Effect of Alloying and Thermo-Mechanical-Treatment on Anisotropic Creep and Deformation of Ti-Alloys

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This renewal award, a renewal of award DMR-0101309, by the Division of Materials Research in the Directorate for Mathematical and Physical Sciences and the Division of Civil and Mechanical Systems in the Directorate for Engineering to North Carolina State University is to study the influence of thermo-mechanical-treatment (TMT) and alloying on deformation and creep anisotropy of titanium alloys. With this award, Professors Murty and Scattergood will characterize the anisotropic biaxial creep of Ti alloys using closed-end internally pressurized thin-walled tubing superimposed with axial load. The project will investigate these behaviors in Ti and Ti-3Al-2.5V following stress-relief anneal and complete recrystallization. Alloying additions such as Al to Ti result in significant modification of crystallographic texture and the operating slip systems. Cold working leads to grain-shape anisotropy of the otherwise equiaxed grain structure of Rx materials. The effects of these variables on the deformation microstructures will be investigated along with deformation anisotropy following biaxial loading under varied stress-states and stress-levels. This award will address transitions in creep mechanisms and the effect of underlying deformation mechanism(s) on creep anisotropy. Such studies would be important since 'blind' extrapolation of short-term data to low stresses could lead to 'non-conservative' estimates of creep strains and life of these structural materials in-service. The broader impacts of the proposed study involve significance to technologically relevant structural materials in various industries such as aerospace, chemical, transportation, etc., where the reliability of thin-walled tubing is of great concern during in-service exposure under multiaxial loading. The mechanical anisotropy of these materials, while making it relatively complex in predicting the life of structures, constitutes interesting examples for demonstration for both undergraduate and high school students thereby giving them a good feel for real life problems. While the outcome of the proposed study is of direct relevance to appropriate technologies, the study involves fundamental aspects of mechanical metallurgy and mechanics.