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Effect of Small Amounts of B and C Additions on Glass Formation and Mechanical Properties of a Zr-Base Alloy

Description: The effect of B and C additions up to 0.4 at. % on glass formation and mechanical properties of a Zr-base alloy Vitreloy 105 was studied using various techniques. All alloys were prepared by arc melting and drop casting. Boron additions increase the glass forming ability by lowering T<sub>m</sub> and increasing T<sub>g</sub>. Carbon additions only lower T<sub>m</sub>, but do not affect T<sub>g</sub>. B and C additions occupy free space and do not harden the glass phase.
Date: November 30, 1998
Creator: Chen, N.G.; Liu, C.T. & Pike, L.M.
Partner: UNT Libraries Government Documents Department

Synthesis, characterization and physical properties of Al-Cu-Fe quasicrystalline plasma sprayed coatings

Description: Our lab has been working with plasma spraying of both high pressure gas atomized (HPGA) and cast and crushed quasicrystal powders. A major component of this research includes comparative studies of PAS coatings formed with starting powders prepared by both techniques. In addition, a thorough investigation of the effects of starting powder particle size on coating microstructure is included. During the course of the overall research, an interest developed in forming Al-Cu-Fe materials with finer grain sizes. Therefore, a brief study was performed to characterize the effect of adding boron to Al-Cu-Fe materials prepared by different techniques. In addition to characterizing the microstructural features of the above materials, oxidation and wear behavior was also examined.
Date: November 9, 1995
Creator: Daniel, S.
Partner: UNT Libraries Government Documents Department

Microstructural characterization of superalloy 718 with boron and phosphorus additions

Description: Boron and phosphorus additions are known to improve the stress rupture properties of IN-718. One possible mechanism to explain this property improvement relies on the boron and phosphorus additions slowing down the growth of {gamma}{double_prime} and {gamma}{prime} precipitates during high temperature service or aging. However, atom probe analysis found no segregation of boron and phosphorus to {gamma}-{gamma}{double_prime} or to {gamma}-{gamma}{prime} interfaces in the alloys with the high boron and high phosphorus levels. No difference in growth rates were found by transmission electron microscopy in the sizes of the {gamma}{double_prime} or {gamma}{prime} in alloys with high phosphorus and high boron as compared to commercial alloys and to alloys with even lower levels of phosphorus and boron. Atom probe analysis further found that much of the phosphorus, boron, and carbon segregated to grain boundaries. Creep curves comparing the alloys with high levels of phosphorus and boron and alloys with low levels of phosphorus and boron show a large difference in strain rate in the first hours of the test. These results suggest that the boron and phosphorus may have a direct effect on dislocation mobility by some pinning mechanism.
Date: June 1, 1997
Creator: Horton, J.A.; McKamey, C.G.; Miller, M.K.; Cao, W.D. & Kennedy, R.L.
Partner: UNT Libraries Government Documents Department

Characterization of segregation in nickel and titanium aluminides

Description: Atom probe field ion microscopy has been used to characterize the distributions of microalloying additions in the microstructure of a variety of nickel and titanium aluminides. In Ni{sub 3}Al, boron additions were found to segregate to dislocations, low angle boundaries, stacking faults, antiphase boundaries, and grain boundaries. The boron and aluminum levels at grain boundaries were found to vary both from boundary to boundary and also along an individual boundary segment. In some cases, a boron-enriched film up to {approximately}3 nm thick was observed. In aluminum-enriched Ni{sub 3}Al, ultrafine clusters containing up to approximately 10 boron atoms were detected in the matrix. In contrast, the majority of the boron additions in NiAl was determined to be in the form of ultrafine MB{sub 2}-type precipitates. These precipitates offset the benefits of the boron segregation to the high angle grain boundaries. In molybdenum-doped NiAl, atom probe analyses indicated extremely low solubilities of the molybdenum and other trace impurities in the matrix and significant enrichments of molybdenum, nitrogen and silicon, boron, and iron at the grain boundaries. In boron-doped two phase {alpha}{sub 2} + {gamma} TiAl containing chromium, niobium, and tungsten, the boron level was found to be significantly depleted from the bulk level in both the {alpha}{sub 2} and {gamma} phases and a variety of coarse borides including TiB, TiB{sub 2} and a finer chromium-enriched (Ti, Cr){sub 2}B precipitate was observed. The tungsten and chromium were determined to partition preferentially to the {alpha}{sub 2} phase and also to segregated to the {alpha}{sub 2}-{gamma} and {gamma}-{gamma} interfaces. These results indicate that a significant proportion of the microalloying elements are consumed by the boride precipitates.
Date: March 1997
Creator: Miller, M. K.; Larson, D. J. & Russell, K. F.
Partner: UNT Libraries Government Documents Department

Oxidation behavior of molybdenum silicides and their composites

Description: A key materials issue associated with the future of high-temperature structural silicides is the resistance of these materials to oxidation at low temperatures. Oxidation tests were conducted on Mo-based silicides over a wide temperature range to evaluate the effects of alloy composition and temperature on the protective scaling characteristics and testing regime for the materials. The study included Mo{sub 5}Si{sub 3} alloys that contained several concentrations of B. In addition, oxidation characteristics of MoSi{sub 2}-Si{sub 3}N{sub 4} composites that contained 20--80 vol.% Si{sub 3}N{sub 4} were evaluated at 500--1,400 C.
Date: April 3, 2000
Creator: Natesan, K. & Deevi, S. C.
Partner: UNT Libraries Government Documents Department

Manufacturing of nickel-base superalloys with improved high-temperature performance

Description: This report summarizes the results of research conducted as part of CRADA ORNL95-0327 between Oak Ridge National Laboratory and Teledyne Allvac (now Allvac, an Allegheny Teledyne Co.). The objective was to gain a better understanding of the role of trace elements in nickel-based superalloys, with the ultimate goal of enhancing performance without significantly increasing production cost. Two model superalloys, IN 718 and Waspaloy, were selected for this study, and the synergistic effects of P and B additions on creep and stress rupture properties were determined. Wherever possible the underlying physical mechanisms responsible for the observed effects were investigated.
Date: January 1, 2000
Creator: McKamey, C. G.; George, E. P.; Liu, C. T.; Horton, J. A.; Carmichael, C. A.; Kennedy, R. L. et al.
Partner: UNT Libraries Government Documents Department

Impurity effects on bonding charge in Ni{sub 3}Al

Description: We have studied the effect of B and H on the charge density in Ni{sub 3}Al employing first-principles electronic structure calculations based on the FLMTO method. The changes in the electronic structure induced by B result from hybridization of d states of the nearest neighbor Ni atoms with adjacent B-{ital PP} states. Thus, boron prefers to occupy Ni-rich octahedral interstices [X(7)]. Boron greatly enhances the intraplanar metallic bonding between the Ni atoms, enhances the interplanar bonding between the NiAl layers in [001] direction, and reduces the bonding-charge directionality near the Ni(3) atoms. It is concluded that B acts to increase crystal cohesion. Hydrogen enhances the bonding-charge directionality near Ni(3) atoms and has virtually no interstitial charge enhancement, suggesting that H does not promote local cohesion. When both B and H are present, the dominant changes in the electronic structure induced by B and H seems to have little effect.
Date: May 14, 1996
Creator: Sun, Sheng N.; Kioussis, N.; Lim, Say-Peng; Gonis, A. & Gourdin, W.
Partner: UNT Libraries Government Documents Department

Irradiation-assisted stress corrosion cracking of HTH Alloy X-750 and Alloy 625

Description: In-reactor testing of bolt-loaded compact tension specimens was performed in 360 C water. New data confirms previous results that high irradiation levels reduce SCC resistance in Alloy X-750. Low boron heats show improved IASCC (irradiation-assisted stress corrosion cracking). Alloy 625 is resistant to IASCC. Microstructural, microchemical, and deformation studies were carried out. Irradiation of X-750 caused significant strengthening and ductility loss associated with formation of cavities and dislocation loops. High irradiation did not cause segregation in X-750. Irradiation of 625 resulted in formation of small dislocation loops and a fine body-centered-orthorhombic phase. The strengthening due to loops and precipitates was apparently offset in 625 by partial dissolution of {gamma} precipitates. Transmutation of boron to helium at grain boundaries, coupled with matrix strengthening, is believed to be responsible for IASCC in X-750, and the absence of these two effects results in superior IASCC resistance in 625.
Date: July 1, 1995
Creator: Bajaj, R.; Mills, W.J.; Lebo, M.R.; Hyatt, B.Z. & Burke, M.G.
Partner: UNT Libraries Government Documents Department

Fracture and fatigue properties of Mo-Mo{sub 3}Si-Mo{sub 5}SiB{sub 2} refractory intermetallic alloys at ambient to elevated temperatures (25-1300 degrees Centigrade)

Description: The need for structural materials with high-temperature strength and oxidation resistance coupled with adequate lower-temperature toughness for potential use at temperatures above {approx} 1000 degrees C has remained a persistent challenge in materials science. In this work, one promising class of intermetallic alloys is examined, namely boron-containing molybdenum silicides, with compositions in the range Mo (bal), 12-17 at. percentSi, 8.5 at. percentB, processed using both ingot (I/M) and powder (P/M) metallurgy methods. Specifically, the oxidation (''pesting''), fracture toughness and fatigue-crack propagation resistance of four such alloys, which consisted of {approx}21 to 38 vol. percent a-Mo phase in an intermetallic matrix of Mo3Si and Mo5SiB2 (T2), were characterized at temperatures between 25 degrees and 1300 degrees C. The boron additions were found to confer superior ''pest'' resistance (at 400 degrees to 900 degrees C) as compared to unmodified molybdenum silicides, such as Mo5Si3. Moreover , although the fracture and fatigue properties of the finer-scale P/M alloys were only marginally better than those of MoSi2, for the I/M processed microstructures with coarse distributions of the a-Mo phase, fracture toughness properties were far superior, rising from values above 7 MPa sqrt m at ambient temperatures to almost 12 MPa sqrt m at 1300 degrees C.
Date: August 1, 2002
Creator: Choe, Heeman; Schneibel, J.H. & Ritchie, R.O.
Partner: UNT Libraries Government Documents Department

Atomic level microstructural characterization by APFIM

Description: Atom probe field ion microscopy has been used to characterize Ni aluminides in addition to changes in microstructure of pressure vessel steels as a result of exposure to neutron irradiation. Ultrafine intragranular Cu precipitates and P segregation to grain and lath boundaries have been quantified in the pressure vessel steels. In boron-doped Ni{sub 3}Al, the B additions were found to segregate to dislocations, low angle boundaries, antiphase boundaries, stacking faults, and grain boundaries. In boron-doped NiAl, B segregation to grain boundaries and ultrafine MB{sub 2} precipitates were observed. In Mo-doped NiAl, enrichments of Mo, C, N/Si, B, and Fe were observed at the grain boundaries together with Mo precipitates and low Mo matrix solubility.
Date: October 1, 1996
Creator: Miller, M. K.
Partner: UNT Libraries Government Documents Department

Recent advances in alloy design of Ni{sub 3}Al alloys for structural use

Description: This is a comprehensive review of recent advances in R&D of Ni{sub 3}Al-based alloys for structural use at elevated temperatures in hostile environments. Recent studies indicate that polycrystalline Ni{sub 3}Al is intrinsically quite ductile at ambient temperatures, and its poor tensile ductility and brittle grain-boundary fracture are caused mainly by moisture-induced hydrogen embrittlement when the aluminide is tested in moisture- or hydrogen-containing environments. Tensile ductility is improved by alloying with substitutional and interstitial elements. Among these additives, B is most effective in suppressing environmental embrittlement and enhancing grain-boundary cohesion, resulting in a dramatic increase of tensile ductility at room temperature. Both B-doped and B-free Ni{sub 3}Al alloys exhibit brittle intergranular fracture and low ductility at intermediate temperatures (300-850 C) because of oxygen-induced embrittlement in oxidizing environments. Cr is found to be most effective in alleviating elevated-temperature embrittlement. Parallel efforts on alloy development using physical metallurgy principles have led to development of several Ni{sub 3}Al alloys for industrial use. The unique properties of these alloys are briefly discussed. 56 refs, 15 figs, 3 tabs.
Date: December 31, 1996
Creator: Liu, C.T. & George, E.P.
Partner: UNT Libraries Government Documents Department

Key microstructures controlling the mechanical properties of two-phase TiAl alloys with lamellar structures

Description: TiAl alloys with the base composition of Ti-47Al-2Cr-2Nb (at.%) were prepared by arc melting and drop casting, followed by hot extrusion above the {alpha}-transus temperature, T{sub {alpha}}. The hot extruded materials were then heat treated above and below T{sub {alpha}} in order to control microstructural features in these lamellar structures. Mechanical properties of these alloys were determined by tensile testing at temperatures to 1000 C. Tensile elongation at room temperature (RT) is strongly dependent on grain size, showing increased ductility with decreasing grain size. Strength at RT and elevated temperatures is sensitive to interlamellar spacing, showing increased strength with decreasing lamellar spacing. Hall-Petch relations hold well for yield strength at RT and elevated temperatures and for tensile elongation at RT. Tensile elongations of about 5% and yield strengths around 900 MPa are achieved by controlling both colony size and interlamellar spacing. Mechanical properties of the TiAl alloys with controlled lamellar structures produced directly by hot extrusion are much superior to those produced by conventional thermomechanical treatments.
Date: December 31, 1996
Creator: Liu, C.T.; Maziasz, P.J. & Wright, J.L.
Partner: UNT Libraries Government Documents Department

Processing and operating experience of Ni{sub 3}Al-based intermetallic alloy IC-221M

Description: The cast Ni{sub 3}Al-based intermetallic alloy IC-221M is the most advanced in its commercial applications. This paper presents progress made for this alloy in the areas of: (1) composition optimization; (2) melting process development; (3) casting process; (4) mechanical properties; (5) welding process, weld repairs, and thermal aging response; and (6) applications. This paper also reviews the operating experience with several of the components. The projection for future growth in the applications of nickel aluminide is also discussed.
Date: May 1, 1997
Creator: Sikka, V.K.; Santella, M.L. & Orth, J.E.
Partner: UNT Libraries Government Documents Department

Evaluation of the intrinsic and extrinsic fracture behavior of iron aluminides

Description: Iron aluminides have excellent corrosion resistance in high-temperature oxidizing-sulfidizing environments; however, there are problems at room and medium temperatures with hydrogen embrittlement as related to exposure to moisture. In this research, a coordinated computational modeling/experimental study of mechanisms related to environmental-assisted fracture behavior of selected iron aluminides has been undertaken. The modeling and the experimental work connect at the level of coordinated understanding of the mechanisms for hydrogen penetration and for loss of strength and susceptibility to fracture. The focus of the modeling component has been on the challenging question of accurately predicting the iron vacancy formation energy in Fe{sub 3}Al and the subsequent tendency, if present, for vacancy clustering. The authors have successfully performed, on an ab initio basis, the first calculation of the vacancy formation energy in Fe{sub 3}Al. These calculations include lattice relaxation effects which are quite large for one of the two types of iron sites. This has significant implications for vacancy clustering effects with consequences for hydrogen diffusion. Indeed, the ab-initio-based estimate of the divacancy binding energy indicates a likely tendency toward such clustering for iron vacancies on the sites with large lattice relaxation. The experimental work has focused on the relationship of the choice and concentration of additives to the improvement of resistance to hydrogen embrittlement and hence to the fracture behavior.
Date: July 27, 1998
Creator: Cooper, B.R. & Kang, B.S.
Partner: UNT Libraries Government Documents Department

Mixing phenomena of interest to boron dilution during small break LOCAs in PWRs

Description: This paper presents the results of a study of mixing phenomena related to boron dilution during small break loss of coolant accidents (LOCAs)in pressurized water reactors (PWRs). Boron free condensate can accumulate in the cold leg loop seals when the reactor is operating in a reflux/boiler-condenser mode. A problem may occur when subsequent change in flow conditions such as loop seal clearing or re-establishment of natural circulation flow drive the diluted water in the loop seals into the reactor core without sufficient mixing with the highly borated water in the reactor downcomer and lower plenum. The resulting low boron concentration coolant entering the core may cause a power excursion leading to fuel failure. The mixing processes associated with a slow moving stream of diluted water through the loop seal to the core are examined in this paper. Bounding calculations for boron concentration of coolant entering the core during a small break LOCA in a typical Westinghouse-designed four-loop plant are also presented.
Date: March 1, 1995
Creator: Nourbakhsh, H.P. & Cheng, Z.
Partner: UNT Libraries Government Documents Department

Advanced far infrared detector and double donor studies in Ge

Description: This has application to astronomy and astrophysics. Selenium in Ge has been studied with a doping technique which limits complex formation. Only one ionization level has been found to correspond to selenium, which presumably occupies a substitutional site. This level is extremely unstable and its concentration decreases after annealing at 400C. Future work is planned to anneal the fast neutron damage before much selenium has formed in the {sup 74/76}Ge samples. It is expected that the observed selenium level can be better characterized and the missing selenium level is more likely to be discovered if other defects are removed before {sup 77}Se formation.
Date: December 1, 1994
Creator: Olsen, C.S.
Partner: UNT Libraries Government Documents Department

Boron strengthening in FeAl

Description: The effect of boron on the strength of B2-structured FeAl is considered as a function of composition, grain size and temperature. Boron does not affect the concentrations of antisite atoms or vacancies present, with the former increasing and the latter decreasing with increasing deviation from the stoichiometric composition. When vacancies are absent, the strength increase per at. % B per unit lattice strain, {Delta}{sigma}/({Delta}c x {epsilon}) increases with increasing aluminum concentration, but when vacancies are present (>45 at. % Al), {Delta}{sigma}/({Delta}c x {epsilon}) decreases again. Boron increases grain size strengthening in FeAl. B strengthening is roughly independent of temperature up to the yield strength peak but above the point, when diffusion-assisted deformation occurs, boron strengthening increases dramatically.
Date: November 1, 1998
Creator: Baker, I.; Li, X.; Xiao, H.; Klein, O.; Nelson, C.; Carleton, R.L. et al.
Partner: UNT Libraries Government Documents Department

Rare earth chalcogenides for use as high temperature thermoelectric materials

Description: In the first part of the thesis, the electric resistivity, Seebeck coefficient, and Hall effect were measured in X{sub y}(Y{sub 2}S{sub 3}){sub 1-y} (X = Cu, B, or Al), for y = 0.05 (Cu, B) or 0.025-0.075 for Al, in order to determine their potential as high- temperature (HT)(300-1000 C) thermoelectrics. Results indicate that Cu, B, Al- doped Y{sub 2}S{sub 3} are not useful as HT thermoelectrics. In the second part, phase stability of {gamma}-cubic LaSe{sub 1.47-1.48} and NdSe{sub 1.47} was measured periodically during annealing at 800 or 1000 C for the same purpose. In the Nd selenide, {beta} phase increased with time, while the Nd selenide showed no sign of this second phase. It is concluded that the La selenide is not promising for use as HT thermoelectric due to the {gamma}-to-{beta} transformation, whereas the Nd selenide is promising.
Date: January 2, 1996
Creator: Michiels, J.
Partner: UNT Libraries Government Documents Department

Results on powder injection molding of Ni{sub 3}Al and application to other intermetallic compositions

Description: Net forming processes are under development to allow affordable production of intermetallic components. Powder injection molding (PIM) mav be employed for the production of complex-shaped intermetallic geometries. Proper choice of powder parameters and processing conditions can lead to the formation of fullv dense structures through pressure-less sintering. In this study, Ni{sub 3}Al with 0.04 wt.-% boron has been successfully injection molded and sintered to full density. A yield strength of 340 MPa, ultimate tensile strength (UTS) of 591 MPa, and 8% elongation were attained for injection molded and sintered tensile bars. Powder characteristics and sintering behavior are given for the nickel aluminide employed in this study to highlight the powder attributes needed for injection molding. Molding parameters, debinding and sintering schedules, along, with mechanical properties are presented to indicate the viability of PIM for intermetallics. This approach based on the understanding of key powder characteristics and use of the reactive synthesis powder process mav be extended to the successful injection molding of other intermetallic systems.
Date: December 31, 1992
Creator: Cooper, R. M.
Partner: UNT Libraries Government Documents Department

An atom probe investigation of the influence of trace impurities on the mechanical behavior of NiAl

Description: Atom probe field ion microscopy (APFIM) and transmission electron microscopy (TEM) have been used to investigate the influence of trace metallic impurities on the enormous increase in the yield stress of boron-doped NiAl. Previous atom probe studies of NiAl containing 0.12 at. % boron had demonstrated that 0.026 at. % of the boron was in solid solution. The remainder reacted with trace metallic impurities, presumably present in high purity Ni, to form ultrafine MB{sub 2} precipitates ranging in size from less than 2 nm to 20 nm. Atom probe measurements had shown that their number densities were significant enough to make the dominant contribution to the observed increase in yield stress. An attempt was made in the present work to minimize the effect of these precipitates by an additional aging treatment. Field ion microscope (FIM) and TEM micrographs revealed that 2 nm precipitates coarsened significantly during aging. Microstructure of aged NiAl was consistent with observed mechanical behavior showing a significantly smaller increase in the yield stress. An approximate value of the Orowan stress, based on TEM estimates of the size and number density of the precipitates, is in reasonable agreement with the measured value. This APFIM/TEM investigation has indicated a practical approach to minimize the detrimental role of trace impurities in NiAl.
Date: November 1, 1993
Creator: Jayaram, R.; Liu, C. T. & Miller, M. K.
Partner: UNT Libraries Government Documents Department

Experimental studies of the structure of grain boundaries. Progress report

Description: Goals are to understand factors affecting structure of grain boundaries in intermetallic compounds, understand how solute segregation affects grain boundary structure and causes embrittlement in Fe-base alloys, and explore control of grain boundary properties. Fe and boron-doped Ni{sub 3}Al and NiAl were studied. 7 figs, 1 tab, 18 refs.
Date: April 1, 1993
Creator: Sass, S. L.
Partner: UNT Libraries Government Documents Department

[Experimental studies of the structure, chemistry, and properties of grain boundaries]. [Annual report, June 1, 1993--May 31, 1994]

Description: Observations have shown that the APB energy in boron-doped grain boundaries in Ni{sub 3}Al decreases with increasing misorientation angle. Boron segregation to a grain boundary in Ni{sub 3}Al has been observed for the first time using EELS. The boron distribution along a large angle grain boundary in Ni{sub 0.76}Al{sub 0.24} was shown to be not uniform. The boron-rich regions of the grain boundary were seen to have similar nickel bonding to bulk Ni{sub 3}Al. Undoped and boron-poor regions of the grain boundary have bonding similar to that in pure Ni (less filled Ni d bands) which suggests these Ni atoms have fewer Al nearest neighbors and weaker Ni-Al bonding than in bulk Ni{sub 3}Al. Finally, radiation damage was seen to occur in freshly prepared specimens at beam voltages as low as 100 kV but could be prevented by carbon coating the samples.
Date: June 1, 1994
Creator: Sass, S. L.
Partner: UNT Libraries Government Documents Department

Neutron-induced microstructural alteration of GlidCop{trademark} alloys at 415{degrees}C and high neutron exposure

Description: GlidCop{trademark} internally oxidized copper alloys remain the leading candidates for high heat flux applications in fusion reactor. This paper presents the microstructural changes incurred in three GlidCop{trademark} alloys exposed to long term, high temperature neutron irradiation. Irradiation at high temperature produced a microstructure containing a much lower dislocation density than the unirradiated specimens. Although 10--50 nm size triangular oxide particles were observed in areas with a very low number density of particles, spherical oxide particles on the order of 5--7 nm in diameter, thought to be CuAl{sub 2}O{sub 4}, were the predominant morphology. The changes in grain size distribution, dislocation density, and precipitate type and distribution saturate in the range of 34 to 50 dpa, as reflected in the saturation of mechanical properties.
Date: October 1, 1993
Creator: Edwards, D. J.; Garner, F. A.; Newkirk, J. W. & Nadkarni, A.
Partner: UNT Libraries Government Documents Department