Elsevier

Materials & Design

Volume 64, December 2014, Pages 102-109
Materials & Design

Mechanical and functional properties of ultrafine grained Al wires reinforced by nano-Al2O3 particles

https://doi.org/10.1016/j.matdes.2014.07.052Get rights and content

Highlights

  • Al wires reinforced with Al2O3 nanoparticles were produce via powder metallurgy.

  • Ball milling led to the fragmentation of the oxide layers that cover Al particles.

  • Ball milling led to the fragmentation of Al2O3 nanoparticles added ex-situ.

  • The nanocomposite wires showed improved tensile properties.

  • The nanocomposite wires exhibited excellent damping behavior at high temperatures.

Abstract

A powder metallurgy route based on high-energy ball milling, powder consolidation by hot extrusion and cold rolling was used to produce Al composite wires reinforced with Al2O3 nanoparticles. The process was capable of preparing fully dense nanocomposites characterized by well dispersed nanoparticles in a ultra-fine grained matrix. Ball milling led to the fragmentation of the passivation oxide layer that covers the aluminum particles and of the alumina particle clusters added ex-situ in addition to embedding these nano-sized particles in the Al matrix and thus producing optimal precursors for subsequent consolidation. The nanocomposites showed improved mechanical performances in term of hardness and tensile strength. They also exhibited excellent damping behavior at high temperatures.

Introduction

Metal matrix nanocomposites (MMnCs) are considered interesting materials since they show higher strength than the corresponding base metals while retaining a good toughness [1], [2], [3]. They are generally made up of a ductile metal matrix reinforced with hard nanoparticles (NPs). Different from precipitates formed in precipitation hardening alloys, the reinforcing NPs are thermodynamically stable, making MMnCs ideal for high temperature applications [1], [2], [3]. Such small particles can obstruct the motion of dislocations and are responsible for the formation of geometrically necessary dislocations due to the mismatch in coefficients of thermal expansion and in elastic moduli between the metal matrix and the NPs [4]. Low wettability and a high surface to volume ratio of ceramic nano-particles are the main issue to face to prepare MMnCs. NPs tend to agglomerate and form clusters, losing their capability to effectively obstruct the movement of dislocations. For this reason, they cannot be prepared by conventional casting methods. To overcome this problem several non-conventional manufacturing methods have been proposed, and they can be categorized into two major groups: ex-situ and in-situ synthesis routes [1], [2], [3]. The former refers to those processes in which the nano-reinforcement is added to the liquid or powder metal whereas the latter refers to those methods that lead to the formation of nano-sized compounds during the process itself, e.g. through reacting gases. Powder metallurgy routes [5], [6], [7], [8], [9], [10], ultrasound assisted casting [11], [12], disintegrated melt deposition [13] are some of the processes commonly used to produce MMnCs.

The high strength of MMnCs can be further improved by decreasing the grain size of the matrix down to the sub-micrometer level (Hall–Petch strengthening) [14]. Indeed, ultrafine grained (UFG) materials, processed by severe plastic deformation methods like equal channel angular pressing or high pressure torsion, have attracted growing interest because of their unique physical and mechanical properties [15]. The combination of properties conferred to the aluminum matrix by the combination of an UFG microstructure and hard NPs would be particularly attractive for all those applications requiring low density and high mechanical properties.

In this investigation, a powder metallurgy route to produce Al-based MMnCs reinforced by Al2O3 NPs is adopted. An UFG microstructure was conferred to the micro Al particles through high-energy ball milling (BM) and preserved during consolidation thanks to the oxide dispersion. Ball milling has proven to be a suitable technique for breaking the surface oxide layer that covers the aluminum particles into nano-sized fragments (in-situ production of NPs). It also revealed able to embed NPs into the ductile Al matrix. The ball milled powder, after canning, were consolidated via hot extrusion. The extruded rods were cold rolled down into wires to verify the formability. The wires were then characterized for mechanical properties (tensile and Vickers hardness) and microstructures including NPs dispersion and grain sizes by electron microscopy analysis.

The damping capacity, or internal friction (IF), was also investigated. IF is a measure of the energy dissipated by a material during imposed mechanical vibration under cyclic loading. IF of the Al/Al2O3 MMnC wires was studied to consider these materials as possible candidates for applications in which the combination of good mechanical properties and high internal friction required. Indeed, vibrations generated in response to a dynamic loading are responsible for high noise levels, premature fatigue failure and wear in most of the frequently used structural materials such as steels and Al alloys which exhibit relatively low IF [16], [17].

Section snippets

Method

A commercial purity Al powder with an average size of 20 μm (supplied by ECKA Granules) and a colloidal solution of alumina particles with an average particle size of 50 nm in isopropyl alcohol (supplied by Sigma Aldrich) were used as starting materials. The aluminum particles were passivated by exposure to air to possess a thin oxide layer. According to previous works [18], [19], [20], [21], [22], [23], the thickness of this layer is considered to be in the range of 2–4 nm. The nominal oxygen

Microstructures

Morphological analysis of powders was carried out before and after milling which was responsible for severe alteration of the shape of metal particles. The as-received Al particles were round, smooth and separated but, after ball milling, they appeared agglomerated and became flat with sharp corners (Fig. 3). The Al–2 wt.% Al2O3 powder had a similar appearance after milling. In Fig. 4a, a close-up of the milled particles. It is reasonable to assume that high-energy ball milling was able to break

Conclusions

Al based nanocomposite wires were successfully produced via a powder metallurgy route based on high-energy ball milling, powder consolidation by hot extrusion and cold rolling. Ball milling led to fragmentation of the surface oxide layers on Al particles and the breakup of alumina clusters added ex-situ into nano-sized alumina particles. It was also able to homogeneously embed these nanoparticles in the Al matrix, producing the optimal precursors for subsequent consolidation. The milled powders

References (32)

  • M. Balog et al.

    Forged HITEMAL: Al-based MMCs strengthen with nanometric thick Al2O3 skeleton

    Mater Sci Eng A

    (2014)
  • Williamson et al.

    X-ray line broadening from filed aluminium and wolfram

    Acta Metall

    (1953)
  • Praveennath G. Koppad et al.

    On shear-lag and thermal mismatch model in multiwalled carbon nanotube/copper matrix nanocomposites

    JALCOM

    (2013)
  • J.N. Wei et al.

    Mater Sci Eng A

    (2002)
  • E. Carreño-Morelli et al.

    Mechanical spectroscopy of thermal stress relaxation at metal–ceramic interfaces in Aluminium-based composites

    Acta Mater

    (2000)
  • S.C. Tjong

    Novel nanoparticle-reinforced metal matrix composites with enhanced mechanical properties

    Adv Eng Mater

    (2007)
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