共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Inoue Y. Takahashi C. Suryanarayana T. Masumoto 《Journal of Materials Science》1982,17(6):1753-1764
Amorphous Hf-Nb-Si and Hf-V-Si alloys have been produced by rapidly quenching the melts using a melt-spinning technique. The silicon content in the amorphous alloys was limited to 14 to 20 at% and the niobium or vanadium content was limited to 0 to 45 at% and 0 to 35 at%, respectively. These amorphous alloys did not show any superconducting transition down to liquid helium temperature (4.2 K). However, a transition was detected above 4.2 K after inducing crystallization in these alloys by annealing at appropriate temperatures. The highest superconducting transition temperatures, T
c, attained were 8.9 K for the Hf45Nb40Si15 alloy annealed for 1 h at 1273 K and 6.7 K for the Hf50V35Si15 alloy annealed for 1 h at 1173 K. The upper critical magnetic field, H
c2, at 4.2 K and the critical current density, J
c, at zero applied field and 4.2 K were about 5.1×106A m–1 (6.4 T) and more than 1×104 A cm–2 for the Hf45Nb40Si15 alloy and more than 8.0×106 A m–1 (10 T) and 5×103 A cm–2 for the Hf50V35Si15 alloy. Detailed transmission electron microscopic studies of the annealed structure of these amorphous alloys established that, after crystallization, these alloys contain a body-centred cubic -Hf(Nb) solid solution and body-centred tetragonal Nb3Si phases in the Hf45Nb40Si15 alloy and hexagonal Hf5Si3, face-centred cubic HfV2 and cubic V3Si phases in the Hf50V35Si15 alloy. Since Nb3Si and Hf5Si3 are not superconducting above 4.2 K, it has been concluded that superconductivity in these crystallized alloys is due to the precipitation of -Hf(Nb) solid solution in the Hf-Nb-Si alloys and to the precipitation of HfV2 and V3Si compounds in the Hf-V-Si alloys. 相似文献
2.
This research studied the fracture toughness of the Fe-7Al-27Mn alloys with increasing carbon contents: 0.5% C, Fl alloy: 0.7% C, F2 alloy (with 4.0% Cr); and 1.0% C, F3 alloy. Fracture toughness experiments were conducted at temperatures of 25, – 50, – 100 and – 150 °C. It was found that plane-stress,K
C, values as measured by the R-curve method, decreased as the temperature dropped. F1 alloy possessed the highestK
C value at all temperatures among the three alloys. TheK
C values of the F2 and F3 alloys were similar at ambient temperatures, but F3 maintained the toughness property and ductility better at sub-zero temperatures. Quantitatively,K
IC values of the F2 alloy at – 150 °C were ca, 60% less than at 25 °C, but F1 and F3 alloys dropped by only ca. 30%. Using a compact-tension specimen, 20.0 mm thick, at –150°C only alloy F2 satisfied the requirement of plane-strain fracture toughness with aK
C value of 106 MPa m1/2. The existence of Cr (4.0%) and the formation of a ferrite phase in an austenite matrix was responsible for the low toughness value observed. 相似文献
3.
Microstructural changes in Fe73.5–xCrxCu1Nb3Si13.5B9 (0x5) alloys with thermal treatment were studied by electron microscopy. In a first stage, around 800 K, an Fe(Si) nanocrystalline phase is formed in the amorphous residual matrix. Crystallization onset is enhanced with the Cr content of the alloy. In a second stage, around 950 K, full crystallization of the samples leads to the formation of a body centred cubic (b.c.c.) boride-type unknown crystal phase with a lattice parameter of a=1.52 nm, and recrystallization of the previous Fe(Si) nanophase also occurs. No qualitative differences were found between dynamic and isothermal crystallization. The size effect for thin samples is limited to a lowering of crystallization temperatures. For isothermal nanocrystallization in the temperature range 775–900 K, the mean grain size of the nanocrystals increases for short annealing times to stabilize at a constant value of about 10–15 nm for long annealing times. The stabilized grain size increases with increasing annealing temperature and slightly decreases with the Cr content of the alloy. 相似文献
4.
Attempts to substitute Bi for Nd in orthorhombic NdBa2Cu3O
y
, prepared in air or oxygen at about 950°C led instead to formation of Ba2NdBiO6, a new cubic compound witha=0.8703 nm. The possibility was then explored of preparing superconducting (Nd1–x
Bi
x
)Ba2Cu3O
y
, by first forming the tetragonal phase at 880–950°C in nitrogen or argon followed by reheating in oxygen or air at 250–500°C in order to insert the additional oxygen required to yield the orthorhombic form while avoiding oxidation of Bi3+ to Bi5+. X-ray diffraction studies, electrical conductivity measurements, and thermogravimetric analysis of products indicate that Bi does not enter the NdBa2Cu3O
y
, lattice in either the tetragonal or the orthorhombic phase. Ba2NdBiO6 clearly forms on reheating in oxygen or air even at low temperatures, and evidence is presented that a poorly crystallized oxygen-deficient form of this compound is already present prior to the reheating. 相似文献
5.
A. Inoue Y. Takahashi C. Suryanarayana T. Masumoto 《Journal of Materials Science》1982,17(11):3253-3262
By rapidly quenching with a melt-spinning apparatus, it has been possible to produce ductile amorphous single-phase ternary Zr85–x
M
x
Si15 (M=IV–VIII group transition metals) alloys in wide composition ranges. The crystallization temperature, activation energy for crystallization and hardness increase significantly only with the addition of group V and VI elements (V, Nb, Ta, Cr, Mo and W). Such a solute element effect could be interpreted on the basis that the chemical bonding between the solute elements and silicon is stronger for the group V and VI elements than for the other group elements. Crystallization studies of the amorphous Zr85Si15 and Zr65Nb20Si15 alloys have been carried out through transmission electron microscopy and differential scanning calorimetry techniques. The binary alloy crystallizes by the uniform precipitation of b c c-Zr over the entire area of the amorphous matrix followed by the appearance of the metastable b c tetragonal Zr3Si compound from the remaining amorphous phase. On the other hand, the ternary alloy transforms by the simultaneous precipitation of-Zr(Nb) and b c tetragonal Nb3Si. The-Zr and Zr3Si phases were found to be in metastable states, the equilibrium structure being a mixture of-Zr and Zr4Si compound in the binary alloy. 相似文献
6.
N. Kumada T. Kyoda Y. Yonesaki T. Takei N. Kinomura 《Materials Research Bulletin》2007,42(10):1856-1862
Perovskite-type KNbO3 powder was prepared by hydrothermal reaction using Nb2O5 in KOH solution. A single phase of KNbO3 was obtained when the molar ratio of KOH/Nb2O5 was above 20 and the reaction temperature was above 160 °C. Three types of KNbO3 powder with the orthorhombic, tetragonal and cubic symmetries were obtained, depending on the reaction temperature and the ratio of KOH/Nb2O5. The molar ratios of K/Nb in the cubic and tetragonal phases were 0.91 and 0.94, respectively and that of the orthorhombic one was 0.98, and the mass loss was observed in the TG curves of tetragonal and cubic phases. The tetragonal and cubic phases were stabilized by OH− and adsorbed water. 相似文献
7.
Young G. Kim Tae Y. Seong Jae H. Han Alan J. Ardell 《Journal of Materials Science》1986,21(4):1357-1362
The effects of applying different solution and ageing conditions on the electrical resistivity and precipitation behaviour of a Cu-1.3Ni-0.3Si-0.03P (wt%) alloy were studied. The electrical resistivity of solution-treated material is greatly reduced, by about 50%, by the ageing processes. The reduction in resistivity is due to depletion of solute atoms from the copper matrix by the formation of precipitates. Double ageing peaks appeared during isothermal ageing due to the formation of Ni3P and Ni2Si precipitates. The first maximum, due to the precipitation of Ni3P, appeared at about 1 h of ageing time, while the second peak, due to Ni2Si, appeared at around 10 h of ageing time when aged at 450°C. The precipitate Ni3P forms early and the alloy starts to over-age before Ni2Si precipitates and the alloy reaches maximum hardness. The maximum hardness produced by the precipitations of Ni3P and Ni2Si decreased with increasing ageing temperature from 450 to 550°C. The time to reach the maximum hardness due to Ni3P precipitation became shorter, while that of Ni2Si became longer, as the solution treatment temperature increased from 780 to 1020° C. The apparent activation energy for Ni2Si precipitation was found to be about 80 kJ mol–1 while that for Ni3P precipitation was about 25 kJ mol–1. 相似文献
8.
T. Yu. Losevskaya V. I. Voronkova V. K. Yanovskii N. I. Sorokina 《Inorganic Materials》2001,37(9):968-970
K2TiNb2P2O13single crystals (monoclinic structure, a= 13.788 Å, b= 6.418 Å, c= 16.927 Å, = 97°) were grown from off-stoichiometric K2O–TiO2–Nb2O5–P2O5melts, and their habit was described. The 300°C electrical conductivity of the crystals was determined to be 5 × 10–4S/cm. 相似文献
9.
A. Inoue Y. Takahashi C. Suryanarayana A. Hoshi T. Masumoto 《Journal of Materials Science》1981,16(11):3077-3086
Amorphous alloys containing 0 to 40 at% Ta and 15 to 20 at% Si have been produced in the ternary Ti-Ta-Si system by rapidly quenching the melts using a melt-spinning technique. The amorphous alloys did not show any superconducting transition down to liquid helium temperature (4.2 K). However, a transition was detected above 4.2 K after inducing crystallization in these alloys by annealing at appropriate temperatures. The superconducting transition temperature, T
c, increased with increasing tantalum content and showed the highest value of 7.6 K for the Ti45Ta40Si15 alloy annealed for 1 h at 1073 K. An upper critical magnetic field, H
c2 of 4.7×106 Am–1 at 4.2 K and a critical current density, J
c, of 1.5×104 A cm–2 at zero applied field and 4.2 K were recorded for this alloy. Detailed electron microscopic studies of the crystallization behaviour of the amorphous alloys established that a supersaturated solid solution of tantalum in -Ti with a bcc structure forms first, followed by the precipitation of the bc tetragonal Ta3Si compound. Since Ta3Si is not superconducting above 4.2 K, it has been concluded that superconductivity in the crystallized alloys is due to the precipitation of -Ti(Ta) solid solution. 相似文献
10.
The thermal expansion of superconducting Bi1.6Pb0.4Sr2Ca2Cu3Ox (BiPbSrCaCuO) and its oxide components Bi2O3, PbO, CaO and CuO have been studied by high-temperature dilatometric measurements (30–800°C). The thermal expansion coefficient for the BiPbSrCaCuO superconductor in the range 150–830°C is =6.4×10–6K–1. The temperature dependences of L/L of pressed Bi2O3 reveals sharp changes of length on heating (T
1=712°C), and on cooling (T
2=637°C and T
3=577°C), caused by the phase transition monoclinic-cubic (T
1) and by reverse transitions via a metastable phase (T
2 and T
3). By thermal expansion measurements of melted Bi2O3 it is shown that hysteresis in the forward and the reverse phase transitions may be partly caused by grain boundary effect in pressed Bi2O3. The thermal expansion of red PbO reveals a sharp decrease in L/L, on heating (T
1=490°C), related with the phase transition of tetragonal (red, a=0.3962 nm, c=0.5025 nm)-orthorhombic (yellow, a=0.5489 nm, b=0.4756 nm, c=0.5895 nm). The possible causes of irreversibility of the phase transition in PbO are discussed. In the range 50–740°C the coefficient of thermal expansion of pressed Bi2O3 (m=3.6 × 10–6 and c=16.6×10–6K–1 for monoclinic and cubic Bi2O3 respectively), the melted Bi2O3 (m=7.6×10–6 and c=11.5×10–6K–1), PbO (t=9.4×106 and or=3.3×10–6K–1 for tetragonal and orthorhombic PbO respectively), CaO (=6.1×10–6K–1) and CuO (=4.3×10–6K–1) are presented. 相似文献
11.
The influence of Ti addition on the high temperature oxidation behavior of FeAl intermetallic alloys in air at 1000°C and 1100°C has been investigated. The oxidation kinetics of FeAl alloys was examined by the weight gain method and oxide products were examined by XRD, SEM, EDS and EPMA. The results showed that the oxidation kinetic curves of both Ti-doped and binary Fe-36.5Al alloys could be described as different parabolas that followed the formula: (W/S)2 = K
p
t + C. The parabolic rate constant, K
p values are approximately 2.4 and 3.3 mg2 cm–4 h–1 for Fe-36.5Al alloy and about 1.3 and 2.0 mg2 cm–4 h–1 for Fe-36.5Al-2Ti alloy when oxidizing at 1000°C and 1100°C respectively. The difference between Fe-36.5Al and Fe-36.5Al-2Ti alloy is not only in the surface morphology but also in the phase components. In the surface there is only -Al2O3 oxide for Fe-36.5Al alloy while there are -Al2O3 and TiO oxides for Fe-36.5Al-2Ti alloy. The effects of Ti addition on the oxidation resistance of FeAl alloy were addressed based on the microstructural evidence. 相似文献
12.
Mechanical and elastic properties of transparent TeO2-based glass-ceramics (15K2O · 15Nb2O5 · 70TeO2) consisting of nanocrystalline particles (each particle size: 40–50 nm) and showing optical second harmonic generation were evaluated by means of usual Vickers indentation and nanoindentation tests. The precursor glass has Vickers hardness H
v of 2.9 GPa, Young's modulus E of 54.7 GPa, the fracture toughness K
c of 0.25 MPam1/2 and Poisson's ratio of 0.24. The transparent nanocrystalline glass-ceramic heat-treated at 420°C for 1 h has H
v = 3.8 GPa, E = 75.9 GPa and K
c = 0.34 MPam1/2, and the opaque glass-ceramic heat-treated at 475°C for 1 h has H
v = 4.5 GPa, E = 82.9 GPa and K
c = 0.68 MPam1/2, demonstrating that poor mechanical and elastic properties of the precursor TeO2-based glass are improved through sufficient crystallization. The fracture surface energy, brittleness and elastic recoveries (about 44%) after unloading (the maximum load: 30 mN) of transparent nanocrystalline glass-ceramics are almost the same as those of the precursor glass, implying that the interaction among nanocrystalline particles is not so strong. 相似文献
13.
A technique of top-cooling-solution-growth (TCSG) has been developed to grow the piezo-/ferroelectric perovskite single crystals of 0.955Pb(Zn1/3Nb2/3)O3-0.045PbTiO3 [PZNT95.5/4.5]. The flux composition and concentration, and the thermal parameters have been optimized, leading to the growth of high quality PZNT crystals with a size up to 20 × 15 × 10 mm3. The perovskite crystals are found to form upon slow cooling down to 1020°C, while the undesirable pyrochlore crystals of Pb1.5Nb2O6.5-type start growing upon further cooling from 1020°C to 950°C. By controlling the growth pathway, the formation of the pyrochlore phase can be avoided. The dielectric properties of the grown PZNT95.5/4.5 crystals have been measured as a function of temperature at various frequencies. Upon heating, the phase transition for the rhombohedral R3m to the tetragonal P4mm phase takes place at 132°C, while the tetragonal to cubic phase transition occurs at 160°C. The TCSG developed in this work provides an alternative technique to grow PZNT piezocrystals of medium size at low cost for transducer applications. 相似文献
14.
A study has been made of the mechanism and kinetics of formation of Nb3Sn from the elemental components. The Nb3Sn forms partly by diffusion and partly by a solution/ deposition mechanism which depends on thermal gradient mass transfer. The effect of this is to modify the growth equation to x = kt
0.36 over the temperature range 950 to 1150° C. The temperature dependence of these two processes, given by the difference between the activation energies for diffusion and solution, is –9.7 kcal/g atom (–0.42 eV/atom) so that the thickness of the Nb3Sn layer produced in any given time decreases with increasing temperature.Various experimental factors are discussed in terms of their influence on the rate of growth of the layer. 相似文献
15.
Al-3.3Fe-10.7Si alloy has been experimentally made with spray deposition technology. The internal friction of the alloy which was directly associated with the microstructures under spray deposited, extruted and heat treated conditions has been investigated using a low frequency inverted torsion pendulum over the temperature region of 10–300 °C. An internal friction peak was observed in the temperature range 50–250 °C in the present alloy. The Q-1 peak decreased after extruted and in subsequent to the earliness of isothermal annealing, which was found to be directly attributed to the precipitation of FeAl2 and Al– Fe– Si intermetallics from the supersaturated aluminium alloy matrix. We suggest that the internal friction peak in the alloy originates from grain boundary relaxation, but the grain boundary relaxation can also be affected by FeAl2 and Al– Fe– Si intermetallics at the grain boundaries, which will impede grain boundary sliding. 相似文献
16.
It has been demonstrated that high rate d.c. magnetron sputtering can easily prepare materials such as Nb3Ge and Nb3Si in a metastable state. This sputtering-system was made in an effort to stabilize the metstable phases. Specimens were quenched just after sputtering from 1100° C to liquid N2 temperature at the rate of 3500° C min–1. The relation between quenching rate and superconducting onset temperture, T
c0, the transition width, T
c, and the lattice constant, a
0 were examined. The results show that quenching just after sputtering is very useful in preparing metastable materials. 相似文献
17.
K. P. Mizgalski O. T. Inal F. G. Yost M. M. Karnowsky 《Journal of Materials Science》1981,16(12):3357-3364
The crystallization behaviour of the Metglas 2826 MB alloy (Fe40Ni38Mo4B18) has been studied using resistance measurements and X-ray diffraction techniques. Three annealing sequences were used to follow the process. Samples were annealed isothermally (a) at 780° C in a vacuum of 2×10–5 torr for times in the range 1 sec to 4 h, (b) for 2 h in an argon atmosphere at temperatures where the resistance curve indicated phase changes to occur, and (c) for 300 h in 100 torr of helium at 400, 600, 700 and 850° C. From these annealing sequences it was found that the alloy did not crystallize below 410° C and followed a crystallization process of: amorphous Fe40Ni38Mo4B18 Fe
x
Ni23–x
B6 (cubic)+glassy matrix Fe
x
Ni23–x
B6+(Fe, Ni) (FCC) (Fe, Ni)3B(bct). This series of transformations was followed for Sequences (a) and (c) above, but was slightly different for Sequence (b). An orthorhombic (Fe, Ni)3 B phase was found in the samples annealed in a vacuum of 2×10–5 torr.Trademark of Allied Chemical Co. 相似文献
18.
Experiments are described in which the fracture toughness,K
c, of PMMA has been determined in the temperature range –190 to + 80° C and over the crack speed range of 10–2 to 102 mm sec–1. Single edge notch tension was used for instability measurements but the other data were obtained using the double torsion method. In the range –80 to + 80°C the variations inK
c may be described in terms of modulus changes and a constant crack opening displacement criterion. Crack instabilities are correlated with isothermal-adiabatic transitions at the crack tip. Below –80° C there is an inverted rate dependence associated with thermal effects during post-instability crack propagation. 相似文献
19.
The microstructure of Fe-Si alloys containing 8 and 15.5 at % Si and heat-treated between 550 and 1200°C is studied by transmission electron microscopy, and the phase composition of alloys containing 19 and 23 at % Si is determined by x-ray diffraction. The Fe-15.5 at % Si alloy heat-treated above 700°C is found to consist of a disordered solid solution and B2 phase. The B2 particles can be thought of as portions of {100} layers consisting entirely of Si atoms and sandwiched between {100} layers of Fe atoms, that is, as a two dimensional phase. At t 675°C, a compositionally modulated microstructure develops in which the Si-enriched zones have the Fe3 Si stoichiometry and DO3 structure. At high temperatures, the Fe-19 at % Si alloy consists of the and B2 phases, and the Fe-23 at % Si alloy consists of the and DO3 phases. These findings are at variance with the generally accepted Fe-Si phase diagram.Translated from Neorganicheskie Materialy, Vol. 41, No. 1, 2005, pp. 28–35.Original Russian Text Copyright © 2005 by Ustinovshchikov, Sapegina. 相似文献
20.
The kinetics of the crystallization of Fe73.5Cu1Nb3Si13.5B9 amorphous alloy was studied using Mössbauer spectroscopy and X-ray diffractometry. During isothermal annealing of the samples, two phases were observed: a crystalline D03-FeSi alloy with fine grains and an amorphous phase enriched with niobium, boron and copper. It was found that the growth rate of the particles of the crystalline alloy was controlled by diffusion. For longer annealing time or at higher annealing temperature the growth process was found to be suppressed, probably by the niobium atoms. The activation energy obtained for the crystallization was about 143 kJ mol–1. 相似文献