稀土渗氮过程中RE-Me-O化合物的形成及其催渗机理

Compared with carburizing, nitriding can reduce the distortion of components effectively, which exhibits an excellent prospect of applications. However, nitriding can not replace the carburizing due to the thin nitrided layer. It has been proved that the thickness of nitrided layers could be dramatically increased with rare earth addition, which enlarges the application of nitriding. Based on a new finding of catalytic phenomena during rare earth nitriding, this project will focus on the formation and catalytic mechanism of RE-Me-O ternary compounds produced during rare earth nitriding. Firstly, the effects of process parameters on the microstructure evolution of the rare earth nitrided layer and the layer thickness will be investigated. The different ways of rare earth addition are also considered. Secondly, based on these researches, the catalytic rare-earth compounds and their catalytic factors will be determined. The studies on the interaction between rare earth and nitrogen atoms during rare earth nitriding will be carried out to clarify the catalytic mechanism of rare earth elements. Finally, the effect of alloy elements on catalytic activity will be confirmed through the researches on the formation mechanism of catalytic RE-Me-O compounds and the interaction between catalytic RE-Me-O compounds and nitrogen atoms. All these works are of great theoretical support for the extensive application of rare earth thermochemical treatment in the deeper modification of alloy steels.

渗氮技术相比于渗碳技术而言，能够有效减小零件的变形，因此更具应用价值。然而受渗层深度的制约，渗氮技术一直无法取代渗碳技术。稀土的引入能够有效增加渗氮层厚度，扩大了渗氮技术的研究范围，然而稀土的催渗机理尚不明确。基于申请人在稀土渗氮过程中发现的一种新的稀土催化途径，本项目聚焦于稀土渗氮过程中RE-Me-O化合物的形成及其催渗机理。通过稀土共渗工艺参数及稀土添加方式对共渗层组织结构及渗层深度影响规律的研究，确定稀土催渗的活性组态及催渗条件，阐明稀土在共渗过程中与氮原子相互作用机理，揭示稀土催化机理。研究RE-Me-O化合物的形成及其与氮原子相互作用机理，阐明钢中合金元素对稀土催化活性的影响，为稀土化学热处理在合金钢深层改性中的全面广泛应用提供理论支持。

渗氮技术是提高零件表面性能的重要手段。相比于渗碳而言，能够有效减小零件的变形，因此更具应用价值。然而受渗层深度的制约，渗氮技术一直无法取代渗碳技术。稀土的引入能够有效增加渗氮层厚度，扩大了渗氮技术的研究范围，然而稀土的催渗机理尚不明确。针对这一问题，开展渗氮过程中稀土催化机理的研究。项目研究过程中，重点开展并完成了：（1）通过不同稀土添加方式下稀土-氮共渗试验的对比研究，明确了具有催化作用的稀土元素存在形式；（2）通过对稀土共渗层的组织结构及表面化学成键的定量分析，结合第一性原理计算，从理论和实验两方面揭示稀土元素对氮原子表面扩散及体扩散的影响规律和作用机理；（3）采用元素掺杂的方式实现稀土化合物催化性能优化，并结合第一性原理计算，阐明合金元素对稀土化合物催化活性的影响机理，研究发现：(1)ABO3钙钛矿氧化物具有渗氮催化活性；（2）ABO3化合物仅在渗氮表面起催化作用；（3）通过元素掺杂可对ABO3化合物的催化活性进行优化；（4）ABO3钙钛矿氧化物的催化效果归因于其促进NH3的吸附分解，同时降低Fe-N键的强度，促进氮原子的扩散。本项目突破了关键科学问题，形成具有实用价值的稀土催化气体渗氮技术，具有重大的科学意义和工程应用价值。