Plasma Source Ion Nitriding Research Articles

Microstructure of perfect nitrogen-expanded austenite formed by unconstrained nitriding

In present work, a perfect nitrogen-expanded austenite free from the deformation defect is prepared by the plasma-based low-energy nitrogen ion implanted (also named plasma source ion nitriding) TEM foil of Fe-Cr-Ni austenitic alloys under an unconstrained condition. The effective area in nano-scale, which is constructed by the perfect nitrogen-expanded austenite without stress and plastic strain, is obtained for TEM observation. The electron diffraction directly proves that the Fe4N-like long-rang ordered transformation is the nature of nitrogen-expanded austenite only dependent on nitrogen concentration, and independent on stress or defect. Moreover, the intrinsic microstructure of the nitrogen-expanded austenite is confirmed without twins and ε-martensite, which were formed from the constrained deformation of the nitrided layer depending on the stacking fault energy.

Controllable friction and wear of nitrided steel under the lubrication of [DMIm]PF6/PC solution via electrochemical potential

The friction and wear properties of the nitrided steel at different electrochemical potentials of the rubbed surface have maintained interesting and still an unsolved problem. This study systematically investigated the friction and wear behavior under different potentials for the nitrided AISI 4340 low alloy steel lubricated by propylene carbonate with an additive of imidazolium ionic liquid. A nitrided layer ~170nm thick, composed of nitrogen expanded austenite (γN) phase, nitrogen-containing martensite (α′) phase and chromium nitride (Cr2N) precipitate, was formed onto the steel substrate via plasma source ion nitriding. The nitrided layer exhibited a higher hardness and corrosion resistance than the steel substrate. It was found that the friction and wear for the nitrided sample could be controlled via electrochemical potential. A stable low friction coefficient, 0.16, was obtained within the potential range of −1 V to −0.6V, and almost no wear appeared at −1V for the nitrided sample. The potential controlled friction was due to the modulation of the adsorption of the lubricant ions ([DMIm]+ cations or [PF6]− anions) by the potential, and the potential controlled wear was due to the adjustment of the anti-wear ability of the lubricant by the potential. The saturated adsorption of [DMIm]+ cations at −1V led to the improved anti-wear ability compared to that at OCP, and the anodic corrosion of the rubbed sample surface was responsible for the degraded anti-wear ability at +1V. Also, the nitrided sample exhibited a much milder wear than the un-nitrided sample at each tested potential, ascribed to the higher hardness and corrosion resistance of the nitrided sample compared to those of the un-nitrided sample.

Wear and corrosion properties of plasma-based low-energy nitrogen ion implanted titanium

Plasma-based low-energy nitrogen ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition, has emerged as a low-temperature surface engineering technique for metal and alloy. In this paper, the pure metal Ti samples have been modified by the plasma source ion nitriding process at a process temperature of 700°C for a processing time of 4h. The nitrided Ti surfaces were constructed of a continuous and dense Ti2N compound layer about 2μm thick and a 7–8μm diffused layer. During tribological test on a ball on disk tribometer against the Si3N4 ceramic counterface, a low friction coefficient of about 0.3 and the faint wear volume were obtained for the nitrided Ti samples. The cyclic polarization curves of the nitrided Ti samples in 3.5% and 6.0% NaCl solutions showed that the improved pitting corrosion resistance with an increase of corrosion potential and a decrease of passive current, compared with that of the unnitrided Ti sample. The plasma source ion nitriding of the Ti samples provided the engineering surfaces for the functional applications with the combined improvement in wear and corrosion resistance.

Surface engineering of biomedical metallic materials by plasma-based low-energy ion implantation

Abstract Plasma-based low-energy ion implantation, including plasma source ion nitriding/carburizing and plasma source low-energy ion enhanced deposition of thin films, for surface engineering of metallic materials was emerged as low-temperature, low-pressure surface modification technique. Plasma source ion nitriding onto AISI 316L austenitic stainless steel produced a high nitrogen face-centered-cubic phase (γ N ) layer about 10 μm thick at the temperature of 380 °C during 4 h with the high microhardness of HK 0.1 N 22.0 GPa. The microhardness of the nitrided surface from the titanium nitride phase [(Ti, Al, V)N] layer on Ti6Al4V alloy at 750 °C during 4 h achieved up to about HK 0.1 N 15.5 GPa. No pitting corrosion in the Ringer’s solution at 37 °C was detected by electrochemical polarization measurement for the nitrided AISI 316L stainless steel and Ti6Al4V alloy, respectively. Plasma source ion nitriding of the metallic materials provided the engineering surfaces with combined improvement in hardness and corrosion resistance.

In vitro corrosion resistance of plasma source ion nitrided austenitic stainless steels

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into steel and alloy. In this work, a single high nitrogen face-centered-cubic (f.c.c.) phase ( γ N) formed on the 1Cr18Ni9Ti and AISI 316L austenitic stainless steels with a high nitrogen concentration of about 32 at % was characterized using Auger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. The corrosion resistance of the γ N-phase layer was studied by the electrochemical cyclic polarization measurement in Ringer's solutions buffered to pH from 3.5 to 7.2 at a temperature of 37°C. No pitting corrosion in the Ringer’s solutions with pH=7.2 and 5.5 was detected for the γ N-phase layers on the two stainless steels. The high pitting potential for the γ N-phase layers is higher, about 500 and 600 mV, above that of the two original stainless steels, respectively, in the Ringer’s solution with pH=3.5. The corroded surface morphologies of the γ N-phase layers observed by scanning electron microscopy are consistent with the results of the electrochemical polarization measurement.

Pitting corrosion resistance of high nitrogen f.c.c. phase in plasma source ion nitrided austenitic stainless steel

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into metal and alloy. In this work, 1Cr18Ni9Ti (18-8 type) austenitic stainless steel was treated at a process temperature of 380°C during a nitriding period of 4 h. A single high nitrogen f.c.c. phase (γ N) with a high nitrogen concentration of 32 at.% was characterized using Auger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. The pitting corrosion resistance of the γ N phase layer was measured by cyclic polarization in a series of 3% NaCl solutions buffered to pH from 0.4 to 13. In the potential–pH diagram of the γ N phase layer, the extended immunity and perfect passivity zones and the narrowed imperfect passivity and pitting zones were obtained, compared with that of the original austenitic stainless steel. No pitting corrosion resistance was observed for the γ N phase layer in the solutions of pH 4–13. The high supersaturation of nitrogen in the γ N phase led to the improvement in the pitting corrosion resistance.

Plasma source low-energy ion-enhanced deposition of thin films

Plasma source low-energy ion-enhanced deposition is a new approach for the deposition of thin films on steel and alloys with specific advantages over ion beam-enhanced deposition (IBED) and the complex combined plasma source ion implantation (PSII) and IBED (PSII-IBED). It may be used to develop a thin film process using the plasma-based low-energy ion implantation including plasma source ion nitriding and plasma source ion carburizing. A deposition apparatus based on an electron cyclotron resonance (ECR) microwave plasma source, a magnetron sputtering target and a pulsed low-voltage power supply from 0.5 to 2 kV has been developed. The magnetron sputter deposition of Ti metal films and plasma source low-energy nitrogen ion implantation under a high nitrogen ion implantation dose rate of 0.65–1.20 mA/cm 2 are used alternately in order to synthesize the stoichiometric TiN films on A3 mild steel and M2 high-speed steel at a deposition rate of 50–110 nm/min. The Knoop microhardness of the 1.2–1.6 μm thick TiN films on the M2 steel is in the range of 18.0–20.0 GPa (0.05 N load). The critical loads of the TiN films on the M2 steel measured by the scratch test are 22–35 N corresponding to the formation of an intermixed layer of about 40 nm thick between the film and the steel substrate. The corrosion resistance of the TiN films in 0.5 mol/l H 2SO 4 solution is evaluated by performing electrochemical polarization measurements. Their superior corrosion resistance is a result of the dense fine-grained microstructure and is independent of the preferential orientation of the films.

Computer controlled plasma source ion nitriding

This paper describes how to realize computer-controlled plasma source ion nitriding (PSIN) and introduces some results of stainless-steel-samples treated by auto-PSIN for the first time.

Phase transformations in plasma source ion nitrided austenitic stainless steel at low temperature

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for low-energy implanting nitrogen ions and then diffusing them into steel and other alloys. In this work, 1Cr18Ni9Ti (18–8 type) austenitic stainless steel was treated at a process temperature from 280 to 480 °C under an average nitrogen implantation dose rate (nitrogen ion current density) of 0.44–0.63 mA cm−2 during a nitriding period of 4 h. The nitrided surfaces of the stainless steel were characterized using Auger electron spectroscopy, electron probe microanalysis, glancing angle X-ray diffraction, and transmission electron microscopy. Below 300 °C, a high nitrogen f.c.c. phase (γN) and an ordered f.c.c. phase (γ′) mixed phase and a γN and a nitrogen-induced martensite (ɛ′N) mixed phase were obtained respectively under lower and higher nitrogen implantation dose rates. In the range of 300–450 °C a single γN phase was observed under various nitrogen implantation dose rates. Above 450 °C, the decomposition of the γN phase to a CrN phase with a b.c.c. martensite was obtained. Phase states and phase transformations in the plasma source ion nitrided 1Cr18Ni9Ti stainless steel at the low process temperatures are dependent on all the process parameters, including process temperature, nitrogen implantation dose rate, nitrogen ion energy, and processing time, etc.. The process parameters have significant effects on the formation and transformation of the various phases.

Cubic-BN-Like Structure of B-C-N Films Synthesized by Plasma Source Ion Nitriding

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for implanting nitrogen ions and then diffusing them into bulk materials. The ion-plating B-C films were nitrided to synthesize B-C-N films at a nitriding temperature from 300 to 500° C. The x-ray photoelectron spectroscopy and diffuse reflectance Fourier transform infrared spectra analyses showed that the amorphous B-C-N films synthesized at 500° C are composed mainly of cubic-BN-like and hexagonal-BN-like plain microdomains. The higher nitriding temperature contributes to the formation of cubic-BN-like B-C-N structure in the B-C-N films.

Tribological studies of plasma source ion nitrided low alloy tool steel

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for implanting nitrogen ions and then diffusing into metallic materials. In this work, an attempt has been made to develop a method for hardening 9SiCr low alloy tool steel at a process temperature of 250 °C by plasma source ion nitriding. The nitrided samples were characterized using optical microscopy, Auger electron spectroscopy, electron probe microanalysis and glancing angle X-ray diffraction. The wear tests were performed on a crank/connecting rod reciprocating tribometer. The dominant wear mechanisms were identified by the worn surface morphologies using scanning electron microscopy. The results indicate that the nitrided surface layers possess the improved abrasive wear resistance and increase the transition load from mild to severe wear, compared with the unnitrided samples. The formations of nitrides and nitrogen-containing solid solution are considered as the main reasons for improved tribological properties.

Plasma source ion nitriding of pure iron: formation of an iron nitride layer and hardened diffusion layer at low temperature

Plasma source ion nitriding is a new low temperature, low pressure nitriding approach for the surface modification of iron and steel. A nitriding apparatus based on an electron cyclotron resonance (ECR) microwave plasma source has been developed. Nitrogen ions are accelerated from the ECR microwave plasma by a pulsed negative bias (typically − 2 kV) applied directly to the sample, are implanted, and are finally diffused to a depth below the surface at elevated temperatures which are regulated up to 450 °C by an auxiliary heater. An experimental investigation of plasma source ion nitriding into pure iron is described. The nitrided samples were characterized using optical metallography, microhardness measurement, glancing angle X-ray diffraction and transmission electron microscopy. The effect of the process temperatures on the surface hardness, the hardness-depth profile and the microstructure of nitrided pure iron has been investigated. On the basis of these findings, it has been established that plasma source ion nitriding of pure iron can produce an iron nitride layer and a hardened diffusion zone at process temperatures from 150 to 450 °C.

Microstructure and corrosion resistance of plasma source ion nitrided austenitic stainless steel

Plasma source ion nitriding has emerged as a low-temperature, low-pressure nitriding approach for implanting nitrogen ions and then diffusing them into metallic materials. In this work, 1Cr18Ni9Ti austenitic stainless steel was nitrided at process temperatures from 280 to 480 °C over a range of nitriding conditions, and the resultant corrosion properties in 1% NaCl solution and in 1 N H2SO4 solution were investigated by cyclic polarization and anodic polarization measurements, respectively. Glancing angle x-ray diffraction and transmission electron microscopy studies were used to determine the crystal structures obtained at different process temperatures. It was found that three different near-surface microstructures were present, they were the face-centered-cubic (fcc)γ-(Fe,Cr,Ni)4N and fcc nitrogen expanded austenite (γN) mixed phases, the γN without precipitation of the nitrides phase, and the α-ferrite, fcc CrN, and γN mixed phase. The hardness-depth profiles exhibit a distinct compound layer with a thickness between 1.5 and 10 μm and the Knoop microhardness varied from 1500 to 2400 HK (0.1 N load), depending on process temperatures. The γN phase layer has a good pitting corrosion resistance in 1% NaCl solution and an equivalent homogeneous corrosion resistance in 1 N H2SO4 solution, compared with the original stainless steel. The formation of the γ-(Fe,Cr,Ni)4N phase from the γN phase layer can be the cause of the poor homogeneous corrosion resistance, while the precipitation of chromium nitride leads to deterioration of both the pitting corrosion resistance and the homogeneous corrosion resistance.

Plasma source ion nitriding: A new low temperature, low-pressure nitriding approach

Plasma source ion nitriding is a new approach for surface modification of steel with certain advantages over conventional plasma nitriding and plasma-based nitrogen ion implantation. A nitriding apparatus based on an electron cyclotron resonance (ECR) microwave plasma source has been developed. Nitrogen ions are accelerated from the ECR microwave plasma by a low-pulsed negative bias (typically −2 kV) which is applied directly to the workpiece, implanted, and finally diffused into the steel at elevated temperatures that are regulated up to 550 °C by an auxiliary heater. An application of plasma source ion nitriding into 1Cr18Ni9Ti austenitic stainless steel is described. The nitriding layer thicknesses are varied continuously from 0.8 to 10 μm at various process temperatures from 230 to 480 °C for a nitriding time of 4 h. A dramatic increase in microhardness has been observed. Glancing angle x-ray diffraction has been used to determine the structural changes that occur in the nitrided surface layer.