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.