Film characterization of titanium oxide films prepared by high-power impulse magnetron sputtering

Surface modification with a high power glow discharge is an emerging technology that can be used to improve the surface characteristics. Titanium oxide films are prepared using a high-power impulse magnetron sputtering (HPPS-M) glow discharge with a current density of 2 A/cm² and a power density of 1 kW/cm². Observing optical emission spectrum confirms that singly-ionized titanium ions are produced in the plasma. Ions are extracted from the HIPIMS glow plasma by a substrate placed near the plasma source. It is found that the substrate is immersed in the HPPS-M glow plasma. The film is deposited by a HPPS-M, and the results are compared to those of magnetron sputtering operated by a stationary dc power source. The deposition rate is lower by HPPS-M than that by DC-MS. The main structure of the films is rutile, however an anatase structure is also observed. The mixed structure is obtained at an oxygen rate as low as 5%. Anatase structure is not significantly observed in HPPS-M compared to that in DC-MS. The intensity of the XRD profiles becomes weaker with increasing the substrate position due to the collisions of metal species with the plasma species and the background gas particles. The deposition rate of the prepared titanium oxide film is significantly influenced by the production rate of titanium ions, distance of the substrate, and the gas mixture ratio. With regard to the effect of the gas ratio, the difference in the deposition rate is probably based on the argon ion density available to sputter titanium atoms that would eventually contribute to the titanium oxide film deposition.     

Effects of reactive gas addition on ionization of metal atoms in droplet-free metal ion sources

This paper reports on influences of reactive oxygen (O₂) or nitrogen (N₂) addition on ionization characteristics of sputtered titanium (Ti) atoms in an argon (Ar)-based novel droplet-free metal ion sources. Although Ti atoms had a pressure dependence of ionization characteristics similar to copper ones in a pure Ar discharge, the ionization characteristics of Ti atoms were affected by adding reactive N₂ and O₂ gases into the Ar plasma. Especially, the reactive gas addition significantly reduced fluxes of Ti atoms and Ti⁺ ions probably due to target-poisoning effect caused by chemical reactivity of Ti. Even adding the reactive gases, the source will still work as a droplet-free metal ion source since the ionization fraction of Ti atoms reached over ∼ 90%. Optimization of discharge conditions and reactive gas provision will be necessary from a metal ion process point of view.     

Formation of oxynitride layers on titanium alloys by gas diffusion treatment

Titanium alloys were oxynitrided in controlled nitrogen-oxygen gas atmospheres between 650 °C and 950 °C for 5 h to 10 h with two different techniques of gas diffusion treatment. One technique was performed in an oxygen-containing (oxygen amount ≥ 0.4 %) nitrogen environment. The other technique was performed in a deoxygenated (oxygen amount < 0.01 % to 0.0005 %) nitrogen environment with subsequent cooling in an oxygen-containing nitrogen environment (with an oxygen pressure of 1 Pa). The surface microhardness of oxynitrided samples increased due to the strengthening effect of titanium oxynitrides (TiN_xO_y). The maximum microhardness of the titanium oxynitrides was obtained with a near-equiatomic composition of nitrogen and oxygen in TiN_xO_y under optimal oxygen partial pressure and temperature-time conditions.     

Reactive sputtering of TiOxNy coatings by the reactive gas pulsing process: Part III: The particular case of exponential pulses

A new and original method, namely the reactive gas pulsing process (RGPP), was optimised to deposit titanium oxynitride thin films by dc reactive magnetron sputtering. Pure titanium target was sputtered in a reactive atmosphere composed of argon, nitrogen and oxygen. Argon and nitrogen gases were injected with a constant mass flow rate whereas oxygen was periodically supplied into the sputtering chamber. An exponential signal was generated to the oxygen mass flow meter with a constant pulsing period T = 45 s. During the injection time of the oxygen gas (t_ON time), the exponential shape was systematically modified in order to better control the amount of reactive gas introduced. Duty cycle was also changed and led to an extended alternation of the process between the nitrided and oxidised sputtering mode. Speed of poisoning of the titanium target surface by oxygen was calculated assuming real time measurements of the target potential. It was clearly shown that duty cycle and shape of the exponential signals used during oxygen injection are fundamental pulsing parameters. Both parameters must be taken into account in order to adjust and improve the monitoring of RGPP system for the deposition of titanium oxynitride coatings. Such approach prevents the full poisoning of the target surface by oxygen or nitrogen, and consequently, a wide range of oxynitride compounds can be easily reached.     

Nitrogen plasma functionalization of low density polyethylene

Low density polyethylene (LDPE) films have been treated with different nitrogen containing plasmas with the purpose of incorporating nitrogen functional groups on its surface and analyzing the changes experienced in their surface tension. Effects of a dielectric barrier discharge (DBD) at atmospheric pressure and a microwave discharge (MW) at reduced pressure are compared with those obtained by using an atom source supplied with N₂ and mixtures Ar + NH₃ as plasma gas. X-ray photoelectron spectroscopy (XPS) analysis has provided information about the chemical surface changes whereas the surface topography of the treated samples has been examined by atomic force microscopy (AFM). Non-destructive depth profiles of oxygen and carbon have been obtained for the treated and one month aged samples by means of the non-destructive Tougaard's method of XPS background analysis. Generally, an oxygen enrichment of the deeper region of treated LDPE surfaces has been observed. Chemical derivatization of the treated samples has shown that a DBD plasma with a mixture of Ar + NH₃ was the most efficient treatment for nitrogen and amine group functionalization. It is argued that the high concentration of NH* species in this plasma is the most important factor in enhancing the nitrogen functionalization of this polymer. It has been also found that the observed increase in hydrophilicity and surface tension cannot be attributed to the anchored nitrogen functional groups formed on plasma treated LDPE. Differences in the plasma activation behaviour of LDPE and that of other polymers subjected to similar treatments are stressed.     

Anodic plasma electrolytic nitrocarburising of VT22 titanium alloy in carbamide and ammonium chloride electrolyte

The structure of alpha- and beta-titanium alloy VT22, its microhardness, surface roughness, wear and corrosion resistance after anodic plasma electrolytic nitrocarburising in an electrolyte containing carbamide and ammonium chloride were investigated. An X-ray diffractometer and a scanning electron microscope were used to characterize the phase composition and structure of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a ball-on-disc tribometer under lubricated testing conditions. The effect of processing temperature on corrosion resistance of the plasma electrolytic nitrocarburising samples was examined by means of potentiodynamic polarization in Ringer’s solution. It was shown that the anodic nitrocarburising provides saturation of the titanium alloy with oxygen, nitrogen and carbon and the formation of TiO₂ with a rutile structure and a nitrogen/carbon solid solution in titanium. The anodic plasma electrolytic nitrocarburising at all treatment temperatures diminishes the wear rate of the titanium alloy samples and the surface roughness. Friction coefficient of treated samples can be reduced by 4.7 times. The anodic nitrocarburising results in an enhanced corrosion resistance since the corrosion potential increases by an order of magnitude.     

Producing titanium powder by continuous vapor-phase reduction

One of the goals of the U.S. Department of Energy’s Albany Research Center is to reduce the cost of titanium parts by developing a continuous titanium process. In this work, titanium powder was produced by feeding liquid TiCl₄, with argon as a carrier gas, and magnesium wire into a shaft reactor at 1,000°C. The magnesium and TiCl₄ vaporized and reacted to produce a mixture of titanium, MgCl₂, and magnesium powder. Ti/Mg/MgCl₂ powder was removed from the argon gas stream by an electrostatic precipitator, and the titanium powder was separated from the magnesium and MgCl₂ by either vacuum distillation or leaching. Vacuum distillation produced sintered titanium powder with lower oxygen levels, but unacceptably high levels of magnesium and chlorine. Leached powder was spherical and free-flowing with low levels of magnesium and chlorine, but the oxygen content was no lower than 0.82%. The high oxygen content of the leached powder is caused by surface oxidation of the submicrometer titanium powder. For more information, contact S.J. Gerdemann, Albany Research Center-Department of Energy, 1450 Queen Avenue S.W., Albany, Oregon 97321-2198; (541) 967-5964; fax (541) 967-5868; e-mail gerdeman@alrc.doe.gov.     

Plasma electrolytic treatment of VT22 titanium alloy in electrolytes with carbon-containing compounds

The study investigates the influence of electrolyte compositions containing acetone, glycerol, sucrose, ethylene glycol and ammonium chloride on the properties of VT22 titanium alloy in the process of the anode plasma electrolytic treatment (PET). An X-ray diffractometer and a scanning electron microscopy (SEM) were used to characterize the phase composition and morphology of the modified surface. Tribological properties of the treated titanium alloy were evaluated using a pin-on-disc tribometer under lubricated testing conditions. The effect of electrolyte compositions on the corrosion resistance of the PET samples was examined by means of potentiodynamic polarization in a solution of Na₂SO₄. It was assumed that the PET provides the saturation of titanium alloy with oxygen and carbon and formation TiO₂ with a rutile structure and carbon solid solution in titanium. The anode PET in an electrolyte with glycerol results in an increase in microhardness to 540 HV and a decrease in the corrosion current density by 2.4 times. The friction coefficient of the treated samples in anelectrolyte with sucrose can be reduced 7.5 times. The anode PET in all electrolytes enables todiminish the wear rate of the titanium alloy samples by 3 orders of magnitude and the surface roughness, too, due to the anode dissolution of titanium.     

Etching mechanisms during plasma jet machining of silicon carbide

The material removal of the C- and Si-face of 4H-SiC using a 13.56 MHz RF excited plasma jet source at atmospheric pressure using helium as feed gas and CF₄ as reactive gas has been investigated. Additionally O₂ is provided together with the peripherally injected N₂ shielding gas and it is shown that a decrease of the etching rate with an increase of the O₂ gas flow occurs.Furthermore, etching experiments under sample heating have been carried out for different [CF₄]/[O₂] mixtures to obtain the activation energy of fluorine and oxygen with the surface. A minimum in the etching rate at a temperature of approximately 150 °C has been found. Therefore XPS and SEM analyses have been carried out for surfaces etched at sample temperatures of 25 °C, 150 °C and 400 °C showing an elevated fraction of silicon oxides and film thickness at 150 °C.     

Investigation of novel low temperature atmospheric pressure plasma system for deposition photo-catalytic TiO2 thin film

The purpose of this study was to develop a novel low-temperature atmospheric pressure (AP) plasma system and to use the system to deposit photo-catalytic titanium dioxide (TiO₂) thin film. In this study, titanium tetraisopropoxide (TTIP) was used as a precursor for TiO₂ thin film deposition. The precursor was vaporized by ultrasonic oscillator and introduced into an atmospheric plasma system by argon (Ar) carrier gas. The main plasma working gas was Ar mixed with O₂. Microstructure evolutions of TiO₂ thin film were investigated by low-angle grazing-incidence x-ray diffraction (GID), x-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), and transmission electron microscope (TEM). The photo-catalytic properties were determined by contact angle and methylene orange de-coloration testing. In this study, the substrate temperature, the precursor flow rate and the O₂ flow rate were varied. TiO₂ thin film grown at a temperature of 350 °C, with precursor and O₂ flow rates of 20 sccm and 200 sccm, respectively, revealed the optimum photo-catalytic properties. It was also found that titanium dioxide thin films synthesized by the AP plasma method possess reasonable photo-catalytic characteristics like other deposition techniques.     

Preparation of Electrode Based on Plasma Modification and Its Electrochemical Application

The carbon nanotubes-manganese oxide (CNTs/MnO₂) composite raw material was synthesized through chemical precipitation, and then was modified by the induction-coupled oxygen plasma source to get the improved materials. The influences of the modification effect on the morphology and constitution of the electrode material were investigated with SEM and FT-IR. An oxygen plasma exposure in the coupled plasma source for 20 min at 450 W and 30 Pa leads to a specific capacitance value of 260.2 F/g, i.e., 1.64 times larger than the initial electrode. Its ESR is 0.35 Ω, which decreases by 70.8%. The composite material modified by the oxygen plasma is an excellent electrode material for the supercapacitor that can be used in the electromagnetic launch system and other fields that require high power and energy density.     

低气压等离子喷涂TiO2涂层结构的研究

本研究分析了在低气压等离子喷涂条件下,TiO_2涂层的结构受等离子弧喷涂过程中氧分解量所影响。氧分解量很大程度上依赖于离子气中氢流量的大小,此外喷涂室压力也有一定影响。而等离子弧功率和喷涂距离对TiO_2涂层的氧分解量没有多大影响。在离子气中氢流量不变的条件下,涂层中Ti_3O_5量随喷涂室压力(从100×133.322Pa至400×133.322Pa)增加而增加。     

Excimer laser surface alloying of titanium with nickel and palladium for increased corrosion resistance

In the electron beam treatment of flue gases, titanium foil is employed as an electron-transparent window. Due to its degradation in the flue gas environment and eventual failure, extension of the life of the window is being sought. Previous studies have indicated significant improvements of corrosion resistance from surface alloying with nickel or palladium, using high intensity pulsed plasma beams, but restricted size of vacuum systems prevents treatment of large surfaces. In the present work, an excimer laser was employed to surface alloy titanium foil with nickel or palladium, using fluences in the range 0.4-1.1 J cm⁻² and either nitrogen or argon as the cover gas. The resultant surfaces provided high resistance to corrosion in 0.1 M H₂SO₄ solution at 80 °C that simulates, under accelerated conditions, the degradation of titanium by the flue gas. The improved behaviour is associated with the corrosion potential being shifted to the region of passivity. Treatments at increased fluences reduced losses of nickel and increased alloying of palladium during processing of the foils. Palladium was largely retained during the subsequent immersion tests, contrasting with the depletion of nickel by corrosion that limits the durability of the treated foils. The corrosion rates of the optimum palladium-alloyed surfaces were about two orders of magnitude lower than that of untreated titanium.     

Nitride formation in synthesis of titanium aluminide matrix composite coatings by reactive RF plasma spraying

This paper presents an in situ process to form intermetallic matrix composite coatings by reactive radio frequency (RF) plasma spraying with premixed elemental powder. The typical splat morphology of impinged titanium droplets on a stainless steel substrate is a disk with an outer peripheral fringe. If the supplied titanium powder size becomes finer or the nitrogen partial pressure in the plasma gas increases, splats containing prominent asperities with a smaller flattening ratio appear along with the plain disk type. An increase in nitrogen content is detected in all the splats sprayed with finer titanium powder and/or higher nitrogen partial pressure. The splats containing prominent asperities, which correspond to TiN, are twice as high in nitrogen content than the plain disk type. Aluminum splats are also classified into two categories: a disk type with an irregular outer periphery and a seminodular type. Oxygen exists on the splat surfaces, on which there are nitrogen concentrated areas corresponding to AlN. Consequently, the nitride formation proceeds on titanium and aluminum droplets during the flight as well as on the substrate. If the substrate temperature is higher than 873 K just before spraying with premixed titanium and aluminum powder, the formation of TiAl and Ti₂AlN proceeds on the substrate because of negligible mutual collisions during the flight. Titanium aluminide matrix in situ composites sprayed with premixed titanium and aluminum powder contain more nitrides than those sprayed with TiAl compound powder, because of the higher nitrogen absorption in titanium and aluminum droplets that results in an exothermic reaction.     

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.     

Effect of Oxidation and SiO<Subscript>2</Subscript> Coating on the Bonding Strength of Ti-Porcelain

Investigations on the effect of oxidation on titanium-ceramic adhesion were performed. Cast pure titanium was subjected to surface modification by preoxidation and introduction of an intermediate layer of SiO₂ by sol-gel process. Specimens were characterized by TG-DSC, XRD, and SEM/EDS. The adhesion between the titanium and porcelain was evaluated by three-point flexure bond test. Failure of the titanium-porcelain with preoxidation treatment predominantly occurred at the titanium-oxide interface. Preoxidation treatment did not affect the fracture mode of the titanium-ceramic system and did not increase the bonding strength of Ti-porcelain. The SEM results revealed the existence of microcracks on the SiO₂ coating surface oxidized at 800 °C in an air furnace. During the porcelain fusion, minute amounts of oxygen were able to penetrate the cracks and caused localized oxidation of the Ti-substrate. Failure of the titanium-porcelain with SiO₂ coating predominantly occurred at the SiO₂ layer. The SiO₂ coating served as an effective oxygen diffusion barrier and improved the mechanical and chemical bonding between porcelain and titanium.     

Spraying TiN by a Combined laser and low-pressure plasma spray system

The formation of a TiN-Ti composite coating by thermal spraying of titanium powder with laser processing of the subsequent coating in a low-pressure N₂ atmosphere was examined. A low-pressure plasma spray system was used in combination with a CO₂ laser. First, the coating was plasma sprayed onto a mild steel substrate using a N₂ plasma jet and titanium powder in a controlled low-pressure N2 atmosphere. The coating was then irradiated with a CO₂ laser beam in a N₂ atmosphere, and the coating was heated with a N₂ plasma jet. The amount of TiN formed in the coating was characterized by X-ray diffraction analysis. The influence of plasma spraying conditions such as plasma power, flow of plasma operating gases, chamber pressure, and laser irradiating conditions on the formation of TiN was investigated. The effect of TiN formation in the titanium coating on Vickers hardness of the coatings was examined. It was evident that coating hardness increased with an increase in TiN content in the coating and that a TiN-Ti composite coating with a hardness of more than 1200 H V can be obtained with the use of laser irradiation processing.     

Initial stages of plasma electrolytic oxidation of titanium

The initial stages of oxide growth on titanium are examined in a recently developed commercial alkaline pyrophosphate/aluminate electrolyte of interest for plasma electrolytic oxidation of light metal alloys. Constant current anodizing was employed, with resultant films examined by scanning and transmission electron microscopies and Rutherford backscattering spectroscopy. The initial film is relatively uniform and composed of TiO₂, with low concentrations of aluminium and phosphorus species incorporated from the electrolyte. With increase in voltage the film breaks down locally, and regions of original and modified film develop simultaneously, with the latter occupying more of the surface as the voltage rises. Porous regions due to dielectric breakdown also become increasingly evident. At 240 V, sparking commences, and the surface reveals extensive, relatively uniform porosity, with the coating now containing much enhanced concentrations of aluminium and phosphorus species compared with the coating at lower voltages. The films develop at low efficiency due to generation of oxygen. The oxygen is produced within the original film material and at sites of dielectric breakdown. The former type of film develops a two-layered morphology, with an outer layer of amorphous TiO₂ and an inner layer with numerous fine and course cavities. The cavities are due to the generation of oxygen that may be associated with the formation of anatase in the inner layer.     

钛合金在Ar与O2气氛中的燃烧行为

以ＤＣＳＢ法点燃钛合金,研究钛合金在Ａｒ气与Ｏ２气氛中的燃烧行为,分析常规钛合金一旦着火应采用什么方法灭火。研究结果表明：钛可在富氧环境中燃烧;钛的燃烧可用Ａｒ气灭火;钛在富氧环境中燃烧的产物及燃烧产物与基体的界面均不致密,燃烧可持续进行。     

Synthesis of As-Cast Ti-Al-V Alloy from Titanium-Rich Material by Thermite Reduction

We present a novel methodology for preparing as-cast Ti-Al-V alloy directly from titanium-rich material through a thermite reduction. The new method is shown to be feasible through a thermodynamics and dynamics analysis. The as-cast Ti-Al-V alloys synthesized from titanium dioxide, rutile, and high-titanium slag were analyzed by an x-ray diffractometer, a scanning electron microscope, an inductively coupled plasma emission spectrometer, and an oxygen/nitrogen/hydrogen analyzer. The results indicate that the alloy is composed of a Ti-Al-V matrix and Al₂O₃ inclusions. The Al and V contents in the matrix are close to the mass ratio of Ti-6Al-4V (Al: 5.5–6.8 wt.%, V: 3.5–4.5 wt.%). The Si and Fe in the alloys synthesized from rutile and high-titanium slag can be used as alloying elements in low-cost titanium alloys. The present method is expected to be useful for preparing Ti-Al-V alloys at a low production cost.