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. ***

9987593Dunand 最近发现的由可逆化学循环引起的相变失配塑性和超塑性现象在钛中进行了实验和理论研究。作为一般的变形机制，已知相变失配塑性和超塑性是由于同素异形相变期间产生的内部失配应力的外部应力偏置的结果而发生的。这些机制在因同素异形温度附近的温度循环而发生相变的金属中是众所周知的。最近，研究表明，通过在钛中重复添加和去除氢，在恒温下循环化学成分可以诱导相同的机制。通过进行单向蠕变实验，在纯钛和钛合金中研究了这种新颖的变形现象，其中所施加的应力和氢循环特性是系统变化的。基于控制失配应变发展的微观力学和金属中氢扩散的基本机制，开发了连续介质力学、闭式模型和有限元数值方法，以允许对这种现象进行定量、预测性描述。实验旨在支持这些模型，这些模型将变形过程中的瞬时应变率和平均应变率描述为实验参数的函数。%%%这是对氢致相变失配塑性这一新现象的首次系统研究。简单金属（钛）及其合金之一（Ti-6Al-4V）作为所有相关化学和机械参数的函数。该计划将证明化学循环下可以诱导超塑性（即，重复循环后应变累积超过 100%，并且平均应变率与施加应力之间呈线性比例）。将开发基于内应力产生和偏置松弛力学的模型，为这种新的变形机制提供理论和预测性的理解。这些知识将促进对非平衡条件下塑性和超塑性的基本科学理解，并最终允许基于氢诱导相变-失配超塑性的超塑性工业过程的发展。 ***