Hot-wire Deposition Research Articles

Influence of printing parameters on the mechanical behavior of 3D-printed SS316L parts manufactured using laser hot wire directed energy deposition

Hybrid manufacturing combines the simultaneous benefits of additive manufacturing (complex geometries, part consolidation, and mass customization) with the advantages of subtractive manufacturing (superior surface finish and enhanced dimensional accuracies) by integrating a suite of complementary traditional processes into a base platform of additive manufacturing. The use of hybrid technology has grown in recent years given its capabilities on repairing metallic structures, producing parts with conformal cooling features, and manufacturing functionally graded products. These kinds of capabilities are of great interest to the medical implant, energy, automotive, maritime, and aerospace industry sectors, among many other fields. This work investigated the mechanical properties of stainless steel (SS) 316L as a function of different tool paths strategies using an integrated 5-axis CNC hybrid Mazak system with a laser hot wire deposition system (LHWDS). This study includes the evaluation of different printing parameters and their impact on the quality of the printed bead as well as the incorporation of a structure–property material relationship based on the mechanical performance of the manufactured coupons.

Highly-efficient additive manufacturing of Inconel 625 thin wall using hot-wire laser metal deposition: Process optimization, microstructure, and mechanical properties

Hot-wire-based laser metal deposition (HW-LMD) technique was used for additive manufacturing of Inconel 625 thin-walled parts. The desired process window was obtained through the Taguchi experiment design, and the defect-free Inconel 625 thin-walled structures were efficiently manufactured with a wire deposition rate of 1.72 kg/h. The microstructure, phase composition, microhardness, and tensile properties of the Inconel 625 thin walls were studied in detail. The results showed that the microstructure of the Inconel 625 thin wall was mainly composed of a large number of columnar dendrites with an average grains size of 12.5 μm, and the growth direction of the columnar dendrites was perpendicular to the substrate surface. γ-Ni was the base phase of the as-deposited Inconel 625 thin walls and irregularly shaped Laves precipitates were observed in the inter-dendritic region. The microhardness of the Inconel 625 thin wall over the build direction was homogenous and the average microhardness was 258 HV1, which was 35.7 % higher than that of the wrought alloy. The tensile strength of the as-deposited Inconel 625 thin walls exhibited anisotropy according to the relationships between stress loading direction and microstructural texture. The maximum tensile strength and elongation of the as-deposited Inconel 625 thin wall were respectively 825.91 MPa and 55.62 %, which were close to the wrought alloy 625. Meanwhile, through comparative analysis, it was found that the tensile properties of the Inconel 625 samples fabricated in this study were superior to samples produced using conventional arc additive manufacturing methods.

Multi sensor monitoring of the wire-melt pool interaction in hot-wire directed energy deposition using laser beam

This study investigates the combination of three sensors to improve in-process monitoring of the liquid bridge between the feedstock wire and melt pool in hot-wire Directed Energy Deposition using Laser Beam. The stability of the deposition process relies on the transfer of metal between the molten feedstock wire and melt pool. Therefore, monitoring the condition of the liquid bridge and the interaction between the feedstock wire and melt pool is crucial. By utilizing a laser-optics-integrated visible range optical spectrometer and electrical sensors measuring voltage and current, relevant process changes and indications of instabilities were detected. Combined information from the current sensor and the spectrometer provided a better understanding of the process and helped to identify deviations leading to unstable deposition modes.

Room-temperature deposited fluorine-doped tantalum pentoxide for stable organic solar cells

Earth-abundant transition metal oxides deposited at room temperature with low-cost methods suitable for large area manufacturing can offer advances in many fields of energy related devices. Here we report the room-temperature deposition of a fluorine-doped tantalum pentoxide using a home-made, low-cost hot-wire deposition system. This novel tantalum oxyfluoride material is super hydrophobic, ultra-transparent within the visible spectrum, and possesses adequate conductivity and suitable valence band and conduction band extrema for acting as efficient hole extraction and electron blocking layer in organic solar cells with the forward architecture. By inserting this material in the form of nanoparticles deposited on top of the commonly used as hole transport layer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate, higher efficiencies compared to the reference cells without the nanoparticles were demonstrated in solar cells based on blends of polymer donors with either a fullerene (where maximum achieved efficiency was improved from 6.07% to 7.90%) or a non-fullerene acceptor (reaching values of 13.48% compared to 11.32% of the reference cell). Moreover, significant improvement in device stability was achievd in unencapsulated devices continuously exposed in a humid environment for 500 h. This work demonstrates the unambiguous potential of well-designed metal oxide materials as charge transport and blocking interlayers and protective buffers in organic solar cells and beyond. Home-grown fluorine-doped tantalum pentoxide nanoparticles deposited on top of PEDOT:PSS hole transport layer results in around 19% improved power conversion efficiency and an improved stability in organic solar cells. • Room-temperature deposition of fluorine-doped tantalum pentoxide. • Improved hole extraction and electron blocking properties. • Ta 2 O 5 :F - an inorganic protective buffer layer. • A 19% improved efficiency in organic solar cells. • Improved stability of fullerene and non-fullerene acceptor.

Effects of laser remelting on microstructural characteristics of Ni-WC composite coatings produced by laser hot wire cladding

The work presented in this paper focused on the effects of laser remelting with varied laser energy densities from 800 J/mm to 1400 J/mm on the phase transformation and microstructural characteristics in the tungsten carbide nickel-based matrix composite (Ni-WC) tracks obtained by laser hot wire cladding. The microstructures of the as-deposited tracks fabricated by laser hot-wire deposition were mainly composed of spherical residual carbons, eutectic Ni/Ni3B, retained WC/W2C particles and the granular in situ W2C particles formed in the interdendritic regions of primary (Ni,Fe) dendrites. When the low laser energy densities of 800 J/mm and 1000 J/mm were applied, the dispersive W2C particles in the as-deposited tracks were dissolved, and the WC particles were successfully in situ synthesized and uniformly distributed in the remelted tracks. When the laser energy density was increased to 1200 J/mm, the feather-like M6C(Ni2W4C) carbides homogeneously precipitated in the remelted tracks. When the laser energy density was further increased to 1400 J/mm, the dissolution degree of the ex-situ WC/W2C particles was significantly increased, resulting in a remelted track with a relative low volume fraction of retained ceramic particles and a high dilution ratio of the base metal. In addition, the dendritic M6C(Fe3W3C) carbides were precipitated around the retained particles, and the eutectic M6C(Fe3W3C) carbides in the herringbone morphology were uniformly distributed in the matrix of the track remelted by a high laser energy density of 1400 J/mm. These experimental results confirmed that the homogenization of the in situ synthesized reinforcements in the tracks could be well realized by laser hot wire cladding and the subsequent laser remelting. The coatings remelted by the low energy densities (800 J/mm and 1000 J/mm) possessed higher wear resistance than that of the as-deposited coating, but the wear performance of the remelted coatings was decreased when the laser energy densities were increased to 1200 J/mm and 1400 J/mm.

Experimental investigation of hot-wire laser deposition for the additive manufacturing of titanium parts

Hot-wire laser welding is additive manufacturing (AM) technique that allows for the direct creation of complicated objects by melting layers of wire. This process is characterized by the use of hot-wire process, unification with the laser welding (LW) process in AM process. The empirical investigation of AM employing a hot-wire laser welding on a titanium alloy (grade 2) workpiece is presented in this research. There are three parameters in the hot-wire laser process namely wire current, welding speed, and wire feeding speed; this research examined porosities, microhardness, tensile stress, and residual stress. The filler metal used titanium AMS (American welding society) 4951F welding wire of grade 2 and measures 1.6 mm in diameter. Finally, the suitable hot wire laser welding parameters should be 0.183 cm s−1 for the welding speed, the wire current of 40 A, and the wire feeding speed of 1.00 m min−1 are 0.183 cm s−1 for welding speed, 40 A for wire current, and 1.00 m min−1 for wire feeding speed, which will give the average Vicker microhardness of 321.00–345.80 HV, the average tensile strength of 432.02 MPa (substrate); 670.30 MPa (horizontal direction), 497.39 MPa (vertical direction).

Empirical Model for the Description of Weld Seam Geometry in Coaxial Laser Hot-Wire Deposition Welding Processes with Different Steel Wires

Claddings are used to protect areas of components that are exposed to particular chemical, physical or tribological stresses. The aim when developing a cladding process is to achieve a cladding with low waviness in order to reduce the amount of machining required. Computational models and FEA simulations can be used to determine process parameters for claddings with low rework including a prediction of the height and width of a single weld seam aswell as the development of welding strategies. In this paper empirical models describing the geometry of single weld seams on a substrate manufactured with a coaxial laser hot-wire cladding process are investigated for three steel wire materials and different welding parameters. The coordinates of surface points of the weld seams were detected using a laser scanning microscope and post-processed by a self-created script. In order to describe the cross sectional shape of the weld seams, the parameters of parabolic, cosinusiodal or circular arc model functions are derived from the surface data using a fitting algorithm. For the tested wire materials, an effect of the wire material on the shape of the weld seam was not observed. The investigations also show that regardless of the varied welding parameter set or wire material, a circular model function appears to be the most suitable model shape for describing the cross sectional weld seam geometry in coaxial laser metal deposition with hot-wire. The regression residua using a circular arc model function ranged from 18.9 upmum to 34.6 upmum, which indicates a good approximation.

Control of wire melting behavior during laser hot wire deposition of aluminum alloy

Laser wire deposition (LWD) is a promising method with a great potential for the fabrication of large open-frame components. Using hot wire in such a process, referred to as laser hot wire deposition (LHWD) would improve the laser absorption and deposition rate. In this work, the LHWD process of aluminum-alloy wire was studied with particular attention to the wire transfer behaviors. The results show that the wire melting rate could still be effectively increased even for the low-resistivity aluminum wire. The preheating current has a great influence on the wire transfer dynamics. Analysis demonstrates that the key to maintaining stable wire melting and transfer is to control the wire tip temperature by matching the wire feed speed and preheating current under certain laser power. A model computing the dynamic preheating process was established to predict the wire tip temperature with or without resistance preheating. A criterion based on the predictions was proposed to determine the optimal match of wire feed speed and wire preheating current, and thereby provided a deeper understanding of LHWD process.

Insights into microstructural evolution and dissolution characteristics of reinforced particles in tungsten carbide‑nickel composite coatings prepared by laser hot-wire deposition

Tungsten carbide‑nickel (WC-Ni) composite coatings were firstly prepared on martensite stainless steel 2Cr13 by laser hot-wire deposition. The microstructural evolution and the dissolution characteristics of ceramic particles in the coatings had been systematically investigated. The results showed that the tungsten carbides' dissolution and microstructures in the coatings were close related to the dilution degree of the base metal. Apart form large retained particles, the coating with a lower dilution ratio (8.4%) was composed of Ni, Ni/Ni3B eutectics, and in-situ W2C particles. The W2C phase was preferentially dissolved while the WC was retained in W2C/WC eutectoid-structured particles, which exhibited the typical thermal damage patterns including the dissolution-diffusion and partially/completely fragmentation-dissolution-diffusion. The amount of M6C carbides was increased with the increment of dilution ratio (from 9.5% to 24%), and the ceramic particles suffered from more severe heat damage which mainly exhibited the characteristics of dissolution-diffusion-precipitation. Not only was the W2C phase was dissolved, the WC phase was also decomposed and reacted into M6C carbides. Due to the reinforcement of retained particles and the precipitated carbides, these coatings showed higher hardness and wear resistance which was about 1.9– 2.3 and 12.1– 26.9 times that of 2Cr13 substrate.

Hot-Wire Laser-Directed Energy Deposition: Process Characteristics and Benefits of Resistive Pre-Heating of the Feedstock Wire

This study investigates the influence of resistive pre-heating of the feedstock wire (here called hot-wire) on the stability of laser-directed energy deposition of Duplex stainless steel. Data acquired online during depositions as well as metallographic investigations revealed the process characteristic and its stability window. The online data, such as electrical signals in the pre-heating circuit and images captured from side-view of the process interaction zone gave insight on the metal transfer between the molten wire and the melt pool. The results show that the characteristics of the process, like laser-wire and wire-melt pool interaction, vary depending on the level of the wire pre-heating. In addition, application of two independent energy sources, laser beam and electrical power, allows fine-tuning of the heat input and increases penetration depth, with little influence on the height and width of the beads. This allows for better process stability as well as elimination of lack of fusion defects. Electrical signals measured in the hot-wire circuit indicate the process stability such that the resistive pre-heating can be used for in-process monitoring. The conclusion is that the resistive pre-heating gives additional means for controlling the stability and the heat input of the laser-directed energy deposition.

Enrichment of in-situ synthesized WC by partial dissolution of ex-situ eutectoid-structured WC/W2C particle in the coatings produced by laser hot-wire deposition

A novel additive manufacturing method for fabricating Ni/WC composite coatings by laser hot-wire deposition was proposed. Finely dispersed WC particles were successfully in-situ synthesized by partial dissolution of the ex-situ eutectoid-structured WC/W2C particles during laser deposition. Under the combination effect of the high-volume fraction of ex-situ particles and in-situ synthesized reinforcements, the coating hardness and wear resistance was improved to about 3.5 times and 45 times more than that of substrate.

Lithography-free and dopant-free back-contact silicon heterojunction solar cells with solution-processed TiO2 as the efficient electron selective layer

Lithography-free interdigitated back-contact silicon heterojunction (IBC-SHJ) solar cells with dopant-free metal oxides (TiO2 and MoOx) as the carriers selective transport layers were investigated. Spin-coating and hot-wire reactive-sublimation deposition together with low cost mask technology were used to fabricate the solar cells. Insertion of a SiOx layer with the thickness of about 2.4 nm between the intrinsic amorphous Si (a-Si:H(i)) passivation layer and the spin-coated TiO2 layer greatly improves the solar cell performance due to the enhanced field-effect passivation of the a-Si:H(i)/SiOx/TiO2 layer stack. Efficiency up to 20.24% was achieved on the lithography-free and dopant-free IBC-SHJ devices with a-Si:H(i)/SiOx/TiO2 layer stack as the electron selective transport layer, a-Si:H(i)/MoOx as the hole selective transport layer, and WOx as the antireflection layer. The novel IBC-SHJ solar cells show significant advantages in simplification of the technology and process compared with the IBC-SHJ devices whose back surface pattering and carrier selective layers relied on photolithography and plasma enhanced chemical vapor deposition (PECVD).

Comprehensive modeling of transport phenomena in laser hot-wire deposition process

Transport phenomena in the molten pool and heat affected zone during the laser hot-wire deposition process are intrinsically complex. These phenomena involve multi-phase flows on the millimeter scale, including surface tension and capillary effects at the gas–liquid interface, solid–liquid phase transition, heat input from the laser beam source, and mass addition from the filler wire. Thus, a comprehensive multi-phase model was proposed in this study, which elucidates the evolution of the gas–liquid–solid interfaces during the laser hot-wire deposition process. A coupled level-set and volume-of-fluid approach was adopted to track the motion of the free surface with high resolution while ensuring that mass conservation was not violated. The mass addition from the preheated filler wire was modeled as the source terms in the continuity and energy equations. The simulation results include the geometries of the molten pool and clad layer, Marangoni outward flow effect and temperature evolution during the deposition. The multi-phase model was validated based on the geometries of the fusion zone and clad layer determined from laser conduction welding and laser hot-wire deposition experiments. The mechanism of cladding formation (specifically the microstructural and microhardness gradients in the deposited FV520B maraging steel) was analyzed based on the temperature profile of various phase transition regions in the heat affected zone.

Characteristics of microstructure and stresses and their effects on interfacial fracture behavior for laser-deposited maraging steel

Laser cladding is one of the most attractive ways to repair or remanufacture high-added-value engineering components. The present paper describes the effect of microstructure and residual stresses on the interfacial fracture behavior of laser-deposited maraging steel. The multi-layer overlapped cladding material was deposited on maraging steel substrates using laser hot-wire deposition. Residual stress profile was measured by X-ray diffraction. Temperature evolution and the induced phase transformation during the process were investigated to reveal the generation mechanism of residual stresses. A novel testing method was developed to analyze the interfacial fracture behavior and evaluate the bonding strength with specially designed T-shaped samples. The compressive stresses derived from martensitic expansion was presented in the clad layer, and tensile stresses in the heat affected zone up to a depth of 4mm, which was caused by thermal shrinkage. Both the solidification micro-voids and steep stress gradient appearing in the interface contributed to the propagation of interfacial crack that will critically affect the mechanical properties of laser deposited material.

Competitive failure analysis on tensile fracture of laser-deposited material for martensitic stainless steel

Sufficient mechanical properties of deposited materials are needed in remanufacturing applications to guarantee the functionality and reliability of repaired parts. The present paper described the tensile fracture behavior of laser-deposited FV520B martensitic stainless steel comprehensively based on evolution of the microstructure and mechanical property. The samples were fabricated by laser hot-wire deposition. The fracture behavior of the deposited samples was characterized using a specially designed uniaxial tension testing approach and investigated on the grain size, microhardness profile, residual stresses and precipitate distribution. The results show that the tensile fracture occurred at the position with high fluctuating microhardness caused by the multi-layer laser heating. Three tensile fracture patterns of deposited material were found: interfacial fracture, heat affected zone (HAZ) fracture and HAZ/interface hybrid fracture. They result from the competitive failure between microvoid coalescence in the heat affected zone and interfacial cracking in the clad layer/HAZ interface. Grain refinement and dissolution of precipitates occurred in heat affected zone, leading to a decrease of strength and increase of toughness.

Performance enhancement of micro-supercapacitor by coating of graphene on silicon nanowires at room temperature

Fabrication of high performance micro-supercapacitor (μ-SC) based on Silicon nanowires (SiNWs) at low temperatures by simple, effective and a scalable technique is always desired. In this regard, the performance of the μ-SC was greatly improved by employing a novel architecture developed by coating SiNWs with Graphene (rGO) in the present work. This coating of Graphene was deposited by an easy and efficient technique, Electrophoretic Deposition (EPD), at the room temperature with no intricate steps. These rGO coated SiNWs electrodes show as much as four times larger capacitance (240 μF/cm2) than the bare SiNWs (60 μF/cm2). Moreover, the key advantage of the architecture is that both rGO and SiNWs structurally complement each other enhancing the electrode performance - EPD deposited rGO fills the empty space between SiNWs by making a bridge type structure, increasing the surface area of the electrodes whereas SiNWs prevent restacking and aggregation of the rGO nano-sheets and also provide support to rGO nano-sheets to stand vertically over the substrate. One more notable bonus of using EPD technique is that the wires are selectively coated. SiNWs were synthesized at a temperature of 320 °C by the Hot-wire assisted SiNW growth technique and deposition of Graphene oxide (GO) and its reduction into reduced Graphene oxide (rGO) was carried out at the room temperature. The results suggest that rGO coated SiNWs could be a promising candidate as an electrode for on-chip integrable μ-SC application.

Experimental study and modeling of H13 steel deposition using laser hot-wire additive manufacturing

The laser hot-wire (LHW) process has the potential to deposit material at high rates using low laser power. An LHW experiment was designed to be able to deposit material at the rate of 3.46kg per hour with less than 10kW of laser power. Four thermocouples were built into the substrate to record the temperature variation during the deposition. The results show that temperature fluctuates in a periodic manner with the deposition layer by layer. Simultaneously, the distortion of the substrate was measured. The substrate is distorted, and the maximum distortion increases gradually during deposition.The equivalent heat conduction coefficient for heat convection in the molten pool is discussed. It becomes apparent that the heat convection of flowing molten metal is 3–5 times that of molten metal at rest. The absorptivity of laser power was determined by comparison between the simulation and a one-pass cladding experiment. The absorptivity of laser power is approximately 15% in this experiment.Numerical simulation of LHW additive manufacturing was conducted to obtain the temperature, stress and strain fields, and the distortion. The outstanding features for numerical simulation are additive geometry and numerous analysis steps. The INP files of ABAQUS are compiled in a Matlab program because of the considerable number of steps and element definitions. Temperature variation and substrate distortion are both measured to validate the FEA model. The verification result indicates that the LHW model is feasible and accurate.The maximum residual stress is located in the junction between the deposit and substrate when the deposition is finished. This junction area becomes the most likely crack position. Deposited material undergoes complicated thermal cycles during the LHW process. Temperature variation determines the phase transformation. The microstructure change of the heat affected zone was analyzed on the basis of computational temperature variation. Such interpretation can effectively explain softened area in the heat affected zone of the substrate. A numerical computation method is used to map the processing window of stable hot-wire deposition. It is shown that the stable deposition has top and bottom limitations under a certain current intensity and wire feed speed.

Degradation of a tantalum filament during the hot-wire CVD of silicon nitride thin films

Electron backscatter diffraction revealed that during the hot-wire deposition of silicon nitride, a tantalum filament partially transformed to some of its nitrides and silicides. The deposition of an encapsulating silicon nitride layer occurred at the cooler filament ends. Time-of-flight secondary ion mass spectroscopy disclosed the presence of hydrogen, nitrogen and silicon containing ions within the aged filament bulk. Hardness measurements revealed that the recrystallized tantalum core experienced significant hardening, whereas the silicides and nitrides were harder but more brittle. Crack growth, porosity and the different thermal expansion amongst the various phases are all enhanced at the hotter centre regions, which resulted in failure at these areas.

A system for measuring complex dielectric properties of thin films at submillimeter wavelengths using an open hemispherical cavity and a vector network analyzer

Quasi-optical (QO) methods of dielectric spectroscopy are well established in the millimeter and submillimeter frequency bands. These methods exploit standing wave structure in the sample produced by a transmitted Gaussian beam to achieve accurate, low-noise measurement of the complex permittivity of the sample [e.g., J. A. Scales and M. Batzle, Appl. Phys. Lett. 88, 062906 (2006); R. N. Clarke and C. B. Rosenberg, J. Phys. E 15, 9 (1982); T. M. Hirovnen, P. Vainikainen, A. Lozowski, and A. V. Raisanen, IEEE Trans. Instrum. Meas. 45, 780 (1996)]. In effect the sample itself becomes a low-Q cavity. On the other hand, for optically thin samples (films of thickness much less than a wavelength) or extremely low loss samples (loss tangents below 10(-5)) the QO approach tends to break down due to loss of signal. In such a case it is useful to put the sample in a high-Q cavity and measure the perturbation of the cavity modes. Provided that the average mode frequency divided by the shift in mode frequency is less than the Q (quality factor) of the mode, then the perturbation should be resolvable. Cavity perturbation techniques are not new, but there are technological difficulties in working in the millimeter/submillimeter wave region. In this paper we will show applications of cavity perturbation to the dielectric characterization of semi-conductor thin films of the type used in the manufacture of photovoltaics in the 100 and 350 GHz range. We measured the complex optical constants of hot-wire chemical deposition grown 1-μm thick amorphous silicon (a-Si:H) film on borosilicate glass substrate. The real part of the refractive index and dielectric constant of the glass-substrate varies from frequency-independent to linearly frequency-dependent. We also see power-law behavior of the frequency-dependent optical conductivity from 316 GHz (9.48 cm(-1)) down to 104 GHz (3.12 cm(-1)).

Deposition of undoped and H doped WOx (x ≤ 3) films in a hot-wire atomic layer deposition system without the use of tungsten precursors

A hot-wire atomic layer deposition system is used for the synthesis of tungsten oxide films with various stoichiometries, undoped and hydrogen doped. For this synthesis, no precursors are used and only a W wire is heated at 660°C at a base pressure of 0,1Torr set by the flow of various gases (O2, N2, H2) or gas mixtures (N2–O2 10% in H2, forming gas, FG) and the pulsed injection of O2 or H2. Four classes of hot-wire tungsten oxide films were synthesized: i) stoichiometric (hwWO3), ii) oxygen deficient (sub-stoichiometric, hwWOx with x<3), iii) stoichiometric and hydrogen doped (hwWO3:H) and iv) sub-stoichiometric and hydrogen doped (hwWOx:H). During deposition, due to the pulsed injection of O2, the W wire re-oxidizes creating continuously WO3 vapors and so films deposited do not suffer by thickness limitations. Moreover, they are highly porous. Each one of the four classes of the deposited tungsten oxides exhibits its own optical properties, which indicates that each class has its own electronic structure. So, hwWO3 films were semiconducting, exhibiting a band gap near 3eV. Sub-stoichiometric hwWOx deposited with up to 2 injections of O2 were semi-metalic, exhibiting some features of the electronic structure of the pure metal, while further injection of O2 leads to stoichiometric films. The injection of H2 during deposition leads to the formation of atomic H, which dopes the films. Depositions carried out with base pressure set by O2 or N2 and with injection of H2, lead to the formation of hwWO3:H films that exhibit optical properties similar to Na lightly-doped WO3 films. In base pressure set by H2 or FG and with H2 injection, substoichiometric, hydrogen-doped films were obtained, exhibiting optical properties corresponding to a metal substantially different than W. Fourier transform infrared spectroscopy and spectroscopic ellipsometry measurements indicated that the hwWOx films grown in the presence of hydrogen in the deposition ambience contain H bonded with the O ions. When these films are doped with hydrogen, protons are bonded not only with the oxygen but also with the tungsten ions.