D. Claves et A. Galerie, KINETIC AND MORPHOLOGIC STUDY OF THE PACK-ALUMINIZATION OF A SERIES OF REFRACTORY ALLOYS, Journal de physique. IV, 3(C9), 1993, pp. 531-539
Five refractory alloys, Fe-20Cr-20Ni, Fe-20Cr-36Ni, Fe-20Cr-45Ni, Fe-2
0Cr-60Ni and Ni-20Cr, were submitted to pack aluminization at 850-degr
ees-C for different durations in a NaF-activated pack. After a short p
eriod to achieve steady state, the coating kinetics were shown to be l
inear. The rate of aluminization was the same for the four alloys cont
aining iron (about 1 mg.cm-2.h-1) and notably higher (1.8 mg.cm-2.h-1)
in the case of the Ni-20Cr alloy. The nature of the formed products a
nd the morphology of the layers were shown to depend on the alloy comp
osition. The most important feature was the presence of external FeAl3
on the four Fe-containing alloys, whereas a mixture of Ni2Al3 + NiAl
was observed on the Ni-20Cr alloy. Kinetic experiments and thermodynam
ic calculations allowed a derivation of the value of the Al-activity a
t the gas-substrate interface. The mechanisms involved in the aluminiz
ation were shown to depend on the Al-concentration in the pack, on gas
eous diffusion for low Al concentration and on interface reaction for
high Al concentration.