The Effect of Hf Addition on the Nitriding Behavior of CoCrFeNi High Entropy Alloys

The effect and improvements of nitriding process on CoCrFeNiHf0,1-0,42 high entropy alloys were investigated in this study. When raising the ratio of added Hf in CoCrFeNiHfx, the structure of the alloys progressively transformed from single phase FCC to initially Ni7Hf2 + FCC and lastly to C15 Laves and FCC phases. The nitriding process concluded the formation nitride layer (NL). Raising the ratio of Hf in the alloys concluded in increased at first the combined layer thickness. On the other hand, NL thickness diminished when the composition (CoCrFeNi)90,5(Hf)9,5 which were determined for (CoCrFeNi)97,6(Hf)2,4, (CoCrFeNi)95,25(Hf)4,75, (CoCrFeNi)90,5(Hf)9,5 to be 23 µm, 28 µm, 25 µm respectively. Moreover, considering the hardness change, depending on the amount of Hf added; it was determined because of the measurements that a direct increase in the hardness of the alloy was obtained with the increasing Hf element.