An investigation was carried out to determine the effect of rapid solidification on the weld meta... more An investigation was carried out to determine the effect of rapid solidification on the weld metal microstructure of austenitic stainless steels and its implication on the ferrite constitution diagram. A wide variety of stainless steels were laser beam welded at different welding speeds and laser power levels. The results indicate that both weld pool cooling rate and the postsolidification solid-state
Growth from the melt of niobium-niobium carbide (Nb-Nb2C) composites at the eutectic and off the ... more Growth from the melt of niobium-niobium carbide (Nb-Nb2C) composites at the eutectic and off the eutectic composition by electron beam floating zone melting and freezing was studied. Composite growth has been successfully achieved for the eutectic composition and for compositions up to four atomic percent above the eutectic. The volume fraction of the carbide phase was increased from 26 to 33 pct by growing off the eutectic composition. The alignment and morphology of the carbide phase are influenced primarily by growth rate and composition. The carbide morphology may be either rod-like or platelike. For a given composition, rod morphology is favored at higher growth rates. For constant growth rate, the plate-like morphology is promoted by increasing carbon content. The transition from plate to rod morphology is gradual. Lamellar and ihter-rod spacings vary from 1 to 6 microns for growth rates varying from 5 to 90 microns per second. Variation of lamellar spacing with freezing rate, R, produces a straight line (on a log-log plot) in agreement with a relationship of the form X2Rn = constant, with n = 0.8. For alloys four at. pet above the eutectic, primary N'b2C dendrites nucleate and grow ahead of the still we11 aligned two phase solid plus liquid interface.
The microstructure change is one of the most important research areas in the field of friction st... more The microstructure change is one of the most important research areas in the field of friction stir welding (FSW). However, in-situ observation of microstructure changes has been extremely challenging because many measurement techniques are not applicable. Recently developed in-situ time-resolved neutron diffraction method, which drastically improves the temporal resolution of neutron diffraction, enables observervation of the transient microstructure changes during FSW. A portable FSW system was installed in the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos Neutron Science Center and the FSW was made on 6.35mm-thickness 6061-T6 Al alloy plate. At the same time, the neutron beam was centered on the mid-plane of the Al plate at 8 mm from the tool center (underneath the tool shoulder). The diffraction peak was continuously measured during welding. The peak broadening analysis has been performed using the Williamson-Hall Method. The result shows that the dislocation density of about 3.2 x 10 15 m -2 in that position duing FSW, which is a significant increse compared to before FSW (4.5 x 10 14 m -2 ) and after FSW (4.0 x 10 14 m -2 ). This quantitatively analysis of the grain structure can provide an insight to understand the transient variation of the microstructure during FSW.
Two papers presented at the Sheffield International Symposium on Solidification are included. One... more Two papers presented at the Sheffield International Symposium on Solidification are included. One paper covers a theory to describe the relation between casting conditions and structure in directionally solidified peritectic alloys. Experiments on Pb-Bi and Sn-Cd alloys are used to check the theory. The second paper describes the application of a computer model of continuous casting to study the effects of ingot diameter and casting rate on heat flow and thermal stresses in an aluminum-magnesium alloy. (Author)
The microstructural development in PWA-1480 superalloy electron beam welds (Ni-11.0at%Al-11.5%Cr-... more The microstructural development in PWA-1480 superalloy electron beam welds (Ni-11.0at%Al-11.5%Cr-l.9%Ti-5. l%Co-4.0%Ta-1.3%W) was characterized. Optical microscopy revealed a branched dendritic structure in the weld metal. Transmission electron microscopy of these welds, in the as-welded condition, showed fine cuboidal (0.05-0.5 /zm) L12-ordered y' precipitates within the y grains. The average volume percentage of the y' precipitates was found to be ~ 75%. Atom probe analyses revealed that the composition of the 3' matrix was Ni-4.6at%A1-25.5%Cr-0.4%Ti-9.4%Co-0.8%Ta-2.9%W and that of the y' precipitates was Ni-18.2at%A1-2.6%Cr-2.4%Ti-2.8%Co-7.1%Ta-l.5%W. These compositions were compared with the previous APFIM analyses of commercial PWA-1480 single crystals that had received conventional heat treatments. Small differences were found in the chromium and aluminum levels and these may be due to the nonequilibrium nature of phase transformations that occur during weld cooling. No solute segregation was detected at the y-y' interface. The APFIM results were also compared with the thermodynamic calculations of alloying element partitioning between the y and y' phases using the ThermoCalc TM program.
Description/Abstract The evolution of temperature and thermal stresses during friction stir weldi... more Description/Abstract The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in situ, time resolved neutron diffraction technique. A method was developed to deconvolute the temperature and stress from the ...
The specification discloses a corrosion-resistant intermetallic alloy comprising, in atomic perce... more The specification discloses a corrosion-resistant intermetallic alloy comprising, in atomic percent, an FeAl iron aluminide containing from about 30 to about 40% aluminum alloyed with from about 0.01 to 0.4% zirconium and from 0.01 to about 0.8% boron. The alloy exhibits considerably improved room temperature ductility for enhanced usefulness in structural applications. The high temperature strength and fabricability is improved
Welding behavior and welding metallurgy of several ordered intermetallic alloys are reviewed comp... more Welding behavior and welding metallurgy of several ordered intermetallic alloys are reviewed comprehensively. Weldability of these alloys has been found to be a strong function of composition, welding process and process parameters. Phase transformations associated with the weld thermal cycle play a critical role in determining the weldability of these alloys. Defect-free welds have been produced in several of these alloys. 31 refs., 11 figs., 3 tabs.
Processes for forming an enhanced material or structure are disclosed. The structure typically in... more Processes for forming an enhanced material or structure are disclosed. The structure typically includes a preform that has a first common surface and a recess below the first common surface. A filler is added to the recess and seams are friction stir welded, and materials may be stir mixed.
This invention is a process for joining metals to ceramics to form very strong bonds using low br... more This invention is a process for joining metals to ceramics to form very strong bonds using low brazing temperature, i.e., less than 750.degree. C., and particularly for joining nodular cast iron to partially stabilized zirconia. The process provides that the ceramic be coated with an active metal, such as titanium, that can form an intermetallic with a low melting point
Processes for friction stir welding, typically for comparatively thick plate materials using mult... more Processes for friction stir welding, typically for comparatively thick plate materials using multiple passes and multiple layers of a friction stir welding tool. In some embodiments a first portion of a fabrication preform and a second portion of the fabrication preform are placed adjacent to each other to form a joint, and there may be a groove adjacent the joint.
An investigation was carried out to determine the effect of rapid solidification on the weld meta... more An investigation was carried out to determine the effect of rapid solidification on the weld metal microstructure of austenitic stainless steels and its implication on the ferrite constitution diagram. A wide variety of stainless steels were laser beam welded at different welding speeds and laser power levels. The results indicate that both weld pool cooling rate and the postsolidification solid-state
Growth from the melt of niobium-niobium carbide (Nb-Nb2C) composites at the eutectic and off the ... more Growth from the melt of niobium-niobium carbide (Nb-Nb2C) composites at the eutectic and off the eutectic composition by electron beam floating zone melting and freezing was studied. Composite growth has been successfully achieved for the eutectic composition and for compositions up to four atomic percent above the eutectic. The volume fraction of the carbide phase was increased from 26 to 33 pct by growing off the eutectic composition. The alignment and morphology of the carbide phase are influenced primarily by growth rate and composition. The carbide morphology may be either rod-like or platelike. For a given composition, rod morphology is favored at higher growth rates. For constant growth rate, the plate-like morphology is promoted by increasing carbon content. The transition from plate to rod morphology is gradual. Lamellar and ihter-rod spacings vary from 1 to 6 microns for growth rates varying from 5 to 90 microns per second. Variation of lamellar spacing with freezing rate, R, produces a straight line (on a log-log plot) in agreement with a relationship of the form X2Rn = constant, with n = 0.8. For alloys four at. pet above the eutectic, primary N'b2C dendrites nucleate and grow ahead of the still we11 aligned two phase solid plus liquid interface.
The microstructure change is one of the most important research areas in the field of friction st... more The microstructure change is one of the most important research areas in the field of friction stir welding (FSW). However, in-situ observation of microstructure changes has been extremely challenging because many measurement techniques are not applicable. Recently developed in-situ time-resolved neutron diffraction method, which drastically improves the temporal resolution of neutron diffraction, enables observervation of the transient microstructure changes during FSW. A portable FSW system was installed in the Spectrometer for MAterials Research at Temperature and Stress (SMARTS) at Los Alamos Neutron Science Center and the FSW was made on 6.35mm-thickness 6061-T6 Al alloy plate. At the same time, the neutron beam was centered on the mid-plane of the Al plate at 8 mm from the tool center (underneath the tool shoulder). The diffraction peak was continuously measured during welding. The peak broadening analysis has been performed using the Williamson-Hall Method. The result shows that the dislocation density of about 3.2 x 10 15 m -2 in that position duing FSW, which is a significant increse compared to before FSW (4.5 x 10 14 m -2 ) and after FSW (4.0 x 10 14 m -2 ). This quantitatively analysis of the grain structure can provide an insight to understand the transient variation of the microstructure during FSW.
Two papers presented at the Sheffield International Symposium on Solidification are included. One... more Two papers presented at the Sheffield International Symposium on Solidification are included. One paper covers a theory to describe the relation between casting conditions and structure in directionally solidified peritectic alloys. Experiments on Pb-Bi and Sn-Cd alloys are used to check the theory. The second paper describes the application of a computer model of continuous casting to study the effects of ingot diameter and casting rate on heat flow and thermal stresses in an aluminum-magnesium alloy. (Author)
The microstructural development in PWA-1480 superalloy electron beam welds (Ni-11.0at%Al-11.5%Cr-... more The microstructural development in PWA-1480 superalloy electron beam welds (Ni-11.0at%Al-11.5%Cr-l.9%Ti-5. l%Co-4.0%Ta-1.3%W) was characterized. Optical microscopy revealed a branched dendritic structure in the weld metal. Transmission electron microscopy of these welds, in the as-welded condition, showed fine cuboidal (0.05-0.5 /zm) L12-ordered y' precipitates within the y grains. The average volume percentage of the y' precipitates was found to be ~ 75%. Atom probe analyses revealed that the composition of the 3' matrix was Ni-4.6at%A1-25.5%Cr-0.4%Ti-9.4%Co-0.8%Ta-2.9%W and that of the y' precipitates was Ni-18.2at%A1-2.6%Cr-2.4%Ti-2.8%Co-7.1%Ta-l.5%W. These compositions were compared with the previous APFIM analyses of commercial PWA-1480 single crystals that had received conventional heat treatments. Small differences were found in the chromium and aluminum levels and these may be due to the nonequilibrium nature of phase transformations that occur during weld cooling. No solute segregation was detected at the y-y' interface. The APFIM results were also compared with the thermodynamic calculations of alloying element partitioning between the y and y' phases using the ThermoCalc TM program.
Description/Abstract The evolution of temperature and thermal stresses during friction stir weldi... more Description/Abstract The evolution of temperature and thermal stresses during friction stir welding of Al6061-T6 was investigated by means of in situ, time resolved neutron diffraction technique. A method was developed to deconvolute the temperature and stress from the ...
The specification discloses a corrosion-resistant intermetallic alloy comprising, in atomic perce... more The specification discloses a corrosion-resistant intermetallic alloy comprising, in atomic percent, an FeAl iron aluminide containing from about 30 to about 40% aluminum alloyed with from about 0.01 to 0.4% zirconium and from 0.01 to about 0.8% boron. The alloy exhibits considerably improved room temperature ductility for enhanced usefulness in structural applications. The high temperature strength and fabricability is improved
Welding behavior and welding metallurgy of several ordered intermetallic alloys are reviewed comp... more Welding behavior and welding metallurgy of several ordered intermetallic alloys are reviewed comprehensively. Weldability of these alloys has been found to be a strong function of composition, welding process and process parameters. Phase transformations associated with the weld thermal cycle play a critical role in determining the weldability of these alloys. Defect-free welds have been produced in several of these alloys. 31 refs., 11 figs., 3 tabs.
Processes for forming an enhanced material or structure are disclosed. The structure typically in... more Processes for forming an enhanced material or structure are disclosed. The structure typically includes a preform that has a first common surface and a recess below the first common surface. A filler is added to the recess and seams are friction stir welded, and materials may be stir mixed.
This invention is a process for joining metals to ceramics to form very strong bonds using low br... more This invention is a process for joining metals to ceramics to form very strong bonds using low brazing temperature, i.e., less than 750.degree. C., and particularly for joining nodular cast iron to partially stabilized zirconia. The process provides that the ceramic be coated with an active metal, such as titanium, that can form an intermetallic with a low melting point
Processes for friction stir welding, typically for comparatively thick plate materials using mult... more Processes for friction stir welding, typically for comparatively thick plate materials using multiple passes and multiple layers of a friction stir welding tool. In some embodiments a first portion of a fabrication preform and a second portion of the fabrication preform are placed adjacent to each other to form a joint, and there may be a groove adjacent the joint.
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