Elsevier

Materials & Design

Volume 50, September 2013, Pages 85-91
Materials & Design

Effect of 10Ce-TZP/Al2O3 nanocomposite particle amount and sintering temperature on the microstructure and mechanical properties of Al/(10Ce-TZP/Al2O3) nanocomposites

https://doi.org/10.1016/j.matdes.2013.03.001Get rights and content

Highlights

  • Increasing the 10Ce-TZP/Al2O3 content up to 7 wt.%, enhanced composites’ hardness.

  • Significant enhancement in compressive strength is obtained with 7% 10Ce-TZP/Al2O3.

  • Sintering at 450 °C, hardness and compressive strength are higher than at 400 °C.

Abstract

A zirconia/alumina nanocomposite stabilized with cerium oxide (Ce-TZP/Al2O3 nanocomposite) can be a good substitute as reinforcement in metal matrix composites. In the present study, the effect of the amount of 10Ce-TZP/Al2O3 particles on the microstructure and properties of Al/(10Ce-TZP/Al2O3) nanocomposites was investigated. For this purpose, aluminum powders with average size of 30 μm were ball-milled with 10Ce-TZP/Al2O3 nanocomposite powders (synthesized by aqueous combustion) in varying amounts of 1, 3, 5, 7, and 10 wt.%. Cylindrical-shape samples were prepared by pressing the powders at 600 MPa for 60 min while heating at 400–450 °C. The specimens were then characterized by scanning and transmission electron microscopy (SEM and TEM) in addition to different physical and mechanical testing methods in order to establish the optimal processing conditions. The highest compression strength was obtained in the composite with 7 wt.% (10Ce-TZP/Al2O3) sintered at 450 °C.

Introduction

Aluminum–matrix composites (AMCs) reinforced with intermetallic compounds have been proposed as substitutes for ceramic reinforced composites due to their attractive mechanical properties. Aluminum matrix composites are potential structural materials for automotive, defense and aerospace applications [1]. Lightweight, environmental resistance, high specific strength and stiffness, high thermal and electrical conductivity, and good wear resistance are some characteristics that encourage research and development to extend their applications by further improvement in the properties [2]. Recently, nanocomposites have drawn the attention of many researchers due to their unique mechanical behavior [3], [4]. It has been reported that the strength of Al matrix composites can be improved by about 20% by decreasing the reinforcement particle size from microscale to nanoscale [5], but the tendency of particle clustering and agglomeration also increases [6], [7], [8]. It is important to note that a homogeneous distribution of the reinforcing particles is essential for achieving the improved properties [9]. It is generally known that powder metallurgy processing of MMCs results in better mechanical properties with homogeneous microstructure compared with casting processing [10]. In addition, mixing the matrix and reinforcements particles via ball milling have been successfully employed to improve particle distribution throughout the matrix [11].

As reinforcing particulates for AMCs, carbides, oxides, nitrides and different intermetallics compounds have been used extensively [12]. Moreover, ceramic–ceramic nanocomposites have both specific advantages of ceramic and nanoparticles such as neutrality, high strength, and improved properties owing to nanoscale particles which have superior homogeneity, extraordinary high strength, electric, dielectric, magnetic and optical besides good thermodynamic properties [13], [14], [15], [16], [17], [18]. Alumina and yttria stabilized zirconia have been used successfully as bearing components [19]. Yttria (Y2O3) or ceria (CeO2) as stabilizer of tetragonal zirconia polycrystalline (TZP) prevent transformation from the tetragonal to the monoclinic phase under the external applied stresses at ambient temperature [20].

Several zirconia–alumina composites have been recently developed to offer enhanced mechanical properties [21], [22], [23]. Recently, Nawa et al. [24] developed a Ce-TZP/Al2O3 nanocomposite (with both phases being of nanometer scale). Ce-TZP/Al2O3 nanocomposite possesses three times the toughness and the equivalent strength of conventional Y-TZP.

Ceria-tetragonal-zirconia-polycrystalline (Ce-TZP) nanocomposite is an entirely tetragonal polycrystalline material. The nanosized grains, together with the Ce stabilizer prevent transformation of the tetragonal phase on cooling to room temperature. The homogeneous dispersion of alumina phase in the TZP matrix not only does improve the mechanical properties but also increases hydrothermal stability of tetragonal zirconia [15].

The powder metallurgy process consists of several stages that need to be controlled to optimize the properties of MMCs. Some researchers [25], [26], [27] investigated the effect of process parameters on mechanical properties of MMCs. The microstructures of composites are sensitively determined by the process conditions and are also closely related to the mechanical properties. Therefore, an understanding of the relationship between microstructure and process condition can explain the variation in the mechanical properties with varying process condition such as, the concentration of reinforcement particles, processing temperature and the pressure of hot pressing. Furthermore, it is expected to be able to predict the mechanical properties by analyzing the relationships between the microstructures and the properties of MMCs. In spite of much attention lately paid to high flexural strength and fracture toughness of AMCs as compared to carbides, oxides, nitrides and different intermetallic compounds, no report on addition of 10Ce-TZP/Al2O3 to Al with the purpose of matrix reinforcement has so far been publicized.

In this work, the effect of different concentration of 10Ce-TZP/Al2O3 nanocomposites synthesized via combustion synthesis on the microstructure and physical/mechanical properties of Al–Ce-TZP/Al2O3 nanocomposites prepared by hot- pressing were investigated. The optimal processing conditions to obtaining the highest compression strength were established.

Section snippets

Experimental procedure

Aluminum nitrate, Cerous nitrate and Zirconyl nitrate were the starting materials as the oxidizers, and also used as a source of cerium, zirconium and aluminum for the combustion synthesis. Glycine, Urea, Ammonium acetate, Hexamethylenetetramine and Ammonium nitrate were used as fuels. 10Ce-TZP/Al2O3 is composed of 70 vol.% Ce-TZP that containing 10 mol.% ceria, and 30 vol.% Al2O3. 10Ce-ZTP/Al2O3 nanocomposite powders were prepared by dissolving stoichiometric Aluminum nitrate, Cerous nitrate,

X-ray diffraction of 10Ce-TZP/Al2O3 powder

A representative X-ray diffraction pattern of the 10Ce-TZP/Al2O3 sample is shown in Fig. 3. The crystallinity of the samples is evidenced by the peaks corresponding to the tetragonal phase Ce 0.12–Zr 0.88–O2 (JCPDS card number: 01-082-1398 and lattice parameters: a = 3.627 Å, b = 3.627 Å c = 5.2336 Å) and monoclinic phase Al2O3 (JCPDS card number: 00-035-0121 and lattice parameters: a = 5.62 Å, b = 2.9 Å, c = 11.7 Å). The broad peaks confirm the nanosized nature of the material and the size of the Ce 0.12–Zr

Conclusions

In the present work, a Al/(10Ce-TZP/Al2O3) nanocomposite with 1, 3, 5, 7, and 10 wt.% of reinforcement 10Ce-TZP/Al2O3 particles was hot pressed with 600 MPa at 400 and 450 °C for 1 h. 10Ce-TZP/Al2O3 nanocomposites powders can be successfully synthesized using the aqueous combustion method at 1150 °C for 8 h. Raising the weight fraction of 10Ce-TZP/Al2O3 from 0 up to 10 wt.% leads to increasing the hardness of specimens to a maximum value of 90 BHN. Increasing 10Ce-TZP/Al2O3 up to 7% led to a

Acknowledgements

The authors gratefully acknowledge Sharif University of Technology and Razi Metallurgical Research Center for financial support of this work.

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