基于共晶转变的高强韧双尺度结构钛合金半固态烧结制备研究

This project will explore a novel semi-solid sintering technology (consisting of two procedures coupling spark plasma sintering and semi-solid processing) for fabricating bimodal structural (including deformation twins) titanium alloys strengthened and toughened by the coexisting of nano-sized or ultra-fine grains and micron-sized grains. Composition design of bimodal structural titanium alloy with high strength and ductility, fabrication of glassy powder and its crystallization mechanism, densification mechanism of glassy powder and related mechanism of its microstructure evolution and its effect on mechanical properties during sintering, are chosen as core research contents. To reveal formation mechanism of bimodal structural titanium alloy and its strengthening and toughening mechanism, and further clarify effect of alloy composition and fabrication parametere on microstructure and mechanical property of bimodal structural titanium alloy, this project will significantly focus on effect of fabrication parametere, such as pressure, pulsed electron current, and holding time, especially pressure condition, on grain size, interface microstructure and deformation twins of bimodal structural grains, and thus on liquid phase in semi-solid state and its solidification mechanism, on solid phase in semi-solid state and formation mechanism of deformation twins, especially on atomic diffusion mechanism on liquid-solid interface. It is expected that this study will supply theory base for composition design of high-strength and ductility bimodal structural titanium alloy with three crystalline phases, among which some two phases can react preferentially in the eutectic transformation at elevated approximate temperature range and thus a semi-solid state containing a liquid phase and remaining solid phase would emerge spontaneously, optimization of fabrication technology, and precise controlling of microstructure and property. Moreover, this study will provide a new preparation route of titanium alloy with high strength and ductility.

本项目以钛合金为研究对象，以探索通过纳米晶（或超细晶）与微米晶共存的双尺度结构（含形变孪晶）强韧化钛合金的半固态烧结（SPS+半固态加工）制备技术为研究主线，以高强韧双尺度结构钛合金的成分设计、非晶粉末的制备及其晶化机制、烧结过程中的致密化机理、微观结构变化规律与机理、及其对力学性能的影响规律等为核心内容。重点研究压力、脉冲电流密度、保温时间等半固态加工参数对双尺度晶粒尺寸、界面和形变孪晶微观结构的影响机理，以揭示对液相的作用机理和凝固机理、液固界面原子扩散的影响机理、以及对固相的作用机理与形变孪晶的形成机理，从而揭示双尺度结构的形成机理及其强韧化机制，进而明确合金成分、制备工艺对钛合金结构性能的影响规律。为具有三个晶态相且某两相可优先发生共晶转变形成半固态的高强韧双尺度结构钛合金的成分设计、制备技术优化和结构性能的精确调控提供理论依据，并为高强韧钛合金的制备提供新途径。

本项目以钛合金为研究对象，以探索通过纳米晶（或超细晶）与微米晶共存的双尺度结构（含形变孪晶）强韧化钛合金的半固态烧结（SPS+半固态加工）制备技术为研究主线，以高强韧双尺度结构钛合金的成分设计、非晶粉末的制备及其晶化机制、烧结过程中的致密化机理、微观结构变化规律与机理、及其对力学性能的影响规律等为核心内容。重点研究压力、脉冲电流密度、保温时间等半固态加工参数对双尺度晶粒尺寸、界面和形变孪晶微观结构的影响机理，以揭示对液相的作用机理和凝固机理、液固界面原子扩散的影响机理、以及对固相的作用机理与形变孪晶的形成机理，从而揭示双尺度结构的形成机理及其强韧化机制，进而明确合金成分、制备工艺对钛合金结构性能的影响规律。为具有三个晶态相且某两相可优先发生共晶转变形成半固态的高强韧双尺度结构钛合金的成分设计、制备技术优化和结构性能的精确调控提供理论依据，并为高强韧钛合金的制备提供新途径。结合非晶粉末的晶化、致密化机制及半固态形成机制，揭示了SSS形成双尺度结构的原理。在连续升温烧结条件下，双尺度钛合金的形成可分为五个阶段：非晶粉末颗粒重排，非晶粉末致密化及晶化，晶化相晶粒长大，共晶反应及液相形成（半固态形成），以及快速冷却后液相转变为超细/纳米层片共晶组织的同时、剩余固相保持其微米晶尺度，从而形成超细/纳米层片共晶与微米晶共存的双尺度结构。力学性能分析表明，(Ti63.5Fe26.5Co10)82Nb12.2Al5.8双尺度合金呈现出2897MPa的压缩断裂强度、2050 MPa的屈服强度、23%的断裂应变，以及920 MPa的拉伸断裂强度与1.6%的拉伸断裂应变。相关研究在Acta Materialia、Scripta Materialia等国际著名期刊发表SCI学术论文30篇；授权国家发明专利10件，申请美国专利3件（授权1件，公开2件）；出版国家科学技术学术著作出版基金资助中文专著1部；在国内外学术会议作大会/主旨/邀请报告17次；培养硕士研究生4名、博士研究生3名。