Hydrogen-Induced Transformation Superplasticity of Titanium and Ti-6Al-4V

钛和Ti-6Al-4V的氢致相变超塑性

• 批准号: 9987593
• 负责人: David Dunand
• 金额: $ 28.94万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-04-15 至 2004-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9987593&HistoricalAwards=false
• 关键词: Hydrogen; Induced; Transformation; Superplasticity; Titanium

9987593DunandThe recently discovered phenomena of transformation-mismatch plasticity and superplasticity induced by reversible chemical cycling are investigated experimentally and theoretically in titanium. As a general deformation mechanism, transformation-mismatch plasticity and superplasticity are known to occur as a result of biasing by an external stress of internal mismatch stresses produced during an allotropic transformation. These mechanisms are well known in metals subjected to a phase change by temperature cycling around their allotropic temperature. Recently, it was shown that the same mechanism could be induced by cycling the chemical composition at constant temperature, upon repeated addition and removal of hydrogen in titanium. This novel deformation phenomenon is examined in pure titanium and in a titanium alloy by performing unidirectional creep experiments, where the applied stress and the hydrogen cycling characteristics are systematically varied. Based on the fundamental mechanisms controlling the micromechanics of mismatch strain development and the diffusion of hydrogen in metals, continuum-mechanics, closed-form models and finite-element, numerical methods are developed to allow a quantitative, predictive description of the phenomenon. Experiments are targeted to support these models, which will describe the instantaneous and average strain-rate during deformation as a function of experimental parameters.%%%This is the first systematic investigation of the novel phenomenon of hydrogen-induced transformation-mismatch plasticity in a simple metal (titanium) and one of its alloys (Ti-6Al-4V) as a function of all relevant chemical and mechanical parameters. The program will demonstrate that superplasticity can be induced under chemical cycling (i.e., accumulation of strains in excess of 100% upon repeated cycling and linear proportionality between average strain rate and applied stress). Models will be developed that provide a theoretical and predictive understanding of this new deformation mechanism, based on the mechanics of internal stress creation and biased relaxation. This knowledge will advance the basic scientific understanding of plasticity and superplasticity under non-equilibrium conditions, and will eventually allow the development of superplastic industrial processes based on hydrogen-induced transformation-mismatch superplasticity. ***

9987593 Dunandthe最近发现了可逆化学循环引起的转化不匹配可塑性和超塑性的现象，在钛中是在实验和理论上研究的。作为一种一般的变形机制，已知转化不匹配的可塑性和超塑性是由于异形体转化期间产生的内部不匹配应力的偏见而导致的。这些机制在金属中众所周知，通过在同素异常温度周围温度循环的金属发生变化。最近，结果表明，可以通过在恒定温度下循环化学成分，重复添加和去除钛中的氢，从而引起相同的机制。通过执行单向蠕变实验，在纯钛和钛合金中检查了这种新型的变形现象，其中施加的应力和氢循环特性系统地变化了。基于控制不匹配应变发展的微力学的基本机制，以及在金属，连续机械，封闭形式模型和有限元中氢的扩散，开发了数值方法，以允许对现象的定量，预测性描述。实验是针对这些模型的，该模型将描述变形过程中的瞬时和平均应变率，这是实验参数的函数。%%％这是对氢诱导的转化转化 - 匹配可塑性在简单金属（钛）中的新现象的首次系统研究（Ti-6al-4v）（Ti-6al-4V）（Ti-6al-4V）（ti-6al-4V）（ti-6al-4v）（ti-6al-4v），其效果是相关的。该程序将证明可以在化学循环下诱导超塑性（即，在平均应力和施加的应力之间重复循环和线性比例时，菌株的积累超过100％）。将基于内部压力产生和偏见的放松的机制，开发出对这种新变形机制的理论和预测理解的模型。这些知识将在非平衡条件下提高对可塑性和极端性的基本科学理解，并最终将基于氢诱导的转化不匹配的超塑性的超塑性工艺发展。 ***