Structural and Mechanical Properties of Radiofrequency Ar-N₂ Plasma Nitrided Aluminium

Aluminium (Al) samples were nitrided in 13.56 MHz radiofrequency (RF) discharge of 70:30 vol.% Ar:N₂ mixture at substrate temperature of 400 °C and RF power of 300 W for different fill pressures and treatment times. The nitrided samples were then characterized for their structural and mechanical properties using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray spectroscopy (EDS), and Vickers micro hardness testing. XRD peaks (110), (111) and (200) of aluminium nitride (AlN) and their downshift confirmed the nitride formation together with nitrogen diffusion. The metastable cubic phase (c-AlN) shows texture growth and re-orientation dependent on fill pressure and treatment time. SEM micrographs showed the surface morphology with micro-pores. EDS results showed that the nitrogen content was significantly increased with nitriding time, along with the removal of oxides. Vickers hardness of the Al surface was increased more than thrice for 30 hours nitriding.

radiofrequency discharge; surface nitriding; structural and mechanical properties; surface hardness