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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Effect of microalloying additions on microstructural evolution and thermal stability in cast Al-Ni alloys

Enhancement of thermal stability in Al-Ni alloys through microalloying with slow-diffusing elements, specifically Zr, has been previously reported which is attributed to Zr segregation at the Al/Al 3 Ni interface. In this study, we explore the influence of microalloying Al-Ni alloys with Zr, Ti, V, and Fe on microstructural evolution, hardness, and electrical and thermal conductivity across a range of heat-treatment temperatures from 300 to 450 °C. The distribution of microalloying elements and precipitates after heat treatment is characterized using atom probe tomography (APT). Our investigation confirms Zr segregation to the Al/Al 3 Ni interface, while similar interfacial segregation is absent with the addition of Ti, V, and Fe. Additionally, our analysis of the Al 3 Ni microfiber morphology reveals that their coarsening and spheroidization rates are similar with and without interfacial segregation; thus, retaining the fiber reinforcement through interfacial segregation of slow diffusing elements may not be an effective strategy. Precipitation of L1 2 nanoparticles was found to be the dominant mechanism affecting enhanced hardness and electrical conductivity in Al-Ni-Zr alloys, attributed to precipitation strengthening and solute depletion, respectively. Similar precipitation was not observed for additions of Ti, V, and Fe following heat treatment. We provide a thermodynamic explanation for this limitation. Furthermore, the findings of this study suggest that an effective approach for designing Al-Ni alloys should involve prioritizing microalloying elements to maximize L1 2 precipitation and minimize solute content in the FCC-Al matrix post heat treatment, rather than focusing on Al/Al3Ni interfacial segregation.

36 MATERIALS SCIENCE↗
NASA NTRS1978

Interdiffusion and intrinsic diffusion in the NiAl /delta/ phase of the Al-Ni system

Interdiffusion coefficients at 950 to 1150 C and the ratio of intrinsic diffusion coefficients at 1100 C were measured as functions of composition in the NiAl (delta) phase of the Al-Ni system, using a vapor-solid technique. Diffusivity values were also obtained for the Ni3Al (epsilon) and Ni (Al) solid solution (zeta) phases from 950 to 1150 C. The interdiffusion coefficient in NiAl (delta) varies several orders of magnitude over the delta phase field with a deep minimum in the diffusivity-composition curve at 48 to 49 at% Al. The ratio of intrinsic diffusion coefficients DNi/DAl, in the delta phase also varies with composition from a value of 3 to 3.5 below 50 at% Al to 0.1 or less above 50 at% Al.

Shankar, S.↗
NASA NTRS1988

Directional solidification of Al-Ni/SiC composites during parabolic trajectories

Aluminum-6.1 wt. pct. nickel-silicon carbide composites containing varying volume fractions and particle sizes of SiC were directionally solidified at different translation rates and temperature gradients, under variable gravity levels. High-gravity, high-volume fractions of particles or high effective viscosity of liquid favored the engulfment of particles by the melt interface. Solidification under low gravity seemed to deflocculate the SiC particle agglomerates, while opposite results were obtained when solidifying under high gravity. Intercellular spacings were higher under low gravity solidfication.

Dhindaw, B. K.↗
DOE OSTI2022

First-principles study of Al/Al 3 Ni interfaces

Al-Ni alloys have shown promise for high-temperature applications due to the strengthening of Al 3 Ni fibers resistant to coarsening and spheroidization up to 400°C. While the interface between Al and Al 3 Ni phases affects the coarsening rate of Al 3 Ni at elevated temperatures, its characteristics are largely unknown to date. Here, we have constructed various supercells to model this interface and performed a first-principles study based on density functional theory (DFT). We have considered three groups of Al/Al 3 Ni interfaces: experimentally reported orientation relationships from the solidification studies, crystallographically similar Fe-Fe 3 C pearlite interfaces, and the family of low-index (100) termination planes. We have analyzed the correlation between the DFT Al/Al 3 Ni interfacial energies and characteristic features, e.g., excess free volume and the number of broken bonds. We outline the further experimental and computational analysis required to improve the interface modeling of Al/Al 3 Ni.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Effects of tensile loading during annealing of alnico melt spun ribbons

Conventional magnetic annealing (MA) of the permanent magnet alloy alnico involves application of an external magnetic field at temperatures within the spinodal decomposition range. This field biases the growth of the Fe-Co rich, ferromagnetic α 1 -phase in an energetically favorable 〈001〉 direction in alignment with the applied field within an Al-Ni rich, paramagnetic α 2 -phase. Utilizing a magnetic field to bias the α 1 -phase may limit alnico from reaching theoretical coercivity due to (1) the field having maximum biasing ability at temperatures near the Curie temperature where large α 1 -phase nanorods form and (2) connectivity of the α 1 -phase occurs unavoidably during MA. Both decrease the effective shape anisotropy of the α 1 -phase, thereby reducing coercivity. Herein, we explore tensile-loading as a biasing mechanism to control and optimize the final alnico nanostructure beyond that achieved by MA. Two samples of melt-spun alnico were heat-treated at 860 °C for 5 minutes: one sample was subjected to 10 MPa tensile stress for comparison with a stress-free control sample. Structural and magnetic characterization revealed that the stress-annealed ribbon sample possessed expected phase assemblages, but was distinguished by a ∼2× larger grain diameter and an elongated anisotropic α 1 -phase within grains that were oriented to a shear stress along 〈001〉 directions at an angle of ∼45° relative to the loading direction. Both types of annealing produced a similar increase in the coercivity and remanence, but a decrease in saturation magnetization.

Rinko, E. A.↗
NASA NTRS1987

High-temperature ordered intermetallic alloys II; Proceedings of the Second Symposium, Boston, MA, Dec. 2-4, 1986

The papers presented in this volume provide on overview of recent theoretical and experimental research in the field of high-temperature ordered intermetallic alloys. The papers are gouped under the following headings: ordering behavior and theory, microstructures, mechanical behavior, alloy design and microstructural control, and metallurgical properties. Specific topics discussed include antiphase domains, disordered films and the ductility of ordered alloys based on Ni3Al; kinetics and mechanics of formation of Al-Ni intermetallics; deformability improvements of L1(2)-type intermetallic compounds; B2 aluminides for high-temperature applications; and rapidly solidified binary TiAl alloys.

Stoloff, N. S.↗
NASA NTRS1990

The influence of buoyant forces and volume fraction of particles on the particle pushing/entrapment transition during directional solidification of Al/SiC and Al/graphite composites

Directional solidification experiments in a Bridgman-type furnace were used to study particle behavior at the liquid/solid interface in aluminum metal matrix composites. Graphite or silicon-carbide particles were first dispersed in aluminum-base alloys via a mechanically stirred vortex. Then, 100-mm-diameter and 120-mm-long samples were cast in steel dies and used for directional solidification. The processing variables controlled were the direction and velocity of solidification and the temperature gradient at the interface. The material variables monitored were the interface energy, the liquid/particle density difference, the particle/liquid thermal conductivity ratio, and the volume fraction of particles. These properties were changed by selecting combinations of particles (graphite or silicon carbide) and alloys (Al-Cu, Al-Mg, Al-Ni). A model which consideres process thermodynamics, process kinetics (including the role of buoyant forces), and thermophysical properties was developed. Based on solidification direction and velocity, and on materials properties, four types of behavior were predicted. Sessile drop experiments were also used to determine some of the interface energies required in calculation with the proposed model. Experimental results compared favorably with model predictions.

Stefanescu, Doru M.↗
NASA NTRS1990

Sulfur at nickel-alumina interfaces - Molecular orbital theory

Previous studies on Al-Ni alloys containing sulfur as an impurity suggest that, when S is in the interface between a metal and an oxide scale, it weakens the chemical bonding between them. This paper investigates factors responsible for this effect, using a molecular orbital theory to predict sulfur structures and electronic properties on the Ni-Al2O3 interface. It is shown that, in absence of S, the basal plane of Al2O3 will bind strongly through the Al(3+) cation surface to Ni (111). When segregated S impurity is present on the Ni surface, there are too few interfacial AlS bonds to effect good adhesion, leading to an inhibition of the oxide scale adhesion in NiCrAl alloys.

Hong, S. Y.↗
NASA NTRS1996

Advancement of Solidification Processing Technology Through Real Time X-Ray Transmission Microscopy: Sample Preparation

Two types of samples were prepared for the real time X-ray transmission microscopy (XTM) characterization. In the first series directional solidification experiments were carried out to evaluate the critical velocity of engulfment of zirconia particles in the Al and Al-Ni eutectic matrix under ground (l-g) conditions. The particle distribution in the samples was recorded on video before and after the samples were directionally solidified. In the second series samples of the above two type of composites were prepared for directional solidification runs to be carried out on the Advanced Gradient Heating Facility (AGHF) aboard the space shuttle during the LMS mission in June 1996. X-ray microscopy proved to be an invaluable tool for characterizing the particle distribution in the metal matrix samples. This kind of analysis helped in determining accurately the critical velocity of engulfment of ceramic particles by the melt interface in the opaque metal matrix composites. The quality of the cast samples with respect to porosity and instrumented thermocouple sheath breakage or shift could be easily viewed and thus helped in selecting samples for the space shuttle experiments. Summarizing the merits of this technique it can be stated that this technique enabled the use of cast metal matrix composite samples since the particle location was known prior to the experiment.

Stefanescu, D. M.↗
DOE OSTI2020

Materials Data on Al3Ni2 by Materials Project

Al3Ni2 crystallizes in the trigonal P-3m1 space group. The structure is three-dimensional. Ni is bonded in a body-centered cubic geometry to eight Al atoms. There are a spread of Ni–Al bond distances ranging from 2.44–2.54 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 6-coordinate geometry to six equivalent Ni atoms. In the second Al site, Al is bonded in a 5-coordinate geometry to five equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlNi by Materials Project

NiAl is Tetraauricupride structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. Ni is bonded in a body-centered cubic geometry to eight equivalent Al atoms. All Ni–Al bond lengths are 2.50 Å. Al is bonded in a body-centered cubic geometry to eight equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al3Ni5 by Materials Project

Ni5Al3 crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. there are three inequivalent Ni sites. In the first Ni site, Ni is bonded in a 12-coordinate geometry to six Ni and six Al atoms. There are two shorter (2.60 Å) and four longer (2.65 Å) Ni–Ni bond lengths. There are a spread of Ni–Al bond distances ranging from 2.39–2.55 Å. In the second Ni site, Ni is bonded to six Ni and six Al atoms to form distorted NiAl6Ni6 cuboctahedra that share corners with twelve equivalent NiAl6Ni6 cuboctahedra, edges with four equivalent NiAl4Ni8 cuboctahedra, and faces with eight NiAl6Ni6 cuboctahedra. Both Ni–Ni bond lengths are 2.50 Å. All Ni–Al bond lengths are 2.50 Å. In the third Ni site, Ni is bonded to eight Ni and four equivalent Al atoms to form distorted NiAl4Ni8 cuboctahedra that share corners with four equivalent NiAl4Ni8 cuboctahedra, edges with eight equivalent NiAl6Ni6 cuboctahedra, and faces with six NiAl6Ni6 cuboctahedra. All Ni–Al bond lengths are 2.52 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 10-coordinate geometry to ten Ni atoms. In the second Al site, Al is bonded in a distorted body-centered cubic geometry to eight Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al4Ni3 by Materials Project

Al4Ni3 crystallizes in the cubic Ia-3d space group. The structure is three-dimensional. Ni is bonded in a body-centered cubic geometry to eight Al atoms. There are a spread of Ni–Al bond distances ranging from 2.44–2.53 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 6-coordinate geometry to six equivalent Ni atoms. In the second Al site, Al is bonded in a 6-coordinate geometry to six equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlNi3 by Materials Project

Ni3Al is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ni is bonded to eight equivalent Ni and four equivalent Al atoms to form NiAl4Ni8 cuboctahedra that share corners with twelve equivalent NiAl4Ni8 cuboctahedra, edges with eight equivalent AlNi12 cuboctahedra, edges with sixteen equivalent NiAl4Ni8 cuboctahedra, faces with four equivalent AlNi12 cuboctahedra, and faces with fourteen equivalent NiAl4Ni8 cuboctahedra. All Ni–Ni bond lengths are 2.52 Å. All Ni–Al bond lengths are 2.52 Å. Al is bonded to twelve equivalent Ni atoms to form AlNi12 cuboctahedra that share corners with twelve equivalent AlNi12 cuboctahedra, edges with twenty-four equivalent NiAl4Ni8 cuboctahedra, faces with six equivalent AlNi12 cuboctahedra, and faces with twelve equivalent NiAl4Ni8 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Al3Ni by Materials Project

Al3Ni is Cementite structured and crystallizes in the orthorhombic Pnma space group. The structure is three-dimensional. Ni is bonded in a 9-coordinate geometry to nine Al atoms. There are a spread of Ni–Al bond distances ranging from 2.43–2.70 Å. There are two inequivalent Al sites. In the first Al site, Al is bonded in a 2-coordinate geometry to three equivalent Ni atoms. In the second Al site, Al is bonded in a 3-coordinate geometry to three equivalent Ni atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on AlNi3 by Materials Project

Ni3Al is alpha bismuth trifluoride structured and crystallizes in the cubic Fm-3m space group. The structure is three-dimensional. there are two inequivalent Ni sites. In the first Ni site, Ni is bonded in a distorted body-centered cubic geometry to four equivalent Ni and four equivalent Al atoms. All Ni–Ni bond lengths are 2.45 Å. All Ni–Al bond lengths are 2.45 Å. In the second Ni site, Ni is bonded in a 8-coordinate geometry to eight equivalent Ni and six equivalent Al atoms. All Ni–Al bond lengths are 2.83 Å. Al is bonded in a distorted body-centered cubic geometry to fourteen Ni atoms.

36 MATERIALS SCIENCE↗