Investigation of the compound layer and diffusion zone of pulsed plasma nitrided 51CrV4-steel

Abstract

51CrV4-steel was pulsed plasma nitrided (PPN) with four sets of parameters. The resulting compound layers and diffusion zones were investigated using visible light microscopy, scanning electron microscopy, hardness measurements and x-ray diffraction. The results showed that the four different PPN treatments resulted in four compound layers and diffusion zones with different thickness. The compound layers ranged from 0.2 µm to 2.3 µm, while the diffusion zones ranged from 62 µm to 138 µm. The PPN treatment that was supposed to result in a sample with no compound layer exhibited a very thin surface layer of about 0.2 µm. To achieve the goal of a PPN process that result in no compound layer, the parameters have to be adjusted with either dilution of the plasma, or reduction of the nitriding time. XRD analysis revealed that all the samples consisted of the three phases α-iron, Fe3N and Fe4N, and the intensities indicated different ratios. One sample, which was PPN with a low temperature process, was investigated with transmission electron microscopy (TEM). TEM imaging revealed grains in the size order of a few 100 nm at the compound layer surface. Electron diffraction showed extra diffraction spots corresponding to a primitive cubic lattice with a cell parameter of 6.58 Å. Further investigation is needed to decide what causes the external ordering and to create a model of the expanded unit cell.

51CrV4-steel was pulsed plasma nitrided (PPN) with four sets of parameters. The resulting compound layers and diffusion zones were investigated using visible light microscopy, scanning electron microscopy, hardness measurements and x-ray diffraction. The results showed that the four different PPN treatments resulted in four compound layers and diffusion zones with different thickness. The compound layers ranged from 0.2 µm to 2.3 µm, while the diffusion zones ranged from 62 µm to 138 µm. The PPN treatment that was supposed to result in a sample with no compound layer exhibited a very thin surface layer of about 0.2 µm. To achieve the goal of a PPN process that result in no compound layer, the parameters have to be adjusted with either dilution of the plasma, or reduction of the nitriding time. XRD analysis revealed that all the samples consisted of the three phases α-iron, Fe3N and Fe4N, and the intensities indicated different ratios. One sample, which was PPN with a low temperature process, was investigated with transmission electron microscopy (TEM). TEM imaging revealed grains in the size order of a few 100 nm at the compound layer surface. Electron diffraction showed extra diffraction spots corresponding to a primitive cubic lattice with a cell parameter of 6.58 Å. Further investigation is needed to decide what causes the external ordering and to create a model of the expanded unit cell.