Thermal Stability and Mechanical Behavior of Ti-base Nanocrystalline Alloys

非技术综述将研究选定的非常小(纳米晶)晶粒度的钛基合金的热稳定性和力学行为。合金将通过球磨粉末来制备，然后通过热压进行固结。将确定添加适量第三元素以稳定细晶组织的钛合金的组织和显微组织。机械性能将通过评估强度和延展性的技术进行测量。将进行退火研究，通过测量细晶的生长来定量确定热稳定性。这些研究的结果应该会对超细晶粒钛合金的加工和高温要求产生重大影响。与传统晶粒度的钛合金相比，钛合金具有优异的力学性能，可以在结构和生物相关(如植入材料)应用方面取得突破性进展。技术综述钛基合金在汽车和航空航天应用中具有极大的兴趣。这些合金是拟议研究的重点。在大多数情况下，为了处理初始的非平衡合金，必须先进行粉末压制，然后再进行高温固结，而高温是最终使用的先决条件。本研究将探讨纳米晶钛基合金高温热稳定性的动力学和热力学机制。用机械合金化的方法合成了含有hcpα稳定剂和bccβ稳定剂的钛合金。一个模型将能够为热力学稳定选择最佳(过大)的溶质。通过溶质拖曳或齐纳钉扎实现的动力学稳定将通过原位(金属间沉淀)或非原位(氧化物掺杂)策略来实现。热稳定机制相互作用和强化机制转变(Hall Petch与Orowan强化)与实现最佳微观结构密切相关。微结构表征将使用与感兴趣的微结构尺度相适应的方法进行。这将包括使用能够进行原子尺度分辨率的最先进的仪器进行结构和化学研究。机械性能的测量将使用评估通过热压实处理的粉末产生的样品尺寸的强度和延展性的技术。将进行等温退火研究，以建立晶粒生长动力学和激活能。这将为在选定的温度区域内稳定机制和相互作用提供更多的洞察和建模。

Non-technical Summary The thermal stability and mechanical behavior of selected titanium-base alloys with very small (nanocrystalline) grain sizes will be studied. The alloys will be prepared by the ball milling of powders that will then be consolidated by hot pressing. The structure and microstructures of the titanium alloys with appropriate additions of third elements that are predicted to stabilize the fine grain structure will be determined. Mechanical properties will be measured with techniques that evaluate the strength and ductility. Annealing studies will be carried out to quantitatively determine the thermal stability by measuring the growth of the fine grains. The results of these studies should have a substantial impact on both the processing and elevated temperature requirements of very fine grain size titanium alloys. Superior mechanical properties compared to conventional grain size titanium alloys can lead to breakthroughs in structural and bio-related (for example, implant materials) applications.Technical Summary Ti-base alloys processed to synthesize nanocrystalline microstructures with superior mechanical properties are of great interest for automotive and aerospace applications. These alloys are the focus of the proposed research. Powder compaction followed by elevated temperature consolidation is necessary to process the initial non-equilibrium alloys in most cases, and elevated temperatures are prerequisite for end-use. The research will investigate the kinetic and thermodynamic mechanisms that can provide high temperature thermal stability for nanocrystalline Ti-base alloys. Ti alloys with hcp alpha stabilizers and bcc beta stabilizers will be synthesized using mechanical alloying. A model will enable selection of optimum (oversize) solutes for thermodynamic stabilization. Kinetic stabilization by solute drag or Zener pinning will be achieved by in-situ (intermetallic precipitates) or ex-situ (oxide dopant) strategies. Thermal stabilization mechanism interactions and strengthening mechanism transitions (Hall Petch vs. Orowan strengthening) are highly relevant for achieving optimum microstructures. Microstructure characterization will be done using methods appropriate to the microstructural scale of interest. This will include structural and chemical investigation using state-of-the art instrumentation capable of atomic scale resolution. Mechanical properties will be measured with techniques that evaluate strength and ductility for the sample sizes produced by hot compaction of the processed powders. Isothermal annealing studies will be undertaken to establish grain-growth kinetics and activation energies. This will provide additional insight and modeling for stabilization mechanisms and interactions in selected temperature regimes.