High-temperature Nitriding Research Articles

Friction and Wear Performance of CF/PTFE Composites in Water Lubrication

Using ring friction testing machine and metallographic and SEM on three formula of carbon fiber reinforced PFFE composite materials (CFRP) and stainless steel under water lubrication tribological properties were studied, and analyses the influence of load, grinding time on friction coefficient and wear quantity. It was found that CFRP with carbon-fiber content of 15% mass fraction and the high temperature nitride treated OCr17Ni14Cu4Nb got a friction coefficient of 0.0ll under 200N load, sliding speed of 5 m/s , which is the lowest one between all of the similar materials in domestic reporting.15 min before testing, the friction coefficient decreased with the increase of load. After 15 min, the friction coefficient basically was stabilized at around 0.011-0.014, Main wear mechanism of the CFRP material containing carbon fiber is fatigue wear, the higher the carbon fiber content, the lower the friction coefficient; the applied load increases from100N to 250N, the wear quantity increases with load decrease, starting from250 N wear increases with load increase.

Solar gas nitriding of Ti6Al4V alloy

The main purpose of this work was to study the activating effect of concentrated solar energy (CSE) on the high-temperature nitriding of Ti6Al4V alloy. Solar nitriding was conducted using a low-cost solar installation based on a Fresnel lens with a maximum density power of 250W/cm2 at its focus. Prior to the solar nitriding study, Ti6Al4V was submitted to high-temperature thermochemical treatments using an electrical furnace in a conventional manner. A comparison between the two processes considering the effect of nitriding time and temperature on the hardness, thickness and composition of the nitrided layer is presented. Characterisation of the treated samples by optical and SEM microscopy, microhardness measurements and XRD analysis reveals an important reduction in the nitriding time when concentrated solar energy is used versus the traditional method. The maximum hardness of the solar nitrided samples (2100HV) was achieved after treatment at 1200°C for 15min. This value is similar to that obtained when samples were heated at the same temperature in the electrical furnace for 8h.

Research on Powder Metallurgy High Nitrogen Stainless Steels

High nitrogen Fe-18Cr-12Mn-3Mo-xN austenitic stainless steels were prepared by mechanical alloying and powder metallurgical pressing-sintering techniques. The microstructures, nitrogen contents and sintering properties of the milled powders and sintered bodies had been also investigated. The results show that high nitrogen and nearly spherical composite powders with good compressibility can be obtained by high-energy vibration ball milling and high temperature nitriding. It is also found that the sintering temperature has a significant effect on the density and the nitrogen content of sintered specimens, and the optimal sintering temperature are determined to be 1250°C, at which a favorable combination of the relative density as high as 97.1% and the final nitrogen content of 0.79wt% in sintered specimens can be obtained. The sintered bodies mainly consist of γ-austenite, α-ferrite and the lamellar Cr2N phase. After solution-annealing at 1150°C for 1.5h followed by water-quenching, high nitrogen austenitic stainless steels reveal a fully austenitic structure.

Specific kinetic features of nitriding of titanium caused by phase-structural transformations

We model analytically the high-temperature (T = 1000°С) nitriding of titanium. The role of nitrogen as an α-stabilizer in the formation of a three-layer diffusion zone is analyzed. The problem of nitrogen diffusion in this inhomogeneous medium is solved with regard for the motion of interfaces. We calculate constants of the parabolic growth of layers, which enables us to predict the distribution of nitrogen in the diffusion zone. The evolution (after holding for 1 and 5 h) of the microstructure of a diffusion layer caused by structural-phase transformation during hydrogen diffusion is detected.

Surface morphology on high-temperature plasma-etched gallium nitride

Surface morphology on high-temperature plasma-etched gallium nitride

Enhanced growth rate for ammonothermal gallium nitride crystal growth using ammonium iodide mineralizer

High-temperature gallium nitride (GaN) crystal growth using the acidic ammonothermal method with ammonium iodide (NH4I) as a mineralizer was investigated. The growth rate reached 105μm/day, which was much higher than that previously achieved using acidic ammonothermal methods, and exceeded 100μm/day, which is the minimum growth rate required for industrial applications. When NH4I was used as a mineralizer, high-speed crystal growth was achieved at a relatively low pressure compared to the case of using an ammonium chloride (NH4Cl) as a mineralizer.

High temperature nitriding of grey cast iron substrates in arc plasma heated furnace

Grey cast iron substrates were case nitrided at 1000–1100°C by varying several process parameters such as nitriding time, flowrate of N2 and nitriding gas configuration. Ar and H2 were mixed with N2 to change the configuration and to observe their influence on the nitrided case. Nitriding was carried out in a specially designed arc plasma heated reactor with water cooled steel casing. X‐ray diffraction studies show that the nitride peaks arise due to growth of iron nitride phases such as γ′ (Fe4N: 5·7–6·1%N), ϵ (Fe3N: 8–11·2%N) and carbon nitride (C3N4). Typical surface morphologies of the 10–30 μm nitride layer were studied by SEM. Microhardness studies exhibited twofold improvement of surface hardness. Nanoindentation test indicated poor plastic behaviour of the surface. Micro‐Raman spectra of the nitided case established the presence of β‐C3N4, a superhard phase. Nitrided grey cast iron may find use in wear and corrosion resistant dies, machine components and parts in various industrial applications.

Self-propagating high-temperature synthesis of silicon-nitride ceramic mix using ferro-silicon and ilmenite

The results of an investigation of the high-temperature nitriding of a mixture of ferro-silicon – ilmenite using a complex method of differential-scanning calorimetry are presented. A ceramic mix with the composition Si3N4 – TiN – Si2N2O – Fe is obtained by the method of self-propagating high-temperature synthesis using as the raw material dust-like ferro-silicon and ilmenite wastes.

Surface characterisation of boron nitride layers on multiwalled carbon nanotubes

AbstractMultiwalled carbon nanotubes (MWCNTs), because of their unique morphology and physico‐chemical properties, have many potential advantages in nanotechnology, electronics, optics and other fields of material science. Their use is limited by their sensibility to oxidation, especially at high temperatures. The chemical resistance of MWCNTs could be increased by coating with non‐oxides, e.g. boron nitride (BN) layers. The aim of the present work was to study the formation of BN thin films on MWCNTs by thermal treatment. Thin films of BN were deposited on MWCNTs surfaces by dip coating of boric acid solutions and high temperature nitriding in ammonia flow. Surface composition and chemical states of the layers were determined by X‐ray photoelectron spectroscopy. The surface layer thickness was also calculated based on XPS data, applying the Layers‐on‐Cylinder model of the XPS MultiQuant program. Resistance of the coated MWCNTs against high temperature oxidation was tested by thermogravimetric analysis. The morphology was investigated by transmission electron microscopy. Copyright © 2010 John Wiley & Sons, Ltd.

High-temperature nitriding of low-carbon martensitic steel 12Kh2G2NMFB in nontoxic salt melts

High-temperature nitriding of steel 12Kh2G2NMFB in ecologically safe salt melts is studied. The structure and phase composition of the formed layers and the kinetics and special features of the process of saturation of the steel are determined.

Zircaloy-4 and M5 ® high temperature oxidation and nitriding in air

For the purpose of nuclear power plant severe accident analysis, degradation of Zircaloy-4 and M5 ® cladding tubes in air at high temperature was investigated by thermo-gravimetric analysis, in isothermal conditions, in a 600–1200 °C temperature range. Alloys were investigated either in a ‘as received’ bare state, or after steam pre-oxidation at 500 °C to simulate in-reactor corrosion. At the beginning of air exposure, the oxidation rate obeys a parabolic law, characteristic of solid-state diffusion limited regime. Parabolic rate constants compare, for Zircaloy-4 as well as for M5 ®, with recently assessed correlations for high temperature Zircaloy-4 steam-oxidation. A thick layer of dense protective zirconia having a columnar structure forms during this diffusion-limited regime. Then, a kinetic transition (breakaway type) occurs, due to radial cracking along the columnar grain boundaries of this protective dense oxide scale. The breakaway is observed for a scale thickness that strongly increases with temperature. At the lowest temperatures, the M5 ® alloy appears to be breakaway-resistant, showing a delayed transition compared to Zircaloy-4. However, for both alloys, a pre-existing corrosion scale favours the transition, which occurs much earlier. The post transition kinetic regime is linear only for the lowest temperatures investigated. From 800 °C, a continuously accelerated regime is observed and is associated with formation of a strongly porous non-protective oxide. A mechanism of nitrogen-assisted oxide growth, involving formation and re-oxidation of ZrN particles, as well as nitrogen associated zirconia phase transformations, is proposed to be responsible for this accelerated degradation.

Impact of Organic Contamination From Partially Fluorinated O-Ring in High-Temperature Nitride Process on DRAM Performance

This paper is concerned with organic contamination from a partially fluorinated o-ring used in a furnace for a high-temperature process. The organic outgas was confirmed by Fourier transform infrared analysis of the furnace exhaust gas. Experiments from practical trench dynamic random access memory disclosed that outgassed organic contaminants from the nitride process would severely worsen the tunneling leakage current performance of the storage dielectric and lead to fatal yield loss even though the cell capacitance was almost uninfluenced. To eliminate this yield detractor requires several test runs prior to real production after installation of the partially fluorinated o-ring; otherwise, a fully fluorinated o-ring is needed. From a cost viewpoint, the latter is highly suggested.

Phase changes of the AISI 430 ferritic stainless steels after high-temperature gas nitriding and tempering heat treatment

This study examined the phase changes, nitride precipitation, heat treatment, hardness variations and tempering effect of AISI 430 ferritic stainless steel after high-temperature gas nitriding (HTGN) at 1050 °C and 1100 °C in a nitrogen gas atmosphere. The strong affinity between nitrogen and Cr enabled the permeation of nitrogen into AISI 430 ferritic stainless steel. The surface layer of the steel was changed into martensite + ferrite and Cr 2N at 1050 °C, while martensite plus a rectangular type retained austenite were observed at 1100 °C after HTGN. When the nitrogen-alloyed AISI 430 steel was tempered, the precipitation of (CrFe)N nitride and a secondary hardening effect resulted in an increase in hardness to a maximum value at 450 °C. Above 450 °C, nitride precipitation decreased the hardness considerably. The HTGN treatment improved the corrosion resistance, while the precipitation of high density of Cr 2N deteriorated the corrosion resistance.

Increasing the wear resistance of stainless steels

AbstractThe wear resistance of martensitic, austenitic and duplex stainless steels is increased by carbon and nitrogen in solid solution and in addition by carbides and nitrides, which are formed during conventional ingot metallurgy or by powder metallurgical processing. High temperature and low temperature nitriding provide a hard surface zone. Characteristic alloys and applications are discussed, which try to optimize the resistance to wear and corrosion.

Formation of nitrogen austenite in steel 08Kh15N5D2T due to quenching in closed volume

The process of high-temperature nitriding of low-carbon steel 08Kh15N5D2T in a medium of nitrogen contained in air is studied. The regular features of formation of nitrogen austenite after quenching in a closed volume are determined.

Lotus-Type Porous Nickel-Free Stainless Steel with High Temperature Nitriding

Lotus-type porous Fe-25wt.%Cr and Fe-23wt.%Cr-2wt.%Mo alloys were fabricated by continuous zone melting technique in pressurized hydrogen gas. After applying a high temperature nitriding treatment, the fabricated Lotus-type porous nickel-free stainless steel absorbed larger amount of nitrogen compared with non-porous alloy of the same composition since the surface area exposed to the gas is larger in the porous samples. In the Lotus-type porous Fe-25wt.%Cr and Fe-23wt.%Cr-2wt.%Mo alloys the nitrogen concentration after the nitriding achieved was approximately 1.2 wt.%. Only austenite peaks were detected in the profile of both Fe-Cr-N alloys after the nitriding treatment. Neither CrN nor Cr2N were identified by XRD in any specimen after the nitriding.

Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high- and low-pressure ion nitriding processes

Ion nitriding is an important surface modification technique used routinely in the advanced technology industries aiming at producing high added value components with increased hardness and wear resistance. To further improve the performance of critical-part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments combining PIII and ion nitriding. In particular, a combination of high-pressure (40 Pa), high-temperature (up to 450 °C) glow discharge nitriding with low-pressure (8×10 −2 Pa) ion nitriding was implemented. Analysis of the SS304 samples treated by this hybrid method was carried out using the technique of grazing incidence X-ray diffraction (GIXRD) and the results were supported by both normal XRD and AES (Auger electron spectroscopy) measurements. Depending on the particular conditions of the treatment and the depth probed, mixed phases of γ N, and γ were measured. The improvement in hardness of the obtained surfaces (up to a factor of 2.7) was also in accordance with the results of other analysis.

High-Temperature Nitriding of Refractory Alloys

Processes of high-temperature internal nitriding of refractory alloys based on nickel and cobalt are described. Thermodynamic backgrounds for formation of zones of internal nitriding with optimum phase compositions in alloys containing alloying elements with different affinity for nitrogen are considered. It is shown experimentally that the structures obtained in zones of internal nitriding with segregations of stable fine nitride phases depend on the ratio of concentrations of the nitride-forming elements, on the nitriding temperature, and on the composition of the saturating atmosphere. The kinetic parameters of the process of internal nitriding and the conditions of formation of through diffusion layers are determined. It is shown experimentally that the refractory characteristics of the nitrided layers are enhanced.

In-line nitrogen PIII/ion nitriding processing of metallic materials

Hybrid surface modification involving plasma immersion ion implantation (PIII) and ion nitriding has been attempted. DC cathode nitrogen glow discharges with 600–1000 V, 50–300 mA were typically obtained using the sample support as the cathode and the vacuum chamber as the anode. In this mode, sample temperatures of 500–600 °C can be reached easily while PIII at 10 kV, 50 μs and 400 Hz alone can provide about 300 °C heating. Combining these two highly conformal treatments and achieving high temperature, high efficiency three dimensional ion implantation is our objective. X-ray diffractions (XRD and high resolution XRD in the glancing mode) showed effects of ion nitriding in the AISI 304 stainless steel samples surface which indicate very thick nitrided layer, especially when operating the glow discharge in the low pressure but with high temperature nitriding mode. Auger electron spectroscopy and microhardness measurements confirmed nitriding in the sample surface. The hybrid treatment (PIII/ion nitriding) is expected to improve further these surfaces.

Predicting Microstructure Development During HighTemperature Nitriding of Martensitic Stainless SteelsUsing Thermodynamic Modeling

Thermodynamic calculations of the Fe-Cr-N System in the region of the Gas Phase Equilibria have been compared with experimental results of maximum nitrogen absorption during nitriding of two Martensitic Stainless Steels (a 6 mm thick sheet of AISI 410S steel and green powder compacts of AISI 434L steel) under N2 atmospheres. The calculations have been performed combining the Fe-Cr-N System description contained in the SGTE Solid Solution Database and the gas phase for the N System contained in the SGTE Substances Database. Results show a rather good agreement for total nitrogen absorption in the steel and nitrogen solubility in austenite in the range of temperatures between 1273 K and 1473 K and in the range of pressures between 0.1 and 0.36 MPa. Calculations show that an appropriate choice of heat treatment parameters can lead to optimal nitrogen absorption in the alloy. It was observed in the calculations that an increased pressure stabilizes CrN at expenses of Cr2N - type nitrides.