Implantation with aluminium ions (Al + ) was investigated for producing amorphous, microcrystalli... more Implantation with aluminium ions (Al + ) was investigated for producing amorphous, microcrystalline and crystalline phases in the refractory metals tantalum, niobium and vanadium. Surface alloys with a substantial aluminum content resulted from the implantation, reaching more than ...
Aluminum ion implantation of vanadium, niobium, and tantalum improved the metals' oxidation resis... more Aluminum ion implantation of vanadium, niobium, and tantalum improved the metals' oxidation resistances at 500 ~ and 735 ~ Implanted vanadium oxidized only to one-third the extent of unimplanted vanadium when exposed at 500 ~ to air. The oxidative weight gains of implanted niobium and tantalum proved negligible when measured at 500 ~ and for times sufficient to fully convert the untreated metals to their pentoxides. At 735 ~ implantation of vanadium only slightly retarded its oxidation, while oxidative weight gains of niobium and tantalum were reduced by factors of 3 or more. Implanted niobium exhibited weight gain in direct proportion to oxidation time squared at 735 ~ Microstructural examination of the metals implanted with selected fluences of the 180 kV aluminum ions showed the following. The solubility limit of aluminum is extended by implantation, the body centered cubic (bcc) phases being retained to-60 at. pct A1 in all three metals. The highest fluence investigated, 2.4 • 1022 ions/m s, produced an-400-nm layer of VA13 beneath the surface of vanadium, and-300-nm layers of an amorphous phase containing-70 at. pct A1 beneath the niobium and tantalum surfaces. All three metals, implanted to this fluence and annealed at 600 ~ contained tri-aluminides, intermetallic compounds known for their oxidation resistances. Specimens implanted to this fluence were thus selected for the oxidation measurements.
Tantalum was implanted with 180 keV Al+ ions to fluences up to 3�1018 Al+/cm2. Subsequent microch... more Tantalum was implanted with 180 keV Al+ ions to fluences up to 3�1018 Al+/cm2. Subsequent microchemical and microstructural observations showed that an amorphous layer covered the surface and extended to depths near 3000 � for fluences above 2.4�1018 Al+/cm2. The layer, comprised of ∼70 at. pet Al and ∼30 at. pet Ta, crystallized at temperatures above 500�C. Oxidation measurements, performed
Ion implantation produces thin films or layers that reside within a substrate rather than on top ... more Ion implantation produces thin films or layers that reside within a substrate rather than on top of it. The layers extend to the surface, differ in chemical composition and/or microstructure as compared with the substrate, and often modify the surface-dependent properties of the substrate material. Selected examples of modified properties are presented in this article and include improvements in oxidation and wear resistance from ion implantation. The shallow depths of the modified layers and the small scales of the implanted microstructures require the use of several modern analytical techniques for their characterization. Examples of such characterizations are also presented in this article. The implanted layers are examined for chemical concentrations versus depth with Auger electron spectroscopy and controlled sputtering, and with Rutherford backscattering spectrometry. Scanning electron microscopy and electron backscattering channeling analysis yield, respectively, information regarding products formed during oxidation and amorphous phase formed during implantation. Transmission electron microscopy and diffraction quantify the microstructures within the implanted layer and identify crystalline, nanocrystalline, and amorphous phases. Finally, it is shown that lattice imaging delineates atomic level defects, including stacking faults in-3 nm implanted rare gas precipitates, and amorphous phase formed during deceleration of the incident ions within intermetallic NiA13 phase.
The manufacture and entrance into service of thin gage gamma-TiAl product has been hampered by th... more The manufacture and entrance into service of thin gage gamma-TiAl product has been hampered by the inherent low room temperature ductility of the material. In the present study a new approach was explored for the efficient manufacture of gamma-TiAl foil with improved ductility. The objective was to produce a very clean material (low interstitial content) with a highly refined, homogeneous microstructure placed in a fully lamellar condition. The processing route involved the use of RF plasma spray deposition of pre-alloyed powders, followed by consolidation via vacuum hot pressing and heat treatment. The approach took advantage of a deposition process which included no electrodes, no binders and high cooling rates. Results and discussion of the work performed to date are presented.
Journal of Materials Engineering and Performance, 1996
Recently, a low-cost near-[3 titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-I.5AI wt%) containing iro... more Recently, a low-cost near-[3 titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-I.5AI wt%) containing iron and molybdenum has been developed. This alloy is cold formable in the [3 microstructure and can be aged to high strengths by precipitating the r phase. Due to its combination of cold formability and high strength, the alloy is a potential replacement for steel components in the automotive industry. The current study was undertaken to evaluate the cold bulk forming characteristics of Timetal LCB for use in lightweight automotive applications. Room-temperature compression tests conducted over a strain-rate range of 0.01 to 5/s indicate that the bulk cold compression of the alloy is affected by two factors: the microstructure and the length-to-diameter aspect ratio of the specimen. In the aged condition, when the microstructure has r particles distributed along flow lines in the ~phase matrix, the alloy has the propensity for shear failure when deformed in compression in a direction parallel to the flow lines. In the solution-heat-treated condition, the microstructure consists of [3 grains with athermal r phase. In this condition, the alloy can be cold compressed to 75 % reduction in height using specimens with aspect ratio of 1.125, but fails by shear for a larger aspect ratio of 1.5. Plastic deformation of the material occurs initially by single slip in most grains, but changes to multiple slip at true plastic strains larger than about 0.15. At a slow strain rate, the deformation is uniform, and the material work hardens continuously. At high strain rates, shear bands develop, and the localized deformation and temperature rise due to deformation heating leads to flow softening during compression. Although there is a considerable rise in temperature (200 to 500 *C) during deformation, precipitation of the r phase was not observed.
The manufacture and entrance into service of thin gage γ-TiAl product has been hampered by the in... more The manufacture and entrance into service of thin gage γ-TiAl product has been hampered by the inherent low room temperature ductility of the material. In the present study a new approach was explored for the efficient manufacture of γ-TiAl foil with improved ductility. The objective was to produce a very clean material (low interstitial content) with a highly refined, homogeneous microstructure placed in a fully lamellar condition. The processing route involved the use of RF plasma spray deposition of pre-alloyed powders, followed by consolidation via vacuum hot pressing and heat treatment. The approach took advantage of a deposition process which included no electrodes, no binders and high cooling rates. Results and discussion of the work performed to date are presented.
Intermetallic compounds based on refractory metals such as Nb, Mo, and W possess properties condu... more Intermetallic compounds based on refractory metals such as Nb, Mo, and W possess properties conducive to high temperature applications. Many of these intermetallics have very high melting points (above 1700 C) and retain their strength and stiffness to a high temperature (\u3e 1000°C). A serious impediment to the application of these materials is their low room temperature fracture toughness. A viable solution to this problem is to form in-situ composites of a brittle intermetallic compound and metallic phase. Room temperature toughness is improved in such composites by the ductile phase ligaments bridging cracks [1]. However, since the deformation of the continuous phase controls the overall deformation behavior of the composite, the role of the intermetallic matrix is also important, especially at temperatures where the intermetallic phase undergoes plastic deformation. Composites based on Nb - niobium silicide can be used as a model system for this class of materials. The room te...
It has been speculated that the beta transus temperature of alpha2-beta alloys will be a function... more It has been speculated that the beta transus temperature of alpha2-beta alloys will be a function of the alloy's oxygen content. An effort is presently made to ascertain the effect of a wide variety of oxygen contents on the beta transus temperature of the Ti-25Al-10Nb-1Mo alloy. The ...
Changes in the microstructure, volume fraction and distribution of phases during different stages... more Changes in the microstructure, volume fraction and distribution of phases during different stages of thermochemical processing of Ti-25Al-10Nb-3V-1Mo (at.%) castings were investigated. Up to 14.5 at.%(0.35 wt.%) of hydrogen was introduced into the material by ...
3. 3. Microstructural evolution during the high the high temperature deformation of Nb-10 a/o Si ... more 3. 3. Microstructural evolution during the high the high temperature deformation of Nb-10 a/o Si alloy indicated that substructure coarsening in the Nb and Nb 3 Si phases is the primary mechanism responsible for the shape of the flow curve. The average subgrain size was ...
Abstract The potential of nial as an elevated temperature material is well established. some of t... more Abstract The potential of nial as an elevated temperature material is well established. some of the positive characteristics of this intermetallic compound are its excellent oxidation resistance, low density, and high melting point. to date, its use has been limited because ...
This paper reports for the first time ordering transformations in the Nb3Si phase in the Nb-10Si ... more This paper reports for the first time ordering transformations in the Nb3Si phase in the Nb-10Si alloy. It was observed that; the Nb3Si phase in the Nb-10Si alloy undergoes two phase transformations during cooling below 1450 deg C. At least one of these transformations is an ordering reaction. The high temperature phases could be metastable or stable phases which, during cooling, transform to Nb3Si phase with the tP-32 structure that is observed at room temperature.
Implantation with aluminium ions (Al + ) was investigated for producing amorphous, microcrystalli... more Implantation with aluminium ions (Al + ) was investigated for producing amorphous, microcrystalline and crystalline phases in the refractory metals tantalum, niobium and vanadium. Surface alloys with a substantial aluminum content resulted from the implantation, reaching more than ...
Aluminum ion implantation of vanadium, niobium, and tantalum improved the metals' oxidation resis... more Aluminum ion implantation of vanadium, niobium, and tantalum improved the metals' oxidation resistances at 500 ~ and 735 ~ Implanted vanadium oxidized only to one-third the extent of unimplanted vanadium when exposed at 500 ~ to air. The oxidative weight gains of implanted niobium and tantalum proved negligible when measured at 500 ~ and for times sufficient to fully convert the untreated metals to their pentoxides. At 735 ~ implantation of vanadium only slightly retarded its oxidation, while oxidative weight gains of niobium and tantalum were reduced by factors of 3 or more. Implanted niobium exhibited weight gain in direct proportion to oxidation time squared at 735 ~ Microstructural examination of the metals implanted with selected fluences of the 180 kV aluminum ions showed the following. The solubility limit of aluminum is extended by implantation, the body centered cubic (bcc) phases being retained to-60 at. pct A1 in all three metals. The highest fluence investigated, 2.4 • 1022 ions/m s, produced an-400-nm layer of VA13 beneath the surface of vanadium, and-300-nm layers of an amorphous phase containing-70 at. pct A1 beneath the niobium and tantalum surfaces. All three metals, implanted to this fluence and annealed at 600 ~ contained tri-aluminides, intermetallic compounds known for their oxidation resistances. Specimens implanted to this fluence were thus selected for the oxidation measurements.
Tantalum was implanted with 180 keV Al+ ions to fluences up to 3�1018 Al+/cm2. Subsequent microch... more Tantalum was implanted with 180 keV Al+ ions to fluences up to 3�1018 Al+/cm2. Subsequent microchemical and microstructural observations showed that an amorphous layer covered the surface and extended to depths near 3000 � for fluences above 2.4�1018 Al+/cm2. The layer, comprised of ∼70 at. pet Al and ∼30 at. pet Ta, crystallized at temperatures above 500�C. Oxidation measurements, performed
Ion implantation produces thin films or layers that reside within a substrate rather than on top ... more Ion implantation produces thin films or layers that reside within a substrate rather than on top of it. The layers extend to the surface, differ in chemical composition and/or microstructure as compared with the substrate, and often modify the surface-dependent properties of the substrate material. Selected examples of modified properties are presented in this article and include improvements in oxidation and wear resistance from ion implantation. The shallow depths of the modified layers and the small scales of the implanted microstructures require the use of several modern analytical techniques for their characterization. Examples of such characterizations are also presented in this article. The implanted layers are examined for chemical concentrations versus depth with Auger electron spectroscopy and controlled sputtering, and with Rutherford backscattering spectrometry. Scanning electron microscopy and electron backscattering channeling analysis yield, respectively, information regarding products formed during oxidation and amorphous phase formed during implantation. Transmission electron microscopy and diffraction quantify the microstructures within the implanted layer and identify crystalline, nanocrystalline, and amorphous phases. Finally, it is shown that lattice imaging delineates atomic level defects, including stacking faults in-3 nm implanted rare gas precipitates, and amorphous phase formed during deceleration of the incident ions within intermetallic NiA13 phase.
The manufacture and entrance into service of thin gage gamma-TiAl product has been hampered by th... more The manufacture and entrance into service of thin gage gamma-TiAl product has been hampered by the inherent low room temperature ductility of the material. In the present study a new approach was explored for the efficient manufacture of gamma-TiAl foil with improved ductility. The objective was to produce a very clean material (low interstitial content) with a highly refined, homogeneous microstructure placed in a fully lamellar condition. The processing route involved the use of RF plasma spray deposition of pre-alloyed powders, followed by consolidation via vacuum hot pressing and heat treatment. The approach took advantage of a deposition process which included no electrodes, no binders and high cooling rates. Results and discussion of the work performed to date are presented.
Journal of Materials Engineering and Performance, 1996
Recently, a low-cost near-[3 titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-I.5AI wt%) containing iro... more Recently, a low-cost near-[3 titanium alloy (Timetal LCB Ti-6.8Mo-4.5Fe-I.5AI wt%) containing iron and molybdenum has been developed. This alloy is cold formable in the [3 microstructure and can be aged to high strengths by precipitating the r phase. Due to its combination of cold formability and high strength, the alloy is a potential replacement for steel components in the automotive industry. The current study was undertaken to evaluate the cold bulk forming characteristics of Timetal LCB for use in lightweight automotive applications. Room-temperature compression tests conducted over a strain-rate range of 0.01 to 5/s indicate that the bulk cold compression of the alloy is affected by two factors: the microstructure and the length-to-diameter aspect ratio of the specimen. In the aged condition, when the microstructure has r particles distributed along flow lines in the ~phase matrix, the alloy has the propensity for shear failure when deformed in compression in a direction parallel to the flow lines. In the solution-heat-treated condition, the microstructure consists of [3 grains with athermal r phase. In this condition, the alloy can be cold compressed to 75 % reduction in height using specimens with aspect ratio of 1.125, but fails by shear for a larger aspect ratio of 1.5. Plastic deformation of the material occurs initially by single slip in most grains, but changes to multiple slip at true plastic strains larger than about 0.15. At a slow strain rate, the deformation is uniform, and the material work hardens continuously. At high strain rates, shear bands develop, and the localized deformation and temperature rise due to deformation heating leads to flow softening during compression. Although there is a considerable rise in temperature (200 to 500 *C) during deformation, precipitation of the r phase was not observed.
The manufacture and entrance into service of thin gage γ-TiAl product has been hampered by the in... more The manufacture and entrance into service of thin gage γ-TiAl product has been hampered by the inherent low room temperature ductility of the material. In the present study a new approach was explored for the efficient manufacture of γ-TiAl foil with improved ductility. The objective was to produce a very clean material (low interstitial content) with a highly refined, homogeneous microstructure placed in a fully lamellar condition. The processing route involved the use of RF plasma spray deposition of pre-alloyed powders, followed by consolidation via vacuum hot pressing and heat treatment. The approach took advantage of a deposition process which included no electrodes, no binders and high cooling rates. Results and discussion of the work performed to date are presented.
Intermetallic compounds based on refractory metals such as Nb, Mo, and W possess properties condu... more Intermetallic compounds based on refractory metals such as Nb, Mo, and W possess properties conducive to high temperature applications. Many of these intermetallics have very high melting points (above 1700 C) and retain their strength and stiffness to a high temperature (\u3e 1000°C). A serious impediment to the application of these materials is their low room temperature fracture toughness. A viable solution to this problem is to form in-situ composites of a brittle intermetallic compound and metallic phase. Room temperature toughness is improved in such composites by the ductile phase ligaments bridging cracks [1]. However, since the deformation of the continuous phase controls the overall deformation behavior of the composite, the role of the intermetallic matrix is also important, especially at temperatures where the intermetallic phase undergoes plastic deformation. Composites based on Nb - niobium silicide can be used as a model system for this class of materials. The room te...
It has been speculated that the beta transus temperature of alpha2-beta alloys will be a function... more It has been speculated that the beta transus temperature of alpha2-beta alloys will be a function of the alloy's oxygen content. An effort is presently made to ascertain the effect of a wide variety of oxygen contents on the beta transus temperature of the Ti-25Al-10Nb-1Mo alloy. The ...
Changes in the microstructure, volume fraction and distribution of phases during different stages... more Changes in the microstructure, volume fraction and distribution of phases during different stages of thermochemical processing of Ti-25Al-10Nb-3V-1Mo (at.%) castings were investigated. Up to 14.5 at.%(0.35 wt.%) of hydrogen was introduced into the material by ...
3. 3. Microstructural evolution during the high the high temperature deformation of Nb-10 a/o Si ... more 3. 3. Microstructural evolution during the high the high temperature deformation of Nb-10 a/o Si alloy indicated that substructure coarsening in the Nb and Nb 3 Si phases is the primary mechanism responsible for the shape of the flow curve. The average subgrain size was ...
Abstract The potential of nial as an elevated temperature material is well established. some of t... more Abstract The potential of nial as an elevated temperature material is well established. some of the positive characteristics of this intermetallic compound are its excellent oxidation resistance, low density, and high melting point. to date, its use has been limited because ...
This paper reports for the first time ordering transformations in the Nb3Si phase in the Nb-10Si ... more This paper reports for the first time ordering transformations in the Nb3Si phase in the Nb-10Si alloy. It was observed that; the Nb3Si phase in the Nb-10Si alloy undergoes two phase transformations during cooling below 1450 deg C. At least one of these transformations is an ordering reaction. The high temperature phases could be metastable or stable phases which, during cooling, transform to Nb3Si phase with the tP-32 structure that is observed at room temperature.
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Papers by Mohammad Saqib