Evaluation of Age Hardening Behavior in Welded Materials of Ti-15V-3Cr-3Sn-3Al Alloy by X-Ray Diffraction

Age hardening was significantly promoted at a weld joint of a conventionally heat-treated Ti-15V-3Cr-3Sn-3Al alloy. This local increase in hardness resulted in a decrease in fracture toughness of the weld joint. So a new heat treatment method has been developed to achieve its high fracture toughness. On the basis of our experimental results, the age hardening behavior of the weld joint has been evaluated by X-ray diffraction. Back-reflection Debye patterns were observed in the weld-metal (WM), heat-affect-zone (HAZ) and base-metal (BM) of welded materials. The Debye patterns of WM and HAZ became wide in comparison with BM. Micro-lattice-strain and total misorientation increased in WM and HAZ. Furthermore, in WM and HAZ, sub-boundaries were observed within a recrystallized β grain. These results may suggest that sub-structures markedly affect the age hardening of the weld joint.