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The effects of replacing Cu or Y by a small-sized B in the Mg 65 Cu 25 Y 10 based alloy are examined. It is found that the replacement of Y by B consistently leads to apparent degradation in GFA; the large sized Y seems to be irreplaceable. In contrast, the replacement of the small sized Cu by the even smaller B to a small amount (1–5%) appears to be beneficial in terms of wider Δ T , higher GFA, thermal stability, and hardness, as well as lower density. In this study, the optimum quaternary alloy composition is identified to be Mg 65 Cu 22 Y 10 B 3 .

The preparation of Mg49Y15Cu36 metallic glass composite powders was accomplished by mechanical alloying of pure Mg, Y, Cu, and WC powder mixture after 10 h milling. In the ball-milled composites, initial WC particles were homogeneously dispersed in the Mg-based alloy glassy matrix. The metallic glass composites powders were found to exhibit a large supercooled liquid region before crystallization. Bulk metallic glass composites were formed by vacuum hot pressing the as-milled WC/ Mg49Y15Cu36 metallic glass composite powders at 473 K in the pressure range of 0.72-1.20 GPa. BMG composite with submicron WC particles homogeneously embedded in a highly dense nanocrystalline/amorphous matrix was successfully prepared under pressure of 1.20 GPa. It was found that the applied pressure during consolidation could enhance the thermal stability and promotes nanocrystallization of WC/ Mg49Y15Cu36 BMG composites.

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.

In the current study, amorphous Ni67−xZr10Ti23Yx alloy powders were synthesized by mechanical alloying technique. The mechanically alloyed powders were amorphous, after 5 h of milling, at compositions of Ni67−xZr10Ti23Yx (x=0–12). The amorphization behavior of Ni59Zr10Ti23Y8 was examined in details. The conventional X-ray diffraction and synchrotron EXAFS results confirm that the fully amorphous powders formed after 5 h of milling. The thermal stability of the Ni67−xZr10Ti23Yx amorphous powders was investigated by differential scanning calorimeter. As the results demonstrated, the amorphous powders with low yttrium concentration (x=0–6) or high yttrium concentration (x=12) exhibit no glass transition behavior. However, the Ni67−xZr10Ti23Yx (x=7–10) amorphous powders were found to exhibit a wide supercooled liquid region before crystallization.

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.

In the current study, we investigated the feasibility of fabricating amorphous Ni 57 Zr 20 Ti 20 Si 3 powders by mechanical alloying, and consolidating them into bulk metallic glasses by a vacuum hot pressing technique. The as-milled and hot-pressed samples were examined by X-ray diffraction, scanning electron microscope, and differential thermal analysis. According to the results, amorphous Ni 57 Zr 20 Ti 20 Si 3 powders were prepared after milling elemental powder mixtures for 5 h. The amorphous powders were found to exhibit a wide supercooled liquid region of 88 K before crystallization. Bulk metallic glasses were prepared successfully by consolidating the as-milled Ni 57 Zr 20 Ti 20 Si 3 amorphous powders using vacuum hot pressing in the supercooled liquid region. Vickers microhardnesses of the as-pressed samples are in the range of 788–830 kg/mm 2 .

This study examined the glass formation range of Ti94–x–yCuxNiySi4B2 alloy powders synthesized by mechanical alloying technique. According to the results, after 5–7 h of milling, the mechanically alloyed powders were amorphous at compositions with (x+y) equal to 20–40%. For the compositions with (x+y) larger than 45% or smaller than 10%, the structure of ball-milled powders is a partial amorphous single phase or coexistent partial amorphous and crystalline phases, respectively. The thermal stability of the amorphous powders was also investigated by differential thermal analysis. As the results demonstrated, several amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between Tg and Tx, i.e. ΔT(=Tx–Tg), are 52 K for Ti74Ni20Si4B2, 74 K for Ti64Ni30Si4B2, 58 K for Ti64Cu20Ni10Si4B2, and 61 K for Ti74Cu10Ni10Si4B2.

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 .

The purpose of this research was to evaluate the performance of a modified rolled homogeneous armor (MRHA) steel during ballistic impact tests. AerMet 100, AISI 1045 and 4130 steels were also tested for comparison with the MRHA results. The “white"‐etched portion of adiabatic shear bands was found on the front surface around penetration cavities in all the impacted armor plates. Scanning electron microscopic observation indicates that the adiabatic shear bands found in 4130, MRHA and AerMet 100 belong to transformed bands while those of 1045 steel are deformed bands. Ballistic test results show that the ballistic limit velocities of the 2.5‐mm thick MRHA steels are higher than those of AISI 1045 and 4130, and possibly compatible with AerMet 100 steel. For 2.5‐mm thick armor plates, the penetration modes were found to be dominated by ductile hole growth and plugging modes.

Cu60Zr30Ti10 metallic glass powder was prepared by mechanically alloying a mixture of pure Cu, Zr, and Ti powders after 5 h of milling. Cu60Zr30Ti10 bulk metallic glass (BMG) was synthesized by vacuum hot pressing the as-milled Cu60Zr30Ti10 metallic glass powder at 746 K in the pressure range of 0.72–1.20 GPa, and the structure was analyzed through X-ray diffraction and transmission electron microscopy. The pressure could enhance the thermal stability, and prolong the existence, of the amorphous phase inside the Cu60Zr30Ti10 powder. Furthermore, the corrosion behavior of the Cu-based BMG in four corrosive media was studied using a potentiodynamic method. The Cu60Zr30Ti10 BMG exhibited a low corrosion rate and current density in 1 N solutions of H2SO4, NaOH, and HNO3. X-ray photoelectron spectroscopy results revealed that the formation of Zr- and Ti-rich passive oxide layers provides a high corrosion resistance against 1 N H2SO4 and HNO3 solutions, and the breakdown of the protective film by Cl− attack was responsible for pitting corrosion in a 3 wt % NaCl solution. The formation of oxide films and the nucleation and growth of pitting were analyzed through microstructural investigations.

Iron nitrides were manufactured by mechanical alloying of Fe2.33N and Fe powder mixtures at starting compositions of Fe12N2 and Fe16N2 and annealed in air at 200 and 240°C. It was found that the supersaturated nanocrystalline α‐Fe solid solution phase was produced after MA, and iron nitrides were formed after heat treatment. The saturation magnetization (σ) of the heat‐treated powders is higher than those of the as‐milled powders. The σ values for the specimens heat treated at 200°C are higher than those heat treated at 240°C, and the highest value among all of the samples is 218 e.m.u./g which is obtained by annealing of as‐milled Fe12N2 powders in air at 200°C for 6 hours. The possible existence of the α”‐Fe16N2 phase is responsible for the high saturation magnetization in mechanically alloyed Fe16N2 and Fe12N2 powders.

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.

The influence of surface modifications on the room-temperature ductility of the Fe-18A1 and Fe-18Al-5Cr alloys was investigated. A variety of surface modification techniques including electroplating, magnetron sputtering and pack treatment were applied to the alloys to produce various protective coatings. From the results of tensile tests in air (70% humidity) at room temperature for the specimens in different surface conditions, several observations can be summarized. 1. The nickel-coating layer by using either electroplating or sputtering deposition had a limited effect on the ductility of alloys. 2. The chromium-coating layer by the electroplating technique had a negative effect on the ductility of alloys, 3. The specimen of Fe-18A1 alloy conducted by packing treatment at 1000°C for 8 hours had the highest elongation (19.6%) among those specimens studied. The significant improvement in the tensile ductility of Fe-18A1 and Fe-18Al-5Cr alloys by pack treatment are related to the forming of alumi...

This study investigated the feasibility of preparing intermetallic-matrix composite powders (NiAl/Al2O3) by mechanical alloying of Ni, Al and Al2O3 powder mixtures with various compositions of (NiAl)x(Al2O3)100–x. The as-milled powders were examined by X-ray diffraction, scanning electron microscopy, and differential thermal analysis. The formation of NiAl phase was noticed after 5 h of milling. Intermetallic-matrix composite powders (NiAl/Al2O3) were prepared successfully at the end of milling for (NiAl)x(Al2O3)100–x (x=79, 66, and 49), but no alumina phase was detected for (NiAl)95(Al2O3)5. It is suspected that the additions of alumina hampered the cold welding and fracturing process. The thermal analysis of (NiAl)x(Al2O3)100–x powders after 1 h of milling revealed that the transition temperature of NiAl phase increased with increasing amount of Al2O3 additions.

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.

Tantalum (Ta) and nitrogen-contained tantalum (Ta–N) thin films are sputter deposited at different argon/nitrogen flow ratios onto (001) silicon-based substrates with and without a titanium adhesion layer. The impact of varying the nitrogen flow rate and the underlying titanium on the phase formation process is also investigated using X-ray diffractometry, resistivity measurement and scanning electron microscopy. In contrast to previous works on bare silicon and thermally oxidized silicon wafers, our results indicate that a thin titanium adhesion layer inhibits the formation of high-resistivity (200 μΩ cm) tetragonal Ta over a wide range of realistic deposition conditions. The titanium layer leads to the deposition of a low-resistivity (29 μΩ cm) body-centered cubic α-Ta arising from its epitaxial orientation on the underlying titanium. The thresholds of nitrogen flow rates for depositing nitrogen-saturated α-Ta, amorphous Ta2N (a-Ta2N) and stoichiometric NaCl-type TaN on silicon are 0.25, 1.0 and 2.0 sccm, respectively. However, the underlying titanium can increase the thresholds for forming nitrogen-saturated α-Ta, a-Ta2N and stoichiometric TaN to 1.0, 1.5 and 2.5 sccm, respectively. Consequently, the electrical properties and microstructures for Ta and Ta–N thin films on Ti are significantly changed. Moreover, the barrier properties of 40-nm-thick stoichiometric a-Ta2N (Ta67N33) and nitrogen over-saturated a-Ta2N thin films are evaluated. According to X-ray diffraction analyses and sheet resistance measurements, all of the a-Ta2N barrier layers degrade in a similar manner, triggered mainly by an entire crystallization of the amorphous barrier layers. This is followed by a phase transformation process, sequentially forming Cu3Si and TaSi2. Cross-sectional transmission electron microscopy reveals that copper can penetrate through the crystallized films either along grain boundaries or thermal-induced crevices to react with silicon, subsequently forming Cu3Si precipitates. As adequately doping nitrogen into stoichiometric a-Ta2N can dramatically increase the crystallization temperature by approximately 150°C, the effectiveness of the nitrogen over-doped a-Ta2N barrier layers can be greatly improved, subsequently elevating the degrading temperature by at least 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.

Formation of nonequilibrium δ-A15 Cr thin films prepared by sputter deposition has been studied. Among processing parameters examined, working pressure, deposition temperature, and time were found to play an important role in affecting the formation of δ-A15 Cr phase. Susceptibility of δ-A15 Cr formation to the processing condition was essentially ascribed to its metastable nature. Since it could irreversibly transform into the equilibrium α-BCC Cr upon heating, the nonequilibrium δ-A15 Cr became unfavorable to form under the processing conditions that led to significant increases in film surface temperature such as lengthy depositions or elevated deposition temperatures. During the lengthy deposition, the film surface temperature inevitably increased as a result of continuous energetic particle bombardmetns. Such film surface temperature increase was analogous to an in situ annealing that was detrimental to the formation of thicker δ-A15 Cr films. To minimize the in situ annealing effect, the deposition with prolonged intermissions has showed very effectively to grow the relatively thick Cr films that had the nonequilibrium δ-A15 crystal structure.

Nickel and silicon powders, of average composition Ni3Si, were mechanical alloyed in a high energy ball mill. The severe plastic deformation produced by mechanical milling induced transformations with increasing milling time as follows: mixture of elemental Ni and Si powder → f.c.c. solid solution → nanocrystalline f.c.c. The structural evolution with milling time was followed by X-ray diffraction, differential scanning calorimetry (DSC), and transmission electron microscopy (TEM). Complete f.c.c. solid solution occurred at a milling time of 4 h and the saturated ΔH (by DSC) peak in the range of estimated enthalpy even after 24 h milling. The similarity of the mechanism of structural development by mechanical alloying of the Ni76Si24 powder mixture, and by mechanical milling of Ni76Si24 compound was also investigated in this study.

Amorphization behaviour of NixTa100−x alloy powders synthesized by mechanical alloying mixtures of pure crystalline Ni and Ta powders with a Spex high energy ball mill was studied. The mechanically alloyed powders were amorphous for the composition range between Ni10Ta90 and Ni80Ta20. This range is larger than amorphous alloys prepared by the rapid-quenching process or by electron-gun deposition technique. A supersaturated nickel solid solution formed for Ni-rich composition. The thermal stability has been investigated by differential thermal analysis. The crystallization temperature of amorphous Ni—Ta powders was proportional to the Ta content, and the activation energy of amorphous Ni—Ta powders exhibited a maximum near the eutectic composition. It is found that the amorphization rate at the early stage of the mechanical alloying process was faster in the intermediate compositions than those at both Ni- and Ta-rich compositions.

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 Fe nitride powders using a combined mechanical alloying and vacuum annealing technique. The results showed that supersaturated Fe and amorphous phases are formed by mechanically alloyed powder mixtures made of Fe2.33N and Fe powders with the starting compositions Fe100 − xNx (x = 11, 14, 20). The saturation magnetization of Fe100 − xNx powders can be improved by vacuum annealing, and reaches a maximum value of 245 e.m.u. g−1 at room temperature for the starting composition Fe86N14. The appearance of the α″-Fe16N2 phase is responsible for the anomalously high saturation magnetization in mechanically alloyed Fe86N14 powder after annealing at 240 °C for 4 h.

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 iron powders were produced by means of gas condensation. Pure nitrogen, or oxygen, or air, was introduced into the as‐made powders before they were taken from the chamber. Different atmospheres produced different layer structures around the iron particles. A high resolution transmission electron microscope was used to analyze the crystal structure and a vibrating‐sample magnetometer was used to measure the magnetic properties of nanocrystalline iron particles. The results showed that a layer of amorphous or nanocrystalline structure was formed initially on the surface of iron particles. This thin amorphous layer crystallized into Fe3O4 after annealing under electron irradiation when the introduced atmosphere was pure oxygen or air. However, it formed a passivated layer of ζ‐Fe2N when nitrogen was introduced. A hydrogen‐reducing process was employed to remove the oxide layer from the surface of nanocrystalline iron particles. The clean surface led to increased magnetization. The exchange an...

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.

Amorphization of TM‐Si (TM: trasition metal) alloy powders by mechanical alloying has been systematically investigated. Pure element powder mixtures were mechanically alloyed for ten hours with a high energy ball mill. The results show that amorphous metallic silicide powders were successfully synthesized in Ti‐Si, Zr‐Si, Nb‐Si, and Ta‐Si systems. Prediction of the amorphization range of mechanically alloyed TM‐Si powders by the Miedema model is inappropriate. The possible criteria for the amorphization of TM3Si powders after mechanical alloying 10 h in a shaker ball mill are (a) the free energy of amorphous state of TM3Si powders is less than −31.95 kJ/mole, and (b) the silicon to trasition metal atomic radius ratio is less than 0.985.

Systematic investigations were carried out on the synthesis of Fe nitride powders using a combined mechanical alloying and vacuum annealing technique. The results showed that supersaturated Fe and amorphous phases are formed by mechanically alloyed powder mixtures made of Fe2.33N and Fe powders with the starting compositions Fe100 − xNx (x = 11, 14, 20). The saturation magnetization of Fe100 − xNx powders can be improved by vacuum annealing, and reaches a maximum value of 245 e.m.u. g−1 at room temperature for the starting composition Fe86N14. The appearance of the α″-Fe16N2 phase is responsible for the anomalously high saturation magnetization in mechanically alloyed Fe86N14 powder after annealing at 240 °C for 4 h.

X-ray diffraction and transmission electron microscopy, along with electrical and film stress measurements, were used to evaluate the effectiveness of 40-nm-thick amorphous Ta2N and microcrystalline TaN diffusion barriers, both single and multilayered, against Cu penetration. Failure of the single-layered Ta2N diffusion barrier upon annealing is initialized by crystallization/grain growth, mainly helped by frozen-in compressive stress (3–4 GPa) to transform itself into a columnar structure with a comparable grain size to the thickness of the barrier. However, when subjected to annealing, the Ta2N/TaN alternately layered diffusion barrier with an optimum bilayer thickness (10 nm) remains almost stress-free (0–0.7 GPa) and transforms itself into an equiaxed structure with grain sizes of only ⩽3 nm. Such quasisuperlattice films can present lengthening and complex grained structures to effectively block Cu diffusion, thus acting as much more effective barriers than Ta2N (and TaN) single-layered films.