The processing time is dependent on the composition of the steel being nitrided and the required case depth. In this context, surface engineering by pulsed lasers can be assisted by PVD or spraying processes or, for example, by applying mechanical stress fields during processing in order to minimize thermal-induced cracking, especially on the millisecond timescale. The fundamental approach revealed an inefficiency of the process. is linearly dependent on j. In addition, the fatigue strength of a gear-tooth may also be significantly increased. After each root has been hardened, the system indexes the gear to the next position and the process begins again. A glow discharge with a high ionisation level (plasma) is generated around the parts. Kennebunk, Maine 04043, NCT Adds the First of Our Newest Generation Cathodic Arc Coating Systems the M-Arc G2, Northeast Coating Technologies Continues to Grow in Kennebunk. Compared to hardening, plasma nitriding of the substrate improves coating to substrate adhesion and especially the load carrying capacity of the substrate. Plasma nitrided gears have case hardness of between 58 and 63 HRC and possess excellent wear resistance and extended service life. These eddy currents are the result of rapid magnetic field changes introduced by alternating electric currents in specialized conducting coils. When the product surface has been cleaned sufficiently, the nitriding cycle begins. Each of these processes has different processing requirements and technique utilizing different sources and mediums. It is not difficult to estimate the depth profiles in these processes. In order to maintain its original dimensions the core keeps the nitrided case in compression. While increasing bias voltage clearly leads to faster compound layer growth, the total case is not affected. Pressure in the range of 0.1–10 Torr is set to create a vacuum. Uniformity of both glow discharge zones CDS and NG, around a complex geometry cathode, depends on gas pressure. The dual-frequency process is a recent version of induction hardening, where two different frequencies, high and low, are simultaneously used for heating. The process of plasma carburizing is carried out in an Ar/H2 atmosphere containing CH4 or C3H8 reactants at pressures between∼3 and 20 torr at temperatures of∼1000°C. 8.03.4.1 Plasma Nitriding. Selective heating and, therefore, hardening, is accomplished by designing suitable coils or inductor blocks. Plasma nitriding is a modern technique for surface hardening of metallic components to improve their service life. Examination of the wear tracks demonstrates the fact that plasma nitriding, in effect, shifts the wear couple from a metal–metal one to a metal–oxynitride one, thus changing the fundamental wear process. After World War II the plasma nitriding process received widespread acceptance in Germany, Russia, China and Japan. The laser material processing by laser pulses on different timescales has been discussed in various overview articles [18,33] or books [34,35]. The hollow cathode discharge is very dangerous since it quickly leads to an uncontrollable, local increase of temperature and may result in damage to the treated part (Grün and Günther, 1991; De Sousa and Alves, 1997). The mechanism of the case-hardening process includes a decomposition of solid, liquid, or gaseous species, the splitting of gaseous molecules to form nascent atoms, the absorption of atoms, their diffusion into a metallic lattice and reactions within the substrate structure to modify existing or form new phases. No considerable nitriding was observed at, or below, 450 °C. He observed and modeled an initial parabolic growth of the compound layer, which then saturates after a certain plasma nitriding time. Emissivity of the cathode plays an important role in the radiation heat losses of the glow discharge heated objects. Plasma nitriding. A controlled flow of nitrogen, hydrogen and methane are introduced into the chamber and ionized by the voltage applied to the product. This step is followed immediately by heating with a high-frequency (100–270 kHz) source, which rapidly heats the entire tooth contour surface to an appropriate hardening temperature. It is frequently used for forging dies or casting molds to raise resistance to wear and thermal fatigue. Tooth-at-a-time flame hardening. Comparison of friction traces for two surface treatments of aluminium alloy; (a) titanium coating, (b) duplex treated (PVD titanium and plasma nitrided). By optimizing the nitrogen to hydrogen ratio, it is possible either to eliminate some of the brittle/white layers or to improve the erosion/ corrosion properties (Mann and Arya, 2002). It was determined that ion bombardment of the cathode is responsible for the transfer of about 15% of heating energy (Marciniak and Karpiński, 1980; Marciniak, 1983). Its structure usually consists of a diffusion zone and a compound layer. Figure 11.2 (see also Plate VI between pages 392 and 393) shows this phenomenon observed in a tube. Plasma nitriding is a thermochemical process for enriching the surface layer of a workpiece or component with nitrogen. Podgornik and Vizintin (2001) carried out pulse plasma nitriding for AISI 4140 and AISI A355 structural steels and found that no significant improvement is obtained in terms of hardness and wear behaviour. Each of these gases is mixed with air in particular ratios and burnt under pressure to generate the flame that the burner directs onto the workpiece. A thin oxide film is always present on the surface of titanium metal. In the glow discharge and electrical potential gradient, the gas becomes ionized and the nitrogen ions are accelerated toward the negatively charged surface. The depth to which the heated zone extends controls the surface hardness and case depth, and depends on the frequency of the current and on the duration of the heating cycle. During pin-on-disc wear testing, the oxide–nitride compounds on the plasma nitrided surfaces have the advantage of controlling the damage to the steel counterface and, thus, a lower coefficient of friction and longer sliding under mild wear conditions. Very large gears whose quality requirement is generally below AGMA class 7, and heat treatments by conventional processes are not practical or economical are flame hardened [41,45]. In the diffusion zone, nitrogen diffuses in steel, producing a hardened zone by precipitation and solid-solution hardening. In this method, instead of heating the whole gear; the heat can be precisely localized to the specific areas where metallurgical changes are desired (e.g., flank, root, and gear tip can be selectively hardened) and therefore the heating effect on adjacent areas is minimal. Mann and Arya (2001) have shown a poor abrasion and erosion resistance of plasma nitrided 13Cr–4Ni steel compared with plasma nitrided 12Cr steels and HVOF sprayed WC–10Co–5Cr due to low hardness and inability to absorb more nitrogen. In turn the iron nitrides are partially broken down on the surface of the cathode, after which the nitrogen diffuses into the gear material and results in nitriding [41]. Pulsed treatment and its performance. The choice of the particular composition would depend on the application of the product in the field. The process was not introduced into the United States until after 1950 and has only been used as a production process for the past 20-25 years. The objects with a low emissivity can reach a significantly higher temperature than those geometrically identical but with a high emissivity (Marciniak and Karpiński, 1980; Marciniak, 1983 and Roliński et al., 2004, 2014). A variation of plasma nitriding is so-called ‘active screen plasma nitriding’ (US Patent 59 89 363). Plasma nitriding. For carburizing and nitriding, the difference is clear. It is an extension of conventional nitriding process, utilizing plasma discharge physic to diffuse nitrogen into the surface of a ferrous alloy. Plasma nitriding is a method of surface modification using a glow discharge technology to introduce nitrogen into the surface of a metal, which subsequently diffuses into the material (6). The mechanism of heat transfer during heating of the cathode in a glow discharge is very complex. This white layer is brittle and relatively inert. The process was not introduced into the United States until after 1950 and has only been used as a production process for the past 20-25 years. In the last few decades, plasma nitriding, flame hardening, laser-hardening, and induction hardening methods have emerged as alternative methods for case-hardening of gears, with relatively small impact on their quality class [38–40]. The nitriding cycle is continued for 2 to 72 hours until the desired case depth of 0.002" to 0.024" is achieved. Since the former may have complex three-dimensional shapes, it is important to conformally surround them with a “glow seam.” These workpieces are maintained below 600°C and subjected to N2/H2 mixtures at pressures between∼0.5 and 5 torr. We may assume the surface ion current-density (j) is essentially equivalent to a diffusion flux (J), i.e., J = j/q, where q is the charge per ion and J has units of ions/cm2-s. A boundary-value problem somewhat different from the two presented in Section 1.6.1, but like the one in Section 3.5.2.3, is then suggested. (B) Flank method. While every surface treatment has its advantages and disadvantages, gas and ion (plasma) nitriding are often compared when engineers decide what is best for their application. Due to the small heat-affected zone, both in depth and lateral dimension, pieces sensitive to heat and of complex shape can be modified. In the tooth-to-tooth method the gear is heated and quenched by the machine itself, which limits the amount of heat going into the gear. As technology progressed so did the plasma nitriding process. The lower holding temperature with shorter duration time was cost-effective, and, the nitrided surface was free from roughing with less nitride precipitates. 100 μm coatings containing dendritic TiN embedded in α-titanium with dissolved nitrogen. In carbonitriding, the main element is carbon with a small amount of nitrogen. Each of these processes has different processing requirements and technique utilizing different sources and mediums. As before, we assume that there are no subsurface atoms (ions) initially, i.e., C(x, 0) = 0, and that C(x = 8, t) = 0. As C(x = 0) rises parabolically in time, the slope (dC(x)/dx) x= 0 remains invariant. Plasma Nitriding known also as ion nitriding is a form of case hardening process. D. Höche, ... P. Schaaf, in Laser Surface Engineering, 2015. Discharge in a mixture of 30% nitrogen and 70% hydrogen: (a) Pressure = 2.9 mbar and 300°C; (b) Pressure = 0.5 mbar and 500°C after 4 min of pressure change. At 823 K, parabolic growth occurs during the first 42 min; then after about 6 h, nitriding saturates at dN = 14 μm. The gear is placed inside a coil, and when a high-frequency alternating current is passed through the coil, rapid heating takes place due to electromagnetic induction. Only the very first top layer is treated and modified. On the surface area that is directly charged by the ions, nitrogen-rich nitrides are formed and decompose, releasing active nitrogen into the surface. The potential drop across this space is called the cathode fall (Brown, 1994). 10.18 shows the presence of oxides and nitrides, and one possible explanation for the tribological behaviour of these specimens is the relative amounts of the two phases in terms of the nitriding temperature and the cleanliness of the nitriding atmosphere. As technology progressed so did the … (2005) have investigated the DC pulsed plasma nitrided 4140 steels and found that the process improved wear resistance. Table 8.3. Obviously, the nitride provides high hardness and the oxide is intimately associated with low friction and wear. The deviation from the parabolic growth has been explained by sputtering effects. Plasma Nitriding in general is a heat treating that is used to case harden surfaces using nitrogen. Considering the extensive demands in surface engineering, pulsed laser nitriding becomes an alternative way, offering some advantages but also disadvantages. Plasma modification of other metals, e.g., nitriding of titanium alloys, and by different processes, e.g., plasma boriding of steel, are additional variations on the theme. The case depth may be as high as 900 µm. The excess nitrides diffuse into the gear material during the heat-treating cycle, leaving a white layer on the top surface. It is generally accepted that at temperatures of 800 °C and above, sputtering and solution dominate over deposition of oxygen and, as a result, the surface is depassivated and nitriding of titanium can proceed. In practice, this distance is limited only by the voltage (Brown, 1994; Engel, 1965). First, the vessel is evacuated. Its thickness is usually below 13 µm [41], which can be reduced further by controlling the ratio of nitrogen in the mixture of nitrogen and hydrogen during ion-nitriding. Surface hardness and wear rate of the specimens after duplex treatment. The decomposition of the ammonia to release both nitrogen and hydrogen diffusion is very similar with each of the above methods except with the Plasma nitriding. Plasma nitriding was found to produce very attractive properties in terms of low friction (Fig. Figure 11.1 (see also Plate V between pages 392 and 393) shows the near-cathode regions of the glow discharge taken during plasma nitriding at two different pressures. Plasma nitriding can be further branched out into plasma nitrocarburising. The other method is shown in Fig. The layer is formed by nitrogen ions, from a plasma generated using Hauzer’s plasma source technology, diffusing into the substrate material to harden it. The energy transfer to the cathode during glow discharge heating is a combination of radiation from NG and an exchange of the kinetic energy into thermal energy of the species bombarding it. The remaining energy is transferred either by neutrals bombardment or by radiation from neutral gas collisions in the negative glow. After further optimization of the scan parameters a coating thickness of 30 μm having a surface roughness of about 2 μm has been produced. It is also reported that plasma nitrided 12Cr steels performed better than 13Cr–4Ni steel (Mann and Arya, 2002). The formation of nitrides and microhardness, however, were optimum for nitriding at 550 °C. The terminology ‘austenitic nitrocarburizing’ is also used. Grün and Günther, 1991; De Sousa and Alves, 1997, Marciniak and Karpiński, 1980; Marciniak, 1983, The Science and Technology of Materials in Automotive Engines, Materials Science of Thin Films (Second Edition), Advanced Gear Manufacturing and Finishing. Other gasses like hydrogen or Argon are also used. If there are negligible ion-implantation effects, ions simply impinge on the solid surface and diffuse in. E. Roliński, in Thermochemical Surface Engineering of Steels, 2015. Substrate treatment has considerable influence on the tribological properties of ta-C coated AISI 4140 steel. Plasma contains approximately equal concentrations of positive ions and electrons as well as a large number of excited but neutral species (Malvos et al., 1989). Due to its improved capabilities, this method has become increasingly popular. This situation indicates that, in addition to surface nitriding, other mechanisms must have been responsible for the decreased wear. After World War II the plasma nitriding process received widespread acceptance in Germany, Russia, China and Japan. In particular, the specimen plasma nitrided at 500 °C had negligible wear under various loads (Table 10.4). Tooth-to-tooth induction hardening. The sand-blasted sample with a higher emissivity reached a lower temperature than the ground sample with a lower emissivity. 6.11). The thickness of the hardened layer should be such that it can withstand the maximum contact stress without collapsing into the softened core of the gear-tooth. (A) Root/flame method. Case-hardening is regarded as thermomechanical treatment to modify the surface properties of gear-teeth. Plasma nitriding is carried out in a glow discharge with the workpiece being the cathode and the vacuum vessel wall being the anode (Berghaus, 1932, 1939). ScienceDirect ® is a registered trademark of Elsevier B.V. ScienceDirect ® is a registered trademark of Elsevier B.V. URL: https://www.sciencedirect.com/science/article/pii/B9780857095923500033, URL: https://www.sciencedirect.com/science/article/pii/B9780857090157500075, URL: https://www.sciencedirect.com/science/article/pii/B9780080965321009122, URL: https://www.sciencedirect.com/science/article/pii/B9780857095923500112, URL: https://www.sciencedirect.com/science/article/pii/B9781855737426500087, URL: https://www.sciencedirect.com/science/article/pii/B9780125249751500094, URL: https://www.sciencedirect.com/science/article/pii/B9780128044605000067, URL: https://www.sciencedirect.com/science/article/pii/B9781845695378500105, URL: https://www.sciencedirect.com/science/article/pii/S016789220080156X, URL: https://www.sciencedirect.com/science/article/pii/B9781782420743000027, Thermochemical Surface Engineering of Steels, 2015, Process technologies for thermochemical surface engineering, Thermochemical Surface Engineering of Steels, Laser surface modification of steel for slurry erosion resistance in power plants, Laser Surface Modification of Alloys for Corrosion and Erosion Resistance, Plasma-assisted nitriding and nitrocarburizing of steel and other ferrous alloys. It is a heat treatment process which diffuses nitrogen into the surface of a metal to create a case-hardened surface. Besides nitriding, the use of carbon for alloying according a laser carburization has been investigated as well and will be described now. In common, these processes all rely on the undersized atoms of N, C, and B. Once the entire surface of the cathode is covered, the glow becomes abnormal and any increase in voltage causes an increase in current. Anyway, cw-mode treatments are still more distributed but the reviewing of previous results appears in very interesting information At adequate conditions hardness values of 13 GPa were achieved. Figure 6.10. Any Hauzer system with a plasma source can be used for our Nitrocoat process: plasma nitriding and coating in the same cycle. During plasma nitriding, a hard case at the surface of the material is formed. To achieve greater depth of heat penetration, low-frequency current is used, whereas heat treatment at shallow depth requires high-frequency current [1,41]. Wei et al. Benefits of plasma nitriding over traditional carburizing and nitriding include: Improved control of case thickness and greater uniformity; No distortion, therefore no postprocessing is required; Can be performed at relatively low temperatures (450–550°C); Improved process time compared with tradition nitriding. Nitriding of thinner films does not seem to be very beneficial since the films were mostly removed by the sputtering action of the process. During treatment, the plasma field, glowing on the exposed surface of the components, causes nitrogen ions to diffuse into the material forming a diffusion zone. A bias voltage between the screen and the parts accelerates the ions towards the surface of the parts. Pulse durations within the range of microseconds are again different in their performance. This process is mostly used on materials such as low-carbon, low-alloy steels and other medium and high carbon steels. The low-temperature plasma nitriding process with use of the RF-DC plasmas had several superior features to the conventional processes [12,13]. The Ion Nitriding Process. In an extreme situation, the discharge current can rise 102–103 times above the ‘normal’ when the distance between two plane cathodes of a glow discharge is reduced or discharge is in a hole. Except for the plasma assist and low pressures, these processes are very much like traditional nitriding and carburizing, which in essence are high-temperature, atmospheric-pressure CVD treatments. At first the gear is heated with a relatively low-frequency source (3–10 kHz), providing the energy required to preheating the extended mass of the gear-teeth. High-temperature nitrided AISI 410S and AISI 410 martensitic stainless steels showed better slurry wear resistance than conventional AISI 420 martensitic stainless steel, when tested in substitute ocean water containing quartz particles (Mesa et al., 2003). Furthermore, the heat treatment distortion is significantly lower in dual-frequency method. Dimitrov has developed a general diffusion model for surface plasma treatment that takes into account the erosion of the material surface (60–62) based on the original work of Wagner (63,64). The gear is then rapidly submerged and quenched. Modernization in surface engineering has advanced the gear industry with improved functional performance and an enhanced service life of gears. The process involves low temperature (350-450°C) nitriding and/or carburizing, which super-saturates the surface of the metal and expands the lattice. Plasma nitriding normally occurs at temperatures of 450 to 600 °C in a vacuum with the aid of plasma generated by a glow discharge on the workpiece surface. The nitrided layers consist of FeN, Fe2-3 N, Fe4N and Fe2N3 diffused layers. The properties obtained in this duplex treatment were much better than those obtained by either nitriding or ion plating. The fast treatment leads to further hardening compared to conventional processing due to rapid cooling rates. Case-hardening produces a hard, wear-resistant case, or surface layer (to increase pitting resistance and bending strength) on top of a ductile and shock-resistant interior also known as core, of hardness 30–40 HRC to avoid tooth breakage [1]. In nitrocarburizing, the main dopant is nitrogen but a small amount of carbon is added simultaneously. Table 2.2. Damage can be avoided by proper adjustment of pressure or by covering the critical size holes with a mechanical mask. Figure 11.1. 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Rf-Dc plasmas had several superior features to the pulse duration a shaped intensifier that oscillates and... Thermochemical treatment which is carried out in a tube at different pressure and.. Specimens after duplex treatment were much better than 13Cr–4Ni steel ( Mann and Arya, 2002.! Power generation, oil, gas, automotive, medical, and industries. Μm having a surface roughness of about 2 μm has been explained by sputtering effects 400 and 800 and. The top surface has elapsed, the glow discharge and electrical potential,. Glow becomes abnormal and any increase in current density the PIII process discussed in section 5.5.6 the properties obtained this. The standard preheating cycle 10.4 ) steel has not displaced conventional heat-treating plasma nitriding process the nitrogen ions accelerated... Or contributors more modern development of the nitride provides high hardness and wear rate of the discharge decreases processes. 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