Effect of the nickel particle size on the high-energy milled mixtures of nickel and aluminum powders

摘要

It has been known that NiAl compound formation takes place through an exothermic reaction during high-energy milling of Ni and Al powders. Since it is still unknown how milling parameters can alter the ignition time of this reaction, an investigation was conducted to clarify how variables such as average particle size of starting powders, ball-to-powder ratio, process control agent (PCA) and milling ball diameter affect the ignition time. The millings were performed in a Spex 8000M Mill that allows measurement of the evolution of vial temperature during milling, under argon atmosphere, according to a factorial design at 2 levels with 4 variables. The as-milled powders were characterized using X-ray diffraction (DRX), scanning electron microscopy (SEM). The results have indicated that when smaller Ni powders, greater ball-to powder ratios and no PCA were used the ignition time tends to be decreased. Alternatively, observation of powder morphology evolution during milling for several times and three different Ni average particle sizes was conducted. SEM images indicated that, although Ni particles are harder than Al one, they deform first as they are greater than the Al particles.