Nonequilibrium Phase Transformations in Titanium Aluminides with Ternary Additions

9616748 Wittig本研究考察了二元和三元Ti-Al合金中的大量相变，以确定母体与产物的结晶学关系，以及三元元素对大量相变产物形核和生长的影响。基合金的成分为Ti-48at%Al。对于该化学计量比，添加了三元元素V、Nb、Cr、Mo、Mn和Fe。最初的工作集中在元素周期表第四行的钒、铬和锰系列上。通过利用范德比尔特大学的过冷快速淬火技术，形成了独特的非平衡微结构，这应该有助于澄清目前关于三元添加伽马TiAl的位置偏好的困惑。用光学显微镜、X射线衍射、扫描电子显微镜和分析电子显微镜对快速冷却、溅射淬火的样品进行了分析。用ALCHEMI方法比较过冷和急冷TiAl三元合金的非平衡组织与平衡状态，可以用化学计量比表征三元元素的占位情况。了解三元原子添加对晶胞结构的影响对于理解三元合金力学性能改善的原子机制是至关重要的。这项研究中探索的高冷却速度、固态转变为其他非平衡过程提供了一些见解，例如在焊接合金的热影响区发现的那些过程。***

9616748 Wittig This research examines the massive phase transformations in binary and ternary Ti-Al alloys to determine the parent to product crystallographic relationships and the effects of ternary elements on the nucleation and growth of the massive transformation product. The base alloy has a composition of Ti-48at%Al. To this stoichiometry, additions of the ternary elements V, Nb, Cr, Mo, Mn, and Fe are added. Initially the work concentrates on the V, Cr, and Mn series from row four of the periodic table. By utilizing the University of Vanderbilt's undercooling, rapid quench technology, unique nonequilibrium microstructures are formed that should help clarify present confusion regarding the site preferences of ternary additions to gamma TiAl. The rapidly cooled, splat- quenched samples are analyzed using optical microscopy, X- ray diffraction, scanning electron microscopy and analytical electron microscopy. By employing ALCHEMI to compare the non-equilibrium microstructures of undercooled and rapidly quenched TiAl ternary alloys with equilibrium conditions, the site occupation of the ternary elements can be characterized as a function of Ti/Al stoichiometry. %%% Knowledge of the influence of ternary atom additions on the unit cell structure is critical to the understanding of the atomic mechanisms responsible for improved mechanical properties observed in the Ti-Al 48at% ternary alloys. The high cooling rate, solid-state transformations explored in this research give some insights onto other nonequilibrium processes such as those found in the heat-affected zones of welded alloys. ***