Abstract
The new in situ fabrication process for Mg-Mg2Si composites composed of interpenetrating metal/intermetallic phases via powder metallurgy was characterized. To obtain the designed composite microstructure, variable nanosilicon ((n)Si) (i.e., 2, 4, and 6 vol.% (n)Si) concentrations were mixed with magnesium powders. The mixture was ordered using a sonic method. The powder mixture morphologies were characterized using scanning electron microscopy (SEM), and heating and cooling-induced thermal effects were characterized using differential scanning calorimetry (DSC). Composite sinters were fabricated by hot-pressing the powders under a vacuum of 2.8 Pa. Shifts in the sintering temperature resulted in two observable microstructures: (1) the presence of Mg2Si and MgO intermetallic phases in α-Mg (580 °C); and (2) Mg2Si intermetallic phases in the α-Mg matrix enriched with bands of refined MgO (640 °C). Materials were characterized by light microscopy (LM) with quantitative metallography, X-ray diffraction (XRD), open porosity measurements, hardness testing, microhardness testing, and nanoindentation. The results revealed that (n)Si in applied sintering conditions ensured the formation of globular and very fine Mg2Si particles. The particles bonded with each other to form an intermetallic network. The volume fraction of this network increased with (n)Si concentration but was dependent on sintering temperature. Increasing sintering temperature intensified magnesium vaporization, affecting the composite formation mechanism and increasing the volume fraction of silicide.
Highlights
Metal matrix composite materials have been intensely examined over the past few decades
The Mg-Mg2Si composites sintered at temperatures below the melting point (580 ◦C) and at the melting point (640 ◦C) were examined and characterized by light microscopy (LM), scanning electron microscopy (SEM), quantitative metallography, open porosity measurements, hardness testing, and nanoindentation. These results showed the in situ formation of Mg2Si in the α-Mg matrix and revealed the role of (n)Si content in the ordered nano/micro-powder mixture and sintering temperature in the composite morphology design
SEM was used to characterize the morphology of the powder mixtures prior to sintering
Summary
Metal matrix composite materials have been intensely examined over the past few decades. The use of nanosized components, mostly ceramic (e.g., SiC [1,2,3,4], SiO2 [5], AlN [6], Al2O3 [5,7,8,9], B4C [10,11], TiB2 [12], TiC [13], or Sm2O3 [14]) or carbon (e.g., fullerene, nanotubes, and graphene [15,16,17,18]), allows for the implementation of Orowan’s mechanism and grain size refinement within the metal matrix Combining these concepts can be used to improve the mechanical properties and wear resistance, in addition to changing the friction coefficient. The primary problem with this process is the agglomeration of nanosized raw components prior to or during the consolidation process with liquid or powder metals
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