Study of microporosity formation in nickel-base superalloys

The susceptibility of nickel-base superalloys to microporosity formation is studied experimentally and theoretically. Analysis of a model introduced herein leads to formulation of a microporosity index, Ap*, which is expressed in terms of solidification parameters and alloy system properties. This index can be determined from information obtained by quantitative differential thermal analysis. The effect of composition on the formation of microporosity is evaluated. Thus, aluminum, titanium, and cobalt are found to increase, and chromium to decrease microporosity. The effect of carbon is beneficial or detrimental depending on the aluminum content in the alloy.