COOLING RATES IN GAS ATOMIZED AL-4WT-PERCENT-CU ALLOY POWDERS

A method is described for measuring alpha-Al cell spacings in helium o r nitrogen atomised Al-4wt%Cu alloy powder particles of different size s. These spacings have been related to cooling rate using an available empirical relationship applicable over a range of cooling rates for t he chill cast alloy and an experimental relationship has been derived between cooling rate and powder particle size. The cooling rates estim ated by this method are higher for helium than for nitrogen atomizatio n and almost two orders of magnitude lower than those determined from heat transfer calculations.