The pack-boronizing of pure vanadium under a controlled atmosphere

Pack boronizing of pure vanadium was performed at 1100 °C for 4, 8, 12 and 16 h under a controlled atmosphere. Characterization of the boride formed on the surface of pure vanadium was carried out by metallographic techniques, profilometry, SEM-EDS, XRD and microhardness measurements. The metallographic studies revealed that a single boride layer with dense, compact and relatively smooth morphology was formed on the surface of pure vanadium. The interface between boride layer and base metal was wavy in nature. The formation of only the VB₂ phase on pure vanadium was confirmed by surface and cross-sectional XRD analysis. The microhardness of the boride layer was approximately 3700 HV for all boriding times. Fracture toughness of the boride layer was evaluated using Vickers indentation, giving the value of 2.1-5.9 and 1.7-3.4 MPa m^1/2 for Palmqvist and median/radial approaches, respectively. Thickness of the boride layer increased almost parabolically from about 23 to 50 μm with boriding time. Surface roughness of the coating was relatively increased from approximately 0.58 to 2.25 μm by boriding duration.     

The effect of surface nanocrystallization on plasma nitriding behaviour of AISI 4140 steel

A plastic deformation surface layer with nanocrystalline grains was produced on AISI 4140 steel by means of surface mechanical attrition treatment (SMAT). Plasma nitriding of SMAT and un-SMAT AISI 4140 steel was carried out by a low-frequency pulse excited plasma unit. A series of nitriding experiments has been conducted at temperatures ranging from 380 to 500 °C for 8 h in an NH₃ gas. The samples were characterized using X-ray diffraction, scanning electron microscopy, optical microscopy and Vickers microhardness tester. The results showed that a much thicker compound layer with higher hardness was obtained for the SMAT samples when compared with un-SMAT samples after nitriding at the low temperature. In particular, plasma nitriding SMAT AISI 4140 steel at 380 °C for 8 h can produced a compound layer of 2.5 μm thickness with very high hardness on the surface, which is similar to un-SMAT samples were plasma nitrided at approximately 430 °C within the same time.     

Cr-Ni-Mo-Co surface alloying layer formed by plasma surface alloying in pure iron

Using double glow plasma alloying technique, a multi-elements alloyed layer containing elements of Cr, Ni, Mo and Co was formed on the surface of pure iron. After undergoing suitable aging treatment followed solid solution treatment, the formed alloying layer keeps a good combination of corrosion resistance and wear resistance. The relationship between the process parameters of heat treatments and the properties of the formed Cr-Ni-Mo-Co alloying layer, such as the chemical composition, hardness, corrosion resistance and wear resistance, was investigated in this study. It was revealed that the formed alloying layer exhibits a better behavior than that of 304 stainless steel and pure iron by employing a suitable heat treatment system. The temperature employed in solid solution treatment is 1453 K (1180 °C) followed by water quenching and the aging temperature is 813 K (540 °C) followed by water cooling.     

Effect of substrate temperature on the surface and interface oxidation of NiTi thin films

NiTi shape memory alloy thin films are deposited on pure Cu substrate at substrate ambient temperatures of 300 °C and 450 °C. The surface and interface oxidation of NiTi thin films are characterized by X-ray photoelectron spectroscopy (XPS). After a subsequent annealing treatment the crystallization behavior of the films deposited on substrate at different temperatures is studied by X-ray diffraction (XRD). The effects of substrate temperature on the surface and interface oxidation of NiTi thin films are investigated. In the film surface this is an oxide layer composed of TiO₂. The Ni atom has not been detected on surface. In the film/substrate interface there is an oxide layer with a mixture Ti₂O₃ and NiO in the films deposited at substrate temperatures 300 °C and 450 °C. In the films deposited at ambient temperature, the interface layer contains Ti suboxides (TiO) and metallic Ni.     

Compositional origin of surface roughness variations in air-annealed ZnO single crystals

We directly investigated the chemical compositional origin of surface roughness variations in air-annealed ZnO single crystal samples for annealing temperatures up to 1000 °C. Atomic Force Microscopy (AFM) showed temperature-dependent changes in surface roughness and morphology, with a maximum in surface roughness of 2 nm found for samples annealed at 400 °C. The O(1s) line, measured by X-ray Photoelectron Spectroscopy (XPS) showed a maximum for Zn(OH)₂ and a minimum for off-stoichiometric ZnO at 400 °C; while the Zn(2p) peaks show an increase in slope at that temperature. These results indicate that the roughness arises from Zn diffusion and loss of surface oxygen.     

Surface characterization of Pd/Ag23 wt% membranes after different thermal treatments

Hydrogen permeation measurements of 1.5-10 μm thick Pd/Ag23 wt% membranes before and after thermal treatments at 300 °C in air (both sides) or in the temperature range 300-450 °C in N₂ (feed side) and Ar (permeate side) were performed. Accompanying changes in surface topography and chemical composition were subsequently investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) depth profiling. For a 2 μm thick membrane, the surface roughness increased for all annealing temperatures applied, while a temperature of 450 °C was required for an increase in roughness of both membrane surfaces to occur for the 5 μm membrane. The thickest membrane, of 10 μm, showed changed surface roughness on one side of the membrane only and a slight decrease in hydrogen permeance after all heat treatments in N₂/Ar. X-ray photoelectron spectroscopy investigations performed after treatment and subsequent permeation measurements revealed segregation of silver to the membrane surfaces for all annealing temperatures applied. In comparison, heat treatment at 300 °C in air resulted in significantly increased hydrogen permeance accompanied by increasing surface roughness. Upon exposure to oxygen, Pd segregates to the surface to form a 2-3 nm thick oxide layer (PdO), with more complex segregation behavior after subsequent reduction and permeance measurements in pure hydrogen. The available permeance data for the Pd/Ag23 wt% membranes after heat treatment in air at 300 °C is found to depend linearly on the inverse membrane thickness, implying bulk limited hydrogen permeation for thicknesses down to 1.5-2.0 μm.     

Nanolayered multilayer coatings of CrN/CrAlN prepared by reactive DC magnetron sputtering

Single-phase CrN and CrAlN coatings were deposited on silicon and mild steel substrates using a reactive DC magnetron sputtering system. The structural characterization of the coatings was done using X-ray diffraction (XRD). The XRD data showed that both the CrN and CrAlN coatings exhibited B1 NaCl structure with a prominent reflection along (2 0 0) plane. The bonding structure of the coatings was characterized by X-ray photoelectron spectroscopy and the surface morphology of the coatings was studied using atomic force microscopy. Subsequently, nanolayered CrN/CrAlN multilayer coatings with a total thickness of approximately 1 μm were deposited on silicon substrates at different modulation wavelengths (Λ). The XRD data showed that all the multilayer coatings were textured along {2 0 0}. The CrN/CrAlN multilayer coatings exhibited a maximum nanoindentation hardness of 3125 kg/mm² at a modulation wavelength of 72 Å, whereas single layer CrN and CrAlN deposited under similar conditions exhibited hardness values of 2375 and 2800 kg/mm², respectively. Structural changes as a result of heating of the multilayer coatings in air (400-800 °C) were characterized using XRD and micro-Raman spectroscopy. The XRD data showed that the multilayer coatings were stable up to a temperature of 650 °C and peaks pertaining to Cr₂O₃ started appearing at 700 °C. These results were confirmed by micro-Raman spectroscopy. Nanoindentation measurements performed on the heat-treated coatings revealed that the multilayer coatings retained hardness as high as 2250 kg/mm² after annealing up to a temperature of 600 °C.     

Influence of annealing temperature on the structural, optical and mechanical properties of ALD-derived ZnO thin films

ZnO thin films grown on Si(1 1 1) substrates by using atomic layer deposition (ALD) were annealed at the temperatures ranging from 300 to 500 °C. The X-ray diffraction (XRD) results show that the annealed ZnO thin films are highly (0 0 2)-oriented, indicating a well ordered microstructure. The film surface examined by the atomic force microscopy (AFM), however, indicated that the roughness increases with increasing annealing temperature. The photoluminescence (PL) spectrum showed that the intensity of UV emission was strongest for films annealed at 500 °C. The mechanical properties of the resultant ZnO thin films investigated by nanoindentation reveal that the hardness decreases from 9.2 GPa to 7.2 GPa for films annealed at 300 °C and 500 °C, respectively. On the other hand, the Young's modulus for the former is 168.6 GPa as compared to a value of 139.5 GPa for the latter. Moreover, the relationship between the hardness and film grain size appear to follow closely with the Hall-Petch equation.     

Effect of oxidation temperature on microstructure, mechanical behaviors and surface morphology of nanocomposite Ti-Cx-Ny thin films

Two nanocomposite Ti-C_x-N_y thin films, TiC_0.95N_0.60 and TiC_2.35N_0.68, as well as one pure TiN, were deposited at 500 °C on Si(1 0 0) substrate by reactive unbalanced dc-magnetron sputtering. Oxidation experiments of these films were carried out in air at fixed temperatures in a regime of 250-600 °C with an interval of 50 °C. As-deposited and oxidized films were characterized and analyzed using X-ray diffraction (XRD), microindentation, Newton's ring methods and atomic force microscopy (AFM). It was found that the starting oxidation temperature of nanocomposite Ti-C_x-N_y thin films was 300 °C irrespective of the carbon content; however their oxidation rate strongly depended on their carbon content. Higher carbon content caused more serious oxidation. After oxidation, the film hardness value remained up to the starting oxidation temperature, followed by fast decrease with increasing heating temperature. The residual compressive stress did not show a similar trend with the hardness. Its value was first increased with increase of heating temperature, and got its maximum at the starting oxidation temperature. A decrease in residual stress was followed when heating temperature was further increased. The film surface roughness value was slightly increased with heating temperature till the starting oxidation temperature, a great decrease in surface roughness was followed with further increase of heating temperature.     

Optical characterization and microstructure of BaTiO3 thin films obtained by RF-magnetron sputtering

BaTiO₃ thin films were deposited on Pt/Ti/SiO₂/Si by rf planar-magnetron sputtering. The films thickness increases with the decrease of both deposition pressure and sample-discharge centre distance. The films annealed at 900 °C, for 8 h, present direct band gap energy ranged between 3.57 and 3.59 eV. The dependence of the structure and microstructure (texture, degree of crystallinity), as well as of the optical characteristics on the deposition parameters, was analysed. Using spectroscopic ellipsometry (SE) measurements coupled with the Bruggeman Effective Medium Approximation (B-EMA), the layer structure and the surface roughness, were determined. The root mean square roughness values of the surface layer, estimated by atomic force microscopy (AFM) analyses, are ranged between 10 and 20 nm and were in good agreement with SE data.The obtained films have tetragonal unit cell and show densely packed, non-columnar morphology and hexagon-like crystallite shape.     

Influence of deposition temperature on the structural and morphological properties of Be3N2 thin films grown by reactive laser ablation

Be₃N₂ thin films have been grown on Si(1 1 1) substrates using the pulsed laser deposition method at different substrate temperatures: room temperature (RT), 200 °C, 400 °C, 600 °C and 700 °C. Additionally, two samples were deposited at RT and were annealed after deposition in situ at 600 °C and 700 °C. In order to obtain the stoichiometry of the samples, they have been characterized in situ by X-ray photoelectron (XPS) and reflection electron energy loss spectroscopy (REELS). The influence of the substrate temperature on the morphological and structural properties of the films was investigated using scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD). The results show that all prepared films presented the Be₃N₂ stoichiometry. Formation of whiskers with diameters of 100-200 nm appears at the surface of the films prepared with a substrate temperature of 600 °C or 700 °C. However, the samples grown at RT and annealed at 600 °C or 700 °C do not show whiskers on the surface. The average root mean square (RMS) roughness and the average grain size of the samples grown with respect the substrate temperature is presented. The films grown with a substrate temperature between the room temperature to 400 °C, and the sample annealed in situ at 600 °C were amorphous; while the αBe₃N₂ phase was presented on the samples with a substrate temperature of 600 °C, 700 °C and that deposited with the substrate at RT and annealed in situ at 700 °C.     

Effect of heat treatment on morphology, crystalline structure and photocatalysis properties of TiO2 nanotubes on Ti substrate and freestanding membrane

Highly ordered titanium oxide (TiO₂) nanotubes were prepared by electrolytic anodization of titanium electrodes. Morphological evolution and phase transformations of TiO₂ nanotubes on a Ti substrate and that of freestanding TiO₂ membranes during the calcinations process were studied by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction microscopy. The detailed results and mechanisms on the morphology and crystalline structure were presented. Our results show that a compact layer exists between the tubular layer and Ti substrate at 600 °C, and the length of the nanotubes shortens dramatically at 750 °C. The freestanding membranes have many particles on their tubes during calcinations from 450 to 900 °C. The TiO₂ nanotubes on the Ti substrate transform to rutile crystals at 600 °C, while the freestanding TiO₂ membranes retain an anatase crystal with increasing temperature to 800 °C. The photocatalytic activity of TiO₂ nanotubes on a Ti substrate annealed at different temperatures was investigated by the degradation of methyl orange in aqueous solution under UV light irradiation. Due to the anatase crystals in the tubular layer and rutile crystals in the compact layer, TiO₂ nanotubes annealed at 450 °C with pure anatase crystals have a better photocatalytic activity than those annealed at 600 °C or 750 °C.     

Surface morphology and luminescence characterization of β-FeSi2 thin films prepared by pulsed laser deposition

β-FeSi₂ thin films were prepared on Si (1 1 1) substrates by pulsed laser deposition (PLD) with a sintering FeSi₂ target and an electrolytic Fe target. The thin films without micron-size droplets were prepared using the electrolytic Fe target; however, the surface without droplets was remarkably rougher using the Fe target than using the FeSi₂ target. After deposition at 600 °C and then annealing at 900 °C for 20 h, XRD indicated that the thin film prepared using the Fe target had a poly-axis-orientation, but that prepared using the FeSi₂ target had a one-axis-orientation. The PL spectra of the thin films prepared using the FeSi₂ and Fe targets at a growth temperature of 600 °C and subsequently annealed at 900 °C for 20 h had A-, B- and C-bands. Moreover, it was found that the main peak at 0.808 eV (A-band) in the PL spectrum of the thin films prepared using the FeSi₂ target was the intrinsic luminescence of β-FeSi₂ from the dependence of PL peak energy on temperature and excitation power density.     

Effect of tin-doped indium oxide film as capping layer on the agglomeration of copper film and the appearance of copper silicide

In this work, the effect of tin-doped indium oxide (ITO) film as capping layer on the agglomeration of copper film and the appearance of copper silicide was studied. Both samples of Cu 100 nm/ITO 10 nm/Si and ITO 20 nm/Cu 100 nm/ITO 10 nm/Si were prepared by sputtering deposition. After annealing in a rapid thermal annealing (RTA) furnace at various temperatures for 5 min in vacuum, the samples were characterized by four probe measurement for sheet resistance, X-ray diffraction (XRD) analysis for phase identification, scanning electron microscopy (SEM) for surface morphology and transmission electron microscopy (TEM) for microstructure.The results show that the sample with ITO capping layer is a good diffusion barrier between copper and silicon at least up to 750 °C, which is 100 °C higher than that of the sample without ITO capping layer. The failure temperature of the sample with ITO capping layer is about 800 °C, which is 100 °C higher than that of the sample without ITO capping layer. The ITO capping layer on Cu/ITO/Si can obstacle the agglomeration of copper film and the appearance of Cu₃Si phase.     

Effect of surface roughness on the development of protective Al2O3 on Fe-10Al (at.%) alloys containing 0-10 at.% Cr

The effect of alloy surface roughness, achieved by different degrees of surface polishing, on the development of protective alumina layer on Fe-10 at.% Al alloys containing 0, 5, and 10 at.% Cr was investigated during oxidation at 1000 °C in 0.1 MPa oxygen. For alloys that are not strong Al₂O₃ formers (Fe-10Al and Fe-5Cr-10Al), the rougher surfaces increased Fe incorporation into the overall surface layer. On the Fe-10Al, more iron oxides were formed in a uniform layer of mixed aluminum- and iron-oxides since the layer was thicker. On the Fe-5Cr-10Al, more iron-rich nodules developed on an otherwise thin Al₂O₃ surface layer. These nodules nucleated preferentially along surface scratch marks but not on alloy grain boundaries. For the strong Al₂O₃-forming Fe-10Cr-10Al alloy, protective alumina surface layers were observed regardless of the surface roughness. These results indicate that the formation of a protective Al₂O₃ layer on Fe-Cr-Al surfaces is not dictated by Al diffusion to the surface. More cold-worked surfaces caused an enhanced Fe diffusion, hence produced more Fe-rich oxides during the early stage of oxidation.     

Phase evolution of an aluminized steel by oxidation treatment

Effects of temperature and time on the microstructure and phase evolution for different thermal treatments were investigated with respect to the measurement of intermetallic layer thickness, phase identification and microhardness distribution in the aluminized zone of a steel substrate. The intermetallic phases present in the aluminized region after hot dip aluminizing is mainly Fe₂Al₅. The thickness of the intermetallic layers increases with increasing oxidation temperature and time. In the oxidation treatments of the aluminized steel in air, the initial Fe₂Al₅ phase remains at the temperature below 950 °C in 2-h, and the Fe₂Al₅ phase is completely transformed into low iron content Fe-Al intermetallics due to oxidation at 950 °C for 4 h. However, the Fe₂Al₅ phase remains in the outer layer of the aluminized samples diffusion-treated in vacuum regardless of diffusion time. The microhardness values of the Al₂O₃ and the intermetallic Fe₂Al₅, FeAl₂, FeAl and Fe₃Al phases are HV1150, HV1010, HV810, HV650 and HV320, respectively. The oxide layer formed on the steel substrate has an extremely fast adherence to the steel substrate and excellent properties of thermal shock resistance, high temperature oxidation resistance and anti-liquid aluminum corrosion.     

Plasticity and ab initio characterizations on Fe4N produced on the surface of nanocrystallized 18Ni-maraging steel plasma nitrided at lower temperature

18Ni-maraging steel has been entirely nanocrystallized by a series of processes including solution treatment, hot-rolling deformation, cold-drawn deformation and direct electric heating. The plasma nitriding of nanocrystallized 18Ni-maraging steel was carried out at 410 °C for 3 h and 6 h in a mixture gas of 20% N₂ + 80% H₂ with a pressure of 400 Pa. The surface phase constructions and nitrogen concentration profile in surface layer were analyzed using an X-ray diffractometer (XRD) and the glow discharge spectrometry (GDS), respectively. The results show that an about 2 μm thick compound layer (mono-phase γ′-Fe₄N) can be produced on the top of the surface layer of nanocrystallized 18Ni-maraging steel plasma nitrided at 410 °C for 6 h. The measured hardness value of the nitrided surface is 11.6 GPa. More importantly, the γ′-Fe₄N phase has better plasticity, i.e., its plastic deformation energy calculated from the load-displacement curve obtained by nano-indentation tester is close to that of nanocrystallized 18Ni-maraging steel. Additionally, the mechanical properties of γ′-Fe₄N phase were also characterized by first-principles calculations. The calculated results indicate that the hardness value and the ratio of bulk to shear modulus (B/G) of the γ′-Fe₄N phase are 10.15 GPa and 3.12 (>1.75), respectively. This demonstrates that the γ′-Fe₄N phase has higher hardness and better ductility.     

Thermal stability of nanoscale silver metallization in Ag/W/Co/Si(1 0 0) multilayer

In this work, we have studied thermal stability of nanoscale Ag metallization and its contact with CoSi₂ in heat-treated Ag(50 nm)/W(10 nm)/Co(10 nm)/Si(1 0 0) multilayer fabricated by sputtering method. To evaluate thermal stability of the systems, heat-treatment was performed from 300 to 900 °C in an N₂ ambient for 30 min. All the samples were analyzed by four-point-probe sheet resistance measurement (R_s), Rutherford backscattering spectrometry (RBS), X-ray diffractometry (XRD), and atomic force microscopy (AFM). Based on our data analysis, no interdiffiusion, phase formation, and R_s variation was observed up to 500 °C in which the Ag layer showed a (1 1 1) preferred crystallographic orientation with a smooth surface and R_s of about 1 Ω/□. At 600 °C, a sharp increase of R_s value was occurred due to initiation of surface agglomeration, WSi₂ formation, and interdiffusion between the layers. Using XRD spectra, CoSi₂ formed at the Co/Si interface preventing W silicide formation at 750 and 800 °C. Meantime, RBS analysis showed that in this temperature range, the W acts as a cap layer, so that we have obtained a W encapsulated Ag/CoSi₂ contact with a smooth surface. At 900 °C, the CoSi₂ layer decomposed and the layers totally mixed. Therefore, we have shown that in Ag/W/Co/Si(1 0 0) multilayer, the Ag nano-layer is thermally stable up to 500 °C, and formation of W-capped Ag/CoSi₂ contact with R_s of 2 Ω/□ has been occurred at 750-800 °C.     

The surface nanostructure of pure iron after combined electrochemical passivation and thermal annealing treatments

The properties of the surface oxide film on pure iron after electrochemical passivation and thermal annealing treatments were investigated using a variety of techniques. Passivation was carried out with an applied potential of 800 mV (vs Ag/AgCl) for 15 min in a pH 8.4 borate buffer solution at 30 °C, whilst annealing was carried out in air in an electric furnace at temperatures up to 300 °C. Analysis of the surface properties was then carried out using X-ray diffraction to determine oxide composition, a spectroscopic ellipsometer to measure the optical properties and oxide thickness, and a scanning probe microscope to measure the surface roughness using tapping mode AFM and to observe the nanoscale structure using constant height mode STM.     

Microstructure and antibacterial properties of microwave plasma nitrided layers on biomedical stainless steels

Nitriding of AISI 303 austenitic stainless steel using microwave plasma system at various temperatures was conducted in the present study. The nitrided layers were characterized via scanning electron microscopy, glancing angle X-ray diffraction, transmission electron microscopy and Vickers microhardness tester. The antibacterial properties of this nitrided layer were evaluated. During nitriding treatment between 350 °C and 550 °C, the phase transformation sequence on the nitrided layers of the alloys was found to be γ → (γ + γ_N) → (γ + α + CrN). The analytical results revealed that the surface hardness of AISI 303 stainless steel could be enhanced with the formation of γ_N phase in nitriding process. Antibacterial test also demonstrated the nitrided layer processed the excellent antibacterial properties. The enhanced surface hardness and antibacterial properties make the nitrided AISI 303 austenitic stainless steel to be one of the essential materials in the biomedical applications.