Microstructure, mechanical and thermal properties of ultrafine-grained Al2024–TiC-GNPs nanocomposite

https://doi.org/10.1016/j.msea.2022.142855Get rights and content

Highlights

  • An ultrafine-grained Al2024–TiC-GNPs hybrid nanocomposite (AlTG) was fabricated.

  • Introducing TiC and GNPs benefits uniform dispersions of TiC and GNPs in AlTG.

  • The hybrid composite (AlTG) shows a superior balance in the strength and ductility.

  • Improved dispersions of TiC and GNPs explain better mechanical properties of AlTG.

  • Excellent thermal conductivity of AlTG is remained compared with other composites.

Abstract

Al matrix composites (AMCs) have gained tremendous interest in the past decades due to their lightweight, superior mechanical and other physical properties. In this study, an ultrafine-grained Al2024/1 wt% TiC/1 wt% graphene nanoplatelets (GNPs) nanocomposite was fabricated through powder metallurgy. Synergetic effects of TiC and GNPs on the microstructural characteristics, mechanical properties and thermal conductivity were investigated in comparison with those of the matrix and TiC or GNPs singly reinforced Al2024 matrix nanocomposites. The Al2024/1 wt% TiC/1 wt% GNPs nanocomposite showed significantly improved mechanical properties with the compression yield strength of 370.2 MPa, ultimate compressive strength of 615.8 MPa and fracture strain of 8.6%, indicating a superior balance in the strength and ductility over TiC or GNPs singly reinforced Al matrix composite, since the distributions of both the TiC and GNPs in Al2024/1 wt% TiC/1 wt% GNPs nanocomposite were improved significantly. The significant mechanical property improvements are attributed to the synergistic reinforcing contributions from TiC and GNPs. The thermal conductivity of Al2024/1 wt% TiC/1 wt% GNPs nanocomposite stables at 55.0 W∙m-1∙K-1 without a further decrease compared with the composite singly reinforced with GNPs.

Introduction

Aluminium and its alloy have been widely used in aerospace and automobile industries due to its lightweight, superior specific strength and wear resistance [[1], [2], [3], [4]]. However, the strength and Young's modulus of monolithic Al alloys are relative low and they cannot meet the requirements for increasing demand for high strength and stiffness in some aerospace and other applications. Thus, AMCs reinforced with fibre, particulate and flaky reinforcements have been developed to overcome the shortcomings of Al alloys [[5], [6], [7]].

In recent years, AMCs reinforced with two or more nano-sized reinforcements have attracted much attention and they have potentials to substitute single reinforced composites [8,9]. On the one hand, the nano-sized reinforcements have a much higher efficiency for strengthening the matrix than that of the micro-sized reinforcements [10,11]. On the other hand, the combination of different reinforcements with different properties may bring beneficial synergistic reinforcing effects that make AMCs more competitive with superior properties [12]. Shan et al. designed a novel AMC reinforced with carbon nanotubes (CNTs) wrapped by γ-Al2O3, the tensile strength of Al−CNTs@Al2O3 composite was significantly improved compared with that of the AMC reinforced with individual CNTs or Al2O3, and its ductility is even better than that of Al–Al2O3 composite. It is believed the synergistic strengthening and toughening effects are attributed to the CNTs@Al2O3 wrapped structure, which improved dislocation strengthening and load transfer ability, and hindered crack propagation [13]. Moreover, a combination of 2D carbonaceous nanomaterials and ceramic nanoparticles are also a common choice for reinforcing Al. AMCs reinforced with GNPs (0.15–0.45 wt %) and BN nanoparticles (0.5–2.0 wt %) were fabricated via powder metallurgy by Şenel et al. Their results show that the compression strength of Al−1.0 wt % BN−0.15 wt % GNP is the highest, an 87% increase compared with that of pure Al. However, when the content of reinforcements exceeds 0.15 wt % for GNPs or 1.0 wt % for BN, the mechanical properties would be deteriorated due to their agglomerations [14]. Therefore, the uniform dispersion of nano-reinforcements is still a challenge in the research of AMCs. Although the previous studies have achieved considerable progress in the study of AMCs, novel AMCs reinforced with different combinations of different nano-sized reinforcing materials, which have uniform dispersed reinforcements and superior properties, are desired to be developed.

TiC and graphene, as reinforcements in Al composites, have been studied by many researchers in the past decades due to their excellent strengthening efficiency for Al matrix among the ceramic and carbonaceous reinforcements, respectively [[15], [16], [17], [18]]. However, researches on composite materials with an Al–TiC-GNPs ternary system are rare, the synergistic effects of nano-sized reinforcements (TiC and GNPs) on the microstructural evolution, compressive properties improvement and thermal properties are still not clear, the relevant mechanisms are needed to be explored further. In this work, the Al2024/TiC/GNPs nanocomposite was fabricated by powder metallurgy. The microstructure, mechanical properties and thermal conductivity of the Al2024/1 wt% TiC/1 wt% GNPs nanocomposite were characterised in comparison with that of unreinforced Al2024, Al2024/TiC and Al2024/GNPs composites. The synergetic influences of TiC and GNPs on the mechanical and thermal performances of the composites were comprehensively studied, and the corresponding possible mechanisms are explored. This study provides a feasible method for designing a new type of AMHNs with superior mechanical and thermal properties.

Section snippets

Composite fabrication

Al2024 powders with a mean size of ∼30 μm supplied by Sichuan Hermus Industry Co. LTD., China were used as the matrix, as shown in Fig. S1. Graphene nanoplatelets (GNPs) with a specific area of 350 m2/g (Sigma Aldrich, Australia) and TiC with an average size of 38 nm (Richest Group LTD., China) were introduced to reinforce the Al2024 matrix. An Al2024/1 wt% TiC/1 wt% GNPs nanocomposite was fabricated via a powder metallurgy (PM) route. First, a mixing process was conducted on a high-energy ball

Powder morphology

Fig. 1 shows microstructures of the as-prepared Al, AlT, AlG and AlTG powders after the ball milling. All of the Al2024 powders had been through severe plastic deformations (i.e. flattening, fracturing and re-welding) from the impact of milling balls during the milling process. As shown in Fig. 1, the powders of Al, AlT and AlG consist of a large number of coarse and flattened lamellar particles and there are many fine cracks on the edges of these particles. The AlTG powders are composed of

Microstructural analysis

It is well known that the oxygen contamination on the powder surfaces during the atomization process of the raw Al alloy powders is unavoidable. Moreover, oxygen contamination (oxygen residue and moisture) would also be introduced during the fabrication of the samples through powder metallurgy in this work. During sintering, the oxygen contamination attached on the powder surfaces would react with Al to form Al oxides, which keeps the prior powder boundaries after sintering. Since the milled

Conclusions

  • (1)

    The fracture of Al alloy powders during ball milling is accelerated and the dispersions of both TiC nanoparticles and GNPs is improved significantly after introducing TiC and GNPs into the matrix simultaneously, compared with TiC or GNPs single-reinforced Al alloy matrix nanocomposites (AlT or AlG), where the agglomerates of TiC and GNPs are clearly found respectively.

  • (2)

    Compared with the unreinforced Al alloy and TiC or GNPs single-reinforced Al alloy matrix nanocomposites, the yield strength and

Data availability

The data included in this study for supporting the findings are available from the corresponding author upon request.

CRediT authorship contribution statement

Fei Lin: Conceptualization, Methodology, Validation, Formal analysis, Investigation, Writing – original draft. Fanghui Jia: Methodology, Formal analysis. Mengyuan Ren: Formal analysis, Investigation. Jun Wang: Investigation. Ming Yang: Resources. Zhixin Chen: Supervision, Writing – review & editing. Zhengyi Jiang: Supervision, Funding acquisition, Writing – review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This work was supported by Australian Research Council (ARC, Grant Nos. DP190100408). The first author thanks the scholarship from China Scholarship Council and University of Wollongong. This research used the JEOL JEM-ARM200F funded by the Australian Research Council (ARC) – Linkage, Infrastructure, Equipment and Facilities (LIEF) grant (LE120100104) located at the UOW Electron Microscopy Centre. Dr Guangsai Yang and Mr. Yao Lu's help in the characterisations is much appreciated.

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