基于可倾转纳米畴基元的高吸能金属材料

Safe and durable structural design requires metals that can absorb high energy elastically (able to absorb energy along with shape recovery) or plastically (i.e. strength-elongation product). However, current metals are not able to fully meet the needs. We have noticed in martensitic alloys that when the martensitic transformation is severely prohibited, nanodomains (<10 nm) form uniformly within parent phase matrix through distortion of the parent lattice. Upon applied stress, the nanodomains can rotate (or reorient) back and forth via collective lattice shear. . In this proposal, we use such nanodomains as the functional basis for materials design. We have synthesized two different alloys, which are respectively denoted as nanodomain/transformation-matrix alloy and nanodomain/dislocation-slip-matrix alloy, by using traditional methods such as casting, forging, wire-drawing and annealing. We have found that the energy absorption of the former alloy (absorbing energy elastically) is two times higher than that of the traditional high-energy-absorbing metals (shape memory alloys) and that of the latter alloy (absorbing energy plastically) exceeds those counterparts reported in high-end journals such as Nature and Science.. This proposal aims at building up the theories and techniques for the development of high-energy-absorbing metals, by focusing on the energy-absorbing mechanisms of the nanodomain/transformation-matrix alloy (elastically absorbing) and the nanodomain/dislocation-slip-matrix alloy (plastically absorbing), as well as fabrication methods.

结构部件的安全性与可靠性要求金属材料在加卸过程中具有高弹性吸能（形状完全恢复并吸能）或高塑性吸能（强度与塑性乘积）特性，然而，现有金属材料难以满足需求。申请者关注到，当金属材料降温马氏体相变受阻时，母相中生成可通过点阵切变而往复倾转的纳米畴（＜10 nm），本项目将此纳米畴设计为高吸能功能基元，采用熔炼、锻造、拔丝及退火（传统冶金方法）制备了纳米畴/相变基体（力致可逆马氏体相变）与纳米畴/位错滑移基体（力致位错滑移）两种合金组织，初步实验结果表明，前者的弹性吸能特性为高吸能金属材料（形状记忆合金）的3倍；后者的塑性吸能特性优于近年Nature、Science等期刊报道，上述优异吸能特性难以用现有原理解释。本项目拟解决“纳米畴/相变基体的高弹性吸能机制”和“纳米畴/位错滑移基体的高塑性吸能机制”2个关键科学问题，并掌握材料制备方法，最终建立基于可倾转纳米畴基元的高吸能金属材料设计理论与方法。

基于纳米畴序构的NiTi基合金具有奇特的相变与力学行为，且展现优异的吸能特性，其物理机制难以在现有相变理论框架内理解。在本项目资助下，项目组综合利用动态力学测试技术、原位同步辐射高能X射线技术、热分析技术、透射电子显微与衍射技术等手段，综合表征了纳米畴序构合金的热、力致相变行为以及塑性变形行为，测算了畴序构合金热弹性马氏体相变的几何相容性，揭示了畴序构导致的非热力学效应，初步明晰了纳米畴序构对塑性变形的影响规律与机制，提出并验证了设计兼具大且循环稳定的弹性吸能合金的两个基本准则。基于上述准则设计制备的合金在30次循环后的吸能高达32.6 MJ/m3（且随循环次数增加吸能水平几乎无变化），比已报道的形状记忆合金至少高出150%。. 本项目初步建立了基于纳米畴序构的高性能金属材料的设计理论与方法，深化了马氏体相变理论并拓宽了现有边界，所获高性能材料在航空航天、土木工程等领域有潜在重要应用价值。项目期间，在Acta Materialia、Materials Research Letters、Nature、Scripta Materialia等国际有影响力学术期刊发表SCI论文 12篇（全部标注，其中以第一或通讯作者身份发表8篇），在国际、国内学术会议宣读论文4次（均为特邀报告），获中国发明专利授权1项，培养博士生4名、硕士生8名（均已获学位）。