Structural evolution of Al/BN mixture during mechanical alloying

The structural evolution of an Al/BN mixture during mechanical alloying (MA) using a planetary ball mill was systematically studied. The X-ray diffraction (XRD) patterns show that the diffraction peaks of hexagonal boron nitride (h-BN) disappeared when the mixture was milled for a period longer than 18 h and no new phases were found in the samples milled even for 72 h. AlN and AlB2 both formed when all the milled samples were annealed at 773 K for 2 h. Characterization of the milled samples was also carried out by means of differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIRS), and scanning electron microscopy (SEM). Experimental results reveal that most h-BN gradually decomposed into boron and nitrogen atoms as MA proceeded. Many of the as-decomposed atoms located at grain boundaries and other lattice defects and then some diffused inwards the grain to form a solid solution with further milling. The forming mechanism of the solid solution is discussed.