| Ion-nitriding for S45C using Al, Cr and Ti subsidiary cathodes was carried out at 823K for 3hours in an atmosphere of 30%N₂-X%H₂-Y%Ar mixing gas at 665Pa. The nitriding layers formed on S45C were characterized by XRD, XPS, microscopic observation and microhardness profile. The surface hardness of S45C was increased with Ar contents up to 20% while N₂ was maintained at 30%. Iron nitride phases of ε-Fe₂-₃N and γ`-Fe₄N were found on the surface of S45C ion-nitrided with each subsidiary cathode. From the results of XPS analysis, Al was found as a combined form with nitrogen in the nitrided layer. Using Al, Cr and Ti subsidiary cathodes, the surface hardness and thickness of compound layer became higher and thicker than the unused layer one. The surface hardness of S45C ion-nitrided without the subsidiary cathodes was about Hv521. On the contrary, the surface hardness of S45C ion-nitrided with Al, Cr and Ti subsidiary cathodes were Hv890, Hv734 and Hv667, respectively. These may be due to the sputtered atoms, which diffused into the iron nitrides and then increased lattice strain. |
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