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Corrosion Tests on Tantalum, Hastelloy C and Duriron in 234-5 Project Solutions

Description: Introduction: "Room temperature and elevated temperature, static immersion and vapor suspicion, corrosion tests were conducted with Duriron, Hastelloy C, and tantalum in hydriotic acid and 234-5 project process supernatant solution (synthetic environments. The data relevant to these tests are contained herein."
Date: February 25, 1949
Creator: Work, J. B. & Koenig, W. W.
Partner: UNT Libraries Government Documents Department

Tantalum-Rich Alloys of Tuballoy

Description: Report discussing "methods for the manufacture of refractory crucibles for use in high temperature work in general." Additionally, "preliminary experiments with the induction furnace to test the action of tantalum on tantalum carbide at 2900°C are described."
Date: January 15, 1946
Creator: Sausville, J. W. & Larson, C. E.
Partner: UNT Libraries Government Documents Department

Mechanical behavior of tantalum and tantalum-tungsten alloys: texture gradients and macro/micro-response

Description: We have examined the mechanical response of unalloyed Ta and Ta-W alloy annealed plates over a wide range of loadings. It was observed in general that Ta exhibits nonuniform mechanical behavior, for example, hourglassing of compression samples and multiple instabilities during tensile deformation. In contrast, the Ta-W alloys do not exhibit any unusual nonuniform behavior. This work presents data revealing the spatial distribution of texture in Ta and Ta-W alloys. Significant variations in texture both through the thickness and from one area of the plate to another were found to be characteristic of Ta. The dominant feature of the texture variations was found to be enhanced <111> crystal direction fractions at the center of the plate, with a decreasing fraction near the surface. We find that the variation in texture in the Ta-W alloys is substantially less than that seen in Ta with primarily a <100> cube texture throughout. This study suggest that the texture gradients are responsible for the nonuniform mechanical response of Ta and that the uniform behavior of the Ta-W alloys is a consequence of the absence of texture gradients.
Date: November 30, 1996
Creator: Lassila, D.H.; Schwartz, A.J.; LeBlanc, M.M. & Wright, S.I.
Partner: UNT Libraries Government Documents Department

Chemistry modification of high oxygen-carbon powder by plasma melting: Follow up to complete the story

Description: State of the art melting of tantalum and tantalum alloys has relied on electron beam (EB) or vacuum arc remelting (VAR) for commercial ingot production. Plasma arc melting (PAM) provides an alternative for melting tantalum that contains very high levels of interstitials where other melting techniques can not be applied. Previous work in this area centered on plasma arc melt quality and final interstitial content of tantalum feedstock containing excessive levels of interstitial impurities as a function of melt rate and plasma gas. This report is an expansion of this prior study and provides the findings from the analysis of second phase components observed in the microstructure of the PAM tantalum. In addition, results from subsequent EB melting trials of PAM tantalum are included.
Date: March 1, 1998
Creator: Dunn, P.S.; Korzekwa, D.R.; Garcia, F.G. & Michaluk, C.A.
Partner: UNT Libraries Government Documents Department

Mechanical properties of Cu/Ta multilayers prepared by magnetron sputtering

Description: The microstructure and mechanical properties of sputtered Cu/Ta multilayers were studied. X- ray diffraction and transmission electron microscopy characterization indicate that both the Ta and Cu in the 2 nm period multilayer are predominantly amorphous, while in longer period samples, the layers are crystalline, with the metastable tetragonal {beta}-Ta observed. No observable microstructure changes upon annealing at 300{degrees}C were found. An average Vickers micro- hardness value of about 5.5 GPa was measured, which increases about 5% upon annealing at 300{degrees}C. Residual stress in the multilayers and its dependence on thermal annealing are reported. The relationships between microstructure and mechanical properties in the multilayers are discussed.
Date: April 1, 1998
Creator: Nguyen, T.D. & Barbee, T.W., Jr.
Partner: UNT Libraries Government Documents Department

The influence of melting process and parameters on the structure and homogeneity of titanium-tantalum alloys

Description: Alloys of titanium with refractory metals are attractive materials for applications requiring high temperature strength and corrosion resistance. However, the widely different characteristics of the component elements have made it difficult to produce sound, compositionally homogeneous ingots using traditional melting techniques. This is particularly critical because the compositional ranges spanned by the micro- and macrosegregation in theses systems can easily encompass a number of microconstituents which are detrimental to mechanical properties. This paper presents results of a study of plasma (PAM) and vacuum-arc (VAR) melting of a 60 wt% tantalum, 40 wt% titanium binary alloy. The structural and compositional homogeneity of both PAM consolidated + PAM remelted, and PAM consolidated + VAR remelted ingots were characterized and compared using optical and electron microscopy and x-ray fluorescence microanalysis. Additionally, the effect of melting parameter, including melt rate and magnetic stirring, was studied. Results indicate that PAM remelting achieves more complete dissolution of lie starting electrode, due to greater local superheat, than does VAR remelting. PAM remelting also produces a finer as-solidified grain structure, due to the smaller molten pool and lower local solidification times. Conversely, VAR remelting produces an ingot with a more uniform macrostructure, due to the more stable movement of the solidification interface and more uniform material feed rate. Based on these results, a three-step process of PAM consolidation, followed by a PAM intermediate melt and a VAR final melt, has been selected for further development of the alloy and processing sequence.
Date: December 31, 1995
Creator: Dunn, P.S.; Korzewka, D.; Garcia, F.; Damkroger, B.K.; Van Den Avyle, J.A. & Tissot, R.G.
Partner: UNT Libraries Government Documents Department

HIGH TEMPERATURE OXIDATION RESISTANT COATINGS FOR TANTALUM BASE ALLOYS. First Quarterly Progress Report, June 1, 1960 to August 31, 1960

Description: The effect of various dipping times, temperatures, and diffusion treatments was determined for tantalum sheet dipped in aluminum alloy baths. Both aluminide and beryllide coatings were produced that will withstand oxidation for 10 hours at 2500 deg F, isothermally and cyclic. Aluminide coatings were obtained on a stressed niobium alloy that meets the same test conditions. (auth)
Date: October 31, 1961
Partner: UNT Libraries Government Documents Department

Phase transformations in some hafnium-tantalum-titanium-zirconium alloys

Description: Phase transformations in hafnium alloys are of interest as a means of achieving a material which exhibits flow softening and high localized strains during deformation at high strain rates. Hafnium transforms from a body-centered-cubic beta phase to a hexagonal alpha phase upon cooling below 1749{degrees}C. Hafnium-based alloys containing up to 17.5% Ti, up to 17.5% Ta, and up to 7.3% Zr by weight were button-arc melted and, in some cases, hot extruded to obtain a refined grain size. A number of alloys were shown to have beta solvus temperatures in the range of 1100 to 1300{degrees}C and showed evidence of a shear transformation upon water quenching. The Vickers microhardness of the quenched materials are typically above 350 HV as compared to 300 HV or less for materials with an alpha plus beta structure. Quenching dilatometry indicates a martensite start temperature of about 750{degrees}C for the Hf-7.5 Ta-10 Ti-1 Zr alloy and 800{degrees}C or more for the Hf-7.5 Ta-7.5 Ti-1 Zr alloy. Tensile tests at 1 s{sup {minus}1} strain rate show a constant ultimate tensile strength for temperatures up to 600{degrees}C for the above two alloys and a rapid decrease in strength with a further increase in temperature.
Date: November 1, 1997
Creator: Ohriner, E.K. & Kapoor, D.
Partner: UNT Libraries Government Documents Department

The Effect of Ramp Rate on the C49 to C54 Titanium Disilicide Phase Transformation from Ti and Ti(Ta)

Description: The C49 to C54 TiSi{sub 2} transformation temperature is shown to be reduced by increasing the ramp rate during rapid thermal processing and this effect is more pronounced for thinner initial Ti and Ti(Ta) films. Experiments were performed on blanket wafers and on wafers that had patterned polycrystalline Si lines with Si{sub 3}N{sub 4} sidewall spacers. Changing the ramp rate caused no change in the transformation temperature for 60 nm blanket Ti films. For blanket Ti films of 25 or 40 nm, however, increasing the ramp rate from 7 to 180 C/s decreased the transformation temperature by 15 C. Studies of patterned lines indicate that sheet resistance of narrow lines is reduced by increased ramp rates for both Ti and Ti(Ta) films, especially as the linewidths decrease below 0.4 {micro}m. This improvement is particularly pronounced for the thinnest Ti(Ta) films, which exhibited almost no linewidth effect after being annealed with a ramp rate of 75 C/s.
Date: September 22, 1999
Creator: BAILEY, GLENN A.; HU, YAO ZHI; SMITH, PAUL M. & TAY, SING PIN
Partner: UNT Libraries Government Documents Department

Oxidation and Volatilization from Tantalum Alloy During Air Exposure

Description: Tantalum alloys are one of the refractory metals with renewed consideration for high temperatures in fusion reactor applications. Tantalum alloys perform well in protective environments but are oxidized readily in gases containing higher oxygen levels. In addition, the radioactive isotope Ta-182 would be produced in tantalum and could be a significant contributor to dose if mobilized. Other isotopes of importance are produced from tungsten and hafnium. Mobilization of activated products during an accident with air ingress is therefore a safety issue. In this study, we measured the extent of oxidation and mobilization from tantalum alloy T-222 oxidized in flowing air between 500 and 1200 degrees C. This alloy nominally contains 10 wt% tungsten, 2.5 wt% hafnium and 0.01 wt% carbon. We found that the mobilization of Ta and Hf was closely linked to the occurrence of oxide spalling. These elements showed no migration from the test chamber. Some W was mobilized by volatilization as evidenced by transport from the chamber. Tungsten volatilization could occur primarily during initial stages of oxidation before the formation of an oxide scale impedes the process. The mobilization of Ta and W are presented in terms of the mass flux (g/m2-h) as a function of test temperature. These measurements along with specific designs, activation calculations, and accident scenarios provide information useful for dose calculations of future fusion devices.
Date: October 1, 2000
Creator: Smolik, Galen Richard; Petti, David Andrew & Schuetz, Stanley Thomas
Partner: UNT Libraries Government Documents Department

Structure and elevated temperature properties of ferritic alloys strengthened by intermetallic compounds

Description: Thesis. An investigation was conducted to develop high-temperature 1Ta-- 6Cr, 1Ta--7Cr, and 1Ta-7Cr--0.5 Mo alloys using a dispersion of the Laves phase in a noncarbon-containing, body-centeredcubic iron matrix. An understanding and application of basic principles of materials science and the use of large amounts of information available in the literature were instrumental in the development of Fe-- Ta-- Cr alloys of the investigation. The phase transformations that occurred in the alloys, and the resulting microstructures were studied. The relations between mechanical properties and structure were also examined. Short- time tensile mechanical properties and long-time creep and stress-rupture tests were conducted on the alloys in which microstructural features were varied by changes in the heat-treating procedure. The mechanical properties were compared with those of several commercially available steels. An examination of substructure and precipitate distribution of the alloys before and after creep tests, the determination of apparent activation energy for creep, and an estimation of the stress sensitivity of steady-state creep rates were carried out in order to investigate the mechanism of creep in dispersion-hardened ferritic alloys. Fracture surface morphology was examined after specimens were tested in short-time tension and in creep. (JRD)
Date: September 1, 1973
Creator: Bhandarkar, M.D.
Partner: UNT Libraries Government Documents Department

Phase stability and elasticity of C15 transition-metal intermetallic compounds

Description: First-principle quantum mechanical calculations based on the local-density-functional theory have been performed to study the electronic, physical and metallurgical properties of C15 intermetallics MV{sub 2} (M = Zr, Hf, or Ta). The elastic constants of C15 HfV{sub 2} + Nb were measured by the resonant ultrasound spectroscopy technique. The phase stability of C15 HfV{sub 2} + Nb was studied by specific heat measurements and by transmission electron microscopy in a low temperature specimen holder. The total energies and their lattice volume dependence were used to obtain the equilibrium lattice constants and bulk modulus. The band structures at the X-point near the Fermi level were employed to understand the anomalous temperature dependence of shear modulus of the C15 intermetallics. It was found that the double degeneracy with a linear dispersion relation of electronic levels at the X-point near the Fermi surface is mainly responsible for the C15 anomalous elasticity. The density of states at the Fermi level, N(E{sub F}), and the Fermi surface geometry were obtained to understand the low temperature phase instability of C15 HfV{sub 2} and ZrV{sub 2} and the stability of C15 TaV{sub 2}. It was proposed that the large N(E{sub F}) and Fermi surface nesting are the physical reasons for the structural instability of the C15 HfV{sub 2} and ZrV{sub 2} at low temperatures. The relation between anomalous elasticity and structural instability of C15 HfV{sub 2} and ZrV{sub 2} is also discussed.
Date: March 1, 1995
Creator: Chu, F.; Mitchell, T.E.; Chen, S.P.; Sob, M.; Siegl, R. & Pope, D.P.
Partner: UNT Libraries Government Documents Department