THERMODYNAMIC STABILITY OF IRON NITRIDES AT TEMPERATURES BELOW 350-DEGREES-C

Although iron nitride coatings are applied for their good tribological properties, their thermodynamic stabilities are unknown in the temperature range in which they are used. We have investigated the s and gamma' nitride phases between 0 and 350-degrees-C with ion implantation and find evidence that while the epsilon-Fe2N1-x with (1 - x) greater-than-or-equal-to 2/3 is stable, gamma'-Fe4N is not. At T less-than-or-equal-to 150-degrees-C, ion irradiation converts gamma'-Fe4N into epsilon-Fe2N1-x, with x -0.5. This epsilon nitride can then be transformed back into gamma'-Fe4N by annealing at temperatures of 150-degrees-C and higher. Ion irradiation assists this process as well.