Effects of Pressure, Temperature and Grain Size on Synthesis and Structures of Fe-N Alloys

Abstract

Effects of pressure, temperature and grain size on the solid state reaction between α-Fe and amorphous BN and crystal structures of the resultant of the reaction were studied by using mechanical milling and high pressure techniques at the temperatures ranging from 580 to 930 K under pressures between 1 × 10-3 Pa and 4 GPa. It was found that the pressures and refinement of grain size can greatly accelerate the solid state reaction process. There is a critical grain size for α-Fe, below which the reaction begins to occur. In the present experiment, this grain size was measured to be about 8 nm. The crystal structures of the resultants change with the variation of pressure and temperature. A new Fe-N alloy with orthorhombic structure was produced firstly at 2 GPa and 800 K. Single phase ε-Feα-N alloy can be obtained in the temperature range of 690 to 800 K at the pressures of 3 to 4 GPa. However, the resultant is not any Fe-N alloy but Fe3B alloy when the pressure is 4 GPa and the temperature is above 930 K.