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Potassium bubbles in tungsten wire 总被引:2,自引:0,他引:2
C. L. Briant 《Metallurgical and Materials Transactions A》1993,24(5):1073-1084
Tungsten filaments for incandescent lamps almost always contain potassium bubbles. These are required to produce the interlocking
grain structure that gives the tungsten lamp filament a long life. In this article, we consider the formation of the bubbles
from the ellipsoids of potassium produced by deformation, the growth of these bubbles as a result of internal pressure created
by the potassium vapor within the bubbles, and the reasons why these bubbles can sometimes grow to very large sizes. In each
case, we present a simple model to describe the process. We finally use nucleation theory to describe the overall process
of bubble growth.
Formerly Visiting Scientist, Institute for Technical Physics, Hungarian Academy of Science, Budapest, Hungary 相似文献
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An anomalous recrystallization behavior has been observed in 0.010 in. diam K?Si?Al doped tungsten wire. Recrystallization to relatively equiaxed grains occurred only in the core at temperatures of 1400° to 1600°C, but not at lower temperatures or higher temperatures up to 1900°C. The anomalous recrystallization reaction was suppressed when the wire was preannealed at 1700° to 1900°C, but not by preanneals at temperatures between 500° and 1100°C. Critically shadowed electron fractographs indicated that linear arrays of microporosity (≈100Å diam) were responsible for the stabilization of the fibrous structures, Recrystallization occurred when these strings of pores were absent. 相似文献
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V. I. Torbov V. N. Troitskii T. V. Rezchikova A. Z. Rakhmatullina A. P. Zuev V. N. Doronin 《Powder Metallurgy and Metal Ceramics》1982,21(1):42-45
Conclusions Vacuum annealing at a temperature above 900°K enables the specific surfaces of very fine loose tungsten and molybdenum powders to be varied in a wide range. The vacuum sintering of compacts pressed from very fine (particle size less than 0.05m tungsten and molybdenum powders is accompanied by severe cracking. In the hot pressing of very fine Mo and W powders produced by the pyrolysis of carbonyls in a stream of high-temperature plasma, a specimen density close to theoretical is reached at 1600°K i.e., at a temperature not less than 400°K lower than the sintering temperatures of powders of particle size more than 1 m. Sintering lowers the amounts of carbon and oxygen in Mo and W by more than half compared with the starting condition.Translated from Poroshkovaya Metallurgiya, No. 1(229), pp. 47–51, January, 1982. 相似文献
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J. L. Walter C. L. Briant E. F. Koch 《Metallurgical and Materials Transactions A》1982,13(8):1501-1510
As-drawn tungsten wire has been known to split and rolled tungsten sheet to delaminate if mishandled. The mechanism of splitting
of tungsten wire in a knife-edge compression test was studied for a number of tungsten wires of different diameter, composition,
processing history, and origin. The micro-structure of these wires was examined by optical, scanning, and transmission electron
microscopy. Grain boundary composition was determined by Auger electron spectroscopy. A correlation between the number of
transverse boundaries in the microstructure and the split load in the knife-edge compression test was observed; the greater
the number of transverse boundaries, the lower the load required to induce a split. This relationship held for all wires,
regardless of the history of the wire. It was concluded that transverse grain or subgrain boundaries are responsible for initiating
splits in the knife-edge compression test. The mechanism of splitting is discussed. 相似文献
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B. P. Bewlay C. L. Briant M. L. Murray 《Metallurgical and Materials Transactions A》1998,29(12):2933-2939
The present article describes the effects of molybdenum contamination on the microstructure of lampgrade potassium-doped tungsten
wire after exposure to temperatures above 2500 °C. Molybdenum is generally used as the mandrel material in the coiling of
single and double coil lamp filaments. During high-temperature heat treatments used during filament manufacture, significant
amounts of molybdenum can diffuse into the tungsten. In this study, tungsten-molybdenum diffusion couples were prepared and
heat treated at temperatures of 2500 °C and above to generate molybdenum contamination of the tungsten. After dissolution
of the molybdenum from the diffusion couple, additional high-temperature heat treatments of the tungsten were performed to
simulate lamp burning; equiaxed grains and excessive potassium bubble growth were observed in the tungsten. Explanations for
these microstructural changes are discussed. Electron beam microprobe data were also obtained to characterize tungsten-molybdenum
interdiffusion, and a Boltzmann-Matano analysis was performed to evaluate the contribution of the concentration dependence
of the interdiffusion coefficient to the measured diffusion profiles. 相似文献
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The creep behavior of 0.018 cm diam doped tungsten wire has been studied over a range of stress from 30 to 90 MPa and temperature
from 2400 to 2800 K. Grain aspect ratio (gar) had a strong influence on creep and rupture of the recrystallized wires, and
separated the creep behavior into two regimes with a transitional gar of about 11 between the two. The low gar regime showed
lower strength and characteristics typical of grain boundary sliding. In the high gar regime, properties were independent
of gar, and evi-dence is presented to show that creep is governed by dislocation-bubble dispersion strengthening.
Formerly with the Lamp Business Division of General Electric Company, E. Cleveland, Ohio 相似文献
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随着对钨细泥特点的不断研究,浮选、重选、磁选、浸出等单一工艺不能满足对钨细泥选别指标的要求,多种选别方法结合的联合工艺应运而生。文中简述了各种流程的特点以及针对钨细泥选别在选厂调研中发现的问题,对未来钨细泥的研究方向以及设备应用进行展望。 相似文献
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随着对钨细泥特点的不断研究,浮选、重选、磁选、浸出等单一工艺不能满足对钨细泥选别指标的要求,多种选别方法结合的联合工艺应运而生.文中简述了各种流程的特点以及针对钨细泥选别在选厂调研中发现的问题,对未来钨细泥的研究方向以及设备应用进行展望. 相似文献
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The microstructures and longitudinal fracture resistances of 0.635 mm diam lamp-doped and undoped tungsten wire were examined
in the as-drawn condition and after anealing at temperatures between 600 and 1500°C. A variety of experimental techniques
were employed, including Auger Electron Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy and a
newly developed mechanical testing technique. The longitudinal fracture mode was intergranular for all wires and a second
phase was observed on the grain boundaries of all doped wires. High concentrations of the dopant element potassium were present
on the fracture surfaces of doped wires and experimental evidence was obtained which suggests they may be due to postfracture
surface diffusion. Doped wires demonstrated increasing amounts of structure coarsening up to 1500°C whereas large equiaxed
grains were formed in undoped wires annealed at 1300 and 1500°C. The longitudinal fracture resistance of undoped wire was
unaltered by annealing at 1050°C and below, but decreased dramatically after annealing at 1300 and 1500°C. In contrast the
fracture resistance of doped wire decreased after annealing at 1050 and 1300°C, but increased after annealing at 1500°C. Fracture
resistance is discussed in terms of microstructure and fracture surface chemistry.
A. W. FUNKENBUSCH, formerly Research Metallurgist with General Electric Refractory Metals Product Department 相似文献
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Density measurements were made on 0.762 mm W-l wt pct ThO2 wires which had been annealed at temperatures between 1000°C and 2000°C for times up to 120 min. Selected specimens were
examined using optical and scanning electron microscopy. The results of this study indicate that the low, as-worked wire density
is a result of large cracks associated with the ThO2 particles. Time-temperature annealing regimes, significantly below those necessary for recrystallization of the wire, result
in partial healing of the cracks. This crack healing process can be followed qualitatively by observing longitudinal fracture
surfaces in the scanning electron microscope and quantitatively by changes in the density of the wire. The apparent activation
energy for the crack healing process was found to be 57.8 kcal/mole. The results suggest that crack closure is a result of
both shear and grain boundary diffusion transport processes. It is concluded that the presence of cracks can influence the
morphology of the recrystallized grains. 相似文献