Influence Of Particle-Size And Surface Nanocrystallite On Nitriding Of Pure Iron

Nitriding technology has more than 80 years history since its appearance at beginning of last century. The research of Fe-N compound experienced a long way, covering the study on surface mechanical property and magnetic property. Although this technology has been greatly developed both in theory and in application, some problems can not still be solved. One of problems lies in the field of preparation of magnetic nitrides, in which the nitriding characteristic of pure iron power has not been clearly revealed . The relation between the nitriding characteristic and the partiele-size of iron powder needs to be studied deeply. On the other side, it is necessary to lower the nitriding temperature and accelerate nitriding speed in industries. I lowever. the development of nitriding technology is provided a greater space due to the emergence of nanocrystallite materials with unique property. Therefore, the bright foreground takes on in this field .Based on the problems concerned, the relationship between nitriding behaviors and the particle-size of iron powder as well as nanostructured surface of pure iron was investigated by means of changing nitriding process. The main results include:1. In gaseous nitriding, the phases constitution and the amount of nitrides not only correlate to the time and temperature of nitriding. but also are influenced by particle-size of iron powder. When the diameter of iron powder is fined to one tenth of original one. the critical temperature for formation of nitrided layer is reduced more than 50℃and the nitriding speed increases significantly.2. The temperature of gaseous nitriding of pure iron with nanostructured surface can be reduced to 350℃. Besides, surface nanostructured of the pure iron can also enhance the nitriding speed within available temperature range. The result can be attributed to nano-scale grains sizes with a large amount of defect such as grain boundaries which can greatly enhanced atomic diffusion.3. In plasma nitriding, the nitriding effect of nanostructured surface is related to temperature, which decreases as nitriding temperature increases. In general, nitriding effect of nanostructured surface on pure iron is weaken by plasma bombing action.