Forming carbonitride coatings on titanium by thermochemical treatment with C-N-O-containing media

The formation of TiC_xN_y coatings on titanium alloys through thermochemical treatment of graphite in nitrogen was investigated in this study. The presence of oxygen in saturating media was found to lower the nitrocarburizing temperature from 1,100°C to 850°C. Two methods to accumulate oxygen in a saturating medium have been proposed: using oxygen-containing nitrogen or oxygensaturated graphite. The sequence of stages of carbonitride formation in the Ti-C-N-O system is explained in this paper.     

Structural, mechanical and corrosion properties of TiOxNy/ZrOxNy multilayer coatings

Results on the deposition and characterization of TiO_xN_y/ZrO_xN_y multilayers, with bilayer periods of 20 and 400 nm, are presented. The coatings were deposited on TiNiNb alloy substrates by the pulsed magnetron sputtering method. The elemental composition, hardness, adhesion and corrosion resistance of the coatings were analyzed.As resulted from the XPS analysis, the individual layers consisted of a mixture of titanium or zirconium oxynitrides and corresponding oxides. X-ray analysis revealed that the coatings were amorphous. Only slight differences between the microhardness and adhesion values of the coatings with small and large bilayer period Λ were found. The experiments also showed that the multilayered coatings improved the corrosion resistance of the uncoated alloy and reduced the amount of ion release in artificial body fluids.     

Nitridation of Ti-6Al-4V powder in thermal plasma conditions and sintering of obtained TiN powder

This study is devoted to plasma nitridation of a Ti-6Al-4V powder, and sintering of reaction products so-obtained.Ti-6Al-4V spherical particles (22-45 μm) were injected in a plasma jet using N₂ as plasma gas and collected in two spots: in a cold area located far from the torch and in a hot area submitted to the plasma thermal effect. After plasma nitridation, particles of substoichiometric titanium nitride (TiN_1−x) with no nitrogen gradient were obtained. The reduction of nitrogen concentration in plasma gas improved the massic output of gathered powders. These powders were not exclusively composed by TiN_1−x, since titanium alloy often remained, and a secondary phase β-Ti containing vanadium and aluminium was always present inside the grains. The nitridation rate depended on the collected area. Titanium oxide (rutile) was detected in powders collected in the hot area.Titanium nitride powders in which no rutile was detected were hot pressed up to 1450 °C under flowing nitrogen. In this case, the densification rate did not overload 83% of theoretical value. This fact can be explained by the nitridation of both TiN_1−x and titanium intermetallic phases during the heat treatment. In the case of inert atmosphere (argon), there was only the densification phenomenon which gave a density close to the theoretical value.This work has to be developed on the one hand to improve powder synthesis and its natural sintering, and on the other hand to approach hot pressing sintering mechanism.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part II: The role of the duty cycle

The reactive gas pulsing process (RGPP) was used to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. A titanium target was sputtered in a reactive atmosphere composed of Ar + O₂ + N₂. Argon and nitrogen gases were continuously introduced into the sputtering chamber whereas oxygen was injected with a well-controlled pulsing flow rate following a rectangular and periodic signal. A constant pulsing period T = 45 s was used for every deposition and the duty cycle α = t_ON/T was systematically changed from 0 to 100%. The operating conditions were investigated taking into account the poisoning phenomena of the target surface by oxygen and nitrogen. Kinetics of poisoning were followed from measurements of the total sputtering pressure and titanium target potential during the depositions. Deposition rate and optical transmittance of titanium oxynitride coatings were also analysed and correlated with the process parameters. Pulsing the oxygen flow rate with rectangular patterns and using suitable duty cycles, RGPP method allows working according to reversible nitrided-oxidised target conditions and leads to the deposition of a wide range of TiO_xN_y thin films, from metallic TiN to insulating TiO₂ compounds.     

Mechanical properties and corrosion resistance of nanocrystalline ZrNxOy coatings on AISI 304 stainless steel by ion plating

Transition metal oxynitrides have become emerging decorative coating materials due to their adjustable coloration and high hardness and corrosion resistance. This research studied the effect of oxygen content on the coloration, mechanical properties and corrosion resistance of ZrN_xO_y thin films deposited on AISI 304 stainless steel using hollow cathode discharge ion plating (HCD-IP). The Zr/N/O ratios of the ZrN_xO_y films were determined using X-ray photoelectron spectroscopy (XPS). The color of the ZrN_xO_y thin film changed from golden yellow to blue and then slate blue with increasing oxygen content. X-ray diffraction (XRD) patterns revealed that phase separation of ZrN and m-ZrO₂ occurred as the oxygen content reached 31.2 at.%. ZrN(O) (ZrN with dissolving oxygen) is dominant at oxygen content less than 18.1 at.%, while m-ZrO₂ phase was prevailed at oxygen content above 40.3 at.%. Phase separation lowered the hardness of the ZrN_xO_y films as the fraction of ZrO₂ was less than 40%. The residual stresses in ZrN phase was higher than that in ZrO₂, and the residual stress decreased for the specimen containing 30 to 37% ZrO₂. For the samples containing more than 44% ZrO₂, the average residual stress was close to that in ZrO₂ phase. The corrosion resistance was evaluated by salt spray test and potentiodynamic scan in two solutions: 0.5MH₂SO₄ + 0.05 M KSCN and 5% NaCl solutions. The results showed consistent trend in the two solutions. From the results of potentiodynamic scan, corrosion resistance increased as the packing density of the film increased, whereas the film thickness was not a crucial factor on corrosion current; moreover, the electrical conductivity of the film may be one of the significant factors in corrosion resistance. Results of salt spray tests suggested that the corrosion of ZrN_xO_y in NaCl may play an important role in corrosion resistance.     

连续氮化硅纤维的氧化行为与高温影响研究

连续氮化硅陶瓷纤维是透波／承载一体化陶瓷基复合材料的关键原材料,也是制约复合材料耐高温性能与力学性能的关键因素。本文系统研究了国防科技大学研制的连续氮化硅纤维的抗氧化性能,分析了高温处理后纤维的组成结构与力学性能变化规律。结果表明：1000°C氧化1h后纤维强度高于原始纤维强度,主要是形成的玻璃相能减少和弥补纤维的表面缺陷。随着空气中处理温度提高,氧含量增加,纤维表面形成的SiO₂层逐渐变厚,纤维强度明显降低。纤维在1200°C氧化1h后强度保留率为63%,表明在此温度以下纤维有较好的服役性能。另一方面,氮化硅纤维在1450°C N₂中处理1h的强度保留率为57%,表现出良好的耐高温性能。纤维表面氧化对其在N₂下的耐高温性能具有不利影响,1000°C氧化的纤维在1450°C处理后丧失强度,1500℃处理后形成氮化硅结晶,失重明显增长,纤维内部也开始产生缺陷。     

Laser chemical vapor deposition of titanium nitride films with tetrakis (diethylamido) titanium and ammonia system

Wide-area and thick titanium nitride (TiN_x) films were prepared on Al₂O₃ substrate by laser chemical vapor deposition (LCVD) using tetrakis (diethylamido) titanium (TDEAT) and ammonia (NH₃) as source materials. Effects of laser power (P_L) and pre-heating temperature (T_pre) on the composition, microstructure and deposition rate of TiN_x films were investigated. (111) and (200) oriented TiN_x films in a single phase were obtained. The lattice parameter and N to Ti ratio of the TiN_x films slightly increased with increasing P_L and was close to stoichiometric at P_L > 150 W. TiN_x films had a cauliflower-like surface and columnar cross section. The deposition rate of TiN_x films increased from 42 to 90 µm/h at a depositing area of 10 mm by 10 mm substrate, decreasing with increasing P_L and T_pre. The highest volume deposition rate of TiN_x films was about 10² to 10⁵ times greater than those of previous LCVD using Nd:YAG laser, argon ion laser and excimer laser.     

Particular properties of Ti2O and TiNx nanoparticles prepared by thermal decomposition

Particular properties of Ti₂O and TiN_x prepared by thermal decomposition were introduced. A precursor prepared by titanium powder reacting with oxalate acid was thermally decomposed in nitrogen atmosphere at 840°C for 15 min, and relatively pure Ti₂O was then obtained. Conductive TiN_x was also prepared after altering reaction conditions. Samples were characterized by resistivity, X-ray powder diffraction, transmission electron microscope, Ultraviolet-Visible diffuse reflection, and electromagnetic shielding efficiency. The results indicate that both Ti₂O and TiN_x have good conductivity. Moreover, Ti₂O shows a better solar photocatalytic activity and TiN_x does well in the electromagnetic shield.     

TiOxNy coatings grown by atmospheric pressure metal organic chemical vapor deposition

Titanium oxynitride coatings were deposited on various substrates by an original atmospheric pressure metal organic chemical vapor deposition (MOCVD) process using titanium tetra-iso-propoxide as titanium and oxygen precursors and hydrazine as a nitrogen source. The films composition was monitored by controlling the N₂H₄ mole fraction in the initial reactive gas phase. The variation of the N content in the films results in significant changes in morphological, structural and mechanical properties. When a large excess of the nitrogen source is used the resulting film contains ca 17  at % of nitrogen and forms dense and amorphous TiO_xN_y films. Growth rates of these amorphous TiO_1.5N_0.5 coatings as high as 14 μm/h were obtained under atmospheric pressure. The influence of the deposition conditions on the morphology, the structure, the composition and the growth rate of the films is presented. For the particular conditions leading to the growth of amorphous TiO_1.5N_0.5 coatings, first studies on the mechanical properties of samples grown on stainless steel have revealed a high hardness, a low friction coefficient, and a good wear resistance in unlubricated sliding experiments against alumina which make them very attractive as protective metallurgical coatings.     

Investigation of the nitrogen-nickel-titanium system: The isothermal section at 900 °C

Phase relations in the ternary system N-Ni-Ti have been established experimentally for the 900 °C isothermal section assisted by thermodynamic modeling. Phase equilibria are characterized by an appreciable amount of up to ≅11 at. % N dissolved in the octahedral interstices of the crystal structure of Ti₂Ni. Two-phase equilibria are formed at 900 °C among the pairs Ti₂N + Ti₂NiN_x, TiN_1-x + Ti₂NiN_x, TiN_1-x + TiNi_1-x, and TiN_1-x + Ni(Ti)_x. The investigation is based on X-ray powder diffraction, metallography, scanning electron microscopy, and electron probe microanalysis techniques on about 50 alloys, which were prepared by arc melting or high-frequency levitation melting of appropriate blends of Ti,Ni-powders with TiN used to introduce nitrogen. Key experiments related to the N solubility in the Ti₂Ni phase have been triggered by an interactively performed thermodynamic modeling. The experimental results are in fine agreement with the thermodynamic calculation.     

Effect of nitriding on the electrochemical behaviour of Ti‐Al‐Mn alloy

The effect of technological conditions of nitriding such as process time duration and chemical composition of saturating medium, on the corrosion behaviour of nitrided coatings in 14 M solution of sulphuric acid was analyzed. The investigations were done on the alloy Ti‐5,0 Al‐2,0 Mn. The nitriding was carried out in nitrogen both at atmospheric pressure and rarefied nitrogen pressure (1 Pa) at the temperature 850°C and time processing in the range from 5 to 20 h in nitrogen‐containing gas only, and in powder electrode graphite and nitrogen‐containing gas. It was shown that technological conditions of nitriding determine the protective properties of nitrided coatings. It was indicated that the optimal structure of the nitride layer for best corrosion protection is the thin nitride TiN_x with high surface quality and a gas‐saturated layer. Nitriding in graphite powder effects positively the protective properties of nitride coatings due to reducing the nitride‐forming process.     

The oxidation of cobalt-chromium-titanium alloys at 1000°C

Cobalt-based alloys containing 3,5,10,15, and 20% Cr with 1 and 3% Ti were oxidized at 1000°C in slowly flowing oxygen gas. In general, titanium additions decreased the oxidation rate with the most pronounced effect being observed at the 10% Cr level. Titanium accelerated the formation of Cr₂O₃ layers at the metal-oxide interface. Faceted Cr_xTi_yO_z spinel particles were found at the metal-oxide interface which varied in composition according to microprobe results. There was no evidence of spalling on the Co-Cr-Ti alloys studied in contrast to the severe spalling normally encountered in Ni-Cr-Ti alloys. Distinct morphological differences existed on the outer CoO layer of the 1% Ti alloys in comparison to the O and 3% Ti alloys.     

Combustion synthesis of Ti(C, N)–TiB2 from a Ti–C–BN system

In this paper, a simple way of fabricating TiC_xN_y–TiB₂ ceramics through the combustion reaction of Ti, C and BN powder mixtures in an argon atmosphere is reported with an emphasis on the effects of the C/(C + N) ratio on the SHS reaction behaviors and mechanism. With the increase in the C/(C + N) ratio, the combustion temperature shows a zigzag variation behavior; the combustion wave velocity displays a similar variation tendency as did in the combustion temperature while the ignition delay time increases progressively. XRD results confirmed that TiC_xN_y–TiB₂ could form in all the samples. Microstructural observations revealed that both TiC_xN_y and TiB₂ grains had fine sizes of less than 1 μm in the products when the C/(C + N) ratio was lower than 0.5. Based on the characterization of quenched samples, the formation mechanism of the titanium carbonitride is proposed. Namely, the formations of TiN_0.3 and TiN are followed by the incorporation of C in TiN_x to form the titanium carbonitride solid solution.     

Self-propagating high-temperature synthesis of TiCxNy–TiB2 ceramics from a Ti–B4C–BN system

An experimental study on direct formation of TiC_xN_y–TiB₂ ceramics by self-propagating high-temperature synthesis (SHS) was conducted using a Ti–B₄C–BN system. The effects of the C/(C + N) ratio on the combustion behavior and reaction products were investigated. Experimental characterizations of quenched samples show that the combustion reaction started with the formation of highly substoichiometric TiN_y and TiB due to the solid-state reaction between Ti and BN; and then the TiN_y precursor and TiB dissolved back into the titanium melt, forming the Ti–B–N liquid, which in turn transformed to the Ti–B–N–C liquid due to the dissolution of the carbon atoms diffused away from B₄C. Finally, the TiC_xN_y and TiB₂ particles are formed from the melt through the dissolution-precipitation mechanism.     

Combinatorial approach to the growth of α-(Al1 − x,Crx)2 + δ(O1 − y,Ny)3 solid solution strengthened thin films by reactive r.f. magnetron sputtering

The design and synthesis of Al–Cr–O–N thin films in a metastable solid solution strengthened α-(Al_{1 − x},Cr_x)_{2 + δ}(O_{1 − y},N_y)₃ microstructure are described. The deposition experiments were carried out by reactive r.f. magnetron sputtering in an argon–oxygen–nitrogen atmosphere for the sputtering from a segmented target, composed of an Al half plate and a Cr half plate. The constitution, microstructure and Vickers micro hardness of the coatings are discussed in dependence of the deposition parameters and the elemental composition. The range of α-(Al_{1 − x},Cr_x)_{2 + δ}(O_{1 − y},N_y)₃ phase formation is shifted to higher Cr/(Al + Cr) ratios with increasing nitrogen gas flow. A γ-Al–Cr–O–N phase is formed at high total gas pressures and low Cr/(Al + Cr) ratios. The solid solution strengthening in the quaternary material system leads to a significant Vickers micro hardness increase compared to α-(Al_{1 − x},Cr_x)₂O₃ coatings deposited in the same PVD machine under corresponding process parameters. The α-(Al_{1 − x},Cr_x)_{2 + δ}(O_{1 − y},N_y)₃ thin films offer an additional restraint of the lattice by the incorporation of nitrogen and therefore higher Vickers micro hardness values are measured compared to the Al–Cr–O material system.     

Deposition of La1?x Sr x Fe1?y Co y O3?δ Coatings with Different Phase Compositions and Microstructures by Low-Pressure Plasma Spraying-Thin Film (LPPS-TF) Processes

Perovskite-type materials with the general chemical formula A_1?x A?? _x B_1?y B?? _y O_3??? have received considerable attention as candidates for oxygen separation membranes. Preparation of La_1?x Sr _x Fe_1?y Co _y O_3??? (LSFC) coatings by low-pressure plasma spraying-thin film processes using different plasma spray parameters is reported and discussed. Deposition with Ar-He plasma leads to formation of coatings containing a mixture of cubic LSFC perovskite, SrLaFeO₄, FeCo, and metal oxides. Coatings deposited at higher oxygen partial pressures by pumping oxygen into the vacuum chamber contain more than 85% perovskite and only a few percent Fe_3?x Co _x O₄, and/or CoO. The microstructures of the investigated LSFC coatings depend sensitively on the oxygen partial pressure, the substrate temperature, the plasma jet velocities, and the deposition rate. Coatings deposited with Ar-rich plasma, relatively low net torch power, and with higher plasma jet velocities are most promising for applications as oxygen permeation membranes.     

Surface characterization of Mo oxynitride films obtained by RF sputtering at various N2 ratios

Molybdenum oxynitride (MoN_xO_y) thin films were deposited on p-type Si(100) wafer by rf magnetron sputtering method at various nitrogen gas ratios. The surface characteristics of deposited thin films were investigated using scanning electron microscopy, atomic force microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. The thickness of films decreased down to 70 from 1000 nm and the roughness was varied with increasing N₂ gas ratio. The formation of MoN_xO_y was confirmed by existence of Mo species between Mo^δ+ and Mo⁵⁺ oxidation state and ON bond in XP spectra. At 0% of N₂ gas ratio, metallic simple cubic Mo structure was observed. As the N₂ gas ratio increased, Mo nitrate and Mo silicate phases were appeared.     

Effect of nitrogen content in amorphous SiCxNyOz thin films deposited by low temperature reactive magnetron co-sputtering technique

Amorphous silicon oxycarbonitride (SiC_xN_yO_z) films have been deposited on Si substrates by low temperature reactive magnetron co-sputtering of silicon and graphite targets in mixed Ar/N₂ atmosphere. Our studies are focused on the influence of nitrogen incorporation on deposition rate, film composition, film structure, chemical bonds, and electrical resistivity of SiC_xN_yO_z films investigated by profilometry, Rutherford Backscattering Spectrometry (RBS), X-ray diffraction (XRD), Raman spectroscopy, X-ray Photoelectron Spectroscopy (XPS), and four-point probe method. RBS results show that all samples contain significant amounts of oxygen (up to 16 at.%) which led to the formation of SiC_xN_yO_z. Further, XPS results show that most of this oxygen is located in the film surface. With the addition of N₂ gas in the plasma, the carbon, and nitrogen contents in the films increase. The increased carbon content is due to the contribution of chemically driven sputtering of the graphite target and the reduction of the sputtering rate of the silicon target owing to poisoning by nitrogen. Raman spectra suggest that the films contain amorphous phases and that the a-C clusters suffer a graphitization with increased N₂ gas flow rate. The XRD analysis confirmed the amorphous structure of these films. According to the XPS analysis, the increase in nitrogen content leads to an increase in SiN and CN bonds, decreasing the SiC, SiSi, and CC bonds. Finally, the films electrical resistivity depends mainly on the nitrogen content, which makes it possible to obtain semiconductor or insulator SiC_xN_yO_z films only by adjusting the N₂ concentration in the gas phase during the deposition process.     

High-temperature oxidation of titanium carbide in oxygen

The kinetics of titanium carbide oxidation in oxygen over the temperature range of 600–1200°C and oxygen pressure from 0.1 to 740 Torr have been studied with a vacuum microbalance. Layer-by-layer x-ray analysis, petrography, metallography, and gas chromatography have been used to analyze the oxidation products. A paralinear nature of the oxidation of material was established, and the rate constants of the process were calculated for the corresponding parabolic and linear portions of the kinetic curves. It was shown that a gaseous product, CO₂, formed, as well as a solid product, TiO₂ (rutile), both stoichiometric and nonstoichiometric. The lower oxides, Ti₃O₅, Ti₂O₃, TiO, were noted in the scale at temperatures from 700 to 800° and low oxygen pressures, their relative quantity rising with decreasing pressure. Based on x-ray analysis and microhardness measurements, it was concluded that titanium oxicarbides formed in the TiC, directly adjacent to the scale. A possible oxidation mechanism of titanium carbide is proposed.     

Influence of deposition conditions on mechanical and tribological properties of nanostructured TiN/CNx multilayer films

Nanostructured TiN/CN_x multilayer films were deposited onto Si (100) wafers and M42 high-speed-steel substrates using closed-filed unbalanced magnetron sputtering in which the deposition process was controlled by a closed loop optical emission monitor (OEM) to regulate the flow of N₂ gas. Multilayers with different carbon nitride (CN_x) layer thickness could be attained by varying the C target current (0.5 A to 2.0 A) during the deposition. It was found that the different bilayer thickness periods (i.e. the TiN layer thickness Λ_TiN was fixed at 3.0 nm while the CN_x layer thickness Λ_CNx was varied from 0.3 to 1.2 nm) significantly affected the mechanical and tribological properties of TiN/CN_x multilayer films. These multilayer films were characterized and analyzed by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), atomic force microscopy (AFM), Rockwell-C adhesion test, scratch test, pin-on-disc tribometer, and nanoindentation measurements. XPS analyses revealed that the chemical states, such as TiN, TiC, TiN_xO_y and TiO_2, existed in a TiN layer. Nanoindentation results showed that the hardness was highly dependent on the bilayer thickness. A maximum hardness of ~ 41.0 GPa was observed in a multilayer film at bilayer thickness Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm. All multilayer films exhibited extreme elasticity with elastic recoveries as high as 80% at 5 mN maximum load. The compressive stresses in the films (in a range of 1.5-3.0 GPa) were strongly related to their microstructure, which depended mainly on the incorporation of nitrogen in the films. By scratch and Rockwell-C adhesion tests, the multilayer films with smaller bilayer thicknesses (Λ_TiN = 3.0 nm, Λ_CNx = 0.3 and 0.6 nm) exhibited the best adhesion and cohesive strength. The critical load value obtained was as high as ~ 78 N for the films with Λ_TiN = 3.0 nm, Λ_CNx = 0.9 nm. The friction coefficient value for a multilayer at Λ_TiN = 3.0 nm and Λ_CNx = 0.9 nm was found to be low 0.11. These adhesive properties and wear performance are also discussed on the basis of microstructure, mechanical properties and tribochemical wear mechanisms.