fu ¨r Metallkunde und Metallphysik, RWTH Aachen University, Kopernikusstr. 14, 52074 Aachen, Germany 123 J Mater Sci (2015) 50:3041–3050 DOI 10.1007/s10853-015-8846-y