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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 1,423 records · Page 79
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DOE OSTI2018

Study of the Al-T-Si (T = Fe, Co, Ni) alloys in the solid, liquid and as-quenched states

Highlights: • Analysis of the formation and evolution of crystalline phases during heat-treatment of as-quenched alloys using in-situ high-temperature XRD. • XRD study and MD simulations of SRO in liquid and amorphous Al-T-Si (T = Fe, Co, Ni) alloys. • Similarity between the CSRO in amorphous Al{sub 65}T{sub 15}Si{sub 20} (T = Fe, Ni) alloys and crystalline Al{sub 9}Fe{sub 2}Si{sub 2} and Al{sub 3}Ni phases. - Abstract: Local atomic structure of liquid and amorphous Al{sub 80 − x}T{sub x}Si{sub 20} (where T = Fe, Co, Ni and x = 10, 15) alloys has been studied by X-ray diffraction (XRD) and molecular dynamics simulations. Chemical short-range order in the liquid and amorphous alloys has been found to be similar to that in the corresponding crystalline counterparts. Formation and evolution of crystalline phases during heat-treatment of the as-quenched ternary alloys up to liquid state were shown using in-situ XRD. Analysis of the morphology of the as-quenched and annealed Al-T-Si ribbons has been performed by transmission electron microscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Mn addition on the microstructure and mechanical properties of a directionally solidified γ-TiAl alloy

Highlights: • Mn addition can significantly improve the yield strength of TiAl alloy. • Introduction of Mn facilitates the operation of twinning-controlled deformation. • Twin-dislocation interactions cause a continuous increase in work hardening rate. - Abstract: TiAl alloys with nominal compositions of Ti-47Al-2Nb-2Cr-(0, 1, 3, 5)Mn were prepared via electromagnetic cold crucible directional solidification (ECCDS), and the influence of Mn addition on the microstructure and mechanical properties of the alloys was investigated. The experimental results showed that the Mn atoms were dissolved within the TiAl alloy, and no Mn compounds were formed. Based on the X-ray diffraction (XRD) analysis results, the peak angle of the Mn-containing sample shifted to a higher value, indicating lattice shrinkage. The Mn addition also increased the volume fraction of the B2 phase. The yield strength of the TiAl alloy monotonically increased as the content of the substitutional-solute Mn atoms increased. The ultimate strengths of the TiAl alloys containing 1 at.%, 3 at.%, and 5 at.% Mn consequently decreased because micro-cracks were preferentially formed in the B2 phase during room-temperature deformation. The introduction of substitutional-solute Mn atoms could result in a reduction of the stacking-fault energy of the γ phase, and facilitate the operation of twinning-controlled plastic-deformation during the intermediate stage of the plastic deformation process. The interaction between the deformation twins and movable dislocations led to a continuous increase in the work-hardening rate.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A study of microstructural evolution of Fe-18Cr-8Ni, Fe-17Cr-12Ni, and Fe-20Cr-25Ni stainless steels after mechanical alloying and annealing

In this study, high-energy mechanical alloying technique was used to produce nanocrystalline stainless steels of three different compositions from elemental powders. The microstructural evolution (grain growth and phase transformation) as a function of alloy compositions and annealing temperatures were investigated by room and high temperature x-ray diffraction experiments, transmission electron microscopy and focused ion beam microscopy. The results revealed that stainless steels with low nickel content (i.e., Fe-18Cr-8Ni) underwent a deformation-induced martensitic transformation during room temperature mechanical alloying. Deformation-induced martensitic transformation with increasing nickel content (i.e., Fe-17Cr-12Ni and Fe-20Cr-25Ni) would not be possible by room temperature milling but was created by high strain rate cryogenic processing, the degree to which was compositional dependent. Post process annealing induced the reverse transformation from martensite-to-austenite the ratio of which was found to be a factor of alloy composition and annealing temperature. The real time in-situ x-ray studies showed that the martensite-to-austenite reverse transformation was completed at around 600 °C and 800 °C for Fe-18Cr-8Ni and Fe-20Cr-25Ni steels, respectively. Microscopy studies revealed a significant enhancement in the resistance to grain growth for Fe-17Cr-12Ni steel over other compositions at elevated temperatures as high as 1200 °C. As such, cryogenic processing following by reverse martensitic transformation of high Ni containing alloys provides a pathway for developing higher heat resistant stainless steel alloys.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electron-irradiation-induced Cr segregation in Fe-Cr model alloy pre-implanted with hydrogen ions

Highlights: • Streaks appeared in the diffraction patterns of hydrogen-implanted Fe-Cr alloy after electron irradiation in an HVEM. • A kind of needle-like Cr precipitates give rise to the streaks. • The streaks are explained reasonably by shape effect of precipitates. - Abstract: Reduced activation ferritic/martensitic (RAFM) steels are widely accepted as the candidate structural materials for fusion reactors. To gain knowledge about Cr behaviour of these steels in such environments, Fe-Cr binary alloys have to be investigated. In this study, Fe-10 at.% Cr ferritic model alloy pre-implanted with hydrogen ions was electron-irradiated in a high voltage electron microscope (HVEM) at the temperature ranging from 300 °C to 600 °C. Streaks were observed in the diffraction patterns in the model alloy after electron irradiation at 450–550 °C and explained reasonably by shape effect. The analysis of transmission electron microscopy (TEM) reveals that the observed streaks are induced by a kind of needle-like precipitates with the directions along <100>. The dependence of the length and density of the precipitates on the temperature were studied. In addition, contrast experiments were conducted with pure Fe and Fe-10 at.% Cr alloy with and without hydrogen ion implantation, respectively. After electron irradiation, no streak was observed in the hydrogen-implanted pure Fe and Fe-10 at.% Cr alloy without the hydrogen implantation. Therefore, it is assumed that the needle-like precipitates could be the complex of Cr and H, which segregate and precipitate along <100> direction.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effects of boron addition on the morphology of silicon phases in Al-Si casting alloys

Highlights: • The influence of boron on Si phase was studied. • Boron addition reduces the length of eutectic Si plates in Al-11Si alloys. • Boron addition promotes the nucleation temperature of primary Si phases in Al-14Si alloys. • Boron addition increases the twin density in the <112>{sub Si} growth direction of eutectic Si in Al-11Si and Al-14Si alloys. - Abstract: The influence of B elements on the morphology of Si phases in Al-11Si and Al-14Si alloys has been investigated employing Optical Microscope, Scanning Electron Microscopy, Transmission Electron Microscopy and Differential Scanning Calorimetry. In Al-11Si alloy, the addition of B element not only refines the primary Al dendrites, but also reduces the length of eutectic Si plates. In Al-14Si alloys, the addition of B element promotes the nucleation temperature of primary Si phases, but shows weak influence on the nucleation temperature of eutectics. The effects of B element on the morphologies of both primary Si particle and eutectics can be attributed to the interaction between B and Si elements during the solidification process.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A comparison of Ti-6Al-4V in-situ alloying in Selective Laser Melting using simply-mixed and satellited powder blend feedstocks

Highlights: • Satelliting mixing is proposed for preparing powder feedstocks for AM. • Satelliting allows the creation of blended feedstocks of improved homogeneity. • Sample homogeneity is affected by particle size distribution and powder mixing technique. - Abstract: In-situ alloying within laser powder-bed fusion, specifically Selective Laser Melting (SLM), has been investigated for the formulation of novel alloys from elemental powders to extend the benefits offered by these technologies. Inadequate preparation of the powder feedstock prior to in-situ alloying can yield inhomogeneous microstructures, often deteriorating the mechanical performance of the deposited parts. The present work was designed to assess the use of the ‘satelliting’ method to create powder feedstocks for in-situ laser powder-bed fusion. The research was carried out on Ti-6Al-4V. Ti-6Al-4V feedstocks obtained by mixing or satelliting elemental powders were investigated and compared to a reference pre-alloyed material. The processability of the different feedstocks was assessed by comparing the microstructure of the deposits originating from the different powder blends. Results show that the powder percolation and particle size distribution of the feedstocks translate in deposited microstructures exhibiting different porosity, elemental segregation, and average grain size, revealing the impact of the powder blend characteristics on the laser energy absorbance and solidification of the alloy. This study provides fundamental insights of how to formulate powder feedstock and aims to support future research activities on the design and development of new alloys for use in powder-based additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy

Highlights: • The grain size was continuously reduced with the increasing Sc content. • No evidence for the formation of the Cu-rich and Sc-containing W phase was observed. • Sc addition could promote the precipitation of S′ in the absence of pre-age stretch. • Sc addition would reduce the growth rate of δ′ and δ′-PFZs. • The highest combinations of strength and ductility were obtained in cast Al-Li alloys. - Abstract: In this work, the influence of Sc content on the microstructure and mechanical properties of cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was investigated. It was found that the grain size of As-cast alloy was significantly reduced in steps with the increase of Sc addition, accompanied by the arising and increasing of cubic primary Al{sub 3}(Sc, Zr) phases. No evidence for the presence of the ternary W (Al{sub 8−x}Cu{sub 4+x}Sc) phase was obtained. The volume fraction of nanoscale Al{sub 3}(Sc, Zr) dispersoids was improved with the increase of Sc content, and the presence of Sc was observed to refine the S′ (Al{sub 2}CuMg) morphology during ageing. The addition of Sc lowered the growth rates of δ′ (Al{sub 3}Li) particles and δ′-Precipitate-free zones (δ′-PFZs) of the base alloy. The tensile property results showed that, with the increasing Sc content and ageing times, the yield strength (YS) and ultimate tensile strength (UTS) were continuously increased, and the highest elongation of 6.0% was obtained in the 0.2Sc-containing alloy aged for 32 h at 175 °C. The results indicated that the optimal Sc addition in cast Al-2Li-2Cu-0.5Mg-0.2Zr alloy was 0.2 wt%.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Intergranular corrosion resistance of Zn modified 5××× series Al alloy during retrogression and re-aging treatment

Highlights: • Increase the strength due to precipitation hardening of T-Mg{sub 32}(AlZn){sub 49} phase in the Zn modified Al-Mg alloy. • Both high corrosion resistance and high strength are achieved by retrogression and re-aging treatment in Al-5Mg-3Zn alloy. • Large Mg and Zn content difference between GBP and PFZ results in relatively high IGC susceptibility. • The intergranular corrosion mechanism of Zn modified Al-Mg alloy during retrogression and re-aging treatment is clarified. - Abstract: The effects of retrogression and re-aging treatment on the intergranular corrosion behavior of Al-5.0Mg-3.0Zn alloys are systematically studied. The alloy's strength increases when retrogression temperature increases from 390 °C to 420 °C. Samples retrogressed at 390 °C then re-aged are very susceptible to intergranular corrosion and those retrogressed at 405 °C and 420 °C express good corrosion resistance. Then the alloy's corrosion susceptibility rises with increasing retrogression temperature. Grain boundary precipitates are coarsened and distributed discontinuously with decreasing retrogression temperature. Higher retrogression temperature results in higher Mg and Zn content difference and intergranular corrosion susceptibility.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Impact of initial temper of base metal on microstructure and mechanical properties of friction stir welded AA 7055 alloy

Highlights: • Friction stir welded 7055-T4 alloy exhibits higher tensile properties than T6 alloy. • Friction stir welded 7055-T4 alloy exhibits more uniform hardness distribution. • Some regions in heat affected zone have higher hardness than base metal in T4-joint. • Effect of initial temper on precipitate evolution in different zones is discussed. AA 7055-T6 and AA 7055-T4 aluminium alloy sheets were friction stir welded to investigate the impact of initial base metal temper on microstructure, hardness and tensile properties of the joints. In the joint of alloy in T6 temper (T6-joint), the hardness of the weld zone is lower than that of base metal; in the joint of alloy in T4 temper (T4-joint), however, some regions in the heat affected zone exhibit higher hardness than base metal. The weld nugget zone in T6-joint exhibits slightly lower hardness compared with that in T4-joint. The hardness minima is slightly higher in T4-joint than in T6-joint. T4-joint exhibits higher yield strength, ultimate tensile strength and elongation compared with T6-joint. Based on microstructure examination by transmission electron microscopy, the impact of initial precipitate state on precipitation behavior in the weld nugget zone, thermo-mechanically affected zone and heat affected zone during friction stir welding and mechanical properties of the joints is discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2022

On the high-temperature stability of the Al 8 Cu 3 Ce intermetallic in an additively manufactured Al-Cu-Ce-Zr alloy

High-temperature resistant eutectic Al alloys are crucial materials for lightweight and energy efficient design in the automotive and aviation industries. Additive manufacturing offers a pathway to refine eutectic microstructures and develop novel alloys with superior high-temperature strength. High-volume fraction intermetallic Al-Cu-Ce alloys have been developed to deliver high-temperature strength in combination with reduced hot-tearing susceptibility. Zr is added to provide additional strengthening via nanoscale Al 3 Zr precipitation, and to stabilize and avoid coarsening of the Al 8 Cu 3 Ce phase. However, the detailed interaction between Zr and Al 8 Cu 3 Ce remains unexplored. In this work, we show with synchrotron X-ray diffraction that laser powder bed fusion fabricated Al-Cu-Ce and Al-Cu-Ce-Zr alloys contain predominantly the Al 8 Cu 3 Ce intermetallic in the as-fabricated condition. Heat treatment of the Al-Cu-Ce alloy results in the Al 8 Cu 3 Ce → Al 8 Cu 4 Ce phase transformation. In the Al-Cu-Ce-Zr alloy, minor fractions of (Al,Cu,Si) 4 Ce and Al 2 Cu-θ are found in the as-fabricated condition, while Al 8 Cu 3 Ce remains stable during heat treatment. Atom probe microscopy quantifies intermetallic stoichiometries and reveals how Zr is enriched at the Al-matrix/Al 8 Cu 3 Ce interface acting as a diffusion barrier against solute exchange. Calibrated thermodynamic modeling underpins this as a kinetic effect. Here, a qualitative microstructural model summarizes, how Zr stabilizes Al 8 Cu 3 Ce against phase transformations and coarsening.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Improved creep performance of CoCrFeNi high entropy alloys by Mo addition

The CoCrFeNi family of high entropy alloys has good mechanical and corrosion properties, performing like stainless steels with low yield stresses. They could, however, benefit from hardening methods for structural and high temperature applications. Here, this work investigates the potential for the CoCrFeNi alloy to be hardened with the addition of Mo. A series of CoCrFeNiMo alloys and their CoCrFeNi counterparts were subsequently manufactured at NETL and then mechanically creep tested at 650°C. The alloys were designed to possess a range of stacking fault energies which influence the mechanical properties of the alloys via the motion of their dislocations under stress. Results show that Mo-containing variants have creep rupture lives ranging from 4000 to 8000 hours, i.e., about two orders of magnitude longer than those for Mo-free variants. The significantly improved creep performance of the Mo-containing alloys is due to a combination of solid solution strengthening and precipitation strengthening from µ-phase and carbides.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Local lattice distortion in NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys investigated by synchrotron X-ray diffraction

Severe lattice distortion is presumptively considered as a core effect of high-entropy alloys, but quantitative measurements are still missing. Here, we demonstrate that the lattice distortion in high-entropy alloys can be quantitatively analyzed based on pair distribution function obtained from synchrotron X-ray diffraction. By applying this method to equiatomic NiCoCr, FeCoNiCr and FeCoNiCrMn concentrated alloys, we found that the local lattice distortion in the NiCoCr (0.23%) and FeCoNiCrMn (0.24%) alloys are comparable while negligible in the FeCoNiCr alloy (0.04%). Furthermore, the origin of local lattice distortion in the NiCoCr and FeCoNiCrMn concentrated alloys was discussed.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Design of Silicide-Strengthened Nb–Si–Cr–(Mo) alloys for additive manufacturing

Three high–intermetallic volume Nb–Si–Cr–(Mo) alloys were designed using CALPHAD modeling with the goal of identifying high–specific strength, oxidation-resistant alloys that can be additively manufactured using powder bed fusion. The silicides Nb 5 Si 3 and Nb 9 Si 2 Cr3 were targeted as the primary strengthening phases, and the addition of Cr promoted the NbCr 2 phase. These alloys were cast and surface-processed with electron beam welding at different speeds to simulate additive manufacturing, and the phases and microstructures of both cast and welded regions were characterized. The weld processing was found to produce fine-grained microstructures in each alloy with fine-scale intermetallics uniformly distributed among a body-centered cubic Nb matrix. Microstructural refinement and hardness were found to increase with weld velocity; one alloy reached its highest hardness of approximately 16 GPa before the brittleness at higher velocities became detrimental. One alloy was found to be qualitatively the least brittle while also attaining a hardness of 13 GPa and was therefore identified as a good candidate for additive manufacturing.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Design of an alumina forming coating for Nb-base refractory alloys

Refractory multi-principal element alloys (RMPEAs) promise to significantly enhance gas turbine engine efficiency, but their poor oxidation performance inhibits their implementation. Alumina-forming bond coat alloys can provide oxidation protection, but discovering suitable chemistries remains a challenge. We employed a design methodology that screens for alumina-formation capability using Al activity and phase constitution predictions from CalPhaD (Thermo-Calc). Alloy down-selection from approximately 7,800 alloys in the Nb-Si-Ti-Al-Hf system was conducted via analysis of calculated thermodynamic properties with number-density topology style maps. This approach is validated by creating and testing the composition Nb 12 Si 23 Ti 24 Al 36 Hf 5 , which forms protective alumina scales up to 1400 °C and resists pesting at 800 °C. Further, the alloy has an average coefficient of thermal expansion of ~10.1 ppm/K, making it well matched to Nb-based refractory alloys. The methodology will be useful for the design of coatings for RMPEAs, enabling their implementation and significant efficiency benefits sooner.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Friction stir processing: A thermomechanical processing tool for high pressure die cast Al-alloys for vehicle light-weighting

This study uses friction stir processing (FSP) for thermomechanical processing of high-pressure die-casting (HPDC) to modify microstructure and improve mechanical properties. FSP is carried out on two different HPDC aluminum alloys: (a) general-purpose, high-iron, HPDC A380 alloy and (b) premium quality, low-iron HPDC Aural-5 alloy in thin wall, flat plate geometry. Subsequent mechanical testing shows ~30 % and ~65 % enhancement in yield strength and tensile ductility. In addition, FSP leads to ~10 times improvement in fatigue life for A380 alloy and ~70 % improvement in fracture toughness for Aural-5 alloy. These findings emphasize the capability of FSP to modify the microstructure of HPDC Al-alloys-based structural components so that they can demonstrate a good combination of strength, ductility, fracture toughness, and high fatigue properties for long-term durability and reliability.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effect of copper content on the tensile elongation of Al–Cu–Mn–Zr alloys: Experiments and finite element simulations

Microstructures of cast aluminum alloys used in automotive engine applications often consist of intermetallic particles that can impact the tensile elongation of these alloys. Here in this paper, we investigate the effect of intermetallic grain boundary particles on tensile elongation by fabricating a series of alloys with Cu content varying between 6.0 - 9.0 wt% in cast Al–Cu–Mn–Zr (ACMZ) type compositions. The tensile elongation of as-aged ACMZ alloys decreases monotonically with increase in Cu content. While the microstructure within the grains and yield stress of the alloy remains invariant with Cu content, the decrease in tensile elongation correlates well with increase in the size and volume fraction of grain boundary particles. Microstructural observations are combined with finite element simulations to explain the trend in tensile elongation with changing Cu content. Crack initiation is found to occur by brittle fracture of the grain boundary particles. Increase in particle size promotes crack initiation by reduction in size dependent particle fracture strength. Lower inter-particle spacing at higher particle volume fraction further facilitates crack initiation by increasing stress within the particles caused by the interaction between stress fields of neighboring particles. Increase in particle volume fraction also accelerates crack propagation through the formation of macro shear zones in the microstructure. The increase in Cu content of cast ACMZ alloys, therefore, decreases tensile elongation by promoting both crack initiation and crack propagation.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The formation and evolution of Ni 2 Cr precipitates in Ni–Cr model alloys as a function of stoichiometry characterized by synchrotron x-ray diffraction

Ni-based alloys containing significant amounts of Cr, may precipitate new phases during long-term service at elevated temperatures. In Ni–Cr model alloys, the formation of Ni 2 Cr has been found to impact the material properties, including the strength and ductility after isothermal aging below the critical temperature of 590°C. In this work, we quantify the formation and evolution of long-range ordering in four Ni–Cr binary model alloys (Ni/Cr = 1.8, 2.0, 2.2, 2.4) after isothermal aging up to 10,000h at temperatures between 373 and 475°C. The alloys were characterized by hardness testing and synchrotron-based x-ray diffraction to quantify the impact of Ni 2 Cr phase fraction and precipitate size on mechanical properties. After 500h of isothermal aging, the formation of Ni 2 Cr was detected in all four alloys at 475°C. In the stochiometric alloy samples (Ni/Cr = 2.0), the formation of Ni 2 Cr was found after 500 and 3000h aging at 418 and 373°C, respectively. We found that the matrix lattice contraction and Ni 2 Cr phase fraction both saturate after early aging times. This is in stark contrast to the hardness and Ni 2 Cr precipitate size that both continue to increase with increasing aging time. Our results highlight that changes in hardness correlate linearly with Ni 2 Cr precipitate size rather than phase fraction. This important structure-property relationship can potentially help define Ni–Cr-based component lifetimes directly through an understanding of how Ni 2 Cr formation impacts strength and ductility. Here, we find that a precipitation hardening model for critical resolved shear stress with weakly coupled dislocations shows good agreement with the material property changes quantified from experimental measurements.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Effect of Re and Al additions on the microstructure and mechanical properties of Nb-18Ti-12W alloy

Microstructure and mechanical properties at 25–1200 °C of new refractory alloys, Nb-18Ti-12W (NTW), Nb-18Ti-12W-5Re (NTW-R) and Nb-18Ti-12W-5Re-1Al (NTW-RA), all compositions are in atomic percent, are reported. The alloys are developed as an alternative to a denser, more expensive and difficult-to-process refractory alloy WC-3009. After production by arc melting and hot isostatic pressing at 1400 °C, 207 MPa for 3 h, the alloys have a BCC crystal structure with the average grain size of ~150–200 μm and contain low volume fraction of (Ti,N)-rich precipitates near grain boundaries. NTW shows excellent malleability at all studied temperatures. Its yield stress at 25 °C, 1000 °C and 1200 °C is 874 MPa, 353 MPa and 202 MPa, respectively. The NTW-R and NTW-RA alloys are stronger at all the studied temperatures; however, they lack in compression ductility at 25 °C. As a result, extensive deformation twinning and formation of intergranular voids precede the fracture of these two alloys at 25 °C.

36 MATERIALS SCIENCE↗