Elsevier

Materials Letters

Volume 264, 1 April 2020, 127361
Materials Letters

Mechanical properties of Al3BC by nanoindentation and micropillar compression

https://doi.org/10.1016/j.matlet.2020.127361Get rights and content

Highlights

  • Al3BC particles with large enough size were synthesized in Al matrix.

  • Mechanical properties of Al3BC were experimentally measured for the first time.

  • The data is important for the design and optimization of Al3BC/Al composites.

Abstract

Mechanical properties of Al3BC are still not sufficiently investigated yet for its synthesis difficulties. In this work, the mechanical properties of single-crystal Al3BC were experimentally measured through nanoindentation and micropillar compression for the first time. The hardness, modulus and compression strength were measured to be 24 GPa, 332 GPa and 8.7 GPa, respectively. The high mechanical properties of Al3BC are one prerequisite for it as the reinforcement of Al alloys. This work is expected to have a profound significance for the design and optimization of Al3BC/Al composites.

Introduction

Ternary aluminum boron-carbide phases in the Al–B–C system, such as Al3BC3, Al8B4C7, AlB24C4, etc. have been reported to be not only promising ceramic materials of high hardness and low density, but also candidates as reinforcements of Al composites [1], [2], [3]. Among them, Al3BC was first discovered as phase X in B4C/Al composites by Halverson et al. [4]. It has a hexagonal unit cell with lattice parameters of a = 3.491(2) Å, c = 11.541(4) Å [5]. Later, Meyer and Hillebrecht fabricated pure compounds of Al3BC and finally determined its specific crystallographic structure. Al3BC has close packed Al atoms (layer sequence of ABACBC) with isolated boron atoms placed in all octahedral voids between layers A and C while isolated carbon atoms occupy trigonal voids in the layer B [6]. Unlike some other ternary M/B/C compounds like Al3BC3 which has C-B-C unit, Al3BC has no B-C covalent bonds, which makes it show more metallic character [6], eg. reaction with diluted HCl etc.

As Al3BC can react with the acid and alkali solution [6], preparation of pure Al3BC powders by etching the Al matrix is impossible. There is no method to get pure Al3BC with sufficient quantities so far. The synthesis difficulty of Al3BC makes it hard to experimentally measure its physical and mechanical properties. As a result, all the properties of Al3BC particles reported so far were all theoretically calculated [7], [8]. Solozhenko et al. [7] calculated the bulk modulus of Al3BC by the equation of state of Al3BC. Through a first-principle calculation, Wang et. al. [8] calculated the bulk modulus, shear modulus and Young’s modulus of Al3BC particles. Obviously, the investigation on the properties of Al3BC is still not sufficient, because of the fabrication difficulties and restriction of measurement methods. Nowadays, thanks for the development of some novel micromechanical methods like nanoindentation and micropillar compression, directly measurement of Al3BC’s properties become possible.

To investigate the mechanical properties of Al3BC particles, the fabrication of Al3BC is one challenge. There were only a few of investigations focusing on the synthesis of Al3BC [9], [10]. However, all these papers did not address the control of Al3BC morphology and there always exist some by-products like AlB2 and Al4C3 etc. In our previous work, a novel liquid-solid reaction method was presented to successfully synthesize Al3BC particles in Al matrix [11], [12]. As the Al3BC particles were in-situ synthesized, the size, morphology as well as the fraction of the particles can be controlled according to the demands.

In this work, Al3BC particles with large enough size for mechanical test were in-situ synthesized, and the mechanical properties of Al3BC including hardness, modulus and compression properties, were quantified experimentally for the first time. This work will have a profound significance for the design and optimization of Al3BC/Al composites.

Section snippets

Experimental methods

Al3BC particles used for mechanical tests in this work were in-situ synthesized through a liquid-solid reaction method in Al matrix. The detail method has been described in our previous work [11], [12]. A longer heat treatment at higher temperature (950 °C for 250 h) was adopted in this work to make the Al3BC particles large enough for mechanical test. The mechanical tests were conducted directly on the Al3BC particles embedded in the Al basement. The microstructures were characterized by a

Results and discussion

To measure the properties of individual Al3BC particles, great efforts were made to synthesize Al3BC particles large enough for mechanical tests. Fig. 1a shows the Al3BC particles fabricated in Al matrix. The size of particles varies from several microns to more than ten microns. To estimate the depth of the particle embedded into the matrix, FIB cross-section on the particles was conducted as shown in Fig. 1b. The Al3BC particle has a polygonal morphology with a size of about 10 μm. The FIB

Conclusion

In summary, Al3BC with large enough size was in-situ synthesized in this work, and the mechanical properties of Al3BC particles were experimentally measured for the first time. The hardness and modulus of the particles were measured to be 24 GPa and 332 GPa by nanoindentation, and the compression strength was measured to be 8.7 GPa by micropillar compression. The high mechanical properties of Al3BC are one prerequisite as the reinforcement of Al alloys. This work will have a profound

Credit author statement

Yongfeng Zhao – conducted most of the work and wrote the manuscript

Arun Sundar S. Singaravelu and Qingdong Zhang – conducted the nanoindentation work and contributed to the manuscript

Xia Ma – conducted the processing work and helped with the manuscript.

Xiangfa Liu – guided the part of the project conducted in China – processing and TEM characterization.

Nikhilesh Chawla – guided the part of the projected conducted in the US – micropillar compression, microscopy, FIB characterization, and helped

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 research was financially supported by the National Natural Science Foundation of China (No. 51731007) and the Key Foundation of Shandong Province (No. ZR2016QZ005). We also acknowledge the Center for 4D Materials Science at Arizona State University for support of this research work.

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