Co-based superalloys for friction stir welding tools

Abstract

Materials commonly used for Friction Stir Welding (FSW) tools are divided into two groups: (1) to weld low melting temperature alloys, such as Al, Mg, and Cu alloys; and (2) to weld high melting temperature alloys, such as steels, Ni, Ti, and Zr alloys. Tool steels are commonly used to join low melting alloys. On the other hand, the processing temperature, stresses, and wear conditions associated to the FSW process of high melting temperature alloys limits the materials that can be used for these tools. The most successful tools available today to join steels and Ni-based alloys are based on W-25Re, reinforced with polycrystalline cubic boron nitride (pcBN). However, such advanced material has very limited supply and elevated production cost, and undergo important wear and presents limited toughness. Therefore, a great effort has been dedicated to the development and test suitable materials for the production of FSW tools for elevated melting temperature alloys. Thus, the recently developed Co-based superalloys, which are hardened by ³2 precipitation are considered some of the most promising materials. This alloy system, based on Co-Al-W, has outstanding wear and mechanical properties, and chemical stability at high temperature, which are fundamental for these FSW tools. This project will study such Co-based superalloys as possible FSW tool material, including detailed microstructural characterization, mechanical performance and even actual FSW tests. (AU)