Biodegradable magnesium (Mg)-based metal matrix composites are promising candidates for orthopaedic applications since magnesium is an abundant mineral in the human body. To improve the bioactivity and cytocompatibility of these Mg composites, hydroxyapatite nanoparticles (HAP) and fluorapatite (FA) microparticles synthesised by a citrate-derived hydrothermal method were introduced into a Mg matrix. These innovative Mg/HAP/FA composites were produced by multi-pass upward friction stir processing (UFSP). Microstructural observation and Micro-CT reconstruction of the composite revealed that HAP and FA particles are well dispersed in the Mg matrix and the magnesium grain size was significantly reduced after the UFSP process. The in vitro bioactivity behaviour of UFSP processed Mg/HAP/FA composites was investigated in simulated body fluid. The results revealed the formation of a fluoride-rich apatite layer on the composites, which was attributed to the release of fluoride ions from the composite and their precipitation in a different configuration. Moreover, cytocompatibility results revealed that the presence of FA particles, together with HAP nanoparticles, were able to favour osteoblasts-biomaterial interaction. 

Fabrication of a biodegradable and cytocompatible magnesium/nanohydroxyapatite/fluorapatite composite by upward friction stir processing for biomedical applications.

Nowadays friction stir processing (FSP) has been used as a surface modification technology. The FSP improves the surface properties of the material by intense plastic deformation, mixing and breaking the base material through stirring action alongside the heat generated by friction to achieve dense and homogenized microstructure. Moreover, FSP is a unique technology to develop surface material matrix composites (MMC) via embedding various reinforcement particles. Recently, many publications have reported the role of various types of reinforcing particles during FSP and their effect on the surface properties such as hardness, tribological and corrosion behaviors. This paper summarizes the state-of-the-art research on FSP technology, providing an in-depth discussion of various types of reinforcement particles to produce surface MMC. This review focusses on the effect of FSP parameters and types of reinforcement particles on the microstructure, mechanical properties, tribological and corrosion behaviors. Finally, it outlines the suggestions and future development directions of FSP as a surface modification technology. 

The influence of reinforcement particles friction stir processing on microstructure, mechanical properties, tribological and corrosion behaviors: A review

The influence of multiple passes during friction stir processing (FSP) on the evolution of microstructure, hardness, compressive strength, and corrosion behavior of a Mg-based bio-composite has been investigated. WE43 Mg alloy was used as the matrix of the composite and nano-sized hydroxyapatite (nHA) was added as the second material to form the composite. After fabrication of the composite by one pass of FSP, the process was repeated six times. Significant grain refinement and fragmentation of secondary phase particles were observed during FSP. Increasing the number of passes of FSP was found to be associated with pronounced grain refinement coupled with the uniformity in distribution of nHAs. Corrosion resistance is enhanced with an increasing number of FSP passes, which is attributed to the fragmentation and redistribution of secondary phase particles in addition to a homogeneous distribution of nHA. 

The effect of multipass friction stir processing on microstructure, mechanical properties, and corrosion behavior of WE43-nHA nano-composite

Although magnesium and magnesium alloys have low elasticity and biodegradable capabilities, the rapid rate of degradation of pure Mg in the body affects the mechanical and corrosion properties. In the current work, the Mg and Mg-1Zr matrix composite reinforced with Eggshell (ES) were synthesized using powder metallurgy. The elemental powders were blended using a milling machine, then compacted at 550 MPa and sintered in an inert atmosphere at 450° C for 2 hr. The synthesized composites were characterized in terms of structure, microstructure, densification, and microhardness. In vitro corrosion, performance was studied in Hank’s medium. The results showed that the sintered samples of Mg-1Zr, Mg-2.5ES, and Mg-1Zr-2.5ES had a relatively homogeneous distribution of reinforcement, with densifications of 99.65%, 98.9%, and 99.2%, respectively. The sintered Mg-1Zr and Mg-1Zr-2.5ES samples showed enhanced microhardness by 13% and 6% respectively compared to pure Mg. The biocorrosion study revealed the beneficial role of reinforcing Mg with Zr and ES particles and their synergetic effect by showing the higher polarization resistance and lower corrosion rate values in Hank’s medium. The finding demonstrates the potential of ES to be used as effective green reinforcement particles in the synthesis of Mg and Mg-Zr-based composite with improved in vitro corrosion properties for biomedical applications. 

Processing and in vitro corrosion analysis of sustainable and economical eggshell reinforced Mg and Mg-Zr matrix composite for biomedical applications

Enriching the microstructure of AZ91D alloy by nano MoO3 composites

In this work, the effects of hybrid (HA + Ag) particles and triple-pass friction stir processing on the microstructure, texture, hardness, and tensile behavior of magnesium matrix bio-nano composite were investigated. The results showed that the mean grain size of samples was in the range of 1-5 μm owing to the occurrence of dynamic recrystallization and suppression of grain growth by second phase particles. All samples exhibited uniform dispersion of particles in the magnesium matrix caused by triple-pass FSP. However, some agglomerations were visible in the microstructure of AZ91/nHA nanocomposite. The average grain size of the AZ91/nHA/smAg sample (1.4 μm) was smaller than that of the AZ91/nHA/mAg sample (2.1 μm), which was attributed to the formation of higher content of MgxAgy precipitates in the AZ91/nHA/smAg composite. By performing the FSP, the content of Mg17Al12 was significantly decreased due to the dissolution of beta into the alpha caused by the breakup effect of mechanical stirring and temperature increase of samples. The AZ91/nHA/smAg sample had the highest texture parameter for the {101‾1} orientation as the high corrosion resistance texture. This was due to the promoting the non-basal slip caused by the dissolution of smAg particles in the magnesium matrix. After the FSP, the microhardness distribution of AZ91, AZ91/nHA, AZ91/nHA/mAg, and AZ91/nHA/smAg samples tended to be uniform and the average hardness was improved owing to the fragmentation of beta particles, grain refinement, and homogeneous dispersion of second phase particles. Compared with the AZ91/nHA/mAg sample, an increase in ultimate tensile strength (291.7 MPa), and a decrease in total elongation (5.6%) and energy absorption (12.3 J/cm3) were observed in the AZ91/nHA/smAg sample due to the formation of a higher content of the silver-rich precipitates in the AZ91/nHA/smAg sample during cooling caused by the higher solubility of silver submicron particles. The fracture surfaces of all processed samples consisted of a large number of fine equiaxed dimples (ductile fracture) owing to the grain refinement and the presence of fine second phase particles. 

Synergistic effects of hybrid (HA+Ag) particles and friction stir processing in the design of a high-strength magnesium matrix bio-nano composite with an appropriate texture for biomedical applications

In this work, the effects of hybrid (HA + Ag) particles and triple-pass friction stir processing on the microstructure, texture, hardness, and tensile behavior of magnesium matrix bio-nano composite were investigated. The results showed that the mean grain size of samples was in the range of 1–5 μm owing to the occurrence of dynamic recrystallization and suppression of grain growth by second phase particles. All samples exhibited uniform dispersion of particles in the magnesium matrix caused by triple-pass FSP. However, some agglomerations were visible in the microstructure of AZ91/nHA nanocomposite. The average grain size of the AZ91/nHA/smAg sample (1.4 μm) was smaller than that of the AZ91/nHA/mAg sample (2.1 μm), which was attributed to the formation of higher content of MgxAgy precipitates in the AZ91/nHA/smAg composite. By performing the FSP, the content of Mg17Al12 was significantly decreased due to the dissolution of beta into the alpha caused by the breakup effect of mechanical stirring and temperature increase of samples. The AZ91/nHA/smAg sample had the highest texture parameter for the { 10 1 ‾ 1 } orientation as the high corrosion resistance texture. This was due to the promoting the non-basal slip caused by the dissolution of smAg particles in the magnesium matrix. After the FSP, the microhardness distribution of AZ91, AZ91/nHA, AZ91/nHA/mAg, and AZ91/nHA/smAg samples tended to be uniform and the average hardness was improved owing to the fragmentation of beta particles, grain refinement, and homogeneous dispersion of second phase particles. Compared with the AZ91/nHA/mAg sample, an increase in ultimate tensile strength (291.7 MPa), and a decrease in total elongation (5.6%) and energy absorption (12.3 J/cm3) were observed in the AZ91/nHA/smAg sample due to the formation of a higher content of the silver-rich precipitates in the AZ91/nHA/smAg sample during cooling caused by the higher solubility of silver submicron particles. The fracture surfaces of all processed samples consisted of a large number of fine equiaxed dimples (ductile fracture) owing to the grain refinement and the presence of fine second phase particles.

Synergistic effects of hybrid (HA+Ag) particles and friction stir processing in the design of a high-strength magnesium matrix bio-nano composite with an appropriate texture for biomedical applications.

Stanislav Pleninger

Papers

Synergistic effects of hybrid (HA+Ag) particles and friction stir processing in the design of a high-strength magnesium matrix bio-nano composite with an appropriate texture for biomedical applications

Synergistic effects of hybrid (HA+Ag) particles and friction stir processing in the design of a high-strength magnesium matrix bio-nano composite with an appropriate texture for biomedical applications.

Achieving high strength and superior ductility in Al–Si alloy by cold rolling and friction stir processing