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The effects of synthesis time on the plasmonic properties of Ag dendritic nanoforests on Si substrate (Ag-DNF/Si) samples synthesized through the fluoride-assisted galvanic replacement reaction were investigated. The Ag-DNF/Si samples were characterized using scanning electron microscopy, energy-dispersive X-ray spectroscopy, reflection spectroscopy, X-ray diffraction and surface-enhanced Raman spectroscopy (SERS). The prolonged reaction time led to the growth of an Ag-DNF layer and etched Si hole array. SEM images and variations in the fractal dimension index indicated that complex-structure, feather-like leaves became coral-like branches between 30 and 60 min of synthesis. The morphological variation during the growth of the Ag DNFs resulted in different optical responses to light illumination, especially those of light harvest and energy transformation. The sample achieved the most desirable light-to-heat conversion efficiency and SERS response with a 30 min growth time. A longer synthesis time or thicker Ag-DNF layer on the Si substrate did not have superior plasmonic properties.

Two kinds of Bi0.4Sb1.6Te3 powder with different particle and grain sizes were fabricated by high-energy ball milling. Powder mixtures with varied weight ratios were consolidated by vacuum hot pressing (HP) to produce nano/ microstructured composites of identical chemical composition. From measurements of the Seebeck coefficient, electrical resistivity, and thermal conductivity of these composites, a figure of merit (ZT) value of up to 1.19 was achieved at 373 K for the sample containing 40% nanograin powder. This ZT value is higher than that of monolithic nanostructured Bi0.4Sb1.6Te3. It is further noted that the ZT value of this sample in the temperature range of 450 K to 575 K is in the range of 0.7 to 1.1. Such ZT characteristics are suitable for power generation applications as no other material with a similar high ZT value in this temperature range has been observed until now. The achieved high ZT value can probably be attributed to the unique nano/microstructure, in which the dispersed nanograin powder increases the number of phonon scattering sites, which in turn results in a decrease of the thermal conductivity while simultaneously increasing the electrical conductivity, owing to the existence of the microsized powder that can provide a fast carrier transportation network. These results indicate that the nano/microstructured Bi0.4Sb1.6Te3 alloy can serve as a high-performance material for application in thermoelectric devices.

In the present study, Ti 50 Cu 28 Ni 15 Sn 7 (at.%) metallic glass and its composite powders reinforced with 4-12 vol.% of added SiC were successfully prepared by mechanical alloying. In the ball-milled composites, an amorphous matrix with a homogeneous dispersion of SiC particles was developed. The metallic glass composite powders were found to exhibit a large supercooled liquid region before crystallization. The presence of SiC particles did not change the glass-formation ability of the amorphous Ti 50 Cu 28 Ni 15 Sn 7 powders. Consolidation of the as-milled Ti 50 Cu 28 Ni 15 Sn 7 composite powders was performed at a temperature slightly higher than the glass-transition temperature under a pressure of ∼1.2 GPa; using this method, the bulk metallic glass composite discs were prepared successfully. However, partial crystallization of the amorphous matrix during the hot-pressing process was noticed. The fracture strength of consolidated composite compacts was increased with SiC additions. The pre-existing particle boundaries may serve as the crack initiation sites which resulted in the brittle failure of the Ti 50 Cu 28 Ni 15 Sn 7 BMG composites.

The corrosion behavior of mechanically alloyed Cu60Zr30Ti10 bulk metallic glass (BMG) in four different corrosive media was studied by the potentiodynamic method. The Cu60Zr30Ti10 BMG shows low corrosion current density and uniform corrosion in 1N H2SO4, NaOH and HNO3 solutions. The Cu60Zr30Ti10 BMG specimen (consolidated at 746K under 1.2GPa) specimen exhibits most corrosion resistance in 1N H2SO4. The formation of the oxide films and the nucleation and growth of pitting will be discussed in light of microstructural investigations.

ZnO thin-film transistors (TFTs) have attracted considerable R&D interest due to their high transparency and low photosensitivity compared with typical a-Si:H TFTs. The electrical characteristics of ZnO thin films may be controlled by doping with ternary element, for instance Al, Ga, In, Mg, Zr, etc. In this study, Zn 1 − x Mg x O ( x = 0 to 0.36) thin films were deposited on glass substrates by spin coating. The as-deposited films were baked at 300 °C for 10 min and then annealed at 500 °C for 1 h in air. The results show that, addition of Mg-species in ZnO films markedly enhanced the uniformity of film thickness and improved optical properties. The Zn 0.8 Mg 0.2 O film exhibited the best transparency of 92%, an increase of ∼ 15% over a pure ZnO film, and the rms roughness value decreased to 1.63. The Zn 1 − x Mg x O TFTs were demonstrated to have n-type enhancement behavior. The optimum device with Zn 0.8 Mg 0.2 O channel layer had a field-effect mobility of 0.1 cm 2 /V s, a threshold voltage of 6.0 V, and an on/off ratio more than 10 7 .

In the present study, pure elemental powders of Fe and S were mixed to give the desired compositions of Fe50S50. A SPEX 8000D high-energy ball mill was used to synthesize iron sulfide powders under an Ar-filled atmosphere. The prepared powders were examined by conventional X-ray diffractometry and synchrotron X-ray absorption spectroscopy. The experimental results revealed that mechanochemical reactions occurred during the ball milling process for all the compositions. The Fe50S50 phase was obtained after ball milling for 20 h. Extended X-ray absorption fine structure (EXAFS) results revealed that the nearest neighbor bond lengths of the radial distribution function (RDF) for iron decreased when iron sulfides formed. X-ray absorption near edge structure (XANES) of S K-edges distinguished better the structural evolution of these iron sulfides.

Amorphous Ti50Cu28Ni15Sn7 alloy powders were synthesized by a mechanical alloying (MA) technique. Differential scanning calorimetry (DSC) results showed that, after 7 hours of exposure to the milling process, amorphous Ti50Cu28Ni15Sn7 alloy powders exhibit a wide supercooled liquid region of 61 K. Consolidation of amorphous powders were performed at a temperature slightly higher than the glass transition temperature under a pressure of ∼1.2 GPa, and bulk metallic glass (BMG) discs can be prepared successfully. However, we noticed partial crystallization during the hot pressing process and were not able to achieve full densification of BMG. The Vickers microhardness of Ti50Cu28Ni15Sn7 BMG was 634 kg/mm2, and the trace of the indentation revealed that pre-existing particle boundaries or interfaces between nanocrystals and amorphous matrix may serve as the crack initiation sites. Thus, typical brittle failure of Ti50Cu28Ni15Sn7 BMG was observed and resulted in relatively low fracture stress compared to that estimated by the microhardness.

Oxide-reduced copper powder can be produced efficiently at low cost. The volume shrinkage, porosity, maximum pore size, permeability and thermal conductivity of wicks sintered from two oxide-reduced (OR) powders were compared with one from water-atomized (WA) powder. The green specimens were sintered at temperatures from 800 to 1000 °C in a tube furnace under a reduction stream of 10% hydrogen and 90% argon. The results show that the property variations of OR − 100 and WA wicks due to porosity changes have a similar tendency and range. Nine hundred degree celsius is a recommended sintering temperature for producing ideal wicks for use in heat pipes. A smaller maximum pore size can be obtained by increasing the green density.

In the current study, the amorphization behavior of mechanically alloyed Ni57Zr20Ti22Pb1 powder was examined in details. The conventional X-ray diffraction results confirm that the fully amorphous powders formed after 5 hours of milling. The thermal stability of the Ni57Zr20Ti22Pb1 amorphous powders was investigated by differential scanning calorimeter (DSC). As the results demonstrated, the glass transition temperature (Tg) and the crystallization temperature (Tx) are 760 K and 850 K, respectively. The supercooled liquid region is 90 K. The appearance of wide supercooled liquid region may be mainly due to the Pb additions which cause the increasing differences in atomic size of mechanically alloyed Ni57Zr20Ti22Pb1 powders.

Mg 45 Y 15 Cu 40 (numbers indicate at.%) metallic glass powders were prepared by the mechanical alloying of pure Mg, Y, and Cu after 10 h of milling. The thermal stability of these Mg 45 Y 15 Cu 40 amorphous powders was investigated using the differential scanning calorimeter (DSC). T g , T x , and Δ T x are 456, 491, and 35 K, respectively. The as-milled Mg 45 Y 15 Cu 40 powders were then consolidated by vacuum hot pressing into disk compacts with a diameter and thickness of 10 and 1 mm, respectively. This yielded bulk Mg 45 Y 15 Cu 40 metallic glass with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix. The pressure applied during consolidation can enhance thermal stability and prolong the existence of amorphous phase within Mg 45 Y 15 Cu 40 powders.

In the present study, mechanical alloying technique was used to prepare (Mg 2 Ni) 100− x Ti x ( x = 0, 2.5, 5, 7.5, and 10 wt.%) powders starting from elemental powder mixture under an Ar atmosphere. The experimental results showed that the absorbed hydrogen content and reversible hydrogen content was 3.14 and 2.40 wt.% for 15 h milled Mg 2 Ni powders, respectively. The maximum hydrogen absorption content was increased to over 3.8 wt.% with Ti additions. The reversible hydrogen content also increased significantly (18–25%) with Ti additions. Meanwhile, 15 h milled Mg 2 Ni–Ti powders can absorb more than 3 wt.% of hydrogen within 1000 s. Not only the hydrogen absorption ability but the hydrogen absorption rate were improved by the additions of titanium and MA treatment in Mg 2 Ni alloy.

The preparation of Ti50Cu28Ni15Sn7 (numbers indicate at.%) metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and WC powder mixture after 5 h milling. In the ball-milled composites, the initial WC particles were homogeneously dispersed in the Ti-based alloy glassy matrix. The metallic glass composite powders were found to exhibit a large supercooled liquid region before crystallization. The bulk metallic glass composite with submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared by vacuum hot pressing the as-milled WC/ Ti50Cu28Ni15Sn7 metallic glass composite powders at 723 K under a pressure of ∼1.2 GPa. A significant hardness increase with the WC additions was observed for the consolidated composite compacts.

The preparation of Ti50Cu28Ni15Sn7 metallic glass composite powders was accomplished by the mechanical alloying of a pure Ti, Cu, Ni, Sn and carbon nanotube (CNT) powder mixture after 8 h milling. In the ball-milled composites, the initial CNT particles were dissolved in the Ti-based alloy glassy matrix. The thermal stability of the amorphous matrix is affected by the presence of the CNT particles. Changes in Tg and Tx suggest deviations in the chemical composition of the glassy matrix due to a partial dissolution of the CNT species in the amorphous phase. The bulk metallic glass composite was successfully prepared by vacuum hot pressing the as-milled CNT/ Ti50Cu28Ni15Sn7 metallic glass composite powders. A significant hardness increase with the CNT additions was observed for the consolidated composite compacts.

In the present study, amorphous Mg 49 Y 15 Cu 36 and Ti 50 Cu 28 Ni 15 Sn 7 alloy powders were synthesized separately by using a mechanical alloying technique. The dual-phase (Mg 49 Y 15 Cu 36 ) 100-x (Ti 50 Cu 28 Ni 15 Sn 7 ), (x = 0, 10, 20, 30, 40, and 50vol%) powders were prepared by mixing the corresponding amorphous powders. The amorphous dual-phase powders were then consolidated into bulk metallic glass (BMG) discs. The amorphization status of as-prepared powders and BMG discs was confirmed by X-ray diffraction and by using a differential scanning calorimeter. The microstructure of the BMG discs showed that the Ti 50 Cu 28 Ni 15 Sn 7 phase is distributed homogeneously within the Mg 49 Y 15 Cu 36 matrix. The (Mg 49 Y 15 Cu 36 ) 50 (Ti 50 Cu 28 Ni 15 Sn 7 ) 50 BMG disc exhibited a relative density of 97.2% and its Vickers microhardness was 526±20 kg/mm 2 .

The hydrogen storage alloy (Mg2Ni)100� xTix (x ¼ 0, 2.5, 5.0, 7.5 and 10.0 at%) powders were synthesized from elemental powder mixture by mechanical alloying (MA) under an Ar atmosphere. The as-milled powders were examined as a function of titanium addition by X-ray diffraction and synchrotron X-ray absorption near-edge structure (XANES) techniques at various milling time. The hydrogen absorption kinetics of the 15 h as-milled powders were evaluated. The maximum hydrogen absorption content of 15 h as-milled Mg2Ni powders can be improved from 3.14 mass% to 3.88 mass% when 5.0 at% of titanium was added. The hydrogenation rate of the Mg2Ni powder was also obviously enhanced by introducing the titanium into Mg2Ni lattices. More than 20% improvement of hydrogen absorption for Mg2Ni intermetallic powders was achieved by adding titanium. [doi:10.2320/matertrans.MER2007169]

Mg55Y15Cu30 metallic glass powders were prepared by the mechanical alloying of pure Mg, Y, and Cu after 10 h of milling. The thermal stability of these Mg55Y15Cu30 amorphous powders was investigated using the differential scanning calorimeter (DSC). Tg ,Tx , and Δ Tx are 442 K, 478 K, and 36 K, respectively. The as-milled Mg55Y15Cu30 powders were then consolidated by vacuum hot pressing into disk compacts with a diameter and thickness of 10 mm and 1 mm, respectively. This yielded bulk Mg55Y15Cu30 metallic glass with nanocrystalline precipitates homogeneously embedded in a highly dense glassy matrix. The pressure applied during consolidation can enhance thermal stability and prolong the existence of amorphous phase within Mg55Y15Cu30 powders.

in the present study, amorphous ti50cu35-xni15snx (x=0~7) alloy powders were synthesized by mechanical alloying technique. the amorphization behavior of ti50cu28ni15sn7 alloy powders was examined in details by scanning electron microscopy, differential scanning calorimeter, x-ray diffraction, and synchrotron x-ray absorption spectroscopy. the results show that fully amorphous powders formed after 7 hours of milling. The thermal stability of the Ti50Cu35-xNi15Snx amorphous powders was investigated by differential scanning calorimeter. The amorphous Ti50Cu35Ni15 powders (i.e., x=0) exhibit no glass transition behavior. However, the amorphous Ti50Cu35-xNi15Snx (x=3~7) powders were found to exhibit a supercooled liquid region before crystallization. Amorphous Ti50Cu28Ni15Sn7 alloy powders exhibits a wide supercooled liquid region of 61 K.

The preparation of Ti50Cu28Ni15Sn7 metallic glass composite powders was accomplished by mechanical alloying of pure Ti, Cu, Ni, Sn and WC for 18 ks. In the ball-milled composites, initial WC particles were homogeneously dispersed in the Ti-based alloy glassy matrix. The metallic glass composite powders exhibited a large supercooled liquid region just below the crystallization temperature. The presence of WC nanoparticles did not change the glass formation ability of amorphous Ti50Cu28Ni15Sn7 powders. The as-milled Ti50Cu28Ni15Sn7 and composite powders were consolidated by vacuum hot pressing into compact discs with a diameter and thickness of 10 and 4 mm, respectively. Microstructural analysis showed that the bulk metallic glass composite contained submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix. Incorporation of WC into consolidated composite compacts resulted in a significant increase in hardness.

In the present study, WC/Cu60Zr30Ti10 metallic glass composite powders were prepared by mechanical alloying of pure Cu, Zr, Ti, and WC powder mixtures. Cu60Zr30Ti10 metallic glass composite powders were obtained after 5 h of milling as confirmed by X-ray diffraction and differential scanning calorimetry. The metallic glass composites powders were found to exhibit a supercooled liquid region before crystallization. Bulk metallic glass (BMG) composites were synthesized by vacuum hot pressing the as-milled Cu60Zr30Ti10 metallic glass composite powders at 723 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense anocrystalline/amorphous matrix was successfully prepared under applied pressure of 1.20 GPa. It was found that the pressure could enhance the thermal stability and promotes nocrystallization of WC/Cu60Zr30Ti10 BMG composites.

The feasibility of preparing amorphous Ni57Zr20Ti20Si3 composite powders by mechanical alloying of pure Ni, Zr, Ti, Si, and ceramic powder mixture after 5 h milling was investigated. The as-milled powders were examined by X-ray diffraction, scanning electron microscopy, and differential thermal analysis. Amorphous Ni57Zr20Ti20Si3 composite powders were prepared successfully at the end of milling for all the compositions studied. The thermal stability of the amorphous matrix is not significantly affected by the presence of the ceramic particles. It is suggested a partial dissolution of the atoms constituting the ceramic species in the amorphous phase can result change of matrix composition and lead to the variation of the glass transition and crystallization behaviors.

This study examined the amorphization behavior and thermal stability of mechanically alloyed Cu 60 Zr 24 Ti 10 Y 6 alloy powders synthesized by using high-energy ball mill. Complete amorphization is feasible after 5 h of milling. The thermal stability of the Cu 60 Zr 24 Ti 10 Y 6 amorphous powders was investigated by differential thermal analysis. As the results demonstrated, the temperature interval of the supercooled liquid region defined by the difference between glass transition temperature ( T g ) and crystallization temperature ( T x ), i.e. Δ T x = T x − T g , is 82 K for Cu 60 Zr 24 Ti 10 Y 6 . The glass transition and crystallization temperatures of mechanically alloyed samples are different from those reported in the literature for samples prepared by melt spinning techniques. The different thermal stability is believed to be due to the introduction of impurities into the ball-milled samples during mechanical alloying (MA) process.

This study examined the amorphization behavior and thermal stability of mechanically alloyed Ni 57 Zr 20 Ti 18 Al 5 alloy powders synthesized by high-energy ball milling. Complete amorphization is feasible after 5 h of milling. The thermal stability of the Ni 57 Zr 20 Ti 18 Al 5 amorphous powders was investigated by differential thermal analysis. As the results demonstrated, the temperature interval of the supercooled liquid region defined by the difference between glass transition temperature ( T g ) and crystallization temperature ( T x ), i.e., Δ T ( = T x − T g ) is 54 K for Ni 57 Zr 20 Ti 18 Al 5 . The glass transition and crystallization temperatures of mechanically alloyed samples are different from those reported in the literature for samples prepared by melt spinning techniques. The different thermal stability is believed to be due to the introduction of impurities into the ball-milled samples during mechanical alloying process. The glass transition behavior in the Ni 57 Zr 20 Ti 18 Al 5 is found to be a kinetically modified thermodynamic phase transformation process.

Conventional transmission electron microscopy is employed to investigate in situ electron-beam-induced phase transformations in vacuum-deposited amorphous aluminum fluoride (a-AlF3) self-developing thin-film resists. The a-AlF3 resists exhibit a very complex sequence of crystallization transitions with three crystalline materials (Al, AlF3, and Al2O3) formed sequentially as the electron dose increases from 105 to 107 Cm−2. Thermally evaporated “dry” a-AlF3 is dissociated into Al crystalline colloids at a threshold dose of ∼1×105 Cm−2, and begins to transform into crystalline AlF3 (c-AlF3) at a dose of ∼1×106 Cm−2. However, water contained in the “wet” films accelerates the transition of a-AlF3 to c-AlF3 at a reduced threshold dose of ∼2×105 Cm−2. Moreover, a-AlF3 films prepared by electron-beam deposition require a markedly different dose for each substance to crystallize, attributed to a microstructure variation. For all of the a-AlF3 films, textured Al2O3 is formed at doses of ⩾1×107 Cm−2, also with the...

The amorphous Cu–Ni–Zr alloys were successfully synthesized by mechanical alloying mixtures of pure crystalline Cu, Ni and Zr powders with SPEX high-energy ball mill. These ranges are similar to those for amorphous alloys produced by melt-spinning techniques. The structure and thermal stability of these alloys were analyzed by X-ray diffraction and differential scanning calorimeter. Several amorphous alloy samples were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between T g and T x , i.e. Δ T x (= T g − T x ), is 34 K for Cu 10 Zr 60 Ni 30 , 48 K for Cu 20 Zr 60 Ni 20 , 78 K for Cu 40 Zr 55 Ni 5 , 81 K for Cu 50 Zr 35 Ni 15 , 61 K for Cu 50 Zr 40 Ni 10 and 64 K for Cu 50 Zr 45 Ni 5 .

This study examined the amorphization feasibility of Zr70−x−y Ti x Al y Ni10Cu20 alloy powders by the mechanical alloying (MA) technique. According to the results, after 5 to 7 hours of milling, the mechanically alloyed powders were amorphous basically in the ranges of 0 to 12.5 at. pct Ti and 2.5 to 17.5 at. pct Al. These ranges are larger than those of bulk amorphous alloys prepared by a squeeze mold casting technique. Most of the amorphous mechanically alloyed powders exhibited a wide supercooled liquid region of more than 60 K before crystallization. The glass-transition and crystallization temperatures of mechanically alloyed samples were different from those prepared by squeeze casting. It is suspected that different thermal properties arise from the introduction of impurities during the MA process. The amorphization behavior of Zr50Ti7.5Al12.5Ni10Cu20 was examined in detail. The X-ray diffraction and extended X-ray absorption fine structure (EXAFS) results show the fully amorphous powders formed after 5 hours of milling. A kinetically modified thermodynamic phase transformation process was observed for the glass-transition behavior in the Zr50Ti7.5Al12.5Ni10Cu20 amorphous powder.

The nanocrystalline Nb 3 Al is prepared by the gas condensation method. The nanocrystalline Nb 3 Al size with injected 0.1mbar helium pressure is about 15nm. During the gas condensation process, the superconductivity disappears at as-prepared NC Nb 3 Al with the mean particle size about 15 nm. After annealing the as-prepared NC Nb 3 Al at 500°C for 30 minutes, the mean particle size of NC Nb 3 Al is about 30 nm and the superconductivity appear with T c about 16K. The results show that superconductivity can be achieved in nanocrystals with a rather smaller size than the typical penetration length of magnetic field. Further study of the influence of gas condensation alloying at high magnetic fields is crucial to the understanding of the superconductivity properties of NC Nb 3 Al.

This study evaluates 40-nm-thick amorphous Ta2N (a-Ta2N) thin films with various compositions and metallurgical designs as diffusion barriers for copper metallization. Results based on sheet resistance measurements, x-ray diffraction analyses, and transmission and scanning electron microscopies consistently follow a sequence of coarsening copper grains, transforming a-Ta2N into a crystalline phase, and finally forming {111}-faceted pyramid Cu3Si precipitates and TaSi2. The degradation of the single-layered stoichiometric Ta2N (a-Ta67N33) barriers is primarily triggered by a premature crystallization of the amorphous barrier layers at temperatures as low as 450 °C. However, as adequately designed double-layered (20 nm Ta67N33/20 nm Ta62N38) amorphous barriers can be subjected to high-temperature annealing without crystallization, the effectiveness of the double-layered barriers can be significantly improved, elevating the degradation temperature by approximately 100 °C.

The progress of the preparation of amorphous Fe50Ta50 alloy powders, starting from elemental Fe and Ta crystalline powder mixtures, by mechanical alloying using a SPEX high energy ball mill was investigated. The as-milled Fe50Ta50 powders were examined as a function of milling time by scanning electron microscopy (SEM), microhardness, X-ray diAraction, diAerential thermal analysis (DTA), and extended X-ray absorption fine structure (EXAFS). The radial distribution functions (RDFs) obtained from Fourier transformation of EXAFS spectra reveal that there are diAerences in local atomic structure after prolong milling. When combined with information from other techniques, the results allow the amorphization process for Fe50Ta50 during the mechanical alloying (MA) to be better understood. ” 1998 Elsevier Science B.V. All rights reserved.

The microstructure and properties of Cu-C pseudoalloy films prepared by R.F. magnetron sputtering have been investigated. As Cu and C are mutually immiscible, nonequilibrium supersaturated solid solutions of C in Cu with nanocrystalline microstructures were observed in as-deposited films. Upon heating of the films, three major transition events took place. Recovery occurred at ∼280 to 300 °C, while at ∼400 °C, crystallites started to growth and coalescence, due to the release of strain energies stored during deposition. Annealing at above 600 °C led to the occurrence of grain growth and altered the microstructure considerably. Although attempts have been made in this study, a possible annealing-induced phase separation could not be unambiguously identified. Yet, the fact of low twin densities and fine grain structures observed in the annealed films suggests that the extensive grain growth was impeded by the presence of carbon. Resistivity and hardness properties correlated well with the film microstructure and were governed by the impurity effect of carbon. Low-carbon Cu-C films yielded relatively low resistivity, attributable to the improved film microstructure. Hardness results indicated the strengthening of films was mainly due to fine structure, presence of carbon, and grain refinement by annealing twins.

The high-temperature corrosion behavior of four iron aluminides containing Fe–18Al (in at.%) and three Fe–18Al–5M alloys (where M was Cr, Mn, or Mo) was studied over the temperature range of 700–900°C in a H 2 /H 2 S/H 2 O atmosphere. The corrosion kinetics followed the parabolic rate law in all cases, regardless of temperature and alloy composition. The parabolic rate constants decreased with decreasing temperature, and the addition of ternary elements resulted in various decreases in the corrosion rate compared with Fe–18Al. It was found that Mo was effective to improve the corrosion resistance at T ≤800°C while Cr had a better improvement at 900°C. The scales formed on all iron aluminides were strongly dependent on temperature and ternary addition.

Le comportement a la sulfuration d'aciers inoxydables 310 modifies (avec differentes quantites de Mo et Al jusqu'a 10 at%) a ete etudie entre 700-900°C sous pressions de soufre egales a 0.01 et 0.1 atm. La cinetique de corrosion de l'acier suit la loi parabolique et diminue quand la quantite de Mo et Al augmente. Les couches formees sur les aciers sont complexes et constituees de deux sous-couches. La couche externe est composee de sulfure de fer (avec du chrome dissous), de (Fe , Ni) 9 S 8 et de sulfures de chromes (Cr 2 S 3 /Cr 3 S 4 avec du fer dissous), tandis que la couche interne est un melange de plusieurs phases: Cr 2 S 3 /Cr 3 S 4 , Fe 1.25 Mo 6 S 77 , MOS 2 , Al 0.55 Mo 2 S 4 et FeS. Des marqueurs de Pt ont ete localises a l'interface entre la couche interne et externe, suggerant que la couche externe croit par transport de cations (Fe, Ni et Cr) vers l'exterieur et que la couche interne croit par transport de soufre vers l'interieur.

Phase transformation of non-BCC δ-A15 Cr thin films prepared by r.f. magnetron sputtering has been characterized. Using differential scanning calorimetry (DSC), we demonstrated for the first time that the phase transformation of the δA15 Cr phase to the equilibrium α-BCC Cr phase is an irreversible, exothermic, first-order transition. At a heating rate of 10 °C min −1 , the onset and peak temperatures of transformation were determined to be 428 and 437 °C, respectively. The enthalpy change of the transformation, Δ H, was estimated to be in a range from −6 to −12 kJ mol −1 . The uncertainty of ΔH was attributed to an ill-defined transition completion temperature and an incorporation of substrate material into the DSC film samples analyzed. Our in situ DSC results confirmed the metastable and allotropie nature of δ-A15 Cr phase, which has been proposed by other prior studies using conventional ex situ X-ray and electron diffraction methods. Our X-ray photoelectron spectroscopy analyses on as-deposited and annealed films showed that while the chrome oxides or carbides were formed inevitably in annealed films the Cr and O were mostly in the unbound states. Hence, it is unlikely that the δ-A15 Cr phase is of an oxide phase.

This study examined the amorphization behavior of Ni x Ta100−x alloy powders synthesized by mechanically alloying (MA) mixtures of pure crystalline Ni and Ta powders with a SPEX high energy ball mill. According to the results, after 20 hours of milling, the mechanically alloyed powders were amorphous for the composition range between Ni10Ta90 and Ni80Ta20. A supersaturated nickel solid solution formed for Ni90Ta10, as well. X-ray diffraction analysis reveals two different types of amorphization reactions. Through an intermediate solid solution and by direct formation of amorphous phase. The thermal stability of the amorphous powders was also investigated by differential thermal analysis. As the results demonstrated, the crystallization temperature of amorphous Ni-Ta powders increased with increasing Ta content. In addition, the activation energy of amorphous Ni-Ta powders reached a maximum near the eutectic composition.

Amorphization of mechanically alloyed TM-Ta (TM: Fe, Co, Ni) powders was performed in this study. The results indicated that complete amorphization was possible for the composition ranges TM 10 Ta 90 -TM 80 Ta 20 (TM: Ni, Co) and Fe 10 Ta 90 -Fe 70 Ta 30 . The range is larger than for amorphous Ni-Ta alloys prepared by the splat-quenching process and compatible with those of amorphous alloys of Co-Ta and Fe-Ta systems produced by vapor quenching methods, A supersaturated solid solution formed for Co-and Fe-rich compositions. The thermal stability was investigated by differential thermal analysis. The crystallization temperature of amorphous Co-Ta and Ni-Ta powders was found to be proportional to Ta content and higher than those of amorphous alloys produced by rapid cooling techniques.

The nanocrystalline AgxNi1−x solid solution is prepared by the gas condensation method. Transmission electron microscopy (TEM) images are used to measure the mean particle size of different AgxNi1−x concentrations. X-ray diffraction (XRD) and electron diffraction patterns of the nanocrystalline particles reveal that only fcc phases exist. These results indicate that the solid solubility in the AgNi system increases in the nanocrystalline state. The coercivity of the nanocrystalline AgxNi1−x solid solution increased with atomic percentage of Ni.

Amorphization behavior of Cox-Ta100-x powders by mechanically alloying mixtures of pure crystalline Co and Ta powder with a high-energy shaker ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Co10Ta90 and Co80Ta20. This range is larger than for amorphous alloys prepared by the r.f. sputtering process and equal to that of electron-gun-deposition method. A supersaturated cobalt solid solution formed for Co-rich composition. Moreover, the thermal stability was investigated by differential thermal analysis. The crystallization temperature of amorphous Co-Ta powders was found to be proportional to Ta content and higher than those of amorphous alloys produced by thin-film techniques. The high values of activation energy of amorphous Co-Ta powders were observed near the eutectic compositions. Experimental results indicated that the amorphization rate in the early stage of mechanical alloying was faster for the middle compositions than for Co- and Ta-rich compositions.

Systematic investigations were carried out on the synthesis of MoSi 2 powders by using a combination of mechanical alloying (MA) and vacuum heat treatment techniques. MA was conducted by two different high-energy ball mills under various milling conditions. The mechanically alloyed powders were characterized by X-ray diffraction and scanning electron microscopy as well as differential scanning calorimetry. The results showed that the preparation of MoSi 2 phase is not successful for all the mechanically alloyed powders after being milled with a less energetic planetary ball mill. However, the low-temperature α -MoSi 2 phase and the high-temperature β -MoSi 2 phase were formed when the same powder mixtures were mechanically alloyed with a more energetic shaker ball mill after a long milling time. Microstructural investigation indicates that cold welding behavior of Mo and Si powders during MA treatment has a pronounced effect on the formation of MoSi 2 phases. Vacuum heat treatment can also promote the formation of MoSi 2 phases in mechanically alloyed powders which are processed with shaker ball mill.

Nanocrystalline (NC) materials, exhibiting a large surface area, may be applied to gas sensors for which an excellent surface effect is required. In this study, tungsten oxide is synthesized by the gas-evaporation method and a mean particle size of about 10 nm is obtained. A step-heating sintering process is used to obtain the porous network-like structure of NC WO3. The results indicate that nanocrystalline WO3 is better than thin-film WO3 in sensing the H2S gas. The amount of dopants influences the sensitivity and the optimum operating temperature. An increasing weight percentage of Pd dopant will at first increase the sensitivity and lower the optimum operating temperature in 100 ppm H2S/air. But if excess dopant is added, e.g., if NC WO3 is 13.5 wt.% Pd-doped, it will oxidize at a high temperature and its characteristics of activating the detected gases on the surface of NC WO3 will disappear. The sensor thus loses the ability to sense at low temperature. Sensitivities of 9.9 and 9.7 can be achieved in 7.7 wt.% Pt-doped NC WO3 at 220 °C and 7.2 wt.% Pd-doped NC WO3 at 170 °C under 100 ppm H2S/air, respectively. The response times of 7.2 wt.% Pd-doped NC WO3 at 170 °C and 7.7 wt.% Pt-doped NC WO3 at 220 °C are less than 0.11 s.

The microstructural change of Ni 40 Zr 60 alloy during mechanical alloying of mixtures of the intermetallic compounds NiZr 2 and Ni 11 Zr 9 has been studied by transmission electron microscopy. A specific “cauliflower” phase was formed during early stage of mechanical alloying process. It is suggested that the solid state reaction between intermetallic compounds NiZr 2 and Ni 11 Zr 9 is not the only origin for the formation of the “cauliflower” phase.

The gas-condensation technique is used to produce the nanocrystalline (NC) WO3−x, Pt/WO3−x, and Pd/WO3−x powders under different atmosphere and pressure. HRTEM images show that a coherently bonded interface exists between Pt or Pd and WO3−x. The nanocrystal WO3−x, Pt/WO3−x, and Pd/WO3−x grow into a needle shape with a plate inside when these as-evaporated powders are compacted and sintered at 900 °C for 2 h. The plate grows preferentially in {220} plane along the 〈0011〉 direction. However, the mean particle size of nanophase Pt and Pd increases only from 3−x powders have better catalytic effects on converting CO to CO2 than nanophase WO3−x and Pd/WO3−x powders.

NixNb1−x alloys were synthesized from pure crystalline Ni and Nb powder by mechanical alloying under a controlled atmosphere. The mechanically alloyed powders were amorphous in the range 0.20