The equilibrium surface equation of gamma prime for nickel base superalloys was suggested by using multiple regression and vector analysis. By application of suggested alloy design technique, precipitation behavior and strengthening effects of gamma prime phase were evaluated for two kinds of designed alloys.
The growth of gamma prime phase in the alloys was controlled by volume diffusion of Al or Ti despite high volume fraction of gamma prime phase. Activation energy for the growth of gamma prime phase was estimated to be 272, 277 kJ/mol, respectively. Since the hardness of alloy was not decreased much after long term exposure at high temperature, it was suggested that the high temperature properties of designed alloys would be excellent. The strengthening effect at high temperature were investigated for four kinds of model alloys designed by adding W continually up to above solution limit of alloy system. In the temperature range between 850 and 950℃, it was observed that compression strength was increased due to the presence of alpha W. It was suggested that strengthening by aging at high temperature was influenced by the precipitation and growth of gamma prime phase. The coarsening of gamma prime was proportional to $t^{1/3}$ and was controlled by volume diffusion of Al or Ti element in the alloy. The activation energy for the growth of gamma prime was estimated to be 271, 259, 260, 266 kJ/mol for four kinds of model alloys, respectively.
The alpha W was stable phase until 950℃ independent of aging time and was composed of W, Ni, Cr and small amount of Al. While the tensile strength was increased linearly upon volume fraction of alpha W in the alloy, the elongation was decreased.
