合金钢等离子体低温共渗无析出纳米晶层形成机理

So far the key basic parts (e.g. gear and bearing) equipped by these high-end equipments such as aerospace-, nuclear power-, and wind power-ones as well as high-speed trains, et al. are still dependent on imports, which results mainly from the lack of the ultra high strengthening and toughening technologies for the surface layer to extend the service life and reliability of the parts. In conventional carburized and nitrided surface layers the grain size is at a level of microns. In carburizing and nitriding, the phase transition and precipitation occurred in surface layer enhance its strength, and at the same time is also along with an increase of brittleness and an decrease of corrosion resistance, which lead to a decrease of service life and reliability of treated parts. The applicant has invented a series of RE thermochemical treatment technologies replaced conventional carburizing and nitriding, which results in a remarkable improvement in strength and toughness of the modified layers. After the invention, the applicant broke through the idea limit of thermochemical treatments and first developed a new idea to produce modified layers at low temperature in which there are no precipitates, and the grains on the level of microns are nanocrystallized. The new technology has been patented (ZL201110031571.8) and applied to a transmission part in an important weapon equipment, the contact fatigue lifetime of this part is increased above 400% and its corrosion resistance is maintained. This application focuses on the grain-nanocrystallized mechanism study of the precipitate-free surface layer of alloying steels treated by low temperature plasma multi-component permeation. This study mainly includes:(1) microstructural design and stability of surface layer, (2) thermodynamics and regulating and non-regulating diffusion in doped and metastable solid solution, (3) microstructure evolution and strengthening and toughening mechanism for the surface layer with and without quasi spinodal decomposition, (4) grains evolution and nanocrystallizing mechanism of surface layer with pseudo spinodal decomposition. The technology that produces a grains-nanocrystallized and ultrahigh strength and toughness surface layer without precipitates for the alloying steels will be applied to manufacture key components of high-end equipment in our country. The researches mentioned above have not been reported until now, and are of significance to theoretical studies and engineering applications.

我国航空航天、核电、风电、高速列车等高端装备关键基础零部件（如齿轮、轴承）依赖进口的"瓶颈"-无表面层超高强韧化技术。常规渗碳、渗氮层晶粒为微米级，其强化源于相变和析出相，渗层脆性高、耐蚀性差，寿命和可靠性低。申请者继发明稀土化学热处理替代现有渗碳渗氮获得高强韧改性层后，突破化学热处理理念局限，首次提出低温共渗无析出、使渗层微米级晶粒直接纳米化的思想，并得以实现（ZL201110031571.8），处理的某杀手锏武器传动件接触疲劳寿命提高400%以上，耐蚀性不降低。本次申请聚焦在钢表面低温共渗无析出纳米晶层形成机理研究，包括共渗层微结构设计与稳定性；亚稳固溶体掺杂伪脱溶热力学与调制扩散、调制与非调制共渗层组织结构与强韧化机制、调制扩散共渗层晶粒演变与纳米化机理；形成低温共渗层无析出纳米化与超高强韧化技术，支撑我国高端装备关键基础零部件制造。上述研究工作未见报道，具有理论研究意义和应用价值。

我国航空航天、核电、风电、高速列车等高端装备关键基础零部件（如齿轮、轴承）依赖进口的"瓶颈"，即表面层超高强韧化技术缺失。常规渗碳、渗氮层晶粒为微米级，其强化源于相变和析出相，渗层脆性高、耐蚀性差，寿命和可靠性低。本项目选用两类典型Fe-M-C系合金合金钢通过预处理获得亚稳固溶体、对其进行低温共渗调制扩散无析出纳米化工艺与相应的微观机理研究。通过低温共渗层微结构设计与稳定性的第一性原理计算，完成了以赝能隙为标识的亚稳固溶体结构设计；研究了Fe-M-C亚稳固溶体渗氮渗碳伪脱溶与调制扩散热力学；对Fe-M-C亚稳固溶体低温共渗非调制扩散层组织结构与性能进行了研究；通过对Fe-M-C亚稳固溶体低温共渗调制扩散无析出纳米晶层表征，揭示了低温共渗调制扩散无析出纳米晶层的形成机理。主要成果如下：（1）得出了以“双势阱函数”为特征的Fe-M-C体系自由能曲线，进而获得Fe-M-C体系准调幅分解临界温度区间为400-590℃。（2）基于亚稳固溶体调幅分解温度区间，设计出Fe-M-C系合金低温共渗表层晶粒纳米化工艺，揭示了亚稳固溶体低温共渗层组织结构演化规律，包括低温共渗纳米晶层增厚动力学和晶粒演变规律规律。（3）阐明了低温共渗元素的调制扩散行为，得出渗入元素的迁移能，揭示了调制扩散纳米晶层形成机制，即N原子渗入导致马氏体中N含量达到调幅分解成分，产生调幅分解；同时产生细小的低氮化合物和高氮马氏体，进而实现表面晶粒纳米化。（4）揭示了低温共渗纳米晶层摩擦学行为及磨损机制。（5）发现低温循环渗氮晶粒纳米化、以及低温共渗纳米晶层的非平衡快速加热深层硬化现象。（6）基于淬火亚稳合金共渗超细化理论，拓展出Cu-Al-Ti亚稳合金的渗氮表层强韧化工艺和相应辅助装置。等离子体低温共渗纳米化工艺技术支撑高端装备传动件长寿命高可靠性制造。