Effect of Nitriding Conditions on Surface Hardening of Nickel Alloy by a Plasma Nitriding Process.

In order to investigate the effect of nitriding conditions on the hardness and thickness of the nitrided layer in nickel alloys, a tentative nickel binary alloy of Ni-30wt %Cr was nitrided in plasma nitriding at different nitriding temperatures ranging from 673 to 1073K nitriding times of 3.6 to 32.4ks, nitrogen gas concentrations in N 2 + H 2 mixed gas of 10 to 100 vol %, gas pressures of 270 to 1330Pa, discharge voltages of 270 to 420V and current densities of 14.2 to 19.5A/m 2.Nitriding temperature was the parameter that affected the hardness of the nitrided layer.The maximum surface hardness was Hv 760 at a nitriding temperature of 823K.The thickness of the nitrided layer depended on the nitriding temperature, nitriding time, and nitrogen gas concentration.Gas pressure, discharge voltage, and discharge current density, however, did not affect surface hardening in the nickel alloy.In this study, we determined that the optimum nitriding conditions for surface hardening of nickel alloys by plasma nitriding were temperature at 823K and 90vol%N 2 + 10vol%H 2 mixed gas atmosphere at 800Pa.