In this study, Al/AlN in-situ nanocomposites were fabricated using Al/BN as the starting composite powders. The impact of adding hexagonal boron nitride (BN) to the Al matrix of commercial purity on the microstructure and mechanical behavior of the fabricated in-situ nanocomposites was investigated. Samples including 1, 2, and 4 wt.% boron nitride nanoparticles were produced by planetary ball milling of the composite powders and a post-process of hot extrusion. Scanning transmission electron microscopy revealed that boron nitride nanoparticles dissolved as a solid solution of B and N in the Al matrix at the as-milled state. Through the process of hot extrusion, AlN as the in-situ phase was formed by a reaction between Al and N. These led to improve the mechanical properties as well as grain refinement of Al/AlN nanocomposite. The average grain size of the fabricated composites with the use of 1, 2 and 4 wt.% BN was measured about 910, 823, and 760 nm respectively. It was found that combined strengthening mechanisms of grain refinement, a solid solution of mostly B and AlN in-situ phase formation improved the mechanical properties of Al/AlN nanocomposite. With the use of 1, 2, and 4 wt.% BN, the tensile strength of nanocomposite samples increased approximately 40, 56, and 57% in comparison with pure Al, respectively. The remarkable change in microstructure and mechanical properties of the nanocomposite was obtained when the content of BN is up to 2 wt.%.
Structural and analytical characterization, in the nanometer scale, has become very important for all types of materials in recent years. Transmission electron microscope (TEM) is a perfect instrument for this purpose, which is summarized in this chapter. Parameters such as particle size, grain size, lattice type, morphological information, crystallographic details, chemical composition, phase-type, and distribution can be obtained by transmission electron micrographs. Electron diffraction patterns of nanomaterials are also used to acquire quantitative information containing size, phase identification, orientation relationship and crystal defects in the lattice structure, etc. In this chapter, typical electron diffraction, highresolution transmission and scanning transmission electron microscope imaging in materials research, especially in the study of nanoscience are presented.
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