Effect of tempering temperature on Z-phase formation and creep strength in 9Cr–1Mo–V–Nb–N steel

The effect of the tempering temperature on Z-phase formation and creep strength in 9Cr–1Mo–V–Nb–N steel was examined with particular attention to the precipitation sequence of MX, M₂X, and Z-phase during creep exposure. Tempering at a lower temperature provided a high dislocation density and a fine lath structure. Tempering at 953, 1003, and 1038 K provided [M₂₃C₆, M₂X, NbX], [M₂₃C₆, M₂X, NbX, VX], and [M₂₃C₆, NbX, VX] phases, respectively. The creep strength of steel tempered at 953 K was the highest among the steels studied, even in the long term. No large decrease in creep strength was observed in steel tempered at 953 K. The Z-phase was observed after long-term creep in steel tempered at 1003 or 1038 K. In steel tempered at 953 K, a VX rather than a Z-phase formed during creep, and this was accompanied by consumption of M₂X. Retardation of the Z-phase formation can retard the creep strength degradation in steel tempered at 953 K.     

Electron microscopy and hardness study of a semi-solid processed 27 wt%Cr cast iron

A semi-solid processed 27 wt%Cr cast iron was studied by electron microscopy and its microstructure was related to the hardness. In the as-cast condition, the primary proeutectic austenite was round in shape while the eutectic M₇C₃ carbide was found as radiating clusters mixed with directional clusters. Growth in the [0 0 1]M₇C₃ with planar faces of {0 2 0}M₇C₃ and was usually observed with an encapsulated core of austenite. Destabilisation heat treatment followed by air cooling led to a precipitation of secondary M₂₃C₆ carbide and a transformation of the primary austenite to martensite in the semi-solid processed iron. Precipitation behaviour is comparable to that observed in the destabilisation of conventional cast iron. However, the nucleation of secondary M₂₃C₆ carbide on the eutectic M₇C₃ carbide was observed for the first time. Tempering after destabilisation led to further precipitation of carbide within the tempered martensite in the eutectic structure. The maximum hardness was obtained after destabilisation and tempering heat treatment due to the precipitation of secondary carbides within the martensite matrix and a possible reduction in the retained austenite.     

Phase evolution in P92 and E911 weld metals during ageing

Phase evolution in the weld metals of P92 and E911 steels weld joints were studied during ageing at 625 °C for up to 9000 h. The phases: ferrite + M₂₃C₆ + MX + Laves found by means of analytical TEM in the annealed states agree with the results of the thermodynamic calculation of equilibrium phases. The cross-weld hardness values, HV10, after 1000, 3000, and 9000 h ageing overlap each other and are approximately 15 units below that of the post-weld heat-treated (PWHT) state. Charpy impact energy with the notch at the centerline of the weld metal was measured. Its values decrease after ageing from approximately 60–80 to 12 J compared to the PWHT state. In 9–12%Cr steel with W this phenomenon can be explained by a priori heterogeneity in the weld metal, its large former austenite grain size, the precipitation and growth of M₂₃C₆ and Laves phase particles on grain and packet boundaries.     

Carburization performance of Incoloy 800HT in CH4/H2 gas mixtures

Carburization performance of Incoloy 800HT has been studied after cyclic and isothermal exposures to CH₄/H₂ carburizing gas mixtures at high temperatures for 500 h. At 800 °C in 2% CH₄/H₂, Incoloy 800HT suffered external oxidation and carburization, the external continuous layer of reaction products consists primarily of Cr₇C₃, Mn_1.5Cr_1.5O₄, and FeCr₂O₄ with Fe(Cr, Al)₂O₄ as a minor phase. At 1100 °C in 10% CH₄/H₂, external carburization did not occur likely due to high carbon dissolution in the alloy substrate at this temperature. A thermodynamic analysis indicated that 1000 °C was an approximate critical temperature, below which the environment should result in mixed oxidizing/carburizing behavior, while above this temperature reducing carburizing behavior should occur. The experimental results approximately agree with the thermodynamic analysis. Metal dusting was not observed under highly carburizing conditions (a_C>1). The size and morphology of Cr-rich phases (or Cr-carbides) are both temperature- and time-dependent, while the external continuity is more temperature-dependent rather than time-dependent.     

Microstructure evolution during dynamic recrystallization of hot deformed superalloy 718

Microstructure evolution during dynamic recrystallization (DRX) of superalloy 718 was studied by optical microscope and electron backscatter diffraction (EBSD) technique. Compression tests were performed at different strains at temperatures from 950 °C to 1120 °C with a strain rate of 10⁻¹ s⁻¹. Microstructure observations show that the recrystallized grain size as well as the fraction of new grains increases with the increasing temperature. A power exponent relationship is obtained between the dynamically recrystallized grain size and the peak stress. It is found that different nucleation mechanisms for DRX are operated in hot deformed superalloy 718, which is closely related to deformation temperatures. DRX nucleation and development are discussed in consideration of subgrain rotation or twinning taking place near the original grain boundaries. Particular attention is also paid to the role of continuous dynamic recrystallization (CDRX) at both higher and lower temperatures.     

Transmission electron microscopy of annealed a-Si1−xCx:H/Al films with different Al grain sizes

The crystallization behavior of a-Si_1−xC_x:H/Al films after annealing has been investigated by transmission electron microscopy and Raman scattering. It is found that the crystallization process is complex and non-uniform, and that both equiaxial and branching Si grains with many twins and stacking faults arise at annealing temperatures as low as 250 °C. Both fine polycrystalline β-SiC grains and fractal-like -SiC aggregates are first observed in a few regions in a-Si_1−xC_x:H/Al films annealed at 350 °C. The increase of the Al grain size can cause a decrease in the crystallization temperature and a rise in the grain growth rate of Si. At higher annealing temperatures, the reaction process SiC+Al→Al₄C₃+Si is predominant.     

Photoluminescence properties of the Yb:Er co-doped Al2O3 thin film fabricated by microwave ECR plasma source enhanced RF magnetron sputtering

The Yb:Er co-doped Al₂O₃ thin film was deposited on oxidized silicon wafers by microwave ECR plasma source enhanced RF magnetron sputtering, and annealed from 800 °C to 1000 °C. The photoluminescence at 1.53 μm of thin film was obtained under room temperature. The mixture phase structure of γ and θ is observed by XRD, and the compositions of the thin film are investigated by EPMA. The maximum PL intensity was achieved with O₂:Ar at 1:1, annealing temperature at 900 °C, and experimental ratio of Yb:Er at 1:3.6. The energy transfer mechanism between Er and Yb ions is supported by theoretical analysis and experiment results.     

Effect of heat treatment on photoluminescence behavior of BaMgAl10O17:Eu phosphors

The blue phosphor of BaMgAl₁₀O₁₇:Eu²⁺ (BAM) powders were prepared by solid-state reaction. The thermal degradation of BAM phosphor significantly reduces the intensity of the blue emission. BAM is reduced by an amount of 50% after heating at around 800 °C for 1 h. Photoluminescence (PL) excitation and emission spectra showed that the blue emission of 450 nm peak decreased with increasing annealing temperature. The ⁵D₀→⁷F₁ and ⁵D₀→⁷F₂ transition of Eu³⁺ were observed at 590 and 615 nm emission lines over 1100 °C. Electron paramagnetic resonance (EPR) spectrum also detected two signals of Eu²⁺, corresponding to g=3.7156(9) for 88 mT, and g=2.9507(9) for 133 mT. X-ray absorption near edge structure (XANES) spectrum decreased the intensity of Eu²⁺ for 6977 eV with increasing annealing temperature, while high-energy peak of Eu³⁺ for 6984 eV was increased. The combined use of X-ray and neutron data by the Rietveld refinement appears to support that the secondary phase of EuMgAl₁₁O₁₉ magnetoplumbite structure in BAM may be formed by heat treatment.     

Effects of substrate temperature on structural, electrical and optical properties of As-doped ZnO films

As-doped ZnO films were prepared by co-sputtering ZnO and Zn₃As₂ targets on glass substrates at various temperatures from 250 to 500 °C. The effects of substrate temperature on structural, electrical and optical properties of the films were investigated. The films grown at temperatures from 250 to 400 °C were c-axis oriented and those deposited above 400 °C exhibited poor crystallinity. Hall measurement showed that p-type ZnO:As films were prepared at different temperatures. With increasing the substrate temperature from 250 to 500 °C, the optical band gap (E_g) first decreased, and then increased. The E_g changes upon the substrate temperature were due to the effect of substrate temperature on the crystallinity of ZnO films.     

Correlation of structure and optical properties of an annealed hydrogenated amorphous silicon-carbon alloy film

A hydrogenated amorphous silicon-carbon (a-Si_0.76C_0.24:H) film has been prepared via the glow discharge decomposition of SiH₄ and C₂H₄. The optical constants of this alloy film have been determined as a function of annealing temperature T_a for photon energies between 1.5 and 4.75 eV. The refractive index n and its imaginary part k show small but significant variation with annealing temperature. The optical energy gap E_opt also exhibits interesting variation with annealing temperature, decreasing with increasing annealing temperature up to T_a = 650°C and then increasing above this temperature. Further, E_opt is found to be correlated with the inverse of the full width at half-maximum of the Si---C and the Si---O IR stretch absorption mode, which seems to indicate that the changes in E_opt are structural in origin and that phonon order correlates well with electronic order.     

Diffusion barrier properties of sputtered TaNx between Cu and Si using TaN as the target

TaN_x films sputtered from a TaN target were used as diffusion barriers between Cu thin films and Si substrates. Material characteristics of TaN_x films and metallurgical reactions of Cu/TaN_x/Si systems annealed in the temperature range 400–900 °C for 60 min were investigated by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, cross-sectional transmission electron microscopy, and sheet resistance measurements. We found that the deposition rate decreased with increasing bias. TaN, β-Ta, and Ta₂N phases appeared and/or coexisted in the films at specific biases. A step change in N/Ta ratio was observed whenever a bias was applied to the substrate. After depositing a copper overlayer, we observed that the variation percentage of sheet resistance for Cu (70 nm)/TaN_x (25 nm, x=0.37 and 0.81)/Si systems stayed at a constant value after annealing up to 700 °C for 60 min; however, the sheet resistance increased dramatically after annealing above 700 and 800 °C for Cu/TaN_0.37/Si and Cu/TaN_0.81/Si systems, respectively. At that point, the interface was seriously deteriorated and formation of Cu₃Si was also observed.     

Effect of β-spodumene on the phase development in an alumina/aluminium-titanate system

The effect of β-spodumene additions on the in situ phase formation and abundances in an Al₂O₃–Al₂TiO₅ system in the temperature range 1000–1400 °C has been studied by neutron diffraction and differential thermal analysis. Results show that β-spodumene began to decompose by phase separation and partial melting at 1290 °C, followed by complete melting at 1330 °C. Formation of Al₂TiO₅ was observed to occur at 1310 °C and its abundance increased with temperature. The addition of β-spodumene as a sintering aid did not cause its reaction with alumina or rutile to form additional phases. Addition of β-spodumene in excess of 5 wt% resulted in pronounced vitrification, which partly recrystallised when cooled to room temperature. The temperatures of Al₂TiO₅ formation and melting of β-spodumene are consistent with the results of differential thermal analysis.     

Direct liquid injection metal-organic chemical vapor deposition of HfO2 thin films using Hf(dimethylaminoethoxide)4

Hf(OCH₂CH₂NMe₂)₄, [Hf(dmae)₄] (dmae=dimethylaminoethoxide) was synthesized and used as a chemical vapor deposition precursor for depositing Hf oxide (HfO₂). Hf(dmae)₄ is a liquid at room temperature and has a moderate vapor pressure (4.5 Torr at 80 °C). It was found that HfO₂ film could be deposited as low as 150 °C with carbon level not detected by X-ray photoelectron spectroscopy. As deposited film was amorphous but when the deposition temperature was raised to 400 °C, X-ray diffraction pattern showed that the film was polycrystalline with weak peak of monoclinic (020). Scanning electron microscope analysis indicated that the grain size was not significantly changed with the increase of the annealing temperature. Capacitance–voltage measurement showed that with the increase of annealing temperature, the effective dielectric constant was increased, but above 900 °C, the effective dielectric constant was decreased due to the formation of interface oxide. For 500 Å thin film, the dielectric constant of HfO₂ film annealed at 800 °C was 20.1 and the current–voltage measurements showed that the leakage current density of the HfO₂ thin film annealed at 800 °C was 2.2×10⁻⁶ A/cm² at 5 V.     

Microstructural, photocatalysis and electrochemical investigations on CeTi2O6 thin films

The properties of sol–gel derived CeTi₂O₆ thin films deposited using a solution of cerium chloride heptahydrate and titanium propoxide in ethanol are discussed. The effect of annealing temperature on structural, optical, photoluminescence, photocatalysis and electrochemical characteristics has been examined. Lowest annealing temperature for the formation of crystalline CeTi₂O₆ phase in these samples is identified as 580 °C. The optical transmittance of the films is observed to be independent of the annealing temperature. The optical energy bandgap of the 600 °C annealed film for indirect transition is influenced by the presence of anatase phase of TiO₂ in its structure. Fourier transform infrared spectroscopy investigations have evidenced increased bond strength of the Ti–O–Ti network in the films as a function of annealing temperature. The photoluminescence intensity of the films has shown dependence on the annealing temperature with the films fired at 450 °C exhibiting the maximum photoluminescence activity. The decomposition of methyl orange and eosin (yellow) under UV–visible light irradiation in the presence of crystalline CeTi₂O₆ films shows the presence of photoactivity in these films. The photocatalytic response of CeTi₂O₆ films is found to be superior to the TiO₂ films. In comparison to crystalline films, the amorphous films have shown superior electrochemical characteristics. The 500 °C annealed amorphous films have exhibited the most appropriate properties for incorporation in electrochromic devices comprising tungsten oxide as the primary electrochromic electrode.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

Annealing effects on microstructure and mechanical properties of chromium oxide coatings

Reactive radio frequency magnetron sputter-deposited chromium oxide coatings were annealed at different temperatures and times. The influence of annealing temperature on the microstructure, surface morphology and mechanical properties was examined by X-ray diffraction, nanoindentation, pin-on-disc wear and scratch tests, respectively. X-ray results show that the chromium oxide sputtered at room temperature in low oxygen flux is primarily amorphous. Annealing below 400 °C did not cause much change, while annealing at higher temperature of 500 °C caused a significant change in microstructure and mechanical properties. Hardness increased from 12.3 GPa to 26 GPa, and the wearability improved with higher annealing temperature due to the formation of crystalline Cr₂O₃ phase, which occurs at 470 °C. Annealing time had little effect on mechanical properties and microstructure, although coating surface roughness increased with a longer annealing time. Coating adhesion was improved by annealing, due to residual stress relief and possible interfacial interdiffusion.     

Preparation and visible-light-driven photoelectrocatalytic properties of boron-doped TiO2 nanotubes

In the present study, chemical vapour deposition (CVD) was applied to dope boron into TiO₂ nanotubes anodized Ti in C₂H₂O₄·2H₂O + NH₄F electrolyte with the goal of improving the photocatalytic (PC) activity under visible light. The undoped TiO₂ nanotubes had a highly self-organized structure. However, after doping through CVD, TiO₂ nanotubes suffered from an observable disintegration of morphological integrity. X-ray diffraction (XRD) results confirmed that annealing temperature had an influence on the phase structure and boron impurities could retard anatase–rutile phase transition. Diffuse reflectance absorption spectra (DRS) analysis indicated that B-doped samples displayed stronger absorption in both UV and visible range. B-doped TiO₂ nanotubes electrode annealed at 700 °C through CVD showed higher photoelectrocatalytic (PEC) efficiency in methyl orange (MO) degradation than that annealed at 400 °C and 550 °C. MO degradation was substantially enhanced with the increasing applied bias potential. Moreover, there was a synergetic effect between the electrochemical and photocatalytic processes, and the synergetic factor R reached 1.45. B-doped TiO₂ nanotubes electrode showed good stability after 10 times by repeating photoelectrocatalysis of MO.     

Characterization and microstructure of highly preferred oriented lead barium titanate thin films on MgO (100) by sol-gel process

Highly preferred oriented lead barium titanate (Pb_1−x,Ba_x)TiO₃ thin film, with particular emphasis on (Pb_0.5,Ba_0.5)TiO₃, can be obtained by spin-coating on MgO (100) substrate by using the precursor sol, which was synthesized from acetylacetone chelating with titanium isopropoxide and ethylene glycol as a solvent, in the sol-gel process. Film thickness, pyrolysis temperature and heating rate were studied systemically to investigate their influences on the formation of preferred oriented thin films. The highly preferred (001)/(100) oriented thin film could be obtained by the pyrolysis of wet film at 500 °C and annealing at 600 °C at a slow heating rate of 5 °C/min. It is confirmed that the tetragonal perovskite structure of the titanate ceramic decreases with an increase of Ba content in (Pb_1−x,Ba_x)TiO₃. The (001)/(100) oriented films were synthesized from all compositions between x = 0.2 and x = 0.8, at a crystallization temperature of 600 °C. In particular, for the Ba content in the range of x = 0.50.6, highly preferred (001)/(100) planes were observed.     

Synthesis of Lanthanofullerenes by Laser Ablation Using Pulsed and CW-Nd:YAG Lasers

Endohedral lanthanum fullerenes, La@C₆₀, La@C₈₂ and La₂C₈₀, were synthesized by ablation of graphite and La₂O₃ in flowing Ar buffer gas with a 1064 nm beam from a pulsed-Nd: YAG laser in which the graphite was heated by the CW-Nd:YAG laser up to 2500 °C. The La-fullerenes were also prepared by laser ablation of a lanthanum-graphite composite rod. The extractant fullerenes from the carbon soot were analyzed by laser-desorption time of flight mass spectrometry (LD-TOF MS). The relative yield of La@C₈₂, increased with increasing temperature of the rod in the range of 700-2300 °C.     

Electrochromic properties of nanocrystalline MoO3 thin films

Electrochromic MoO₃ thin films were prepared by a sol–gel spin-coating technique. The spin-coated films were initially amorphous; they were calcined, producing nanocrystalline MoO₃ thin films. The effects of annealing temperatures ranging from 100 °C to 500 °C were investigated. The electrochemical and electrochromic properties of the films were measured by cyclic voltammetry and by in-situ optical transmittance techniques in 1 M LiClO₄/propylene carbonate electrolyte. Experimental results showed that the transmittance of MoO₃ thin films heat-treated at 350 °C varied from 80% to 35% at λ = 550 nm (ΔT =  45%) and from 86% to 21% at λ ≥ 700 nm (ΔT =  65%) after coloration. Films heat-treated at 350 °C exhibited the best electrochromic properties in the present study.