Predicting growth of γ′ in nickel alloys

AbstractIndividual experiments on the growth at elevated temperature of γ′ particles in nickel alloys do not cover a range of conditions sufficient to permit unambiguous discrimination between the growth laws a = (kt)⅓ and a = (k′t)½, where a is half the mean particle size (half the cube edge or sphere diameter as appropriate), k and k′ are constants, and t is time. This paper assembles six studies of Ni-Al binary alloys, Ni-Cr-Al ternary alloys, and the commercial IN 738 alloy, which together cover temperatures from 500 to 1000°C. By compensating for temperature and composition according to the theory from which the growth laws are derived, the experimental times are converted to equivalent times, which range from a few minutes to 50 years. The plot of a = (kt)⅓ over this considerable time span is linear, but that of a = (k′t)½ has the curved form to be expected when the former is linear. Growth of γ′ particles in these alloys, therefore, is correctly described, within the experimental times, by the firs...