Papers by Keyword: Chromium Nitride

Abstract: A constitutive equation of flow stress based on the Norton-Hoff equation has been developed for the high chromium and nitrogen containing super duplex stainless steel, ZERON® 100 (UNS S32760). This was then used to model, using the finite element method, the strain distribution within a uniaxial compression test under typical two-phase forging conditions. Predictions from the model were used to correlate deformation history to microstructure morphology. The microstructure consisted of austenite, γ islands (both primary and secondary) within a ferrite, δ matrix that contained chromium nitride precipitates. For deformation temperatures of 1050°C and 1120°C, the small secondary austenite was equiaxed, whilst at 1280°C the secondary austenite exhibited a Widmanstätten morphology. The highest level of nitride precipitation occurred at the highest deformation temperatures, i.e. highest volume fraction of ferrite, independent of strain rate. This suggests that nitride precipitation appears to be driven to a greater extent by thermal factors than deformation substructure.

Abstract: In the past decade, Al 5083 has attracted considerable attention due to its promising potential applications in military vehicles. This paper reports the improvement of mechanical and tribological properties of Al 5083 coated with chromium nitride. Chromium nitride thin films were deposited by DC magnetron sputtering technique on Al 5083 substrate at different deposition powers (150 to 300 W in steps of 50 W). A FESEM was used for surface morphology and chemical composition studies. The thickness of the films was determined by quartz crystal monitor and checked with FESEM cross-section images. Films thickness was 2±0.01 μm for all samples. The mechanical and tribological properties were investigated by nanoindentation and scratch tests, respectively. The results showed that grains size decreases with the deposition power, while the samples produced at higher powers had a denser structure. The results also showed that by increasing the deposition power film hardness increased and the friction coefficient and scratch volume decreased.

Abstract: Nitride based hard coatings are widely used for mechanical applications. Among these coatings, chromium nitrides are especially interesting because of its good mechanical and tribological properties. In this work we have studied the influence of nitrogen gas flow on mechanical and tribological properties of chromium nitride thin films. The chromium nitride thin films were deposited on Al 5083 by DC magnetron sputtering technique at different nitrogen gas flows in the range of 5-20 sccm. Surface morphology and chemical composition of the films were studied using field emission scanning electron microscope (FESEM). The thickness of the films was determined by quartz crystal monitor and checked with FESEM cross-section images. The mechanical and tribological properties of the samples were investigated by means of nanoindentation and scratch tests. The results showed that films hardness increased with nitrogen gas flow, while coefficient of friction and scratch volume decreased. The structural investigations showed that these behaviors were due to the decrease of dislocation density and improvement of crystal quality.

Abstract: This article presents the distribution of the varying magnetic field and its effect by magnetron sputtering on mechanical properties of CrN films. The magnetic field variations in the sputtering processes were explored, and the strength of magnetic field in the unbalanced magnetic sputtering systems is controlled. In addition, the microstructure, composition and surface properties of CrN films prepared by magnetron sputtering were investigated. At a GDMT of 27mm, the highest wear rate value and hardness values seems to be appeared, while the higher critical force value appears to occur at 49mm GDMT during 18 tests. The experimental results have showed that in the enhancement in overall intensity at the gap distance of 27mm between magnet set and the target surface (GDMT), magnetic field strength varied having a significant influence on the CrN structures was readily noticeable, while the wear scar curve at 49mm GDMT possessed better tribological properties than those of the others. Thus, magnetic field variations play a crucial role in determining the properties of the films

Abstract: This paper describes the results of gaseous thermochemical treatment of nitriding duplex stainless steel using tube furnace. The nitriding was performed in temperature range between 400°C and 500°C for 6 hours, forming a dual layer structure with hard nitrogen layer. The nitriding gas composition used for this process is 50% NH4 + 50% N2 and 25% NH4 + 75% N2. The structural development was characterised using hardness tester, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on the experimental results, it was found that nitrided layer produced maximum thickness nitrided layer about 13.96µm and hardness 666.3 HV0.025 at 450°C with 50% NH4. The formation of expanded austenite was observed in temperature range between 400°C and 500°C. However, the cromium nitride has been developed at temperature 500°C which decreased the corrosion properties of duplex stainless steel.

Abstract: Chromium nitride and silicon doped chromium nitride thin films have been deposited by r.f. reactive magnetron sputtering. The effect of processing parameters on the properties of chromium nitride films and the correspondent influence of the addition of silicon on the chromium nitride matrix in the films structure and mechanical properties have been investigated. The characterization of the coatings was performed by X-ray diffraction (XRD), and nano-indentation experiments. These studies allow analyzing the crystalline phases, crystal orientation/texture, crystallite size, mechanical properties and the relations between the characteristics of the films. The increase of the nitrogen partial pressure in the working atmosphere produces changes from a body-centered cubic (bcc) Cr structure, to hexagonal Cr₂N to face-centered cubic (fcc) CrN structure, with CrN (111) preferred orientation. For the films with a dominant Cr2N phase the hardness has a relative maximum (42 GPa). The highest hardness was measured for a coating with dominant CrN phase (45 GPa) with a crystallite size around 18 nm. The addition of Si, in the films with CrN dominant phase, maintains the CrN (111) preferred orientation and produced variable changes in films hardness, depending on deposition conditions.

Abstract: This paper reports the effects of varying magnetic field strength on CrN films, deposited by a magnetic sputtering process. The strength of magnetic field in unbalanced magnetic sputtering processes is controlled by adjusting the gap distance between the magnet set and the target surface (GDMT). An improvement in overall intensity, at low GDMT, was observed by adjustable magnetic field distributions. In the chamber, it was readily noticeable that varying the magnetic field strength has an influence on the CrN structures. In experiments, at low GDMT, a high hardness value and lower wear rate become visible in the CrN films. In addition, the CrN films formed have a smooth surface with a dense tiny structure and display preferential orientation in the Cr2N(111) and Cr2N(002) planes, whereas CrN films prepared at higher GDMT exhibit more roughness and the CrN (200) plane is evident. Furthermore, the Cr2N (111) (002) plane possessed better tribological properties than that of the CrN(200) plane, where the wear scars show little failures on the coating surface.

Abstract: This paper presents the optimal chromium nitride (CrN) deposited performance by tuning magnetic systems on die steel in PVD. The strength of magnetic fields was controlled by adjusting the gap distance between magnet sets and target surfaces of the unbalanced magnetic field of sputtering systems. In L18 orthogonal experiments, the effect of control factors were explored such as gap distance between magnet set and target surface (GDMT), target current, argon and nitrogen flow rate, DC pulse frequency, and work distance. Hardness and wear behavior of the CrN films were analyzed using a statistical method. The wear rate was estimated by Pappus’s theorem. Among the results, the Cr2N phase with the mixture crystallographic orientations of (111) and (002) exhibited better wear resistance than CrN(200) with a single preferential orientation. In addition, variance analysis exhibited the largest percentage contribution to friction coefficient in comparison with the other two properties of friction coefficient and GDMT, which showed that GDMT is extremely sensitive to friction coefficient.

Abstract: Bipolar plate of stack in polymer electrolyte membrane fuel cell (PEMFC) has high cost and heavy weight. In this study, low carbon steel was used as a base metal of bipolar plate for the lower cost than stainless steels, which are widely researched as bipolar plate. Low carbon steel has not a good corrosion resistance. In order to improve the corrosion resistance and electrolytic conductivity, low carbon Steel needs to be surface modified. We made chromium electroplated layer of 5㎛ and 10㎛ thickness on the surface of low carbon steel, and it was thermally nitrided for 3hours at 1173K in a furnace with 50torr nitrogen gas pressure. Cross-section and surface microstructures of surface treated low carbon steel were investigated using OM and SEM. Also crystal structures are observed by XRD. Interfacial contact resistance and corrosion test were considered to simulate the internal operating conditions of PEMFC stack. The corrosion test was performed in 0.1N H₂SO₄ + 2ppm F- solution at 80°C. The results show that the surface modified steel plates have good corrosion resistance and relatively low interfacial contact resistance, and it should be candidate material as a bipolar plate of PEMFC.

Abstract: In this paper, the Fe-based cladding layer was prepared on 42CrMo substrate by laser cladding mixture containing chromium nitride. The effects of chromium nitride on microstructure and property of cladding layer were studied. The experimental results indicate the chromium nitride is unstable during the process of laser cladding. It is very difficult to obtain chromium nitride in the laser cladding layer. However, the addition of chromium nitride in cladding powders could promote the formation of austenite phase, and increase the microhardness of cladding layer. The reason about increasing the microhardness of cladding layer is the formation of little carbide and solution strengthening of nitrogen, not the strengthening from chromium nitride.