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

这个续展奖项是DMR-0101309奖的续展，由数学和物理科学局的材料研究部和北卡罗来纳州立大学工程局的土木和机械系统部负责研究热机械处理和合金化对钛合金变形和蠕变各向异性的影响。获得这一奖项后，Murty和ScatterGood教授将研究钛合金的各向异性双轴蠕变，该蠕变采用封闭式内压薄壁管材，并叠加轴向载荷。该项目将在去应力退火热处理和完全再结晶后研究钛和钛-3Al-2.5V的这些行为。添加Al和Ti等合金化元素会显著改变合金的晶体织构和操作滑移系统。冷加工导致了Rx材料等轴晶组织的晶形各向异性。研究了这些变量对变形组织的影响，以及在不同应力状态和应力水平下双轴加载后的变形各向异性。该奖项将涉及蠕变机制的转变和潜在变形机制(S)对蠕变各向异性的影响。这类研究将非常重要，因为将短期数据“盲目”外推到低应力可能导致对这些在役结构材料的蠕变应变和寿命的“非保守”估计。拟议研究的更广泛影响涉及到对航空航天、化工、交通等不同行业中与技术相关的结构材料的重要意义，在这些行业中，薄壁管道在多轴载荷下的服役暴露期间的可靠性非常令人担忧。这些材料的力学各向异性虽然使其在预测结构寿命方面变得相对复杂，但也为本科生和高中生提供了有趣的演示示例，从而使他们对现实生活中的问题有了很好的感觉。虽然拟议研究的结果与适当的技术直接相关，但这项研究涉及机械冶金和力学的基本方面。

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.