Effect of sample diameter and withdrawal rate on microstructure and hot tensile behavior of directionally solidified PWA 1483 superalloy

Microstructure and mechanical properties of a PWA 1483 superalloy directionally solidified in a Bridgman furnace are investigated. The effects of sample diameter, i.e. 13, 33 and 55 mm, and withdrawal rate, i.e. 1.5, 3 and 4.5 mm/min, on primary dendrite arm spacing were evaluated using standard metallographic techniques. Morphology and size of different microstructural constituents were studied by the scanning electron microscopy. Hot tensile tests at 850 °C was utilized to evaluate the mechanical properties of the heat treated samples. While primary dendrite arm spacing decreased with increasing withdrawal rate, it increased with increasing sample diameter. The cubic gamma prime precipitates formed in the interdendritic region were smaller than those formed in the dendrite core. The hot tensile strength of aged samples increased with reduced sample diameter and increased withdrawal rate. In addition, the reduction of sample diameter resulted in increasing of the hot ductility. However, the tensile ductility did not change significantly with the withdrawal rate.