Exploring Mg-Zn-Ca-Based Bulk Metallic Glasses for Biomedical Applications Based on Thermodynamic Approach
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MAGNESIUM (Mg) promises to be an interesting candidate for biodegradable implants in orthopedic application due to its high biocompatibility, biodegradability, and mechanical properties that closely match with that of natural bone.[1,2] Mg plays a vital role in bone formation since it increases osteoblast adhesion.[3] Unlike conventional implants, Mg-based implant does not show a stress shielding effect since its elastic modulus nearly equals to that of the natural bone tissue. Despite these advantages, one major difficulty associated with Mg is its rapid degradation behavior. The corrosion resistance of Mg is very poor making it to degrade before the complete bone formation can occur.[2] Alongside, the rapid degradation of Mg alloys M. RAMYA, Senior Research Fellow, and K.R. RAVI, Associate Professor, are with the Structural Nanomaterials Laboratory, PSG Institute of Advanced Studies, Coimbatore, Tamil Nadu 641 004, India. Contact e-mail: [email protected] SYED GHAZI SARWAT, Undergraduate Student, and V. UDHAYABANU, Assistant Professor, are with the Department of Metallurgical Engineering, PSG College of Technology, Coimbatore, Tamil Nadu 641 004, India. BALDEV RAJ, Director, is with the Structural Nanomaterials Laboratory, PSG Institute of Advanced Studies, and also with the National Institute of Advanced Studies, Bangalore, Karnataka 560 012, India. Manuscript submitted March 27, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
leads to hydrogen evolution and alkalization of solution that causes necrosis of the tissue.[4] This necessitates the need to slow down the biocorrosion rate of Mg alloys. Among the various strategies[5] used to circumvent this difficulty, Mg-based metallic glasses are gaining considerable attention as biodegradable implant material, owing to their superior strength, elasticity, and higher corrosion resistance than their crystalline counterparts.[2,6] By virtue of their chemical homogeneity, the lack of second phases and the absence of grain boundaries,[7–9] Mg metallic glasses slow down the generation of Mg2+ ions, H2 bubbles, and OH- ions.[6] Various Mg-based metallic glasses such as Mg-Cu-Y,[10,11] Mg-Ni-Nd,[12] Mg-Ni-Y,[13] Mg-Cu-Gd,[14] Mg-Ni-La,[15] Mg-Cu-Nd,[16] Mg-Ni-Gd[17] Mg-Ni-Pr,[18] Mg-Al-Ni,[19] Mg-Cu-Er,[20] Mg-Cu-Tb[21] Mg-Al-Ga[22] Mg-Pd-Yb,[23] Mg-Zn-Al,[23] and Mg-Zn-La[23] have been developed but based on the physiological biocompatibility of the alloying elements,[24, 25] it is the Mg-Zn-Ca metallic glass system which is concurred as a favorite choice for bio-implant applications.[26] Contemporary processing routes for Mg-Zn-Ca-based metallic glasses include solid-state processes (i.e., Mechanical alloying/milling) and liquid-state processes (i.e., Melt spinning, copper mold induction melting). In case of solid-state process, the amorphous powder synthesized through mechanical alloying or milling has to be consolidated using techniques such as spark
plasma sintering, hot and cold pressing, hot and cold isostatic pressing,[27] etc. The compaction of these powder
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