铁基合金离子渗氮与激光淬火深层硬化机制

Iron-based alloys are utilized widely in manufacturing the key components used in many fields such as aerospace-, wind power- and nuclear power. How to obtain high obdurability and the high-depth hardening layer (＞1.0mm) by nitriding has drawn world-wide interests of research. Employing the steel M50NiL and the steel 17-4PH as model materials, this proposal is based on the thought that nitriding treatment could decrease the martensite transformation temperature according to the Fe-C and Fe-C-N phase diagrams, which is therefore the key to trigger the martensite transformation during the following laser quenching treatment, resulting in the high-depth hardening layer. Accordingly, we propose to study the laser quenching of the nitriding layer and to obtain the multiplication in both hardness and layer depth, as well as finer grains. Combining with thermodynamic calculations and finite element simulations of nitrogen and temperature profiles in the laser quenched layer, the objective is to reveal the mechanism of the formation of high-depth hardening layer, and to form a mature nitriding - laser quenching technology, contributing to the manufacture of the key components of high-end equipments.

铁基合金广泛应用于航空航天、风电、核电等领域中关键件(齿轮、轴承等)制造，上述关键件通过渗氮实现表层高强韧及深层硬化（＞1.0mm）是国内外研究热点。本申请针以M50NiL钢与17-4PH钢为对象，基于Fe-C和Fe-C-N相图，在合金钢表面氮掺杂降低马氏体转变点，结合氮掺杂层激光淬火与深层相变硬化思想，开展渗氮层激光淬火研究，实现表面硬化层硬度、厚度倍增和改性层组织细化，借助热力学计算与有限元模拟等方法，获得渗氮层氮分布与激光淬火层温度分布耦合模型，试图揭示复合改性深层硬化机制，形成相应的渗氮与激光淬火复合工艺技术，支撑高端装备关键件制造。

针对铁基合金构件表面离子渗氮与激光淬火复合处理深层硬化的问题，本项目在国家自然科学基金青年项目的资助下，经过3年理论和试验研究，全面完成了项目计划研究内容：（1）通过基于疲劳性能的改性层深度计算，明确了为达到预定疲劳性能所需的改性层深度；（2）通过对渗氮生成相表征，并结合热力学计算与第一性原理计算，从理论和实验两方面揭示了生成相择优取向机制，实现了渗氮表面相结构的调控；（3）通过对渗氮与激光复合改性层组织结构及性能表征，结合有限元模拟，阐明了渗氮层氮浓度分布，激光温度场以及改性层中相变规律，揭示复合改性深层硬化机制，形成了渗氮与激光复合表面改性技术。通过研究内容的深入开展，突破了立项时提出的两个关键科学问题，实现了项目计划中的所有目标，具有很强的科学意义和工程应用价值。