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.

The Cooling Rate and Residual Stresses in an AISI 310 Laser Weld: A Meso-Scale Approach

“…In agreement with these previous numerical results, in ref. [16], it is also shown through weld micrographs that the solidification microstructure becomes finer from the fusion line to the centerline.…”

“…The uncertainties in the calculation procedures include the inaccuracies in the calculation of the thermal cycles as well as the approximations in the general frame for the mechanical model, especially when important solid-state transformations take place [12][13][14][15]. In previous works [10,16], it was well established that the cooling time from liquid-to-solid temperatures is longer at the fusion line and shorter at the weld centerline. As such, the cooling rate through the solidification temperature range increases and the dendrite arm spacing decreases from the fusion line to the centerline.…”

Consolidation mechanism, microstructural evolution and corrosion resistance of Inconel 625 coatings

“…A scanning electron microscope (SEM), Jeol JSM-7100F, was used to observe the substrate-coating interface, the geometry of the dilution zone and the microstructure showing the formation of the secondary dendrite arm spacing (SDAS). Quantitative evaluation of the SDAS between adjacent sides of branches (see Equation ( 1)) on the longitudinal section of a primary dendrite was carried out as described in [13,14] via the linear intersection method. This method entails drawing a straight line perpendicular to the growth direction of the secondary dendrite arms and counting the number of intercepts of dendrite regions along the line.…”