Impact of the Morphology of Micro- and Nanosized Powder Mixtures on the Microstructure of Mg-Mg2Si-CNT Composite Sinters

Abstract

The problem of preparing a ternary powder mixture, which was meant to fabricate sintered heterophase composite, and consisted of micro- and two nanosized powders, was analyzed. The microsized powder was a pure magnesium, and as nanocomponents, a silicon powder (nSi) and carbon nanotubes (CNTs) with 2% and 1% volume fractions, respectively, were applied. The powder mixtures were prepared using ultrasonic and mechanical mixing in technological fluid, and four mixing variants were applied. The morphology of the powder mixtures was characterized with scanning electron microscopy (SEM), and then, composite sinters were fabricated in a vacuum with hot temperature pressing at 580 °C under 15 MPa pressure, using a Degussa press. The reaction between the nSi and the Mg matrix, which caused the creation of the Mg2Si phase in the fabricated Mg-Mg2Si-CNT composite, was confirmed with X-ray diffraction (XRD). The porosity and hardness of the composite sinters were examined, and optical microscopy (OM) and quantitative image analyses were carried out to characterize the microstructure of the composites. In the manufacturing process of the Mg-nSi-CNT mixtures, the best results were the following: first separate de-agglomeration of nanocomponents, then their common mixing, and finally, the deposition of nanocomponents at the surface of the microsized magnesium powder. The applied procedure ensured the uniform layer formation of de-agglomerated nanocomponents on the Mg powder, without re-agglomerated nSi and CNTs. Moreover, this type of powder mixture morphology allows to obtain sinters with lower porosity and higher hardness, which is accompanied by precipitation of a finer Mg2Si phase. In the Mg-Mg2Si-CNT composite, the carbon phase was present, and it was located in the magnesium matrix and in silicide.

Residual Stress Induced by Addition of Nanosized TiC in Titanium Matrix Composite

“…Nanoscale grain size in material plays an important role in microstructural changes during sintering at a faster rate due to the larger reaction area [ 16 , 17 , 18 , 19 , 20 ]. Composites reinforced with nanoceramic particles may be categorized into two groups that are mainly based on microstructural evaluation: (1) nanocomposites fabricated through the dispersion strengthening process of nanosized particles within micron-sized matrix grains or dispersed at the boundary of the grains within the matrix, and (2) nanometer scale with nanocomposites where both matrix grains and reinforcement are in the nanoscale [ 21 , 22 ].…”

Microstructure and Mechanical Properties of Hypo- and Hypereutectic Cast Mg/Mg2Si Composites

“…According to this diagram, eutectic transformation proceeds at 1.48 wt% silicon, and materials from the Mg–Si system are divided into hypoeutectic, eutectic and hypereutectic. These composites can be fabricated by both powder metallurgy [ 22 , 23 , 24 , 25 , 26 , 27 , 28 ] and the casting process [ 6 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. Compared to other methods, casting is a method that can be easily adapted to the required commercial scale of production and is the most economical.…”

“…Recently, Mg/Mg 2 Si composites have been intensively investigated due to the number of properties of the Mg 2 Si phase such as low density (1.99 g/cm 3 ), a comparatively low thermal expansion coefficient (7.5 × 10 −6 K −1 ), relatively high Young’s modulus (120 GPa) and high hardness (4.5 × 10 9 Pa) [ 17 , 18 , 19 , 20 , 21 , 30 , 31 , 32 , 33 , 34 , 35 , 36 ]. It should be additionally noted that the Mg 2 Si compound is also used as a reinforcing phase of aluminum matrix composites [ 37 , 38 , 39 , 40 , 41 , 42 , 43 ] or as a component of magnesium matrix composites with SiC or aluminosilicate microspheres [ 27 , 44 , 45 ]. However, Mg/Mg 2 Si materials were most often investigated in separate experiments where composites with different weight fractions of silicon (i.e., the Mg 2 Si phase) were analyzed.…”

Impact of Carbon Foam Cell Sizes on the Microstructure and Properties of Pressure Infiltrated Magnesium Matrix Composites

“…Ceramic–metal interpenetrating network materials are a group of composite materials that have previously defined component distribution and a defined microstructure that can be obtained by different technologies. Manufacturing solutions for the sintering of ordered ceramic–metal powder mixtures include conventional [ 1 , 2 ] or SHS (self-propagating high temperature synthesis) [ 3 , 4 ] methods as well as infiltration of the porous preforms formed by sintered ceramic particles or short fibers [ 5 , 6 , 7 , 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 ] and infiltration of open-celled foams of defined geometry and smooth walls on a microscopic scale [ 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. The mechanism of ceramic network formation imposes and limits foam characterization features such as cell size, geometry, wall thickness and roughness as well the fraction of open pores; this defines the maximum volume fraction of the second component in interpenetrating network composite materials.…”