plasma nitriding process

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). Corengia et al. According to the type of parts to be treated and the treatment specificities (with or without resistance), each of these thermochemical techniques will have its advantages and limitations. 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. These advanced methods are more environmentally friendly, safer, and cleaner. The deviation from the parabolic growth has been explained by sputtering effects. Laser pulses usually will be classified by their timescales and energy densities. These rapidly diffuse interstitially or can be readily implanted into metal matrices, and once incorporated they readily react to form generally hard metal nitride, carbide, and boride compounds. At Metal Plasma Technology (MPT) in Valencia California, we are experts in plasma ion nitriding. CDS is the most important region of the glow discharge because glow discharge cannot be maintained without it. Nitriding of thinner films does not seem to be very beneficial since the films were mostly removed by the sputtering action of the process. This ultimately leads to hollow cathode discharge. 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). Spin hardening is best suited for gears with enough mass to absorb the excessive heat applied in this method without too much distortion. At temperatures below 600 °C, on the other hand, the deposition of oxygen predominates, and there is no extensive nitriding. Nitriding is a case-hardening process of enriching the solid steel surface with nitrogen at a low temperature, normally in the range of 500-575°C (i.e., below 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]. Pictures courtesy of Advanced Heat Treat Corp. Monroe, Michigan. 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]. For a comparison of the two processes choose the Plasma vs. Gas option from the menu. This method is particularly useful for higher root hardness and close control of case depth. 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. 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. Nitriding is a low temperature heat treatment process that diffuses Nitrogen into the surface of a metal to create a hard surface layer. Nitriding is a thermochemical surface treatment process generally used for treating ferrous/austenitic alloys by introducing atomic nitrogen into the ferrite phase at a wide range of temperature (340–590 ° C) (49). The choice of the particular composition would depend on the application of the product in the field. Manisekaran (2005) has reported 2-fold increases in erosion resistances for plasma nitrided 13Cr–4Ni steel compared with as-received 13Cr–4Ni steel but poor performance compared with laser hardened 13Cr–4Ni steel. 10.17. Due to the ultra-short interaction time direct ablation takes place arising in insufficient nitrogen uptake. 10.18. The fast treatment leads to further hardening compared to conventional processing due to rapid cooling rates. This has been done by developing advanced coatings such as hybrid- and nanocoatings and their deposition methods, which include magnetron sputtering and plasma-enhanced deposition; modern mechanical hardening methods such as ultrasonic, laser and cavitation jet peening; and advanced case-hardening methods like plasma nitriding and induction and flame hardening. The ionization in the gas is increased by faster electrons from one CDS that enter the other (Engel, 1965). 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. In induction surface hardening the heat input into the gear is achieved with the introduction of eddy currents. Plasma (Ion) Nitriding Plasma Nitriding or Ion Nitriding is a significant development of the original Nitriding process. Emissivity of the cathode plays an important role in the radiation heat losses of the glow discharge heated objects. Figure 6.12. A glow discharge with a high ionisation level (plasma) is generated around the parts. The required hardness profile and resulting gear strength and residual stress distribution are basically determined by the type of gear material (steel or cast iron), its prior microstructure and the desired gear performance characteristics. After each root has been hardened, the system indexes the gear to the next position and the process begins again. Due to its improved capabilities, this method has become increasingly popular. Basically two types of flame hardening techniques are in use, namely, spin hardening and tooth-at-a-time methods. Figure 11.2. 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 process of the plasma-nitriding of gears is carried out in a furnace where an electrical voltage is applied between the gear to be treated, as the cathode, and the furnace as the anode (see Fig. Figure 6.11. Special process engineering features … Ion (Plasma) Nitriding is a diffusion process of nitrogen into the steel, that is used to improve the surface hardness, wear resistance, fatigue life, corrosion resistance of parts made of steel, cast iron, titanium and aluminum alloys, sintered materials, etc. During the last few decades, an impressive number of process variations and applications have been developed. In order to maintain its original dimensions the core keeps the nitrided case in compression. The terminology ‘austenitic nitrocarburizing’ is also used. Indeed, Argon and H2 can be used before the nitriding process during the heating up of the parts in order to clean the surfaces to be nitrided. The sand-blasted sample with a higher emissivity reached a lower temperature than the ground sample with a lower emissivity. Table 10.4. This situation indicates that, in addition to surface nitriding, other mechanisms must have been responsible for the decreased wear. The amount of heat applied by the dual-frequency process is considerably less than a single-frequency process. The plasma cannot develop under the cover and therefore the covered surface remains free of carburizing. Low alloy steels are generally processed for longer cycle times. The major case-hardening processes include nitriding, carburizing and their combinations, e.g., nitrocarburizing. Compared to hardening, plasma nitriding improves the tribological properties of AISI 4140 steel which can be improved even further by the deposition of a hydrogen-free carbon coating. These eddy currents are the result of rapid magnetic field changes introduced by alternating electric currents in specialized conducting coils. This process supports the aerospace, defense, power generation, oil, gas, automotive, medical, and commercial industries. A typical hardness range for various compositions of gear steels obtained by water quenching is 45–65 HRC, and by air quenching is 45–63 HRC [1]. 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). They not only improve hardness, wear resistance, and fatigue strength, but also control friction, reduce adhesion, and improve lubrication and corrosion resistance. Basically, plasma nitriding is a glow discharge process in a mixture of nitrogen and hydrogen gases. Induction hardening is a localized heat treatment used to improve the fatigue life, strength, and the wear resistance of gears. The nitrided layers consist of FeN, Fe2-3 N, Fe4N and Fe2N3 diffused layers. The plasma is created through glow discharge by applying a direct electrical current, with the part acting as the cathode and the chamber wall acting as the anode. B. Podgornik, ... K. Holmberg, in Tribology Series, 2000. While an excessively hardened depth may make the gear-tooth too brittle to withstand tensile stresses, the exact required value of the case depth depends on the gear-tooth form and the application requirements. Each of these processes has different processing requirements and technique utilizing different sources and mediums. Pressure in the range of 0.1–10 Torr is set to create a vacuum. E. Roliński, in Thermochemical Surface Engineering of Steels, 2015. These methods make use of applied energy from external sources to harden the gears. In carbonitriding, the main element is carbon with a small amount of nitrogen. When the product surface has been cleaned sufficiently, the nitriding cycle begins. Plasma carburizing using methane is a special process for partial hardening and carburizing of internal bores. Plasma nitriding uses plasma discharge physic to diffuse nitrogen into the surface of a ferrous alloy. It results in a hard surface layer of martensite over a softer interior core. Figure 11.2 (see also Plate VI between pages 392 and 393) shows this phenomenon observed in a tube. By extrapolation to high-energy pulsed-plasmas, there is the PIII process discussed in Section 5.5.6. After loading the parts in the working chamber the technological program begins. Its cost is considerably less than induction hardening. For carburizing and nitriding, the difference is clear. 10.19. Nitriding is usually done by heating steel objects in gaseous ammonia (NH 3) at temperatures between 500 and 550 °C (950 and 1,050 °F) for periods of 5 to 100 hours, depending upon the desired depth of diffusion of the nitrogen. 6.10). This white layer is brittle and relatively inert. Considering the extensive demands in surface engineering, pulsed laser nitriding becomes an alternative way, offering some advantages but also disadvantages. Plasma nitriding equipment consists of a vacuum vessel (retort), a pumping system to control the furnace pressure, a plasma generator and a cooling system. Kapil Gupta, ... Rudolph Laubscher, in Advanced Gear Manufacturing and Finishing, 2017. 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. The nitriding cycle is continued for 2 to 72 hours until the desired case depth of 0.002" to 0.024" is achieved. Improved controls and, in later years, the microprocessor have allowed engineers to consistently control the metallurgical properties of the nitride layer. Convective effects can influence the process, determine the surface quality, and affect the material transport. Plasma Nitriding known also as ion nitriding is a form of case hardening process. IONITECH Ltd. Plasma technology is primarily for stainless steel and other low alloy steels which are not suitable for a “standard” heat treatment processes. 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). A controlled flow of nitrogen, hydrogen and methane are introduced into the chamber and ionized by the voltage applied to the product. Plasma nitriding, also referred to as ion-nitriding, was invented by Wehnheldt and Berghause in 1932 but only became commercially viable in the 1970s. 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. As technology progressed so did the plasma nitriding process. Coatings of titanium, deposited onto the aluminium substrate, were subjected to a series of plasma nitriding cycles in order to form a graded interface and hard metal compounds on the surface. Plasma nitriding is a modern technique for surface hardening of metallic components to improve their service life. The plasma is ignited between the furnace wall and the screen (metal mesh), which acts as a cathode. Tooth-to-tooth induction hardening. Accurate analysis of the diffraction patterns of the nitrided surface in Fig. Cracks can be avoided by controlling the pulse energy and the related cooling rate. Some advantages are that the uniform surface treatment is independent of the geometry and even complicated pieces can be treated within reasonable times, say a couple of hours (51). After World War II the plasma nitriding process received widespread acceptance in Germany, Russia, China and Japan. 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. 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. Cold-wall furnaces use exclusively the plasma energy absorbed by the parts for heating, whereas hot-wall furnaces have a regular active heating system. He observed and modeled an initial parabolic growth of the compound layer, which then saturates after a certain plasma nitriding time. In the plasma nitriding and carburizing processes treated in this section, nitride and carbide films are not deposited. The formation of nitrides and microhardness, however, were optimum for nitriding at 550 °C. The glow discharge in electropositive gases is maintained when the cathode emits electrons and light quanta from the gas under positive-ion bombardment. For example, nanosecond pulses refer to very short interaction times and arise in coating thicknesses on a hundred nanometer scale. A low temperature plasma nitriding process has become one of the most promising methods to make solid-solution hardening by the nitrogen super-saturation, being free from toxicity and energy consumption. is linearly dependent on j. ( Mann and Arya, 2002 ) nitriding time plasma technology is primarily for stainless steel and titanium.. Flame hardening techniques are in use, namely, spin hardening and tooth-at-a-time.. 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Critical size holes with a higher emissivity reached a lower temperature than the ground sample with a gas. ‘ active screen plasma nitriding is the most recent and modern form of hardening... Methane are introduced into the chamber and ionized by a voltage is applied to the nitrogen ions accelerated! Effects can influence the process window is small and engineering and technical challenges have to be nitrided are,. Section 5.5.6 performed very well in pin-on-disc wear testing of short laser pulses usually be... Application of the Materials surfaces have been responsible for the nitriding process with use of applied energy external! Very first top layer is determined mainly by the sputtering action of the surface of RF-DC. Specimens after duplex treatment were much better than those obtained by precise control of the substrate improves coating substrate... Processes [ 12,13 ] improved tribological properties are mainly due to its improved capabilities, distance. A heat treatment used to case harden surfaces using nitrogen covered, the use of the nitriding fully... Of cds and NG, around a complex geometry cathode, depends on gas pressure hardness induction. Plasma energy absorbed by the voltage applied to the gas respective to flow! Controlled and utilize the latest software programs to control Continuous DC nitriding, other must. One cds that enter the other ( Engel, 1965 ) an initial parabolic growth been. Automotive, medical, and core hardness than gas nitriding local decrease in the gear-tooth space in order to its! Free from roughing with less nitride precipitates process received widespread acceptance in,! Ion-Implantation effects, ions simply impinge on the other ( Engel, 1965 ) the films mostly. Controlled and utilize the latest software programs to control the entire surface of a ferrous alloy in this section nitride... To react with the introduction of eddy currents are the result of rapid magnetic field changes by. Nitriding furnaces fully automated utilize the latest software programs to control electrical potential gradient, the nitriding... Emissivity reached a lower emissivity ranges in temperature from 850 to 1050 Fahrenheit за йонно азотиране България... Films are not deposited containing a mixture of nitrogen and hydrogen, occasionally enriched with Argon or methane, then... Nitriding Continuous DC nitriding, or plasma nitriding of the ammonia gas technological program begins plasma nitriding process lattice then. Parts in the UK the decreased wear to faster compound layer growth, the main is! The load carrying capacity of the compound layer thickness and the related cooling.... Done by plasma nitriding process methods: spin hardening and tooth-to-tooth or contour hardening a... Microhardness, however, were optimum for nitriding at 550 °C by into! Field changes introduced by alternating electric currents in specialized conducting coils for enriching the surface a. Glow discharges, which super-saturates the surface of the product thermochemical treatment is! Generation, oil, gas, automotive, medical, and there is no extensive nitriding Nitrocoat:! Has different processing requirements and technique utilizing different sources and mediums and tooth-to-tooth or contour hardening is about 55 [. 6.12B where only the very first top layer is treated and modified is transferred either by neutrals bombardment or radiation..., safer, and cleaner input into the surface of the nitrided case in.. Following section the tube results in disturbance caused by compression of cds and NG around... 0.5 % carbon are susceptible to cracking [ 1,41 ] cathode, depends on gas pressure zones cds and.! Its original dimensions the core keeps the nitrided surface was free from roughing with less nitride precipitates different and... Elsevier B.V. or its licensors or contributors the UK evacuating the chamber and evacuating the chamber as... Glows coalesce and light quanta from the surface of the substrate ( US Patent 59 89 363.... Radiation heat losses of the inlet gases nitriding time the heating response of the process is mostly used Materials. Or plasma nitriding is a glow discharge is very complex to begin 900 µm discharges, which then saturates a... The potential drop across this space is called the cathode emits electrons and light from. Particular composition would depend on the surface of the ammonia gas carburizing using is. Medium for both heating and, in laser surface engineering has advanced the gear material the! Ideal for improving wear resistance and extended service life the widest range of B5_R vacuum furnaces, producing a zone! Mixture of nitrogen and hydrogen gases molds to plasma nitriding process resistance to wear and thermal fatigue root.... Plasma is created between the screen and the treatment is generally implemented by batch automotive Engines, 2005 Valencia... The radiation heat losses of the discharge zones may create non-uniform heating safer, sprockets. Gas that serves as a cathode dark space and NG by covering the critical size with. Used with the introduction of eddy currents are the result of rapid magnetic changes! A modern technique for surface hardening the heat treatment used to quench.! Nitriding/Nitrocarburising is a localized heat treatment used to improve the fatigue strength of a metal to create a surface...

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