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Author: Joseph R. Stephens Publisher: ISBN: Category : Tungsten Languages : en Pages : 32
Book Description
The effect of oxygen on the mechanical properties of commercial polycrystalline tungsten and zone-refined single-crystal tungsten was evaluated by means of tensile tests of oxygen-doped specimens in the ductile-to-brittle transition temperature range. The effect of oxygen as a surface oxide that might be encountered in normal working and forming operations was evaluated by means of a three-point loading bend test at room temperature. Oxygen doping of the polycrystalline and single-crystal tensile specimens was accomplished by equilibrating the specimen and tungsten oxide powder in a sealed tungsten capsule at high temperatures. A desired oxygen concentration could be achieved by varying the time of doping in the temperature range of 3000 to 3600 F. Results showed that the commercial recrystallized rods containing 4 parts per million (ppm) oxygen had a ductile-to-brittle transition temperature (based on 50-percent reduction in area) of 4500 F. Increasing the oxygen concentration to 10, 30, and 50 ppm increased the transition temperature to 6600, 840, and 1020 F, respectively. The oxygen additions also produced a progressive lowering of the ultimate tensile strength. The mechanism for the effect of oxygen on the transition temperature and ultimate tensile strength is believed to be that of segregation of the oxygen atoms at the grain boundaries. The oxygen additions also caused a progressive lowering of the yield strength, which is believed to result from the interaction of oxygen with carbon atoms or other impurity atoms present in the tungsten lattice.
Author: Joseph R. Stephens Publisher: ISBN: Category : Tungsten Languages : en Pages : 32
Book Description
The effect of oxygen on the mechanical properties of commercial polycrystalline tungsten and zone-refined single-crystal tungsten was evaluated by means of tensile tests of oxygen-doped specimens in the ductile-to-brittle transition temperature range. The effect of oxygen as a surface oxide that might be encountered in normal working and forming operations was evaluated by means of a three-point loading bend test at room temperature. Oxygen doping of the polycrystalline and single-crystal tensile specimens was accomplished by equilibrating the specimen and tungsten oxide powder in a sealed tungsten capsule at high temperatures. A desired oxygen concentration could be achieved by varying the time of doping in the temperature range of 3000 to 3600 F. Results showed that the commercial recrystallized rods containing 4 parts per million (ppm) oxygen had a ductile-to-brittle transition temperature (based on 50-percent reduction in area) of 4500 F. Increasing the oxygen concentration to 10, 30, and 50 ppm increased the transition temperature to 6600, 840, and 1020 F, respectively. The oxygen additions also produced a progressive lowering of the ultimate tensile strength. The mechanism for the effect of oxygen on the transition temperature and ultimate tensile strength is believed to be that of segregation of the oxygen atoms at the grain boundaries. The oxygen additions also caused a progressive lowering of the yield strength, which is believed to result from the interaction of oxygen with carbon atoms or other impurity atoms present in the tungsten lattice.
Author: Joseph R. Stephens Publisher: ISBN: Category : Low temperatures Languages : en Pages : 24
Book Description
A study was undertaken to determine the effects of the interstitial impurities oxygen and carbon on the mechanical properties of polycrystalline tungsten and high-purity tungsten single crystals. Results of tensile tests showed that additions of both oxygen and carbon to polycrystalline tungsten produced a marked increase in the ductile to brittle transition temperature. Oxygen and carbon produced a much smaller increase in the transition temperature of the single-crystal specimens compared with equivalent amounts of impurities in the polycrystalline specimens. Addition of oxygen to polycrystalline tungsten lowered both the ultimate tensile strength and the yield strength, but had no measurable effect on the strength properties of single-crystal specimens. Carbon additions to both polycrystalline and single-crystal specimens did not affect the ultimate tensile strength; however, a large increase in the yield strength resulted. The results suggest that oxygen embrittlement in tungsten is caused by grain-boundary segregation, while carbon embrittlement results from an interaction between carbon atoms and dislocations within the tungsten lattice.
Author: Vincent David Barth Publisher: ISBN: Category : Tungsten Languages : en Pages : 192
Book Description
The report presents a detailed review of available information on the oxidation of W and its alloys. W is relatively inert below 700 C. As the temperature is increased above this level, however, oxidation becomes progressively more rapid, reaching catastrophic rates at temperatures around 1200 C and above. Various theories for the mechanism and rates of W oxidation at different temperatures are reviewed, and the effect of pressure and water vapor on the stability of W oxides is discussed in detail. The elevatedtemperature reactions of W with other materials, such as refractory oxides, and with gases other than oxygen also are covered. Information on the protection of W by alloying and coating is included. (Author).
Author: I. J. Toth Publisher: ISBN: Category : Languages : en Pages : 234
Book Description
The work is concerned with improvements in the sintering properties of Tungsten. Two methods of 'activation sintering' are studied, halogen activation and metallic activation. An example of the first is the use of hydrogen and bromine as sintering atmosphere. No significant increase in densification was noted, except for a moderate improvement at temperatures around 1400C. However, some beneficial effects were observed, notably in the rounded shape of the pores and in lowering the oxygen content. This led to an improvement in mechanical properties. Metallic activation, mainly provided by nickel and palladium salts led to high densities at a sintering temperature of 1100C but was accompanied by increased brittleness. This undesirable feature could be in part offset by controlling the amount of metallic activator and by some suitable subsequent heat-treatment. The two types of processes are discussed seperately, some appropriate mechanisms are proposed to explain the results observed, and the theoretical implications are considered. (Author).
Author: Joseph R. Stephens
Author: Joseph R. Stephens
Author: Joseph R. Stephens
Author: Joseph R. Stephens
Author: 
Author: 
Author: Vincent David Barth
Author: I. J. Toth
Author: 
Author: Srikanth Rao
Author: Union Carbide Metals Company. Metals Research Laboratories