Solidification structure in Ti–5Ta–1·8Nb weld

Abstract

Solidification structure of a weld in a manual gas tungsten arc welding of 3 mm thick Ti–5Ta–1·8Nb plates has been examined using optical/scanning electron microscopy, EDX spectroscopy and electron backscattered diffraction techniques. The weld exhibited columnar grains of prior β, with a substructure of martensitic α′. The backscattered electron image revealed the solidification mode to be cellular–dendritic, and the EDX analysis confirmed the partitioning of Ta atoms between the dendrites. The crystal orientation of the product α′ obtained by electron backscattered diffraction and the Burgers orientation relationship (for β→α′ transformation) were used to predict the orientation of parent β grains in the weld zone, and the long dendritic arms were found to be aligned parallel to β<100>. Analytical solution based on Rosenthal equation was used to calculate the temperature cycle of the welding process. The solidification mode predicted from calculated G/R ratio (where G is solidification gradient and R is rate of solidification) and Kurz–Fischer map matched with the observed cellular–dendritic solidification structure.