Microstructure Development during Controlled Directional Solidification in Alloy 718

Abstract

To better understand solidification in large ingot superalloy remelting processes, controlled directional solidification experiments were conducted to examine the effect of solidification time on microstructural evolution. Alloy 718 Cylinders, 25 mm in diameter, were directionally solidified at rates ranging from 0.75 mm/min to 3 mm/min. Each casting was sectioned, characterized, and correlations were developed, relating the microstructural features to solidification time. Results indicate that in alloy 718, as the solidification time increases, the dendrite arms spacing, Laves and carbide size also increases. The exponent of the solidification time correlation ranges from 0.4 to 0.55, which is higher than earlier estimates. Developing a thorough experimental technique, and correlations between observed microstructural features and ingot casting parameters is key in generating solidification defect maps. This data is vital to Integrated Computational Materials Engineering (ICME) efforts in determining theoretical limits on processing parameter used during superalloy remelting using process models.