Investigation of grain refinement in Al/Al2O3/B4C nano-composite produced by ARB

doi:10.1016/j.compositesb.2013.10.037

Composites Part B: Engineering

Volume 58, March 2014, Pages 438-442

https://doi.org/10.1016/j.compositesb.2013.10.037 Get rights and content

Abstract

In this study, Al/Al₂O₃/B₄C nano-composites were fabricated via the accumulative roll bonding (ARB) process. The grain refinement of the Al/Al₂O₃/B₄C nano-composite strips during the ARB process was studied. Microstructural characterizations of the fabricated composites after 2, 5, and 9 cycles were performed by transmission electron microscopy (TEM). The results showed that the composite sample, after 9 cycles, was filled with homogenously distributed ultra fine grains with an average grain size of 230 nm. The findings also revealed that the increase in the dislocation density due to the presence of the nano-sized particles resulted in the grain refinement of the specimens. It was also found that the grain refinement is accelerated by the presence of the refinement particles.

Introduction

Ultra-fine grained (UFG) materials with very small grains (smaller than 1 μm) and outstanding mechanical properties have been the focus of a considerable amount of research for potential use in structural materials in the industry [1], [2]. UFG materials have found a wide range of usage in different fields such as automotive, aerospace and engineering applications [1], [2]. This includes ultra-fine grained metal matrix composites (UFGMMCs) which can be used in important applications such as structural neutron absorbers, armor plate materials, and also as a substrate material for computer hard disks [3], [4]. In particular, particle reinforced Al matrix composites have excited a good deal of interest due to its attractive properties such as being light weight, having a high elastic modulus and wear resistance, having a low thermal expansion coefficient, and the possibility of fabrication by many well-known methods [5]. The mechanical properties of these materials are highly dependent on following parameters: (a) the particle characteristics, (b) the particle distribution, and (c) the matrix mean grain size [6]. It has been reported that the mechanical properties of these materials can be improved by grain refinement [7]. Depending on the metal matrix, size and volume fraction of particles, and work conditions, different types of grain refinement can occur in the UFG materials [8], [9], [10], [11].

To date, much research for obtaining a nano-scale ultra-fine microstructure has been done utilizing various severe plastic deformation (SPD) processes, such as equal channel angular pressing (ECAP) [12], high pressure torsion (HPT) [13], [14], accumulative roll-bonding (ARB) [15]. In the mentioned SPD processes, the ARB process has good potential to fabricate the material in the form of sheets. Recently, this process has been widely applied for production of UFG materials, such as Al, Al alloys [15], [16], Mg [17], and some metal matrix composites (MMCs) [10], [18]. It has been found that the formation mechanism of UFG by ARB is explained in terms of grain subdivision at a submicron scale [19], [20], [21]. In fact, grain refinement during the ARB process occurs by continuous fragmentation of the microstructure. The fragmentation results in the formation of low angle boundaries (LABs), which may eventually convert to high angle boundaries (HABs) [22]. In the ARB process, the formation of a large fraction of HABs at rolling stages can considerably refine the microstructure, whereby the mean grain size is reduced to a few hundred nanometers. The addition of nano-sized reinforcement ceramic particles to the matrix during the ARB process increases the fraction of HABs in the microstructure and accelerates grain refinement [6]. Furthermore, the microstructure is affected by the particle volume fraction. Kang and Chan [7] indicated that by increasing the reinforcement nano-particles from 0 to 4 vol.%, the average grain size of the matrix decreases and its strength is increases. However, as the content of reinforcement exceeded 4 vol.%, the average grain size remained unchanged and the strengthening effect leveled off because of the clustering of the reinforcement [7]. In the present work, we attempt to explain grain refinement mechanisms of alumina and boron carbide nano-particles reinforced aluminum matrix composite (Al/Al₂O₃/B₄C). The microstructural evolution during the ARB process was investigated by TEM.

Section snippets

Experimental

As-received commercial purity aluminum sheets (specifications are given in Table 1), Al₂O₃ and B₄C particles (with an average size of 50 nm) were used as raw materials. Strips of 1050-aluminum were cut into 200 mm × 40 mm × 0.5 mm pieces parallel to the rolling direction and were annealed at 623 K in an ambient atmosphere. The strips were degreased in acetone and scratch brushed with a 90 mm diameter stainless steel circumferential brush with a 0.35 mm wire diameter and surface speed of 14 m s⁻¹. To

Result and discussion

The microstructural changes of the Al/Al₂O₃/B₄C nano-composite during the ARB process was investigated by TEM. Fig. 2 demonstrates the TEM microstructure and the corresponding selected area diffraction patterns (SAD) of the aluminum matrix observed in RD–TD plane of the Al/Al₂O₃/B₄C nano-composite after the 2nd, 5th, and 9th cycles. It is clear that the ARB process leads to a significant refinement of the microstructure after nine ARB cycles. In the SAD pattern of the deformed sample after 2

Conclusion

In this study, Al/Al₂O₃/B₄C nano-composites and monolithic Al were fabricated in the form of sheets via the ARB process, and the effect of the Al₂O₃/B₄C nano-particles on the microstructure evolution during the ARB process was investigated. The conclusions drawn from the results can be summarized as follows:

1.
The ultra fine grained Al/Al₂O₃/B₄C composites with average grain size of 230 nm were fabricated by the ARB process after nine cycles.
2.
Microstructural characterization shows that finer matrix

Acknowledgment

The authors gratefully acknowledge the financial support received from Iran National Science Foundation (INSF).

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Investigation of grain refinement in Al/Al2O3/B4C nano-composite produced by ARB

Abstract

Introduction

Section snippets

Experimental

Result and discussion

Conclusion

Acknowledgment

Composites Part B

Composites Part B-Eng

J Alloys Compd

Composites Part B-Eng

J Mater Process Technol

Scr Mater

Mater Chem Phys

Mater Sci Eng A

Mater Sci Eng A

Mater Des

Mater Sci Eng A

Mater Sci Eng A

CIRP Ann-Manuf Technol

Mater Sci Eng A

Investigation of grain refinement in Al/Al₂O₃/B₄C nano-composite produced by ARB