Matrix Structure Evolution and Nanoreinforcement Distribution in Mechanically Milled and Spark Plasma Sintered Al-SiC Nanocomposites

Abstract

Development of homogenous metal matrix nanocomposites with uniform distribution of nanoreinforcement, preserved matrix nanostructure features, and improved properties, was possible by means of innovative processing techniques. In this work, Al-SiC nanocomposites were synthesized by mechanical milling and consolidated through spark plasma sintering. Field Emission Scanning Electron Microscope (FE-SEM) with Energy Dispersive X-ray Spectroscopy (EDS) facility was used for the characterization of the extent of SiC particles’ distribution in the mechanically milled powders and spark plasma sintered samples. The change of the matrix crystallite size and lattice strain during milling and sintering was followed through X-ray diffraction (XRD). The density and hardness of the developed materials were evaluated as function of SiC content at fixed sintering conditions using a densimeter and a digital microhardness tester, respectively. It was found that milling for 24 h led to uniform distribution of SiC nanoreinforcement, reduced particle size and crystallite size of the aluminum matrix, and increased lattice strain. The presence and amount of SiC reinforcement enhanced the milling effect. The uniform distribution of SiC achieved by mechanical milling was maintained in sintered samples. Sintering led to the increase in the crystallite size of the aluminum matrix; however, it remained less than 100 nm in the composite containing 10 wt.% SiC. Density and hardness of sintered nanocomposites were reported and compared with those published in the literature.

Microstructure and Properties of Spark Plasma Sintered Aluminum Containing 1 wt.% SiC Nanoparticles

“…It reveals a free pore microstructure, Figure 7a, and homogenous dispersion of SiC particles, Figure 7c. This confirms that the uniform distribution of SiC particles achieved with milling time of 24 h [4] was maintained in the sintered specimen.…”

“…On the other, XRD spectra did not reveal the presence of phases other than the aluminum matrix [25,32,35]. More details on the synthesis and characterizations of samples were reported elsewhere [4]. The relative density and microhardness, as function of heating rate and pressure, of samples sintered at 550 °C for 5 min are presented in Figure 3.…”

“…SiC nanoparticles appears agglomerated because of their small particle size. More information on powders' characteristics was presented elsewhere [4]. The SiC nanoparticles were uniformly dispersed in the aluminum powder through ball milling for 24 h. Typical XRD spectra of pure un-milled aluminum, Al-1wt.% SiC milled for 24 h, and Al-1wt.% SiC sintered at 600 °C for 10 min using a pressure of 50 MPa and heating rate of 200 °C/min are presented in Figure 2.…”

“…MMCs have excellent properties, such as high fatigue strength, high specific modulus, stability at elevated temperatures, lower coefficient of thermal expansion, high specific strength, and better wear resistance [3,4]. Metal Matrix Nanocomposites (MMNCs), where at least one of the constituent phases has a dimension less than 100 nm, have been developed and their properties were evaluated and found to be better than the properties of metal matrix composites [5][6][7][8][9].…”

Influence of Milling Time on the Crystallite Size of AlSi5Cu2/SiC Composite Powder

“…This high-energy ball milling of powders is being used to produce several materials, alloys and composites. The interest of reduced particle size is needed for improving sintering abilities, which provide to: decreased sintering temperature, increased density or decreased reaction time when we compared with classical methods [5][6][7][8]. However, it is important to keep in mind the fact that "crystallite size" is not synonymous with "particle size".…”