Glow Discharge Optical Emission Spectroscopy Research Articles

Improvement of the Tribocorrosion Properties of Cemented Carbide (WC-Tic-Co) Samples with PVD Coating

This study aims to investigate the improvement of the tribocorrosion properties of WC-TiC-Co substrates by coating them with hard coatings such as AlCrSiN using cathodic arc deposition. WC-TiC-Co is commonly used in the fabrication of machining and cutting tools; however, there are some materials such as titanium or stainless steel that are difficult to work with; furthermore, in aggressive environments or under high temperatures the performance of the machining tools can be affected, and a failure may occur. This coating is intended to ensure the correct performance of the tools in any conditions. The coatings were characterized by glow discharge optical emission spectroscopy (GDOES), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Tribocorrosion, tribology and corrosion tests were performed to evaluate the tribocorrosion properties of the samples. Furthermore, mechanical and adhesive properties of the coating were studied using scratch and nanoindentation tests. The results showed improved tribocorrosion properties in the samples combined with good adhesive and mechanical properties. These results show the possibility of using these coated materials in the most demanding cutting and machining applications.

Glass Film Formation on GOES Surface during High-Temperature Annealing: The Mechanism with Amorphous Phase Formation

Ceramic insulation coating (glass film) is an important constituent of grain-oriented electrical steel (GOES) designed for use in transformers. Within the scope of this study, the glass film was obtained by means of interaction between the surface of GOES containing 0.5 wt. % Cu and a heat-resistant MgO coating during annealing up to 1100 °C in the 75%H2 + 25%N2 atmosphere. The structure of glass film was analyzed using X-ray diffraction, glow-discharge optical emission spectroscopy, scanning probe microscopy, scanning electron microscopy, differential scanning calorimetry and thermodynamic calculations. After annealing, the glass film contained the following phases: crystalline (MgFe)2SiO4 and amorphous Fe-based solid solutions. The multi-stage mechanism of the glass film formation on GOES surface during high-temperature annealing was determined.

Determination of K, Na, and Mg in Brine by Liquid Cathode Glow Discharge—Optical Emission Spectrometry (LCGD-OES) with Interference Suppression

The determination of K, Na, and Mg in brine is important for its effective utilization. Liquid cathode glow discharge—optical emission spectrometry (LCGD-OES) is a successful approach for the determination of these elements in brine. However, matrix interferences reduce the accuracy using a standard curve. Here a correction method based upon the mutual interferences between K, Na, and Mg is reported to improve the accuracy of brine analysis. To verify the performance, LCGD-OES was employed to analyze four samples using the optimized operating voltage and sample flow rate. The results showed that the relative errors of the concentrations of K and Na in the brine were from 1.79% to 8.65% and 3.88% to 6.49% compared to inductively coupled plasma optical—emission spectrometry (ICP-OES). The reported correction method significantly reduced matrix interferences for the determination of K and Na. Additionally, Mg in brine was determined using Al as the internal standard.

Investigation of electrical transport across the CIGSSe/Mo(Se,S)2 interface of a CIGSSe-based solar cell by experiment and device simulation

In this work, we investigated the electrical transport across the valence band injection barrier at the interface between the Cu(In,Ga)(S,Se)2 absorber layer and the Mo(Se,S)2 layer of the back contact of a chalcopyrite solar cell with respect to their different sulfur contents. For this purpose, samples and modules with three different [S][S]+[Se] (SSSe) ratios in the near vicinity of the interface were produced. The valence band offsets at this interface were determined by means of glow-discharge optical emission spectroscopy and ultraviolet photoelectron spectroscopy (UVPES). Measured current–voltage (IV) characteristics allowed to correlate the roll-over behavior related to the injection barrier with the SSSe composition. We discuss two contradictory findings in literature concerning the layer primarily responsible for the valence band edge offset and the injection barrier it creates, of which both findings could be confirmed in our experiments. We conclude that this could be explained by the sensitivity of the UVPES measurement to local differences in the Mo(Se,S)2 crystal properties. Furthermore, we employ a device simulation model to gain insight into the mechanisms at play at that interface, arriving at the following conclusions: (1) Thermionic emission by itself does not suffice to reproduce the measured IV data under the influence of said barrier. (2) The influence of Na doping on the hole density of the absorber narrows the injection barrier at this interface so that tunneling currents contribute considerably to the injected current, even for significantly large valence band edge offsets of 0.8eV. (3) Light soaking (LS) drastically reduces the roll-over effect, although the difference in bulk carrier concentration and its effect on IV behavior are negligible. Instead, the experimental IV data after LS could be reproduced by a higher interface acceptor trap occupation.

Effects of Metal Hydride Coatings at the Electrodes on Neutron Production Rate in a Discharge-Type Fusion Neutron Source

A glow discharge (GD) fusion neutron source that utilizes nuclear fusion reactions of deuterium has been upgraded. The fusion reactions in this device mainly occur by collisions between the charged or neutral particles and the hydrogen isotopes trapped at the surface of electrodes. In addition, it is known that the metal hydride coating on the electrode enhances the neutron production rate (NPR). Therefore, the elemental distribution, including deuterium, in the depth direction on the electrode is an essential factor in neutron production. However, the distribution on the electrode has not been experimentally investigated. This study aims to analyze the distribution experimentally and indicate the effect of the metal hydride coatings. To achieve this purpose, we prepared the titanium (Ti)-coated cathode and the uncoated cathode, of which the base material was stainless steel. After that, the neutron production test was performed in the range of from 5- to 40-mA currents and from 20- to 60-kV applied voltage. This test indicated that the NPR was improved by coating the cathode with Ti than the uncoated cathode. In addition, depth profiling on the cathodes by glow discharge optical emission spectroscopy (GD-OES) was performed. While the analysis indicated that the concentration of deuterium on both cathodes was increased after the test, there was no significant difference in the concentration of deuterium between both cathodes. Furthermore, the concentration of Ti on the Ti-coated cathode was vastly decreased. The cause of these changes needs to be investigated.

Frequency Effect on the Structure and Properties of Mo-Zr-Si-B Coatings Deposited by HIPIMS Using a Composite SHS Target

Mo-Zr-Si-B coatings were deposited by high-power impulse magnetron sputtering at a pulse frequency of 10, 50, and 200 Hz. The coating structure was studied by scanning electron microscopy, energy-dispersive spectroscopy, glow-discharge optical-emission spectroscopy, transmission electron microscopy, and X-ray diffraction. The mechanical characteristics, adhesive strength, coefficient of friction, wear resistance, resistance to cyclic-dynamic-impact loading, high-temperature oxidation resistance, and thermal stability of the coatings were determined. The coatings, obtained at 10 and 50 Hz, had an amorphous structure. Increasing the frequency to 200 Hz led to the formation of the h-MoSi2 phase. As the pulse frequency increased from 10 to 50 and 200 Hz, the deposition rate rose by 2.3 and 9.0 times, while hardness increased by 1.9 and 2.9 times, respectively. The Mo-Zr-Si-B coating deposited at 50 Hz was characterized by better wear resistance, resistance to cyclic-dynamic-impact loading, and oxidation resistance at 1500 °C. Thermal stability tests of the coating samples heated in the transmission electron microscope column showed that the coating deposited at 50 Hz remained amorphous in the temperature range of 20–1000 °C. Long-term annealing in a vacuum furnace at 1000 °C caused partial recrystallization and the formation of a nanocomposite structure, as well as an increased hardness from 15 to 37 GPa and an increased Young’s modulus from 250 to 380 GPa, compared to those of the as-deposited coatings.

What Can Glow Discharge Optical Emission Spectroscopy (GD-OES) Technique Tell Us about Perovskite Solar Cells?

The emerging broad range of applications of the glow discharge optical emission spectroscopy (GD-OES) technique in the field of perovskite solar cells (PSCs) research is reviewed. It can provide a large palette of information by easily and quickly tracking the depth distribution of light to heavy elements. After a discussion of the advantages and the limitations of the technique and a comparison with other analytical techniques, how GD-OES is employed to give structural information on perovskite solar cells is shown. GD-OES has allowed the full perovskite film formation process investigation, from the initial precursor layers containing soaking and complexed solvent to the final crystallized 3D perovskite layers. The A-site elemental cations distribution is followed-up during the film formation. In addition, this technique gives a deep insight into the action mechanism of additives and their effects on the film formation. It provides fruitful information on optimized light absorbing layers and on the selective contact layers which ensure the charge transport in PSCs. It allows to directly visualize halide ions migration and their blocking by ad-hoc chemical engineering and to study the films and PSCs ageing. GD-OES opens new perspectives to explain the final performances of the devices.

Detection of Li Deposition on Si/Graphite Anodes from Commercial Li-Ion Cells - a Post-Mortem GD-OES Depth Profiling Study

A new semi-quantitative method based on Post-Mortem glow discharge optical emission spectroscopy (GD-OES) depth profiling was developed to detect Li deposition on Si/graphite anodes. By means of the detected amounts of Li, Si and O in the GD-OES depth profiles, a corridor is determined, in which the minimum amount of Li deposition is found. Three different commercially available 18650 cell types containing Si/graphite as anode active material were acquired to evaluate the newly developed method. Those three cell types were initially characterized in detail by means of SEM/EDX, GD-OES, ICP-OES, and Hg porosimetry regarding their cell chemistry and electrode properties. One cell type was a high-power cell due to its high anode porosity and low anode coating thickness. The other two cell types were high-energy cells, which have thick anode coatings and low porosities.We aged the cells at 45 °C until their SOH was 80% and analysed the aging behaviour using SEM, DVA, GD-OES, and in coin half-cells. GD-OES depth profiling revealed that no Li plating occurs during cycling aging at 45 °C. Contrary to this, Li plating was detected on the anodes of all three cell types by the new GD-OES method after the high-power cell was aged at -20 °C and the high-energy cells were aged to 0 °C.Cells, which were previously aged at 45 °C until 80% SOH have afterwards been cycled under the same conditions, which led to Li plating in the fresh cells. Cell types exhibiting predominantly loss of anode active material (LAAM) as aging mechanism during the first aging at 45 °C, still suffered from Li plating during the second aging. However, if the main aging mechanism during the initial aging was loss of cyclable Li inventory (LLI), the cells did show a significantly reduced tendency for Li plating, even though the same conditions caused Li plating in the fresh cells.Analysis of the aged anodes using coin half-cells revealed that the loss of anode material was caused by the deactivation of Si anode material. SEM images of the anode cross-section indicate that the deactivation is most likely mainly induced by the formation of a thick film surrounding the Si particles.In combination with complementary methods like SEM, ICP-OES, and coin half-cell analysis, the newly developed GD-OES method yields in profound understanding of the aging behaviour of state-of-the-art Li-ion cells contain Si/graphite anodes. Figure 1

The Effect of Microstructural Evolution on the Brazeability of Two-Layer Al Sheets

In this study, the microstructural evolution and the interaction between the clad and the core alloys that occurs during the brazing process of two-layer Al sheets with equiaxed grains were examined. The study was carried out using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron backscatter diffraction (EBSD) and glow discharge optical emission spectrometry (GDOES). The effects of microstructure on the brazing performances of two-layer sheets were clarified. Although the grains were fine and equiaxed before brazing, three typical microstructural evolutions happened during brazing, corresponding to three kinds of interactions between the clad and core alloys of the aluminum brazing sheets. In the alloys, which had either relatively uniform grain growth or no grain growth, the interaction between the clad alloy and the core alloy was weak; accordingly, they showed a smooth surface, an even microstructure, faint element mutual diffusion, and eventually good brazeability. Meanwhile, in the alloy with obvious abnormal grain growth (AGG), strain-induced liquid-film migration (SILFM) occurred when the energy was too low to cause strain-induced boundary migration (SIBM). This led to rough and uneven surface morphology, significant mutual diffusion, and surface segregation of elements; eventually, this produced the worst brazeability.

Distributions of deposits and hydrogen on the upper and lower TDUs3 target elements of Wendelstein 7-X

Distributions of deposits and hydrogen (H) on the graphite divertor target elements TM4h4 and TM3v5 in the test divertor units 3 (TDUs3) of Wendelstein 7-X (W7-X) are studied. The TM4h4 and TM3v5 are located at the magnetically symmetric positions in the upper and lower divertor. The microstructure of the deposition layer is characterized by a transmission electron microscope (TEM) combined with a focused ion beam (FIB). Metallic deposits such as iron (Fe), molybdenum (Mo), chromium (Cr) are detected in the deposition layer by energy-dispersive x-ray spectroscopy (EDS). The depth-resolved distribution patterns of boron (B) and metallic deposits on upper and lower horizontal (h) divertor target elements TDUs3-TM4h4 as well as upper and lower vertical (v) divertor target elements TDUs3-TM3v5 are clarified by glow discharge optical emission spectrometry (GDOES). Results for both TDUs3-TM4h4 and TDUs3-TM3v5 show that the B deposition regions exhibit higher H retention due to the co-deposition with deposits. On the other hand, up-down asymmetries in B deposition caused by particle drift exist on both TDUs3-TM4h4 and TDUs3-TM3v5. The B deposition amount on upper TDUs3-TM4h4 is 40% smaller than that on lower TDUs3-TM4h4. While for the vertical target elements, the B deposition amount on upper TDUs3-TM3v5 is 35% larger than that on lower TDUs3-TM3v5. Meanwhile, a shift of around 3 cm in B deposition peaks is observed on upper and lower TDUs3-TM4h4 and TDUs3-TM3v5. Results of numerical simulation of carbon deposition/erosion profiles on the target elements using ERO2.0 code and power flux measured by infrared cameras are shown and compared with the above mentioned B profiles.

Structure and properties of protective amorphous Zr[sbnd]B[sbnd]N coating

This article presents a comprehensive study of the ZrBN coating characterized by high transmittance. The coating was deposited by magnetron sputtering of a ZrB2 target in nitrogen atmosphere. The coating structure was studied by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, and glow-discharge optical emission spectroscopy. The mechanical properties were assessed by nanoindentation. The transmittance and reflectivity, as well as the refractive index, were measured by spectrophotometry. Special attention was paid to in situ transmission electron microscopy studies of thermal stability of the coatings at different heating temperatures and exposure times. Due to the high volume fraction of the BN phase and low defect density, the coating was characterized by transmittance of 70–90 % in the wavelength range of 600–2500 nm. The films exhibit high elastoplastic characteristics (H/E = 0.076 and H3/E2 = 0.057 GPa) and thermal stability at temperatures up to 800 °C.

Multi-spectroscopic analysis of high temperature oxides formed on cobalt-chrome-molybdenum alloys

Thanks to their thermal stability, resistance to oxidation and mechanical strength, cobalt-chrome molybdenum alloys are considered an ideal alloy for high temperature applications. The surface oxide layer evolves as a function of time and temperature, changing its chemical structure and increasing its thickness from a few nanometers to various microns. Making use of various diffractographic and spectroscopic techniques, namely X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and glow-discharge optical emission spectroscopy, coupled with complementary analysis, this work gives new insights on the chemical bonding, crystallographic structure, thickness and elemental composition of the oxide layers as a function of both time and temperature of oxidation. Results show that the initial nanometric passive layer of Co3O4 evolves into a metastable, sub-micrometric CoCrO4 structure and finally stabilizes into a micrometric Cr2O3 at the highest temperatures. This paper fills a fundamental gap in the understanding of the chemistry and stability of Cobalt-based alloys used for high temperature applications, such as in poppet or exhaust valves, aerospace components or hot gas turbines. Once calibrated, this innovative, complete surface characterization approach can be ideally extended to other metallic alloys.

Formation and structure of ZIF-8@PEO coating on the surface of zinc

Recently, plasma electrolytic oxidation (PEO) found broad application as a multi-purpose process to create effective corrosion and wear resistant coatings on various metallic substrates. The exceptional properties of metal organic frameworks (MOFs) put them also in focus as perspective materials for corrosion protection. In this work, the formation of a novel ZIF-8@PEO coating is reported for the first time. It was synthesized by controllable recrystallization of a PEO layer formed on zinc alloy Z1 into ZIF-8 in the presence of 2-methylimidazole organic linkers. The multi-stage mechanism of PEO to ZIF-8 rearrangement is proposed. Cross section, glow discharge optical emission spectroscopy and nano-focused synchrotron X-ray diffraction demonstrated that varying of synthesis parameters, the ZIF-8@PEO coating with different distribution of ZIF-8 through PEO layer can be prepared. Based on the results of laser scanning microscopy, the surface smoothing was observed with increasing the degree of the PEO-to-ZIF-8 rearrangement. Containing two components, the novel ZIF-8@PEO coating is expected to combine admirable physical-chemical properties of both PEO and ZIF-8. Such a feature can open the way for its potential application not only for corrosion protection, but also for photo- and heterogeneous catalysis.

Emergence and annihilation of Kirkendall holes during magnetron sputtering aluminum coating to twinning induced plasticity steel

It is important to design a strong interface, i.e., with the inner-diffusion of elements and without fragile compounds/large holes, between a coating and its substrate. In this work, a hot-wire enhanced plasma magnetron sputtering technique was used to deposit Al coatings on the surface of TWIP at various deposition times (1 h, 2 h, and 4 h) at a controlled temperature of 400 °C. The diffusion behavior of the Al coatings/TWIP substrate under the same temperature was investigated. The X-ray diffractometer (XRD) results showed a typical Al recrystallized morphology with the preferred orientation (1 1 1). Combining the results of transmission electron microscope (TEM) morphology and glow discharge optical emission spectroscopy (Pulsed RF GD-OES), the Kirkendall holes were seen at the interface between the TWIP substrate and Al coating deposited for 1 h, which were generated by the diffusion of Al atoms through the interface and into the surface of TWIP substrate. Extending the deposition time to 4 h, the holes were annihilated by the delayed diffusion of iron (Fe) and manganese (Mn) atoms from TWIP steel to the Al coating. It was confirmed by the calculation of GD-OES that the diffusion rate of Al atoms (0.12 µm2/h) was slower than that of Fe (0.34 µm2/h) and Mn atoms (0.37 µm2/h). This investigation of the inner-diffusion behavior and the finding of the emergence/annihilation of Kirkendall holes will be helpful to guide the setting of deposition parameters to establish a strong interface between the Al coating/TWIP substrate.

Multi-angle spectrophotometry as a tool for determination of film parameters on single-layer structures

Ta–Si–C–N single-layer films have been synthesized by direct current magnetron sputtering on fused quartz substrates. The structural perfection of the films has been studied using X-ray diffraction, scanning electron microscopy and glow discharge optical emission spectroscopy. The optical parameters of the films have been studied using multi-angle spectrophotometry. The spectral dependences of the transmission coefficients of substrates and structures were measured for normal incidence of light in the wavelength range 200–2500 nm. We show that the transmittance spectrum of the specimen has an oscillating pattern due to interference phenomena that are typical for layered structures. The reflectance of the films and the substrates has been measured in the 200–2500 nm region for small incidence angles. The difference between the reflection coefficient at the maximum of the interference of the film and the corresponding reflection coefficient of the substrate at the same wavelength shows that the absorption in the film is low. A formula for determination of the film absorption index based on the measured parameters has been derived. The experimental and calculated data have been used for plotting the absorption spectra of the substrate, structure and film. Discrete refractive indices in the 400–1200 nm region have been calculated for reflections at two incidence angles by determining the positions of interference maxima in the reflectivity spectral responses. The results have been approximated using the Cauchy equation. The film thickness has been estimated to be df = 1046 nm ± 13%. The spectra of film extinction coefficients have been plotted with and without allowance for reflection. Obtained values of the refractive and absorption indices with and without reflection have been summarized in a table.

Metal-ceramic diffusion barrier nanocomposite coatings on nickel based superalloys for corrosion and high temperature oxidation resistance

Ceramic diffusion barrier coatings are inevitable in high temperature aerospace and nuclear applications to protect superalloys from oxidation and hot corrosion. Compositionally graded coating (CGC) of Ni-YSZ with five layers was deposited on an Inconel-690 substrate through electron beam physical vapor deposition (EBPVD) method. After heat treatment, the phase formation and crystallite determination in each layer of the CGC were studied by X-ray diffraction. Pulsed radio frequency glow discharge optical emission spectroscopy (RF-GDOES) showed outward diffusion of Ni towards the surface of the CGC. High resolution transmission electron microscopy (HRTEM) studies of the cross-sectional region of the heat-treated coating at 1273 K revealed no secondary phases within the coating as well as at substrate-coating interface. The corrosion behavior of Ni-YSZ coating under 3 M HNO3 medium showed that the heat-treated CGC of Ni-YSZ exhibited better corrosion resistance due to the formation of NiO than as-deposited Ni-YSZ coating.

From cathode to substrate: Plasma diagnostics on high power pulsed magnetron sputtering deposition of titanium nitride

The present study focuses on an approach to measure the plasma properties from cathode to substrate parallel at three different positions in the coating chamber with activated substrate bias. High power pulsed magnetron sputtering is a powerful tool for the application in various coating systems with advantageous properties. For this reason it was investigated by countless studies during the last years. Several of these studies focusing on investigating the coating and plasma properties. Moreover, they investigated the plasma properties either at a high distance from the target or at different points in time at different chamber positions. The investigated positions were in front of the substrate, in front of the target and between both of them. After the plasma diagnostic measurements by optical emission spectroscopy, titanium nitride coatings were deposited. The coating thickness and deposition rate were investigated by scanning electron microscope. The indentation modulus EIT, the indentation hardness HIT as well as the plastic Wpl and elastic work Wel were investigated by nanoindentation. The chemical composition of the coatings was investigated by glow discharge optical emission spectroscopy (GDOES). For a pulse-on time ton variation of the cathode pulse, the relative deviation between the optical emission spectroscopy and GDOES results was determined for the different chamber positions. The best fit between the optical emission spectroscopy and GDOES results were found for the optical emission spectroscopy measurements conducted closest to the substrate. The present study shows that optical emission spectroscopy measurements close to the substrate are more suitable for the prediction of coating properties than optical emission spectroscopy measurements in front of the cathode.

Characteristics of oxide film formed on cavitation-treated steel surface in water

Rust in rust-prone steel is promoted in water by corrosive factors. Therefore, to prevent the formation of rust, it is necessary to eliminate various corrosive factors before plating or other rust prevention measures. In this study, we investigated improvement of the corrosion resistance of steel surfaces by mechanochemical-multifunction cavitation (MC-MFC) with a sodium hypochlorite solution and MFC in water. The compounds formed on the steel surface after MFC and MC-MFC were α-FeOOH and β-FeOOH. Furthermore, red rust was less likely to occur on the surface after MC-MFC; therefore, it was concluded that the amount of β-FeOOH was relatively high. In combined cycle tests conducted to evaluate the rust resistance, red and black regions were formed on the unprocessed and MC-MFC processed surfaces, respectively. The MC-MFC treated surface effectively suppressed rust formation because the amount of Fe compounds was less in the depth direction than on the untreated surface, as determined by glow-discharge optical emission spectroscopy analysis.

Quantitative analysis of trace N2, Ar in O2 using glow discharge optical emission spectroscopy.

A trace level of N2 and Ar gases in O2 ambience were quantitatively analyzed for the first time by glow discharge optical emission spectroscopy. Microplasma was generated in a compact gas cell by a metal (Au) electrode pair of 1mm diameter and ∼1mm separation with the driving voltage of ∼0.9kV and the current of ∼5 mA in ∼60 Torr. 358 and 813nm optical emission bands were used for N2 and Ar detection, respectively. A spectroscopy fiber bundle having a circular input cross section of ∼700 µm in diameter and an output of 100 µm in width and 3mm in height was employed to promote the signal collection efficiency while preserving high spectral resolution. As a result, the detection sensitivities <1 ppm (3 - σ) were attained for both N2 and Ar within 10s. The detection accuracy was also promoted by correcting the N2 and Ar band signal intensities using the neighboring O emission band intensities, which led to detection errors <2% (3 - σ) for both N2 and Ar.

Gaseous nitriding of Co-10 at% and -15 at% Cr alloys at 400 °C and 450 °C

Co-10 at% and -15 at% Cr with the stable hexagonal close packed (hcp) crystal structure at room temperature have been subjected to gaseous nitriding treatment using nitriding temperatures of 400 °C and 450 °C far below the austenite start temperature. Using X-ray and electron backscatter diffraction (EBSD), structural changes as a result of nitrogen incorporation into the initial hcp lattice can be divided into the following steps: (i) expansion of the lattice due to N uptake yielding hcp (hcpexp) at nitriding temperature of 400 °C, (ii) gradual transformation of hcpexp into an expanded face-centered cubic phase (fccexp) by increasing time at 400 °C/ or temperature to 450 °C (mixture of two phases), (iii) development of stable nitrided layer containing fccexp using moderate nitriding times up to 3 h at 450 °C and (iv) decomposition of fccexp layer into CrN nitrides and less expanded austenite and the reverse transformation from fcc to hcp at near-surface regions at 450 °C after prolonged nitriding time of 24 h. Due to occurrence of step (iv), the square-root treatment-time dependence of the nitrided layer thickness breaks down. Nitrogen-depth profiles obtained for Co-15 at% Cr by glow-discharge optical emission spectroscopy (GDOES) along with the Non-Rutherford MeV proton backscattering spectrometry reveal a nitrogen supersaturation of around 20 at% at surface-adjacent areas in hcpexp. A relatively large unit volume expansion has been recognized for hcpexp with a change of c/a ratio of around 0.6%. Hardness-depth profiles obtained for nitrided Co-10 at% and -15 at% Cr alloys using nanoindentation evidence an increase in hardness inside the nitrided layer, compared to the untreated core.