Abstract
The dimensionless Niyama criterion was used to predict the formation of microporosity in nickel-based superalloy casting, which extended the model application from a simple plate casting to complex thin-wall superalloy casting. The physical characteristics of the superalloy were calculated by JMatPro software. The relation between the volume percentage of microporosity and the dimensionless Niyama values were constructed. Quantitative metallographic measurements of the microporosity of the practical thin-wall casting were carried out. The prediction agreed well with the experiment in general, except for some thick-wall sites in the casting.
Highlights
A nickel-based superalloy always behaves well at high temperatures and has been widely used for critical structural components in aerospace and other industries for many years because of its good mechanical property balance, malleability and weld ability
Based on Darcy’ law, Carlson and Beckermann proposed dimensionless Niyama criterion, where local thermal conditions, melt properties, and solidification characteristics were taken into consideration; this criterion can predict feeding-related microporosity caused by shallow temperature gradients other than gas porosity [18]
Once the specific Ny is obtained in the casting, the volume percentage of microporosity can be ensured by the Ny − f p function
Summary
A nickel-based superalloy always behaves well at high temperatures and has been widely used for critical structural components in aerospace and other industries for many years because of its good mechanical property balance, malleability and weld ability. The volume fraction of microporosity has been predicted quantitatively for a simple plate casting based on the transmission of solutes and Sievert’s law [12]. Based on Darcy’ law, Carlson and Beckermann proposed dimensionless Niyama criterion, where local thermal conditions, melt properties, and solidification characteristics were taken into consideration; this criterion can predict feeding-related microporosity caused by shallow temperature gradients other than gas porosity [18]. According to Equations (3)–(6), the volume percentage of microporosity (fp) can be expressed as the function of threshold dimensionless Niyama values ( Ny * ). The Ny * can be calculated directly using local solidification parameters and alloy properties, as shown in Equation (7). Once the specific Ny is obtained in the casting, the volume percentage of microporosity can be ensured by the Ny − f p function
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