Depth sensing indentation of magnesium/boron nitride nanocomposites

Abstract

Magnesium nanocomposites, considered as energy-saving lightweight materials of future, are a fairly new family of composite materials with enhanced specific strength and ductility compared to pure magnesium and/or magnesium alloys. In the present study, time-dependent plastic deformation of novel light-weight magnesium/boron nitride nanocomposites containing 0.5, 1.5 and 2.5 vol% of nano-boron nitride particulates is studied through a depth-sensing indentation approach against monolithic pure magnesium. The synthesis of magnesium–boron nitride nanocomposites was accomplished using powder metallurgy technique coupled with microwave sintering, followed by hot extrusion (end products are 8-mm diameter rods). The depth sensing indentation creep tests were conducted at room temperature (∼0.32Tm of magnesium) using an instrumented indentation platform via a self-similar pyramidal (Berkovich) indenter. To assess the influence of loading rate on the indentation-induced deformation behavior of the materials, a dual stage indentation creep including a constant loading rate followed by a constant load-holding scheme was used; indentation tests were performed on the specimens. The specimens were loaded at rates of 0.05, 0.5, 5, and 50 mN/s to a peak load of 50 mN then force was held constant for 400 s while load/displacement/time data were recorded continuously. The results of the depth sensing indentation tests were correlated and explained using the microstructural characteristics placing special emphasis on the volume fraction of reinforcement and the indentation loading rate. Finally, the controlling creep mechanisms of the magnesium–boron nitride nanocomposites and the base metal (pure magnesium) were discussed in the present paper. The results of this paper can be used as a baseline for high-temperature creep analysis of magnesium–boron nitride nanocomposites which is of engineering significance.

Characterization and Biocompatibility Assessment of Boron Nitride Magnesium Nanocomposites for Orthopedic Applications

“…A similar effect can be observed in BN, with BN nanotubes promoting osteogenic differentiation in vitro, and implants coated with BN had enhanced bone fracture healing in mouse models [37,38]. It has also been previously demonstrated that Mg nanocomposites fabricated with low BN percentages using powder metallurgy demonstrated high levels of grain refinement, and enhanced localized recrystallization compared with pure Mg [39][40][41]. As a result of the expected microstructural characteristics of Mg-BN nanocomposites imparted via BN addition to Mg, we hypothesize that Mg-BN nanocomposites will have the improved mechanical properties and increased corrosion resistance needed for orthopedic implant applications.…”

“…BN nanoparticles, 50 nm in diameter, were incorporated in Mg powder to synthesize BN-Mg nanocomposites of Mg-0.5%BN and Mg-1.5%BN vol.% through powder metallurgy and microwave-assisted rapid sintering methods [39,42]. Mg powder with >98.5% purity and 60-300 µm particle size (Merck, Darm-stadt, Germany) was used as the base metal.…”

“…The mechanically mixed powders were then cold compacted uniaxially at 1000 psi before being sintered at 630 • C in a 2.45 GHz, 900 W Sharp microwave oven. The resulting material was then deformed through hot extrusion at 350 • C at a 20 to 1 ratio, producing 8 mm rods that were finally machined into 7.2 mm diameter and 3 mm thick coupons for their characterizations [39]. In a similar fashion, 0%BN Mg (pure Mg) was synthesized using this method to generate a control for mechanical testing.…”

“…This represents an approximately 1.2 times increase in the microhardness after the addition of 1.5 vol.% of the BN nanoparticles. The enhancement in the mechanical properties after the addition of the BN nanoparticles can be attributed to the presence of the hard BN nanoparticles along the interfaces of the magnesium matrix grains, which limited the deformation of the matrix grains caused by dislocation movement and twining [33,34,39]. To further investigate mechanical properties, a compression test was performed.…”

Effects of processing conditions on solidification characteristics and mechanical properties of in situ magnesium metal matrix composites derived from polysilazane precursor

“…Recently, Haghshenas et al 31 investigated the effects of volume fraction of reinforcement on the depth sensing nanohardness behavior of Mg/BN nanocomposites. They concluded that hardness of the nanocomposites increases with increasing volume fraction of the reinforcement and decreasing activation volume beneath the indenter.…”