Anodic Plasma Nitriding in Hollow Cathode (HCAPN)

Abstract

A study of a proposed plasma nitriding system, exploiting the hollow cathode effect, with treated part biased to anodic potential (Anodic Plasma Nitriding in Hollow Cathode – HCAPN) is presented. The aim of the study was to investigate the differences and similarities with conventional Active Screen Plasma Nitriding (ASPN). At the same time, the experimental results i. e. optical and scanning electron microscopy study of white and diffusion layer along with micro-hardness measurements are presented. Furthermore, the ammonia formation during the nitriding process was studied at different temperatures. We showed that the amount of ammonia reaches a maximum value at 700 K and at higher temperatures the amount of ammonia gradually decreases. This indicates that at the higher temperatures more and more of the formed ammonia dissociates (decomposes) on the hot surfaces of the sample and cathode, transferring the nitrogen to these surfaces, as in the case of classic gas nitriding.

Verification of the Simulated Carburizing Process in Different Bore Sizes

“…Four different bore dimension was used for the investigation, which can be seen in Figure 1. A small (d = 4 mm) and a larger (d = 20 mm) bore were manufactured as a blind and through version; 4 mm is a critical bore size, especially plasma nitriding, where the loss of electrons is low due to the special geometry [29,30]. To find out the differences between a critical and a higher diameter, 4 and 20 mm were chosen.…”

“…The carburized layer thickness was determined by hardness testing, which showed the end of the diffusion zone, where the hardness reached the base plus 50 HV [30]. The hardness was measured on the inner surface of the hole and the top of the sample in the cross-section.…”

The Role of the Material of Active Screen During the Plasma Nitriding Process

“…As soon as the gas ionization begins, the ions start to bombard the surface, which also called vaporization, because the precipitation of ions from the metal surface can rip off the atoms and contaminations. After the bombarding, which also serves the cleaning of the surface, the acce-lerated nitrogen ions heat the workpiece to the nitriding temperature with the controlling of the voltage, then the diffusion of nitrogens into the material and formation of nitrides starts [5][6][7][8]. [5][6][7][8].…”

“…After the bombarding, which also serves the cleaning of the surface, the acce-lerated nitrogen ions heat the workpiece to the nitriding temperature with the controlling of the voltage, then the diffusion of nitrogens into the material and formation of nitrides starts [5][6][7][8]. [5][6][7][8]. Three different types of plasma nitriding exist: DcPn -direct current plasma nitriding, AsPn -active screen plasma nitriding and AsbPn -active screen biased plasma nitriding.…”

Effects of Different Variants of Plasma Nitriding on the Properties of the Nitrided Layer

“…The process is popular because it requires less gas compared to gas nitriding and is more environmentally friendly compared to salt bath nitriding. In the DCPN treatment, plasma is generated directly on the workpiece leading to various problems: (1) edge effect ( Ref 8,9) and (2) hollow cathode effect ( Ref 10,11). Typical technological problem is the edge effect that can be observed along the edges and corners of the samples, where nitrogen can diffuse into these parts from multiple directions which result in a nitride network along the particle boundaries.…”