Enhancing mechanical properties of surface hardness and abrasion resistance of Fe-Mn-Al alloy by using atmospheric pressure plasma jet nitriding

Abstract

This study investigates the use of a N2/H2 mixture gas and an atmospheric pressure plasma jet (APPJ) for nitriding Fe-Mn-Al alloy. Pure metals, iron, manganese, and aluminum, were used as the reference metallic substrates. Various characterization techniques, including X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), Vickers hardness test, and optical emission spectroscopy (OES), were employed to analyze the material properties and plasma species. XRD analysis revealed the formation of nitride compounds on metals after the nitriding process. The plasma-nitrided Fe-Mn-Al alloy showed the mixture phases of Fe4N and Al, while plasma-nitrided pure metals possessed their specific metal nitrides. After nitriding process, the surface hardness increased to approximately 596 ± 6 HV0.025 for the Fe-Mn-Al alloy, 1307 ± 9 HV0.025 for manganese, 467 ± 4 HV0.025 for aluminum, 646 ± 5 HV0.025 for iron, and, compared to the pristine values of around 346 ± 4 HV0.025, 972 ± 6 HV0.025, 145 ± 3 HV0.025, and 125 ± 3 HV0.025, respectively. After the nitriding process, the Fe-Mn-Al alloy exhibited notable enhancements in both its resistance to abrasion and its capacity to endure impact loads, as indicated by the conducted tests. The OES test results identified NH radicals generated by the atmospheric pressure plasma jet beam as the active chemicals responsible for the success of the nitriding process. Overall, this study provides valuable insights into the strengthening of metal surfaces through nitriding using an N2/H2 mixture gas and APPJ. The results demonstrate significant improvements in surface hardness and surface free energy for iron, manganese, aluminum, and Fe-Mn-Al alloy, highlighting the effectiveness of NH radicals in the nitriding process.