High Density Plasma Nitriding Research Articles

Fine piercing of electromagnetic steel sheets by micro-punches under nearly zero clearance

The fine piercing process under the nearly zero-clearance die-punch set-up was proposed as a non-traditional process with use of the plasma-nitrided SKD11 punch – die pair. With use of the high density plasma nitriding system, the SKD11 punch was nitrided to have the surface hardness up to 1600 HV. The annealed SKD11 die-substrate was shaved into a core die by accurately piercing the diamond-coated and the nitrided punches, respectively. After shaping and plasma-nitriding the shaved core die, both the punch and core-die was placed into the cassette die set for piercing experiments under the nearly-zero clearance. The electromagnetic steel sheets with the thickness of 0.5 mm were prepared to describe the shearing behavior in piercing. The piercing load and stroke histories were traced with increasing the number of shots. The engineering durability was also discussed with comments on the wear of punch and die. The brittle electromagnetic sheets were accurately blanked with the burr height ratio by 10% and the burnished surface area ratio by 70% when using the diamond-coated punch. Fine piercing process with less heights and fractured surface area ratio in dry was put into practice by using the plasma nitrided punch and die-core set with rational compliance under nearly zero clearance.

Pembentukan Titanium Nitrida (TiN) dengan Proses Nitriding pada Titanium Murni Menggunakan Plasma Densitas Tinggi

Pure titanium has been widely utilized in industry but its products suffered from low wear and erosion resistance. The plasma nitriding was selected as a tool to harden the pure titanium products but typically high temperature processing was required to attain high hardness. In the present study, high density plasma nitriding system was applied to make low temperature plasma nitriding at 723 K (or 450°C) for 14.4 ks (or 4 hours). The average measured hardness reached to 624 HV. This high hardness of plasma-nitrided pure titanium at low temperature was attributed to formation of fine TiN precipitates and nitrogen solid solution into vacancy sites in the HCP crystalline structure of titanium.

Microtexturing Into AISI-SUS420 Molds for Injection Molding Via Plasma Nitriding

The initial microdot and microline patterns were first ink-jet printed onto the surface of polished AISI420 stainless steel mold. This masked mold substrate was nitrided at 693 K for 7.2 ks at 70 Pa by using the high-density plasma nitriding system. The unmasked parts were selectively nitrided to have higher hardness than 1200 HV. This hardness-profiled substrate was mechanically sand-blasted to fabricate the microtextured mold. Microdisk patterned plastic cover-case for cellular phones were injection-molded by using this method for practical demonstration. Both the selective hardening and anisotropic inner nitriding processes were experimentally discussed as a key step in the present processing.

Development of a novel resistance heating system for microforming by modifying surface of dies

Abstract Application of resistance heating in micro forming processes is effective for improving formability of thin foils and accuracy of products. Current flows to thin foils can achieve a rapid heating time with very low heating energy owing to the size effect of heat capacity and electrical resistance. To control the temperature distribution of such as thin foils, the heating property depending on the dimensions and electrical resistance of the workpiece has to be taken into account. Furthermore, the positioning of electrodes and shape of the products might affect the current distribution. In this study, a novel heating system, controlling the electrical resistance of die surface by using high density plasma nitriding and annealing processes, was proposed. In addition, finite element (FE) analysis was applied to simulate the heat temperature evolutions in dies and heat transfer to workpieces for designing this heating system. As results, the nitrided layer in depth of 50 μm with a nitrogen concentration of 9 at.% in a steel die was achieved by this nitriding process. After annealing of this nitride layer, the electrical resistance increased to 3*106 Ω. By using this nitrided tool steel die a workpiece of a SUS304 sheet in thickness of 0.1 mm was successfully heated to around 700 °C with the heat convection from the die, which a current of 40A was applied.

Fine piercing of electromagnetic steel sheets by the plasma-nitrided tools

Abstract The fine piercing process under the nearly zero-clearance die-punch set-up was proposed as a non-traditional process with use of the plasma-nitrided punch – die pair as well the diamond-coated WC (Co) – plasma nitrided die pair. With use of the high density plasma nitriding system, the SKD11 punch was nitrided to have the surface hardness up to 1000 HV. The annealed SKD11 die-substrate was shaved into a core die by accurately piercing the nitrided punch. After shaping and plasma-nitriding the shaved core die, both the punch and core-die was placed into the cassette die set for piercing experiments under the nearly zero-clearance. The electromagnetic steel sheets with the thickness of 0.5 mm were prepared to describe the shearing behavior in piercing. The piercing load and stroke histories were traced with increasing the number of shots; the engineering durability was also discussed with comments on the wear of punch and die. The brittle electromagnetic sheets were accurately blanked with the burr height ratio of 10 % and the burnished surface area ratio of 70 %. With increasing the clearance from nearly zero to 4 % or 8 % in thickness, this piercing process turned to be normal shearing one with much higher burr height ratio and fractured surface ratio.

Low temperature high density plasma nitriding of stainless steel molds for stamping of oxide glasses

Various kinds of stainless steels have been widely utilized as a die for mold- and direct-stamping processes of optical oxide glasses. Since they suffered from high temperature transients and thermal cycles in practice, they must be surface-treated by dry and wet coatings, or, by plasma nitriding. Martensitic stainless steel mold was first wet plated by the nickel phosphate (NiP), which was unstable at the high temperature stamping condition; and, was easy to crystalize or to fracture by itself. This issue of nuisance significantly lowered the productivity in fabrication of optical oxide-glass elements. In the present paper, the stainless steel mold was surface-treated by the low-temperature plasma nitriding. The nitrided layer by this surface modification had higher nitrogen solute content than 4 mass%; the maximum solid-solubility of nitrogen is usually 0.1 mass% in the equilibrium phase diagram. Owing to this solid-solution with high nitrogen concentration, the nitrided layer had high hardness over 1400 HV within its thickness of 50 μm without any formation of nitrides after plasma nitriding at 693 K for 14.4 ks. This plasma-nitrided mold was utilized for mold-stamping of two colored oxide glass plates at 833 K; these plates were successfully deformed and joined into a single glass plate by this stamping without adhesion or galling of oxide glasses onto the nitrided mold surface.

Plasma-nitriding assisted micro-texturing into stainless steel molds

Micro-texturing has grown up to be one of the most promising procedures. This related application required for large-area, fine micro-texturing onto the stainless steel mold materials. A new method other than laser-machining, micro-milling or micro- EDM was awaited for further advancement of this micro-texturing. In the present paper, a plasma nitriding assisted micro-texturing was developed to make various kinds of micro- patterns onto the martensitic stainless steels. First, original patterns were printed onto the surface of substrate by using the ink-jet printer. Then, the masked substrate was subjected to high density plasma nitriding; the un-masked surfaces were nitrided to have higher hardness. This nitrided substrate was further treated by sand-blasting to selectively dig the soft, masked surfaces. Finally, the micro-patterned martensitic stainless steel substrate was fabricated as a mold to duplicate these micro-patterns onto the work materials. The spatial resolution and depth profile controllability of this plasma nitriding assisted micro-texturing was investigated for variety of initial micro-patterns. The original size and dimension of initial micro-patterns were precisely compared with the three dimensional geometry of micro-textures after blasting treatment. The plastic cover case for smart cellular phones was employed to demonstrate how useful this processing is in practice.

Plasma assisted nitriding for micro-texturing onto martensitic stainless steels

Micro-texturing method has grown up to be one of the most promising procedures to form micro-lines, micro-dots and micro-grooves onto the mold-die materials and to duplicate these micro-patterns onto metallic or polymer sheets via stamping or injection molding. This related application requires for large-area, fine micro-texturing onto the martensitic stainless steel mold-die materials. A new method other than laser-machining, micro-milling or micro-EDM is awaited for further advancement of this micro-texturing. In the present paper, a new micro-texturing method is developed on the basis of the plasma assisted nitriding to transform the two-dimensionally designed micro-patterns to the three dimensional micro-textures in the martensitic stainless steels. First, original patterns are printed onto the surface of stainless steel molds by using the dispenser or the ink-jet printer. Then, the masked mold is subjected to high density plasma nitriding; the un-masked surfaces are nitrided to have higher hardness, 1400 Hv than the matrix hardness, 200 Hv of stainless steels. This nitrided mold is further treated by sand-blasting to selectively remove the soft, masked surfaces. Finally, the micro-patterned martensitic stainless steel mold is fabricated as a tool to duplicate these micro-patterns onto the plastic materials by the injection molding.

Structural materialization of stainless steel molds and dies by the low temperature high density plasma nitriding

Various kinds of stainless steels have been widely utilized as a mold substrate material for injection molding and as a die for mold-stamping and direct stamping processes. Since they suffered from high temperature transients and thermal cycles in practice, they must be surface-treated by dry and wet coatings, or, by plasma nitriding. Martensitic stainless steel mold was first wet plated by the nickel phosphate (NiP), which was unstable at the high temperature stamping condition; and, was easy to crystalize or to fracture by itself. This issue of nuisance significantly lowered the productivity in fabrication of optical elements at present. In the present paper, the stainless steel mold was surface-treated by the low-temperature plasma nitriding. The nitrided layer by this surface modification had higher nitrogen solute content than 4 mass%; the maximum solid-solubility of nitrogen is usually 0.1 mass% in the equilibrium phase diagram. Owing to this solid-solution with high nitrogen concentration, the nitrided layer had high hardness of 1400 Hv within its thickness of 40 μm without any formation of nitrides after 14.4 ks plasma nitriding at 693 K. This nitrogen solid-solution treated stainless steel had thermal resistivity even at the mold-stamping conditions up to 900 K.

Comparison of AISI 316L Plasma Nitriding Behavior in Low and Medium Temperature

Plasma nitriding is a widely used technique to improve the mechanical properties and tribological properties of AISI 316L steel because it has many advantages over other surface treatment techniques. One of this advantage is plasma nitriding allows nitrogen introduce to steel at low temperature (below 500°C).In this study, nitriding of an AISI 316L was performed in high density plasma nitriding system using 70%N2:30%H2 gas mixture at 400°C and 480°C for 2, 4, and 8 hours. Optical Emission Spectroscopy (OES) with optical probe was used for plasma diagnosis. The properties of nitrided sample were investigated through microhardness measurement. The results show that N2 ions and radicals are species predominantly formed in plasma.

プラズマ窒化処理がステンレス刃物鋼の表面性状に及ぼす影響

Plasma nitriding treatment is very effective for the hardening of precision metal parts. Especially, high density plasma nitriding can efficiently generate a high density ion with installed hollow cathode, which decreases the damage of the workpiece. As a result, the parts can be cleaned, etched, heated, and nitrided effectively. In this study, an improvement of surface integrity of stainless steel SUS440C is experimentally investigated by nitriding. The experimental analysis made it clear that the surface hardness of workpiece increased due to the generation of nitrided layer even under the low temperature condition like 513K. The nitrided layer was hardened with an increase of process temperature and process time, until a maximum surface hardness of 1700HV.

Synchrotron Radiation Photoemission Study of Ge3N4/Ge Structures Formed by Plasma Nitridation

Chemical bonding states and energy band alignment of pure germanium nitride (Ge3N4) layers formed on Ge(100) surfaces by high-density plasma nitridation were characterized by synchrotron radiation photoemission spectroscopy (SR-PES). The core-level shift of 2.31 eV originating from Ge–N bonds (Ge4+) with respect to the bulk Ge 3d5/2 peak position (Ge0+) was determined by peak deconvolution of Ge 3d core-level spectra. In situ SR-PES study on changes in Ge 3d, N 1s, and O 1s core-level spectra during thermal annealing under ultrahigh vacuum (UHV) conditions revealed that oxidized surface layer on Ge3N4 film could be selectively removed at around 500 °C, which was 50 °C lower than the decomposition temperature of Ge3N4. Ge3+ component was found to increase with decreasing Ge4+ component during thermal decomposition of Ge3N4 while no significant change in Ge1+ and Ge2+ components. The Ge3N4 energy bandgap of 3.68 eV was experimentally determined from energy loss spectra of N 1s photoelectrons. The valence band offset at Ge3N4/Ge(100) interfaces were also estimated to be 1.65 eV from valence band spectra, and thus, the energy band alignment between Ge3N4 dielectrics and Ge substrate was determined.

Electrical Characteristics of Ge-Based Metal-Insulator-Semiconductor Devices with Ge<SUB>3</SUB>N<SUB>4</SUB> Dielectrics Formed by Plasma Nitridation

We have fabricated pure germanium nitrides (Ge3N4) using high-density plasma nitridation and investigated electrical properties of Au/Ge3N4/Ge capacitors. We achieved equivalent oxide thickness (EOT) of 1.4 nm, and dielectric constant of Ge3N4 was estimated to be 9.7. The gate leakage current density of 4.3 A/cm2 in the accumulation condition at V(fb)-1 V, where V(fb) is the flatband voltage, was one order of magnitude lower than that of conventional poly-Si/SiO2/Si stacks. The interface state density (D(it)) of Ge3N4/Ge interfaces evaluated by a low-temperature conductance method exhibited a minimum value of 9.4 x 10(11) cm(-2)eV(-1) at E - E(v) = 0.27 eV. Furthermore, the insulating property and interface quality of Ge3N4/Ge system was found to be thermally stable up to 650 degrees C. These results indicate that Ge3N4 is a promising candidate for either a gate insulator or an interfacial layer under high-k dielectrics for Ge-MIS devices.

High-density plasma nitriding of AISI 316L for bipolar plate in proton exchange membrane fuel cell

Austenitic stainless steel (AISI 316L) is nitrided by inductively coupled plasma using a gas mixture of N2 and H2 at temperatures between 530 K and 650 K, and the corrosion resistance as well as the interfacial contact resistance (ICR) are measured in a simulated proton exchange membrane fuel cell (PEMFC) environment.After plasma nitriding, a nitrogen-expanded austenite layer, the so-called S-phase is formed in all nitrided samples. The ICR value of the nitrided samples decreases to approximately 10 mΩcm2 after plasma nitriding. The sample nitrided at 590 K shows the best corrosion property, while the corrosion resistance of the sample nitrided at higher temperatures decreases because of the formation of Cr-depleted regions in the nitrided sample. By using high-density plasma, the process temperature can be reduced to such a low temperature that Cr depletion is not significant, but a dense S-phase is formed.

Surface hardening utilizing high-density plasma nitriding on stainless steel alloys

By using a plasma nitriding procedure at the PUPR Mirror Cusp Plasma machine, surface hardness is increased in 302/304-type stainless steel samples by exposing them to high-ion-density plasma at high vacuum. This method successfully dopes the surface of the material with strengthening nitrogen ions, without the use of chemical procedures that sacrifice the resistance to corrosion of the given material. A 500 V negative bias is placed on the sample exposed to the nitrogen plasma, where high-energy ions are therefore attracted and immersed into the metallic matrix microns into the surface of the stainless steel. This potential maintains a constant surface temperature at approximately 800 °C. The plasma parameters including ion density and plasma temperature were diagnosed using single Langmuir probes. The stainless steel samples were then tested using scanning electron microscopy (SEM), and Vickers micro-hardness testing to determine the increment in the surface harness of the material. The SEM showed a significant presence of nitrogen imbedded in the grains of the stainless steel surface.

Characteristics of Pure Ge3N4 Dielectric Layers Formed by High-Density Plasma Nitridation

We have demonstrated the direct nitridation of Ge substrates to obtain pure germanium nitrides (Ge3N4). Physical characterization revealed that 3.5-nm-thick amorphous Ge3N4 layers with smooth surfaces and abrupt nitride/Ge interfaces were formed by the high-density plasma nitridation of Ge(100) substrates. We have investigated the thermal stability of the Ge3N4 layers, and found that the nitride was stable up to 550 °C and started to decompose around 580 °C under an N2 ambient, while maintaining smooth nitride surfaces during thermal decomposition. We also found that vacuum annealing did not affect the decomposition temperature and that nitrogen was the only desorption species during Ge3N4 decomposition, which led to the regrowth of smooth and crystalline Ge surfaces after the nitrides had been completely removed at 700 °C. These results demonstrate both the superior thermal stability of pure Ge3N4 as a gate insulator and feasibility of using nitride as a surface passivation layer in the fabrication of Ge-based devices.

Low-pressure, high-density plasma nitriding: mechanisms, technology and results

This paper reviews the low-pressure (<10 Pa), high-density plasma-assisted nitriding processes recently developed for metallurgical surface modification to improve wear, hardness and fatigue resistance of ferrous and non-ferrous materials. For that purpose, plasma generation is most frequently ensured by d.c. glow discharges at relatively high pressure (100–1000 Pa) with the underlying limitations associated with this technology. Nevertheless, more flexibility and control are required for plasma nitriding of promising non-ferrous materials such as titanium, aluminium and their alloys. These requirements are fulfilled by the recently developed enhanced or intensified plasma nitriding processes that operate at lower pressures (<10 Pa) such as: thermionically assisted d.c. triode arrangements (TAT), plasma immersion ion implantation (PIII) or plasma source ion implantation (PSII), electron cyclotron resonance (ECR) systems and thermionic arc discharges (TAD). The purpose of this paper is to review these new nitriding processes from both technological and fundamental points of view. Plasma parameters and plasma–surface interactions are considered for these processes.