Toughening of aluminum matrix nanocomposites via spatial arrays of boron carbide spherical nanoparticles

Abstract

To enhance the toughness of metal matrix nanocomposites, we demonstrate a strategy that involves the introduction of spatial arrays of nanoparticles. Specifically, we describe an approach to synthesize a microstructure characterized by arrays of fiber-like nanoparticle-rich (NPR) zones that contain spherical nanoparticles of boron carbide (sn-B 4 C) embedded in an ultrafine grained (UFG) aluminum alloy matrix. A combination of cryomilling and hot-extrusion was used to obtain this particular microstructure, and the mechanical behavior and operative strengthening and deformation mechanisms were investigated in detail. When compared to an equivalent unreinforced material, the presence of the array of NPR zones contributed to a 26% increase in tensile strength. Moreover, when compared to a nanocomposite containing 2 a homogeneous distribution of nanoparticles, a 30% increase in toughness was observed. High nanohardness values obtained for the NPR zones and the observation of "pull-out" phenomena on fracture surfaces, suggest that the NPR zones behave as "hard" fiber-like units that can effectively sustain tensile loading and thereby enhance the strengthening efficiency of sn-B 4 C. Also, the presence of the array of NPR zones surrounded by nanoparticle-free (NPF) zones led to an enhancement in strength with limited loss in ductility. This behavior was rationalized on the basis of a low value of the Schmid factor in regions adjacent to NPR zones, coupled with the ease of dislocation movement in NPF zones. Finally, the ratio of the plastic zone size to the size of the "hard" NPR zones is proposed as an important factor that governs the overall toughness of the nanocomposite.

Reinforcement Size Dependence of Load Bearing Capacity in Ultrafine-Grained Metal Matrix Composites

“…Additional previously reported data on cryomilled 100 pct UFG AA 5083 [13] are also reported in Table II, as a point of comparison. The elastic modulus values for Samples 1, 2, and 3 were 78.1 ± 0.3, 82.7 ± 0.2, and 71.5 ± 0.3 GPa, respectively.…”

“…But in real systems, the interfaces between the reinforcement and the matrix are not perfect and, furthermore, are influenced by microstructure and the placement of the relative phases. The micrograph in Figure 4(a) illustrates that for Sample 1, the n-B 4 C 71.5 ---100 pct UFG [13] -558 0.30 -particles can be located either at grain boundaries or at grain interiors since the particles are smaller in size than the grains. In contrast, in Sample 2 (see Figure 4(b)), the sl-B 4 C particles are larger than the matrix grains, so they must be located at grain boundaries.…”

“…[1][2][3][4][5][6][7][8][9][10][11] In a drive to further enhance the properties of MMCs, recent research has focused on reducing the reinforcement particle size from the micrometric regime to submicron and nanometric length scales. [6,9] The strength and hardness of nanoparticle-reinforced composites have been extensively studied and the operative strengthening mechanisms have been thoroughly described [6,9,12,13] with the general finding that as the reinforcement particle size decreases, the strength of the composite increases. The reduction in the reinforcement particle size also reduces stress concentrations at the reinforcement particle corners and leads to a consequential increase in work hardenability due to reinforcement-dislocation interactions, which results in enhanced ductility.…”

Enhanced mechanical behavior and fabrication of silicon carbide particles covered by in-situ carbon nanotube reinforced 6061 aluminum matrix composites

“…Adding this novel reinforcement into magnesium matrix by microwave-assisted rapid sintering and hot extrusion, this hierarchical composites exhibited significant simultaneous enhancement of strengthening, hardening and failure strain compared with properties of matrix. Moreover, Jiang et al [14] fabricated fiber-like B 4 C nanoparticles reinforced 5083Al composite to enhance the toughness of composites. In their method, 5083Al powder and spherical B 4 C nanoparticles were initially cryomilled for 12 hours in liquid nitrogen so as to uniformly embed B 4 C nanoparticles into the aluminum, and precursor was kept in a quartz boat and then placed in a horizontal quartz tube reactor.…”

Bioinspired Aluminum Composite Reinforced with Soft Polymers with Enhanced Strength and Plasticity

“…In previous AMMC design, the matrix is reinforced with high hardness and high‐temperature stable materials (e.g., tungsten, molybdenum, titanium, ceramics, etc. ), which resulted in superior properties . But such reinforcements lead to increase in density and exhibit limited load transfer due to differential stiffness in the interfacial regions .…”