In situ synchrotron X-ray diffraction experiments on Al–15%BN mechanically alloyed powder: Observation of AlN nanoparticles precipitation and enhanced thermal stability of nanostructured Al matrix

• Published in: Journal of alloys and compounds 2009-11, Vol.486 (1), p.653-659
• Main Authors: Lonardelli, I., Zadra, M., Ischia, G., Barreiro, J. Gomez, Bortolotti, M., Molinari, A.
• Format: Article
• Language: English
• Subjects: Aluminum; Aluminum base alloys; Aluminum nitride; Condensed matter: structure, mechanical and thermal properties; Cross-disciplinary physics: materials science; rheology; Defects and impurities in crystals; microstructure; Diffraction; Exact sciences and technology; Grain and twin boundaries; Materials science; Mechanical alloying; Nanoscale materials and structures: fabrication and characterization; Nanostructure; Nanostructured aluminum; Other topics in nanoscale materials and structures; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Precipitation; Structure of solids and liquids; crystallography; Synchrotrons; Thermal expansion; thermomechanical effects and density; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermal stability
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2009.07.024

Two different in situ experiments using high energy X-ray diffraction from synchrotron source were performed in order to understand carefully the phase transformation in nanostructured Al–15%BN mechanically alloyed powder. After milling at room temperature for 10 h, a solid solution of Al, B and N was achieved. During the heating, the formation and the evolution of the metastable trigonal Al 2B 3 and a very fine precipitation of hexagonal AlN ( d < 8 nm) within Al grains were detected quantitatively. We found a stabilization of Al 2B 3 between 225 °C and 550 °C and, only around 600 °C the hexagonal AlB 2 starts to form. A detectable decreasing of the Al crystallite size between 420 °C and 470 °C was attributed to the precipitation of AlN nanoparticles that reduce the Al volume fraction and, at the same time, hinder the grain boundary propagation. The powder loses the nanostructure above 600 °C exhibiting an exceptional thermal stability at temperatures close to 0.9 T m .