Improving the Interfacial Microstructure Evolution of Ti/Stainless Steel GTA Welding Joint by Employing Cu Filler Metal

Abstract

In the present work, Cu alloys as filler metals were applied to improve interfacial microstructural evolution during the process of gas tungsten arc (GTA) welding of TA15 titanium alloy with 18-8 stainless steel (SS). Results indicated that the interfacial brittle microstructure evolution of Ti/SS GTA welding joint was improved by adopting Cu alloy as the filler metal. Microstructure in the reaction zone (RZ) is composed of massive precipitations including brittle phosphide (Ti₃P), Ti₂Cu₃ and Ti(Cu, Fe) intermetallic compounds (IMCs), while the fusion zone (FZ) near SS is mainly composed of Cu-rich clumps and α-Fe+(Fe, Cr)₃P skeleton eutectic microstructure. Ti₂Cu₃ precipitations provided substrate for the heterogeneous nucleation of Ti₃P whose regular tetragonal and irregular morphologies are attributed to the proposed two kinds of forming mechanism. During the reaction of P with Ti₂Cu₃, the dropping of residual Ti₂Cu₃ contributed to the formation of macroporous in the middle of irregular Ti₃P precipitations. The dispersive distribution of massive brittle precipitations in the RZ leads to the fluctuant distribution of microhardness, which is up to about 700HV_0.5.

Keywords:

• Alloys
• Interfaces
• Intermetallics
• Microstructure
• Steels
• Titanium
• Welding