电弧增材原位制备Fe3Al合金的组织等轴化及强韧化机理

Fe3Al-based alloy is significantly meaningful for improving the energy efficiency of our country. Compared to traditional high-temperature alloys, Fe3Al intermetallic has a combination of advantages including excellent high-temperature strength and corrosion resistance, low density and low cost. However, the industrial application of Fe3Al is largely limited due to its intrinsic low room-temperature ductility, which also decreases the flexibility of fabricating such material. The present research project proposes to solve the mentioned problems using the innovative wire-arc additive manufacturing process to flexibly fabricate the Fe3Al in-situ. To refine the large columnar grains and eliminate the anisotropic microstructure induced by the additive manufacturing process, quenching-tempering heat treatment has been applied. Also, to improve the room-temperature ductility and high-temperature strength, alloying elements including B, Ti and Cr have been used with specific ratios. Finally, optimal heat treatment method and alloying element ratio will be found for in-situ additive fabrication of high-performance Fe3Al alloy. Project findings have great significance in revealing the mechanisms of the Fe3Al large columnar grain refinement, anisotropic microstructure modification using heat treatment; and mechanical property improvement using B, Ti, Cr alloying elements. Furthermore, the present research project will provide technical and theoretical support for in-situ fabrication of Fe3Al alloy with higher performance.

Fe3Al相比传统高温合金具有高温强度与抗氧化腐蚀性能好、密度与成本低等优势，对于我国提升能源效率具有重要意义，然而Fe3Al的低温脆性使其制备加工和应用范围受到限制。本项目针对Fe3Al难以灵活原位制备与室温延展性差等问题，以Fe3Al为研究对象，采用电弧熔丝增材制造原位制备方法，研究热处理与合金元素（硼、钛、铬）配比在等轴细化原位增材制备的Fe3Al合金的粗大柱状晶与各向异性组织、提升其室温延展性与高温强度的作用，并确定最优热处理工艺与合金元素配比，项目成果对揭示热处理对Fe3Al中粗大柱状晶等轴细化与组织各向异性消除机理，探明元素配比对Fe3Al合金的强韧化机理，具有重要意义，为原位增材制备更高性能的Fe3Al合金提供可行的技术途径和理论支撑。

以Fe3Al为代表的铁铝金属间化合物（IMC）合金具有良好的室温和高温耐腐蚀、耐磨损、抗硫化、抗氧化性能，且相比传统不锈钢与镍基合金其材料成本很低，适宜石油化工领域的管道内壁涂层及各类高温阀门件。然而铁铝IMC合金的实际应用却受限于其IMC自身的高室温脆性，导致其加工极易开裂，其低成本优势也被高成本的加工过程抵消，所以对于Fe3Al合金的进一步发展来说，新的成形制造方法是关键。本项目使用异种双丝电弧增材制造技术，在钨极氩弧焊（GTAW）电弧熔池内，同步按一定比例填入铁、铝异种双丝，原位制备成形目标Fe3Al基IMC合金。通过对过程参数的灵活控制，可以实现无裂纹的高效增材沉积。.在研究内容方面，本项目研究热处理与合金元素（硼、钛、铬）配比在等轴细化原位增材制备的Fe3Al合金的粗大柱状晶与各向异性组织、提升其室温延展性与高温强度的作用，并确定最优热处理工艺与合金元素配比。.研究发现，通过定制含TiB2粉末芯的ER70S焊丝，向原位制备成形Fe3Al合金中添加2at%的B，实现了延伸率达到4.6%的结果。在粗大柱状晶等轴细化方面，通过采取沉积一层，空扫热处理一层的增材策略，实现了粗大柱状晶细化超80%。后热处理相关研究发现，原位制备增材的Fe3Al合金内部在晶界处出现长程有序的D03结构富铝相，且对于该富铝相的热处理调控可实现粗大晶粒的进一步细化，增材Fe3Al合金的性能各向异性也得到了明显改善。.通过本项目的执行与研究，基于对相应关键科学问题的解决，实现了原位制备成形Fe3Al合金性能的有效提升，为该合金和异种双丝电弧增材制造进入实际应用阶段提供了完整的技术途径与理论支撑。