Ganesh Kumar Meenashisundaram

Enhancing the hardness/compression/damping response of magnesium by reinforcing with biocompatible silica nanoparticulates

Abstract Low volume fraction silica nanoparticulate-containing magnesium composites targeting structural and biomedical applications were synthesized using the blend–press–sinter powder metallurgy technique followed by hot extrusion, and subsequently characterized for their microstructural, mechanical and damping properties. The results of microstructural characterization revealed a maximum ∼32% reduction in grain size with 2 vol.% addition of SiO2 nanoparticulates. The compressive properties of pure magnesium increased with the addition of SiO2 nanoparticulates with Mg-2 vol.% SiO2 nanocomposite exhibiting the maximum 0.2% compressive yield strength and compressive fracture strain. The addition of SiO2 nanoparticulates enhanced the damping characteristics of pure magnesium with Mg-2 vol.% SiO2 nanocomposite exhibiting the maximum damping capacity and damping loss rate with a minimum change in elastic modulus which is favorable when targeting magnesium for biomedical applications. An attempt has also been made in this study to compare the biomechanical properties of synthesized Mg–SiO2 nanocomposites with those of natural bone.

Effects of Primary Processing Techniques and Significance of Hall-Petch Strengthening on the Mechanical Response of Magnesium Matrix Composites Containing TiO2 Nanoparticulates

In the present study, Mg (1.98 and 2.5) vol % TiO2 nanocomposites are primarily synthesized utilizing solid-phase blend-press-sinter powder metallurgy (PM) technique and liquid-phase disintegrated melt deposition technique (DMD) followed by hot extrusion. Microstructural characterization of the synthesized Mg-TiO2 nanocomposites indicated significant grain refinement with DMD synthesized Mg nanocomposites exhibiting as high as ~47% for 2.5 vol % TiO2 NPs addition. X-ray diffraction studies indicated that texture randomization of pure Mg depends not only on the critical amount of TiO2 NPs added to the Mg matrix but also on the adopted synthesis methodology. Irrespective of the processing technique, theoretically predicted tensile yield strength of Mg-TiO2 nanocomposites was found to be primarily governed by Hall-Petch mechanism. Among the synthesized Mg materials, solid-phase synthesized Mg 1.98 vol % TiO2 nanocomposite exhibited a maximum tensile fracture strain of ~14.5%. Further, the liquid-phase synthesized Mg-TiO2 nanocomposites exhibited higher tensile and compression properties than those primarily processed by solid-phase synthesis. The tensile-compression asymmetry values of the synthesized Mg-TiO2 nanocomposite was found to be lower than that of pure Mg with solid-phase synthesized Mg 1.98 vol % TiO2 nanocomposite exhibiting as low as 1.06.

Reinforcing Low-Volume Fraction Nano-TiN Particulates to Monolithical, Pure Mg for Enhanced Tensile and Compressive Response

Novel Mg (0.58, 0.97, 1.98 and 2.5) vol. % TiN nanocomposites containing titanium nitride (TiN) nanoparticulates of ~20 nm size are successfully synthesized by a disintegrated melt deposition technique followed by hot extrusion. Microstructural characterization of Mg-TiN nanocomposites indicate significant grain refinement with Mg 2.5 vol. % TiN exhibiting a minimum grain size of ~11 μm. X-ray diffraction studies of Mg-TiN nanocomposites indicate that addition of up to 1.98 vol. % TiN nanoparticulates aids in modifying the strong basal texture of pure Mg. An attempt is made to study the effects of the type of titanium (metal or ceramic), size, and volume fraction addition of nanoparticulates on the microstructural and mechanical properties of pure magnesium. Among the major strengthening mechanisms contributing to the strength of Mg-Ti-based nanocomposites, Hall-Petch strengthening was found to play a vital role. The synthesized Mg-TiN nanocomposites exhibited superior tensile and compression properties indicating significant improvement in the fracture strain values of pure magnesium under loading. Under tensile and compression loading the presence of titanium (metal or ductile phase) nanoparticulates were found to contribute more towards the strengthening, whereas ceramics of titanium (brittle phases) contribute more towards the ductility of pure magnesium.

Using lanthanum to enhance the overall ignition, hardness, tensile and compressive strengths of Mg-0.5Zr alloy

Abstract Near dense Mg 0.5 wt.% Zr (0, 1, 2.5 and 4) wt.% La alloys were successfully synthesized by disintegrated melt deposition technique followed by hot extrusion and were characterized for their microstructural, ignition, hardness, tensile and compression properties. Combined effects of Zr and La assisted in significant grain refinement of Mg and Mg 0.5 wt.% Zr 4 wt.% La exhibited an average grain size as low as ∼2.75 µm. High ignition temperature of ∼645 °C was realized with Mg 0.5 wt.% Zr (1, 2.5 and 4) wt.% La alloys. Microhardness value as high as ∼103 Hv was observed with Mg 0.5 wt.% Zr 4 wt.% La alloy. Under room temperature tensile and compression loading, significant improvements in the strength properties of pure Mg with the addition of 0.5 wt.% Zr (0, 1, 2.5 and 4) wt.% La was observed. Mg 0.5 wt.% Zr 4 wt.% La exhibited the maximum 0.2% tensile and compression yield strengths of ∼283 MPa and ∼264 MPa, respectively. The tensile and compression fracture strain values of synthesized pure Mg were found to be unaffected with the addition of 0.5 wt.% Zr. But the tensile fracture strain reduced with the addition of La while the compressive fracture strain was unaffected. Minimal tensile-compression asymmetry (∼1) was exhibited by Mg 0.5 wt.% Zr (1 and 2.5) wt.% La alloys.

Synthesis of Magnesium-Based Biomaterials

Owing to the advantages of magnesium as a biomaterial, study on synthesis of magnesium materials is of prime importance. This chapter introduces potential synthesis techniques for synthesizing both impermeable and porous magnesium-based biomaterials. Primary processing of magnesium-based materials (alloys and composites) can be classified into liquid-state and solid-state processes. The advantages and disadvantages of synthesis techniques are presented and discussed. Even though there are many synthesizing methodologies for magnesium-based alloys and composites, very few were adopted for synthesizing biomaterials, especially porous magnesium materials. Recent technology advancements enable the researchers and engineers to synthesize homogeneous magnesium alloys and composites utilizing high-purity raw materials and continuously strive to achieve repeatability of material properties at all times.

Insight into cytotoxicity of Mg nanocomposites using MTT assay technique

In the present study, Youngs modulus measurements and indirect cytotoxicity test were performed on Mg (0.97, 1.98, 2.5) vol% TiO2, Mg (0.58, 0.97, 1.98) vol% TiC, and Mg (0.58, 0.97, 1.98) vol% TiN, synthesized using the Disintegrated Melt Deposition technique to determine the cytotoxicity of low volume nano-particulate reinforcement on magnesium. The results of the indirect MTT assay on Day 3 and Day 5 indicate that 2.5vol% TiO2, TiC and TiN has little effect on the cytotoxicity when added as low volume fraction reinforcement to magnesium. While (0.97, 1.98) vol% TiO2 negatively affected the cytotoxicity when added to Mg. The Youngs modulus of the materials was found to remain close to that of cortical bone which would suggest that the stress shielding effect would be reduced as the increase in Youngs modulus was mitigated by the low volume addition of reinforcements.

Selection of Alloying Elements and Reinforcements Based on Toxicity and Mechanical Properties

An important criterion to assess and biologically evaluate a biomaterial is to study its local toxic effects at the implantation site and systemic toxic effects (distant from the implantation site) due to transportation of the particles or metal ions. When the intake of even a very essential element of human body is beyond the recommended dosage level, adverse effects obstructing the normal functioning of organs are still possible. It is important to design biomaterials such that the compounds generated during degradation of implants due to wear or corrosion are still completely assimilated within the human body without any harmful effects. Biomaterials should possess sufficient mechanical properties to sustain within human body until performing its intended functions. With exhaustive information on toxicity and the effects of varying amounts of elements on mechanical properties of magnesium materials, this chapter will enable the readers to select alloying elements and reinforcements for effective design of magnesium-based biomaterials. In this chapter, major emphasis is on the effects of readily absorbable and advantageous alloying elements such as calcium, zinc, strontium, silicon, and zirconium on the mechanical properties of pure Mg. Due to the toxicity risks of aluminum and rare earth metals on human body, even though few of their alloys are classified “biodegradable,” more investigations especially on their in vivo behavior are required therefore at this moment, they are not primarily addressed in this chapter.

Effects of Ti and TiB2 Nanoparticulates on Room Temperature Mechanical Properties and In Vitro Degradation of Pure Mg

Mg 1 vol.% Ti and Mg 1 vol.% TiB2 composites containing Ti (30–50 nm) and TiB2 (~ 60 nm) nanoparticulates were successfully synthesized using disintegrated melt deposition technique followed by hot extrusion. In vitro degradation of synthesized pure magnesium and composites were assessed by immersion testing in Dulbecco’s Modified Eagle’s Medium (DMEM) + 10% Fetal Bovine Serum (FBS) solution for a maximum duration of 28 days. Determination of corrosion rates by weight loss technique reveals that after 28 days of immersion testing, Mg 1 vol.% Ti exhibited the best corrosion resistance followed by pure magnesium and finally by Mg 1 vol.% TiB2 composite. The room temperature mechanical properties of the synthesized composites were found to surpass those of pure magnesium. On tensile and compressive loading, substantial strengthening of pure magnesium was observed with 1 vol.% Ti addition whereas appreciable increase in tensile and compressive fracture strains of pure magnesium was observed with 1 vol.% TiB2 addition.

Selection of Alloying Elements and Reinforcements Based on Degradation Properties

Magnesium is a potential metallic degradable material which can be gradually dissolved, consumed, or absorbed within the human body. Secondary surgery increases human fatigue and health cost. In case of orthopedic fixation devices such as plates, screws, and pins, it is desirable for the devices to completely degrade within the physiological medium so that secondary surgery for the removal of devices may be avoided. Corrosion of magnesium within a physiological medium may lead to the generation of large volume of hydrogen gas and may increase pH of the body fluid. This limitation may be mitigated by effectively controlling the corrosion rate of magnesium materials. By choosing suitable alloying elements and reinforcements, the degradation properties of magnesium may be appropriately designed. This chapter carefully analyzes the effects of alloying elements and reinforcements on the in vitro degradation and cytotoxicity of pure Mg. Further, significance of absorbable elements such as Ca, Zn, Sr, Mn, and Zr on in vivo degradation of pure magnesium is also discussed. With the combined information on toxicity, mechanical and degradation properties of alloying elements and reinforcements on pure magnesium, magnesium alloys, and composites may be effectively designed targeting potential futuristic biomaterials.