Friction Stir Processing of Beta Titanium Alloys: Challenges and Opportunities

Beta titanium alloys offer a wide range of physical-chemical-mechanical property combinations compared to other classes of Ti alloys, making them attractive for a variety of aerospace applications. Mechanical properties of beta Ti alloys are very sensitive to key microstructural parameters such as beta grain size, grain boundary alpha layer, and secondary alpha platelets. Control of these parameters by conventional thermo-mechanical processing is challenging and limits the property combinations that can be obtained in some cases. In recent years, friction stir processing (FSP) has evolved as a novel tool to create unique microstructures in structural metal alloys that offer improved performance. In this presentation, the influence of FSP on the microstructure and mechanical properties of high strength metastable beta titanium alloys will be discussed. Aspects of FSP tool materials and understanding of issues associated with them will be presented. FSP of beta Ti alloys creates refined microstructures that open up the domain available for fundamental investigation of microstructure-property relationships. Screening results obtained show the feasibility of obtaining tensile strengths up to 1500 MPa along with 5% tensile elongations.