铁镍基合金中B/Ti、B/H交互作用及对η相的抑制机制

This project is applied for the definite item of NSAF (No.37) which theme is interaction of boron with titanium or hydrogen atom and its effect on precipitation of η phase at grain boundary in Fe-Ni based alloy. Two reasons are responsible for lingering application of the Fe-Ni based austenitic alloys such as J75, which one is their hydrogen damage and another is susceptibility to weld heat-affected-zone liquation cracking. Investigations showed that the improvement of ductility and hydrogen-resistant performance of the alloy, as well as decrease in liquation cracks were related to addition of boron. The Fe-Ni based alloys with different levels of boron will be prepared by means of a proprietary technique. Distribution of titanium and boron atom in the alloys and welds will be analyzed by EBSD、EPMA、SIMS and 3DAP methods. Both internal friction experiments and first principle calculation will be conducted in order to explore the interaction of boron with titanium atom which can make clear the effect of boron on the precipitation of η phase. Otherwise, positron annihilation, internal friction experiments and first principle calculation will be employed in order to determine the interaction of boron or hydrogen atom with dislocation and their distribution at incoherent interface. Diffusion coefficient of hydrogen in the alloys with different levels of boron will be measured by means of hydrogen penetrating equipment.

本申请针对“培育项目”的明确目标课题-37：“铁镍基合金中B/Ti、B/H交互作用及对η相的抑制机制”提出。氢损伤较大和易形成接头热影响区液化裂纹是妨碍铁镍基合金（如J75）工程应用的瓶颈问题。研究发现：添加微量元素B可显著提高合金室温塑性、降低氢损伤和接头热影响区晶界液化裂纹形成倾向。本项目拟通过均质化技术，制备不同B含量J75合金。采用EBSD、EPMA、SIMS和3DAP技术表征合金与接头中Ti、B分布及与晶界类型关系，结合内耗实验和第一原理计算结果，查明B/Ti交互作用，澄清对接头热影响区晶界液化及裂纹形成影响机理，揭示抑制晶界η相析出机制。采用内耗和正电子湮没实验分析B、H与位错交互作用及内在关联，结合第一原理计算、氢渗透实验关于B含量影响H扩散系数的结果，探究B、H在非共格界面竞争占位规律，澄清B降低氢损伤机理，为推动铁镍基合金（J75）工程应用奠定理论基础。

本项目为NSAF联合基金明确目标课题，旨在为解决铁镍基合金氢损伤较大和易形成焊接接头热影响区晶界液化裂纹问题提供理论指导。本项目系统性的完成了B/Ti交互作用及对晶界相抑制作用机制、B/H交互作用及对抗氢损伤行为的影响，以及B、Ti与接头热影响区晶界液化裂纹形成关系研究。研究发现，相对于Ti，B的晶界偏聚能力更强，其在晶界优先占位阻碍Ti向晶界偏聚，抑制η相析出；B钉扎位错，而H促进位错运动，且二者存在位置竞争，B降低H在合金中的扩散能力、提高抗氢损伤能力；B是强致接头液化裂纹形成元素，硼化物/基体低熔点共晶是导致接头液化裂纹的主因，而Ti虽是接头晶界液化的重要原因，但其致裂作用弱于B元素。项目资助期期间，已在国内外的期刊上公开发表研究论文8篇（SCI）、申请国家专利5项，已授权3项。基于项目的研究结果，进行了GJB 5724-2006《抗氢钢棒规范》的修订工作。