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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 1,279 records · Page 71
All sourcesNASA NTRSDOE OSTI
NASA NTRS1965

Development of high temperature nickel-base alloys for jet engine turbine bucket applications

A program has been initiated to develop a material with superior properties at elevated temperatures for utilization in turbine blade applications. A nickel-base superalloy can provide the necessary high temperature strength by using the maximum capability of the three available strengthening mechanisms - intermetallic gamma prime precipitation (Ni3Al), solid solution strengthening with refractory and precious metals, and stable carbide formations through the addition of strong carbide forming elements. A stress rupture test at 2000 deg F and 15,000 psi was formulated to approximate the desired properties. By adding varying amounts of refractory metals (Mo, W and Ta) it was possible to statistically analyze the effects of each in a basic superalloy composition containing fixed amounts of Co, Cr, C, B, Sr, and Ni at three separate levels of AL and Ta. Metallographic analysis correlated with the mechanical properties of the alloys; those with few strengthening phases were weak and ductile and those with excessive amounts of intermetallic phases present in undesirable morphologies were brittle.

SUPERALLOY↗
DOE OSTI2018

Magnetic and Electrical Properties of Hg{sub 1–x–}Mn{sub x}Fe{sub y}Te{sub 1–z}S{sub z} Crystals

Electrical and magnetic properties of the semimagnetic semiconductor Hg{sub 1–x–y}Mn{sub x}Fe{sub y}Te{sub 1–z}S{sub z} solid solutions were studied in the ranges of temperatures 77–320 K and magnetic fields 0.25–6 kOe. In the crystals under study, the effect of giant magnetoresistance was observed that reached 75% at low temperatures. This is due to the fact that charge carriers that participate in the current transfer interact with a magnetized ferromagnetic cluster subsystem (Fe–Fe–Fe) and become spin-polarized. It is these spin-polarized charge carriers that are strongly scattered on antiferromagnetic Mn–S–Mn–S and Mn–Te–Mn–Te clusters, since the magnetic moments inside the clusters and the resulting magnetic moments of these clusters are randomly oriented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Giant dielectric constant in TiO{sub 2}/Al{sub 2}O{sub 3} nanolaminates grown on doped silicon substrate by pulsed laser deposition

High quality amorphous nanolaminates by means of alternate Al{sub 2}O{sub 3} and TiO{sub 2} oxide sublayers were grown with atomic scale thickness control by pulsed laser deposition. A giant dielectric constant (>10 000), strongly enhanced compared to the value of either Al{sub 2}O{sub 3} or TiO{sub 2} or their solid solution, was observed. The dependence of the dielectric constant and the dielectric loss on the individual layer thickness of each of the constituting materials was investigated between 0.3 nm and 1 nm, in order to understand the prevailing mechanisms and allow for an optimization of the performances. An impedance study confirmed as the key source of the giant dielectric constant a Maxwell–Wagner type dielectric relaxation, caused by space charge polarization in the nanolaminate structure. The current work provides better insight of nanolaminates and their sublayer thickness engineering for potential applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Understanding the solidification and microstructure evolution during CSC-MIG welding of Fe–Cr–B-based alloy

The present is a study of the solidification and microstructure of Fe–28.2%Cr–3.8%B–1.5%Si–1.5%Mn (wt.%) alloy deposited onto a 1020 plain carbon steel substrate using the controlled short-circuit metal inert gas welding process. The as-solidified alloy was a metal matrix composite with a hypereutectic microstructure. Thermodynamic calculation based on the Scheil–Gulliver model showed that a primary (Cr,Fe){sub 2}B phase formed first during solidification, followed by an eutectic formation of the (Cr,Fe){sub 2}B phase and a body-centered cubic Fe-based solid solution matrix, which contained Cr, Mn and Si. Microstructure analysis confirmed the formation of these phases and showed that the shape of the (Cr,Fe){sub 2}B phase was irregular plate. As the welding heat input increased, the weld dilution increased and thus the volume fraction of the (Cr,Fe){sub 2}B plates decreased while other microstructural characteristics were similar. - Highlights: • We deposit Fe–Cr–B-based alloy onto plain carbon steel using the CSC-MIG process. • We model the solidification behavior using thermodynamic calculation. • As deposited alloy consists of (Cr,Fe){sub 2}B plates embedded in Fe-based matrix. • We study the effect of the welding heat input on the microstructure.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Atomic substitution effects on the structural and vibrational properties of Ni{sub x}Pb{sub 1-x}TiO{sub 3}: X-ray diffraction and Raman scattering investigations

The effects of the atomic substitution of Pb by Ni in the PbTiO{sub 3} ferroelectric perovskite on the vibrational and structural properties was studied using x-ray diffraction and Raman scattering. It was observed that for Ni concentrations between 0.0 and 0.4, there is the formation of a solid solution with reduction of the Raman wavenumber of the E(TO1) soft mode and the tetragonallity factor, which influence directly the temperature of the tetragonal ferroelectric to cubic paraelectric phase transition, the Curie temperature. For concentrations greater than 0.4, it is observed the formation of a PbTiO{sub 3} and NiTiO{sub 3} composite, denounced by the recovering of the both, tetragonallity factor and the E(TO1) soft mode wavenumber. The values of the Curie temperatures were estimated by the Raman scattering measurements for temperatures ranging from 300 to 950 K.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Specific features of magnetoresistance during the antiferromagnet-paramagnet transition in Tm{sub 1-x}Yb{sub x}B{sub 12}

The transverse magnetoresistance {Delta}{rho}/{rho}(H, T) of Tm{sub 1-x}Yb{sub x}B{sub 12} single crystals is studied in the ytterbium concentration range corresponding to the antiferromagnet-paramagnet transition in a magnetic field up to 80 kOe at low temperatures. A magnetic H-T phase diagram is constructed for the antiferromagnetic state of substitutional Tm{sub 1-x}Yb{sub x}B{sub 12} solid solutions with x {<=} 0.1. The contributions to the magnetoresistance in the antiferromagnetic and paramagnetic phases of the dodecaborides under study are separated. Along with negative quadratic magnetoresistance -{Delta}{rho}/{rho} {proportional_to} H{sub 2}, the magnetically ordered phase of these compounds is found to have component {Delta}{rho}/{rho} {proportional_to} H that linearly changes in a magnetic field. The negative contribution to the magnetoresistance of Tm{sub 1-x}Yb{sub x}B{sub 12} is analyzed in terms of the Yosida model for a local magnetic susceptibility.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Short-Range Order in Amorphous and Crystalline Ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2}

The microstructures of amorphous and polycrystalline ferroelectric Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films are studied by X-ray spectroscopy and ellipsometry. EXAFS spectra demonstrate that the amorphous film consists of an “incompletely mixed” solid solution of metallic oxides HfO{sub 2} and ZrO{sub 2}. After rapid thermal annealing, the mixed Hf{sub 0.5}Zr{sub 0.5}O{sub 2} oxide films have a more ordered polycrystalline structure, and individual Hf and Zr monoxide islands are formed in the films. These islands are several nanometers in size and have a structure that is similar to the monoclinic structure of HfO{sub 2} and ZrO{sub 2}. The presence of the HfO{sub 2} and ZrO{sub 2} phases in the Hf{sub 0.5}Zr{sub 0.5}O{sub 2} films is also detected by ellipsometry.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Phase Evolution and Mechanical Properties of AlCoCrFeNiSi{sub x} High-Entropy Alloys Synthesized by Mechanical Alloying and Spark Plasma Sintering

In the current investigation, AlCoCrFeNiSi{sub x} (x = 0, 0.3, 0.6 and 0.9 in atomic ratio) high-entropy alloy systems are prepared by mechanical alloying and subsequently consolidated by spark plasma sintering. The microstructural and mechanical properties were analyzed to understand the effect of Si addition in AlCoCrFeNi alloy. The x-ray diffraction analysis reveals the supersaturated solid solution of the body-centered cubic structure after 20 h of ball milling. However, the consolidation promotes the transformation of body-centered phases partially into the face-centered cubic structure and sigma phases. A recently proposed geometric model based on the atomic stress theory has been extended for the first time to classify single phase and multi-phases on the high-entropy alloys prepared by mechanical alloying and spark plasma sintering process. Improved microhardness and better wear resistance were achieved as the Si content increased from 0 to 0.9 in the present high-entropy alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Cd content in barriers on the threshold energy of Auger recombination in waveguide structures with HgTe/Cd{sub x}Hg{sub 1 – x}Te quantum wells, emitting at a wavelength of 18 μm

The threshold energy of Auger recombination in HgTe/Cd{sub x}Hg{sub 1 – x}Te heterostructures with quantum wells (QWs) is analysed numerically for different compositions of the solid solution in barriers. It is demonstrated that the threshold energy depends nonmonotonically on the cadmium content in barriers and reaches a maximum at x ∼0.6 – 0.7. A comparison of the results of numerical calculations with experimental data on the temperature quenching of stimulated emission in a Cd{sub 0.1}Hg{sub 0.9}Te/Cd{sub 0.65}Hg{sub 0.35}Te structure gives grounds to expect a more than twofold increase in the quenching temperature of stimulated emission in structures with pure HgTe QWs and barriers with a high (∼0.6) cadmium content. (paper)

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Laser assisted high entropy alloy coating on aluminum: Microstructural evolution

High entropy alloy (Al-Fe-Co-Cr-Ni) coatings were synthesized using laser surface engineering on aluminum substrate. Electron diffraction analysis confirmed the formation of solid solution of body centered cubic high entropy alloy phase along with phases with long range periodic structures within the coating. Evolution of such type of microstructure was a result of kinetics associated with laser process, which generates higher temperatures and rapid cooling resulting in retention of high entropy alloy phase followed by reheating and/or annealing in subsequent passes of the laser track giving rise to partial decomposition. The partial decomposition resulted in formation of precipitates having layered morphology with a mixture of high entropy alloy rich phases, compounds, and long range ordered phases.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Effect of Mo Particles Addition in Ag-Cu-Ti Filler Alloy on Ti(C,N)-Based Cermet/45 Steel-Brazed Joints

Reliable brazing of Ti(C,N)-based cermet and 45 steel was successfully achieved by using the Mo-particle-reinforced Ag-Cu-Ti composite filler. The effects of Mo content on the interfacial microstructure and mechanical properties of Ti(C,N)-based cermet/45 steel joints were analyzed. The results showed that the joint microstructure was primarily composed of Ni{sub 3}Ti+Cu{sub 3}Ti{sub 2}, Ag(s,s)+Cu(s.s), CuTi+Mo, Ti-based solid solution, and FeTi+Fe{sub 2}Ti. With the increase in Mo content in filler, the thickness of the Ni{sub 3}Ti+Cu{sub 3}Ti{sub 2} layer adjacent to the Ti(C,N)-based cermet decreases, while more blocky Ti-Cu intermetallic were observed in the brazing seam. The shear strength of the joint could be significantly improved by adding suitable amounts of Mo into the Ag-Cu-Ti filler, and the peak value of 263 MPa was achieved when the alloys were brazed with Ag-Cu-Ti+8wt.%Mo composite filler at 920 °C for 20 min.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural Evolution and Mechanical Behavior of Lead-Free Silicon Brass Manufactured by Low-Pressure Die Casting

Low-pressure die casting (LPDC) has been widely used to process aluminum and magnesium alloys; however, it has yet to be applied to manufacture brass alloys. This study investigates the microstructural evolution and mechanical behavior of a lead-free CuZnSiAl silicon brass via a variable-controlling approach on the basis of a faucet casting by LPDC. The manufactured silicon brass castings are predominantly composed of bcc β-CuZn(Si, Al) and minor fcc α-Cu(Zn, Si) solid solutions. The silicon brass castings also predominantly exhibit short rod-like or granular α phases, which distinctly differ from the acicular α morphology obtained by conventional gravity casting. The manufactured silicon brass castings which contain finer β grains and short rod-like or granular α phase exhibit superior mechanical properties. Their optimal mechanical properties—elongation of 15.0%, yield strength of 359.8 MPa, and ultimate tensile strength of 598.9 MPa—are far superior to those of the typical lead brass HPb59-1. The results obtained in this study provide insight into the manufacture and design of lead-free silicon brass castings by LDPC.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study on Microstructure and Properties of AZ31/6061 GTAW Butt Joints According to Mg-Cd-Al Ternary System

AZ31 Mg and 6061 Al were successfully joined by GTAW method with Cd as filler metal. The tensile strength of the joints reached 170 MPa through this alloying method according to Mg-Cd-Al ternary system. The microstructure, phases, element distribution and fracture mechanism of alloyed joints were studied. The results suggest that the fusion zone is mainly composed of CdMg compounds and Al-based solid solution. A transitional zone thickness of 40-80 μm with few primary Al{sub 12}Mg{sub 17} and fine Al{sub 12}Mg{sub 17}-MCMS (MCMS represents a mixture of CdMg and CdMg{sub 3} compounds) eutectic is formed between the AZ31 base metal and fusion zone. The fracture surface presents three distinct regions because of the different distribution of Al{sub 12}Mg{sub 17} compounds in the transitional zone. The alloying with Cd filler metal can disperse Al{sub 12}Mg{sub 17} intermetallic compounds and form CdMg ordered compounds with excellent plasticity. Thus, the mechanical properties of alloyed joints have been significantly enhanced.

36 MATERIALS SCIENCE↗
DOE OSTI2024

High-throughput approach for investigating interdiffusion in medium- and high-entropy alloys

Interdiffusion experiments are usually time-consuming and tedious since diffusion couples must be annealed at several temperatures for a long time. The efforts required to study interdiffusion in multicomponent alloys increase dramatically as multiple diffusion couples are required to cover broad composition ranges and determine the diffusivities of individual elements in different chemical environments. To circumvent this challenge, we present a high-throughput approach applicable to single-phase and compositionally complex alloys, which are assumed to approximate ideal solid solutions. Here, a simple diffusion-multiple experiment combined with a physically based kinetic model is proposed to efficiently determine the diffusion coefficients of the constituent elements in quaternary CrFeCoNi alloys. Compared with tracer diffusivities reported in the literature, the results, thus, obtained do not differ by more than a factor of 2 and were obtained from a single interdiffusion experiment. In contrast, the diffusivities simulated with commercial mobility and thermodynamic databases are strongly overestimated by a factor ranging from 1 to 16. Therefore, our approach enables high-throughput determination of diffusivities and can help in the design of alloys for high-temperature applications where diffusion plays a key role.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Temperature evolution of the dielectric response function of Pb(Fe{sub 0.95}Sc{sub 0.05}){sub 2/3}W{sub 1/3}O{sub 3} relaxor ceramics in a wide frequency range

Electrodynamic properties of Pb(Fe{sub 0.95}Sc{sub 0.05}){sub 2/3}W{sub 1/3}O{sub 3} solid solution belonging to A(B'B'')O{sub 3} perovskite structural family have been investigated by broadband dielectric spectroscopy in a wave-number range of (4 × 10{sup –9}–4 × 10{sup 3}) cm{sup –1} and a temperature range of 100–600 K. The influence of low-frequency relaxations on the vibrational spectrum is determined within the four-parameter factorized dispersion model. Anomalies in the behavior of the dielectric response function are found near the temperature-diffuse maximum of permittivity.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Defect evolution in Ni and NiCoCr by in situ 2.8 MeV Au irradiation

The evolution of radiation-induced defects in Ni and the single-phase concentrated solid solution alloy, NiCoCr, were investigated during in situ 2.8 MeV Au ion irradiation and post-irradiation analysis using transmission electron microscopy. Compared to Ni, both the size and area density of defect clusters decreased in NiCoCr under the same irradiation conditions, suggesting that the chemical complexity, i.e., randomness of lattice site occupations, of NiCoCr suppressed radiation-induced damage. One-dimensional glide of defect clusters was observed in Ni but not in the NiCoCr alloy. The structural nature of small defect clusters in NiCoCr were further investigated using high-angle annular dark field scanning transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Phase evolution in the ferroelectric relaxor Ba ( Ti 1 - x , Zr x ) O 3 from atomistic simulations

We develop and/or use a combination of first-principles density functional theory and first-principles-based effective Hamiltonian approaches to investigate phase evolution in Ba(Ti 1–x ,Zr x )O 3 ferroelectric relaxor. Our simulations reveal two competing effects, which are associated with substitution of Ti with Zr and primarily responsible for the unusual phase evolution and the properties of this family of solid solutions. They are the negative chemical pressure that Zr exerts on the BaTiO 3 matrix and the ferroelectric “inactivity” of Zr itself. While the former has a stabilizing effect on ferroelectricity, the latter disrupts the ferroelectric cooperation. These competing effects are responsible for the so-called pinched phase transition, where the three phases of parent BaTiO 3 merge together, and the loss of ferroelectricity at the onset of relaxor behavior. Here, the origin of the controversial diffuse phase transition is attributed to the coexistence of the three ferroelectric phases. In the region of the diffuse phase transition, we detect polar nanoregions, which often exhibit unusual nanopillar geometry.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Mechanical and Tribological Behavior of ZrB{sub 2}-TiB{sub 2} System Prepared by Mechanical Activation Spark Plasma Sintering Technique

ZrB{sub 2}-TiB{sub 2} system among varying amount of TiB{sub 2} loading (5, 10, 15, 20 and 30 wt.%) was prepared by mechanical activation spark plasma sintering at 2100 °C for 15-min dwell time under 50 MPa uniaxial pressure in argon atmosphere. The effect of the TiB{sub 2} loading on properties like physical, mechanical and tribological of the prepared samples was studied and evaluated with monolithic ZrB{sub 2} ceramic. Finally, almost fully dense samples (> 96% of theoretical density) were fabricated. Microstructural observation and XRD phase analysis of sintered compact revealed that TiB{sub 2} completely went into the ZrB{sub 2} structure by formation of solid solution with ZrB{sub 2} phase. ZrB{sub 2}-TiB{sub 2} (30 wt.%) showed the highest Vickers micro-hardness (H{sub V}) of 20.64 GPa at 10 N load. On addition of TiB{sub 2}, the fracture toughness of the ZrB{sub 2}-TiB{sub 2} improved up to 4.69 ± 0.43 MPa m{sup 1/2} over monolithic ZrB{sub 2} at 10 N load. At 10 N load, the scratch resistance coefficient, wear rate and wear resistance coefficient of ZrB{sub 2}-TiB{sub 2} (30 wt.%) reached a lowest value of 0.32, 0.35 mm{sup 3}/N m and 0.008, respectively, at 10 N load than other ZrB{sub 2} compositions.

36 MATERIALS SCIENCE↗