摘要
以纯铁为对象,采用增重测量、X射线衍射分析和扫描电镜显微分析方法就充分预氧化对渗氮的作用进行研究。结果表明,渗氮初期,预氧化纯铁表面发生Fe3O4氧化层向εFe3N相的转化;氮原子极易穿过Fe3O4氧化层渗入基体,并在氧化层之下的铁基体形成γ′氮化物;γ′氮化物呈指状延伸生长,使得纯铁渗氮时的化合物层平直界面失稳。渗氮后,与未预氧化试样相比,扣除氧化层本身氮化带来的贡献,预氧化试样的催渗增重达45%,证实较厚的Fe3O4氧化层不仅不会阻碍渗氮,反而具有明显的催渗作用,并提出了两种可能的催渗机理。
Kinetics of gaseous nitridation and microstructure of nitrided case of pre-oxidized pure iron were investigated by measuring weight gain,XRD and SEM.The results show that,at the beginning,Fe3O4 formed during pre-oxidation reacts with ammonia,converting toΕ-Fe3N phase.Nitrogen can easily penetrate the Fe3O4 scale into ferrite formingγ'nitride underneath,coexisting with the outer layer oxide.Co-diffusion of oxygen with nitrogen occurs in the pre-oxidized sample,resulting in precipitation of nitride in the metal and fingering of the compound layer.The general weight gain measurement proves that a pre-formed thick Fe3O4 scale does not resist,but significantly enhance the nitriding process.A net increase of 45%in nitrogen weight gain is obtained.Two possible mechanisms for the enhancement are proposed.
出处
《材料热处理学报》
EI
CAS
CSCD
北大核心
2005年第4期102-105,共4页
Transactions of Materials and Heat Treatment
基金
教育部重点科技项目计划资助(02077)
关键词
气体渗氮
预氧化
纯铁
催渗
Iron
Iron oxides
Kinetic theory
Microstructure
Nitrides
Oxidation
Scanning electron microscopy
X ray diffraction analysis
