Crystallographic structure of Al3Nb in laser-processed Al-Nb alloys

The aim of the present work is to study the influence of the solidification rate of Al3Nb on the crystallographic structure and on the order parameter of Al3Nb in Al-Nb coatings produced by laser-alloying, using a CO2 laser. The laser treatments were performed using a laser power density of 1.7x10(3 ) W/mm(2) and scanning speeds of 5, 10, 20 and 40 mm/s, corresponding to in teraction times in the range 0.03-0.24 s. The microstructure of all the sur face coatings consists only of the phases predicted by the phase diagram, i .e. alpha-Al and Al3Nb. X-ray diffraction on polished bulk samples revealed a strong (001) texture, which increases with increasing scanning speed. Af ter filing, the particles of Al3Nb become randomly oriented, leading to a b etter agreement between the relative intensities the experimental and calcu lated diffraction patterns. The long-range order parameter of Al3Nb varies in the range 0.8-0.9 and does not depend on the solidification rate, within the limits of experimental error. (C) 1999 Elsevier Science Ltd. All right s reserved.