Determination of Secondary Dendrite Arm Spacing for In-738LC Gas-Tungsten-Arc-Welds

Abstract

Microstructure and defect development in the gas tungsten arc weld process is influenced by the solidification and melt-pool dynamics. Melt-pool geometrical parameters which depend mainly on heat input have profound influence on the dendrite growth velocity and growth pattern in the melt pool. Temperature magnitude and history during the process directly determine the molten pool dimensions and surface integrity. However, due to the transient nature and small size of the molten pool, the temperature gradient and the molten pool size are very challenging to measure and control. The proposed research aims to establish a methodology for characterizing direct energy deposited metals by linking processing variables to the resulting microstructure and subsequent material properties. Secondary Dendrite Arm Spacing (SDAS) optical metallographic measurements of equiaxed solidified IN-738LC gas tungsten arc welds were conducted to find a new expression that links the cooling rate that is imposed on the welding during solidification, and the resultant scale of the grain substructure.