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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 757 records · Page 42
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Microstructure and mechanical properties of an ultrafine Ti–Si–Nb alloy

In this study, Nb-modified ultrafine Ti–Si eutectic alloy was made by cold crucible levitation melting, tested in compression at room temperature, and characterized by electron microscopy. Compression tests of (Ti 86.5 Si 13.5 ) 97 Nb 3 specimens measured an ultimate compressive strength of 1180 MPa and a compressive plastic strain of 12%, both of which are higher than in eutectic Ti 86.5 Si 13.5 alloy. Electron microscopy showed that the Ti–Si–Nb alloy had a bimodal microstructure with micrometer-scale primary α-Ti dendrites distributed in an ultrafine eutectic (α-Ti + Ti 5 Si 3 ) matrix. The enhanced ductility is attributed to the morphology of the phase constituents and to the larger lattice mismatches between α-Ti and Ti 5 Si 3 phases caused by the Nb addition. The crystallographic orientation relationship of Ti 5 Si 3 with α-Ti is ($1\bar{1}00$)[$\overline{11}$26]Ti 5 Si 3 ∥($01\bar{1}1$)[5$\overline{143}$] α–Τi.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Hexagonal OsB 2 : Sintering, microstructure and mechanical properties

In this study, the metastable high pressure ReB 2 -type hexagonal OsB 2 bulk ceramics was produced by spark plasma sintering. The phase composition, microstructure, and mechanical behavior of the sintered OsB 2 were studied by X-ray diffraction, optical microscopy, TEM, SEM, EDS, and nanoindentation. The produced ceramics was rather porous and contained a mixture of hexagonal (~80 wt.%) and orthorhombic (~20 wt.%) phases as identified by X-ray diffraction and EBSD analysis. Two boron-rich phases, which do not contain Os, were also identified by TEM and SEM/EDS analysis. Nanoindentation measurements yielded a hardness of 31 ± 9 GPa and Young’s modulus of 574 ± 112 GPa, indicating that the material is rather hard and very stiff; but, it is very prone to crack formation and propagation, which is indicative of a very brittle nature of this material. Improvements in the sintering regime are required in order to produce dense, homogeneous and single phase hexagonal OsB 2 bulk ceramics.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effect of post-weld heat treatment on microstructure and mechanical properties of rotary inertia friction welded dissimilar 422-4140 martensitic steel piston joints

The study investigated how post‐weld heat treatment (PWHT) temperature affects the microstructure and localized deformation/fracture during bend testing of rotary inertia friction welds (RIFW) between AISI 422 stainless steel and AISI 4140 steel. RIFW produced a fully martensitic interface with approximately 550 HV hardness in both the thermo-mechanically affected (TMAZ) and heat‐affected zones (HAZ). Due to differences in temper resistance, the 4140 TMAZ/HAZ softened progressively under PWHT temperatures from 525 °C to 700 °C, while the 422 TMAZ unexpectedly maintained about 550 HV up to 600 °C before significantly softening at temperatures ≥625 °C. This asymmetric softening generated steep hardness gradients across the interface at temperatures ≤600 °C. Furthermore, carbon migration across the interface was minimal up to 600 °C, moderate at 625 °C, and by 700 °C produced a carbide‐rich eutectoid layer in the 422 TMAZ alongside a carbon‐depleted soft ferrite layer in the 4140 TMAZ. Strain during bending was PWHT‐dependent, concentrating on the 4140 side; in as-welded joints, the high hardness led to deformation and crack initiation in the base metals, whereas in PWHT samples, cracking initiated in the softened 4140 TMAZ near the interface. The intermediate PWHT temperature of 625 °C offered the best balance of limited carbon diffusion across the interface, relatively low peak weld hardness and minimized hardness gradients across the interface, more homogenous deformation, and good bend test performance.

4140 low-alloy steel↗
DOE OSTI2012

Impact of the surface-near silicon substrate properties on the microstructure of sputter-deposited AlN thin films

In micro-/nanomachined devices and systems, aluminum nitride (AlN) thin films are widely used due to their piezoelectric properties. This work evaluates the potential of modifying the interface between the AlN thin film and the silicon (Si) wafer serving as bottom electrode for optimized crystallographic orientation and, hence, improved electrical and piezoelectric properties. The films were analyzed using temperature-dependant leakage current measurements, transmission electron microscopy, and x-ray diffraction. By preconditioning of the Si substrate surface applying sputter etching prior to film deposition, leakage current levels are substantially decreased and an increased (002) orientation of the AlN grains is observed.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructure and electrical properties in W/Nb co-doped Aurivillius phase Bi{sub 4}Ti{sub 3}O{sub 12} piezoelectric ceramics

Highlights: • W/Nb codoped BIT ceramics were prepared by the mixed oxides route. • High nd{sup 0} electronic configuration of W/Nb reduces the lattice distortion and T{sub C}. • Oxygen vacancy is responsible for dielectric relaxation and DC conduction process. • W/Nb additives significantly enhanced the piezoelectric coefficient d{sub 33} value. • BWNb-10 ceramics possessed large remnant polarization and a wide sintering window. - Abstract: Aurivillius-type Bi{sub 4}Ti{sub 3-x}W{sub x/2}Nb{sub x/2}O{sub 12} ceramics were prepared by a conventional solid-state sintering method. The XRD patterns demonstrated that all compositions were a single three layered crystalline structure, involving a reduction of lattice distortion with an increase in W/Nb doping level. The electrical properties including dielectric, electrical conduction and piezoelectric properties were tailored by W/Nb additives. The Curie-temperature decreased, whereas the electrical resistivity drastically increased with introduction of W/Nb donor dopants. As a result, a high electric field can be applied during the poling process. The Bi{sub 4}Ti{sub 2.9}W{sub 0.05}Nb{sub 0.05}O{sub 12} ceramics exhibited optimum piezoelectric coefficient (d{sub 33} ∼22.8 pC/N), large remnant polarization (2P{sub r} ∼26.8 μC/cm{sup 2} @ 200 °C) together with a high Curie temperature (T{sub C} ∼635 °C). Furthermore, this composition possessed a wide sintering window with outstanding piezoelectric properties. These parameters indicate that Bi{sub 4}Ti{sub 2.9}W{sub 0.05}Nb{sub 0.05}O{sub 12}-based ceramic is a promising candidate for high temperature piezoelectric applications.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Towards an integrated experimental and computational framework for large-scale metal additive manufacturing

In this work using the Metal Big Area Additive Manufacturing (MBAAM) system, a thin steel wall was manufactured from a low carbon steel wire. The wall was then characterized comprehensively by high-throughput high-energy X-ray diffraction (HEXRD), electron backscatter diffraction (EBSD), and in-situ HEXRD tensile tests. With the predicted temperature histories from the finite element-based additive manufacturing process simulations, the correlations between processing parameters, microstructure, and properties were established. The correlation between the final microstructure with the predicted temperature history is well explained with the material's continuous cooling transformation (CCT) diagram calculated based on the composition of the low carbon steel wire. The final microstructure is dependent on the cooling rate during austenite to ferrite/bainite transformation during initial cooling and the subsequent reheating cycles. Fast cooling rate resulted in small ferrite grain size and fine bainite structure at the location closest to the base plate. Slower cooling rate at the side wall location and repeated reheating cycles to the ferrite-pearlite regions resulted in all allotriomorphic (equiaxed) ferrite with medium grain size with small amount of pearlite. With no reheating cycles, the top location has the slowest cooling rate and a large grained allotriomorphic ferrite and bainitic structures. The measured mechanical strength is then related to the microstructural feature size (grain or lath size) observed in those locations. Thus, a good correlation is found between the mechanical properties, microstructure features and the temperature history at various locations of the printed wall.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microstructure and mechanical properties of friction stir weld performed on neutron-irradiated 304L steel with helium

As nuclear power plants (NPPs) approach or exceed 40–60 years of service, it may become necessary to repair damaged neutron-irradiated components to prolong longevity. However, fusion welding repair of irradiated steels and metallic materials is challenging because of helium-induced cracking. This study used friction stir welding (FSW) to address helium-related issues, such as helium bubble formation and grain boundary cracking. The microstructure, helium-induced degradation, and mechanical properties of a friction stir weld produced on neutron-irradiated 304L stainless steel with approximately 5.2 appm of helium were characterized. The analysis focused on variations in grain size, texture, and the morphology of helium-induced damage in the friction stir weld. Mechanical properties were characterized on the irradiated base metal (BM) and metallurgical zones of the friction stir weld: the stir zone (SZ), the thermo-mechanically affected zone (TMAZ), and the heat affected zone (HAZ). Only minor scattered porosity in the SZ and TMAZ and a few short microcracks (below 20 μm in length) in the TMAZ were observed, indicating limited helium-induced degradation. Tensile tests revealed good mechanical properties and fractography analysis demonstrated predominantly ductile fracture. In conclusion, the results highlight the immediate and substantial benefits of the FSW approach for repairing or joining helium-containing irradiated materials in NPPs.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effects of build orientation and heat treatment on the evolution of microstructure and mechanical properties of alloy Mar-M-509 fabricated via laser powder bed fusion

We present the main results from an experimental investigation into the consequences of various microstructural features, created by laser powder bed fusion (LPBF) and subsequent heat treatments (HTs), in alloy Mar-M-509 on several aspects of plastic deformation including mechanical anisotropy and elongation-to-fracture (ETF). To ensure successful manufacturing of the alloy, porosity fraction and distribution are first characterized using micro X-ray computed tomography. Next, grain structure, crystallographic texture, and regions of recrystallization in the studied microstructures are measured using electron backscattered diffraction (EBSD). Lastly, chemistry, distribution, and morphological features of carbide phases are extracted using electron microscopy and X-ray diffraction. Strength in tension and compression are measured at room temperature for different initial microstructures created by variations in manufacturing conditions and sample orientations with respect to sample processing frame. While the strength of the alloy varies with sample orientation by approximately 30% in the as-built condition, the alloy is softer, more ductile, and approximately isotropic after HT. These results are discussed and critically compared with the data reported for the as-cast material. The alloy manufactured via LPBF is found to be significantly stronger and more ductile than the same alloy produced by casting. The interesting deformation behavior characteristics of the samples in different conditions are explained in terms of their microstructures. EBSD measurements reveal evolution from columnar grains along the build direction favoring a moderately strong <001> fiber texture in the as-built material to equiaxed grains favoring the {110}<001> Goss texture component after subsequent HTs. The major change in grain structure and texture is a result of recrystallization. While carbide phases precipitate primarily at dendrite and cellular interfaces in the as-built material, these phases are both intra-and inter-granular within the HT materials and coarsen with HT duration. These microstructural observations formed bases to rationalize the observed mechanical behavior of the alloy. With this being said, tailoring the alloy performance characteristics with HTs is reported on.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Rotation Speed on the Microstructure and Mechanical Properties of Friction-Stir-Welded CuSn6 Tin Bronze

Four-mm-thick CuSn6 tin bronze plates were friction stir welded at a constant tool traverse speed of 100 mm min{sup −1}. Favorable joints could be obtained with rotation speeds ranging from 600 to 1000 rev min{sup −1}, and groove was found on the surface of the joint under 400 rev min{sup −1}. The microstructure of the weld nugget zone was characterized by equiaxed recrystallized grains with heterogeneity along the thickness direction. Moreover, the grain size of the thermo-mechanically affected zone and stir zone increased with the increase in rotation speed. Hardness of the stir zone was higher than that of other zones due to microstructural refinement. There was little change in tensile properties of the defect-free welded joints. During tensile test, all of the defect-free joints were fractured at heat-affected zone with typical plastic fracture.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Microstructure and photoluminescent properties of Sr{sub 2}SiO{sub 4}:Eu{sup 3+} phosphors with various NH{sub 4}Cl flux concentrations

Graphical abstract: This paper describes effects of NH{sub 4}Cl concentration on microstructural and luminescent characteristics of Sr{sub 2}SiO{sub 4}:Eu{sup 3+} phosphors using microwave assisted sintering at 1200 °C for 1 h. The results showed the improved photoluminescence properties of microwave sintered Sr{sub 2}SiO{sub 4}:Eu{sup 3+} phosphors by adding NH{sub 4}Cl flux. Highlights: ► NH{sub 4}Cl flux improved the luminescence properties of microwave sintered phosphors. ► The particle sizes were enlarged from 1 μm to 10 μm as the NH{sub 4}Cl flux was added. ► The maximum photoluminescence intensity was appeared as adding 1 wt% NH{sub 4}Cl flux. ► The decay times of Sr{sub 2}SiO{sub 4}:Eu{sup 3+} phosphors with NH{sub 4}Cl flux were around 2.47–2.52 ms. -- Abstract: In this paper, effect of NH{sub 4}Cl flux concentrations (0, 1, 2, 3 and 4 wt%) on the crystal structure, morphology and photoluminescent properties of Sr{sub 2}SiO{sub 4}:Eu{sup 3+} phosphors synthesized by a microwave sintering at 1200 °C for 1 h was investigated and discussed. X-ray powder diffraction analysis showed the crystal structure was not affected and the pure Sr{sub 2}SiO{sub 4} phase was formed without second phase or phases of starting materials when adding with the NH{sub 4}Cl flux. The SEM images indicated that increase of the NH{sub 4}Cl flux enlarged the particle size of the phosphor particles. The photo-luminescence results showed the addition of 1 wt% NH{sub 4}Cl flux much improved the emission intensity at λ{sub em} of 617 nm as the excitation spectrum at λ{sub ex} of 395 nm. The decay times of Sr{sub 2}SiO{sub 4}:Eu{sup 3+} phosphors with different NH{sub 4}Cl flux concentrations were obtained around 2.47–2.52 ms.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Bi on the microstructure and mechanical properties of Sn-Zn alloys processed by rolling

Highlights: • Sn-Zn-Bi is proposed for the first time as the cladding in linear explosive device. • Bi can significantly refine the microstructure of Sn-Zn. • Bi can enhance both strength and ductility of Sn-Zn processed by rolling. • The 5 wt% Bi in Sn-3Zn leads to finest and most homogenous grains after rolling. - Abstract: Sn-Zn based alloys including Sn-3Zn, Sn-3Zn-1Bi, and Sn-3Zn-5Bi were prepared by casting and rolling, in efforts to assess their feasibility for the application as cladding materials in detonating and explosive cords. It was found that Bi significantly refined the solidification microstructure, changing the configuration of Sn-Zn eutectic from well-aligned Zn-rich precipitates/needles to misaligned Zn-rich flakes. During deformation, second phases like Zn-rich precipitates and Bi particles, and Bi solutes were effective in grain refinement since second phase particles provided more sites for nucleation and more obstacles to growth of new recrystallized grains. Tensile results revealed that Bi addition enhanced both strength and ductility of the rolled Sn-Zn-Bi alloys. The Sn-3Zn-5Bi alloy possessed superior strength and ductility (UTS: 84.4 MPa; Yield strength: 68.3 MPa; Elongation: 75.2%) due to its finest and most homogeneous equiaxed grains. Based on decent mechanical properties, the Sn-Zn-Bi alloys could be well qualified for the application as cladding materials.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Evolution of microstructure and mechanical properties of selective laser melted Ti-5Al-5V-5Mo-3Cr after heat treatments

Titanium alloy Ti5553 (Ti-5Al-5Mo-5V-3Cr) is an excellent candidate for structural applications and additive manufacturing processes, since, unlike Ti6Al4 V, when built via selective laser melting and/or post additive manufactured welding, it maintains a near-beta microstructure that is both ductile and high strength. Another feature is that Ti5553 properties are adaptable through post build heat treatment. This study explores the heat treatability of selective laser melted Ti5553 up to temperatures approaching the β-transus. Here the results show strength increases while maintaining ductility at high temperatures (700–800°C), but embrittlement occurs at intermediate temperatures (400–600°C) likely due to changes in volume fraction and morphology of the α-phase and/or the presence of the ω-phase. Microstructure and X-ray diffraction are reported after heat-treating to better understand this mechanical response.

42 ENGINEERING↗
DOE OSTI2019

An Investigation on Microstructure Evolution, Mechanical Properties, and Strain Aging of Mg-1.8Zn-0.7Si-0.4Ca Biomedical Alloy Processed by Equal Channel Angular Pressing

The influence of equal channel angular pressing (ECAP) on microstructure and mechanical behavior, as well as, strain aging during ECAP and post-ECAP of Mg-1.8Zn-0.7Si-0.4Ca biomedical alloy was examined. The alloy in solid solution heat-treated condition was processed by ECAP with route B{sub C} at 350 and 400 °C. The specimens ECAPed at 350 °C were aged at 125 and 150 °C for different times. The hardness and shear punch test results indicated that performing ECAP at 350 °C for 4 passes increases the hardness and shear strength of the alloy from 48 HV and 110 MPa to 71 HV and 188 MPa, respectively. It was revealed that the average grain size of the alloy decreases from 78 µm to about 3 µm after 4 passes of ECAP. Three precipitates of CaMgSi, Ca{sub 2}Mg{sub 6}Zn{sub 3}, and Mg{sub 2}Si were detected in the solid solution specimen. After 4 passes of ECAP at 350 °C, Ca{sub 2}Mg{sub 6}Zn{sub 3} was completely dissolved and the morphology of Mg{sub 2}Si changed from Chinese script to fiber-shaped particles. Dynamic strain aging occurred at high-temperature ECAP, and the specimens were overaged during post-ECAP aging. Small MgZn particles were detected in the overaged sample.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Optimization Using Metamodeling in the Context of Integrated Computational Materials Engineering (ICME)

Predictive Design Technologies, LLC (PDT) proposed to employ Integrated Computational Materials Engineering (ICME) tools to help the manufacturing industry in the United States regain the competitive advantage in the global economy. ICME uses computational materials science tools within a holistic system in order to accelerate materials development, improve design optimization, and unify design and manufacturing. With the advent of accurate modeling and simulation along with significant increases in high performance computing (HPC) power, virtual design and manufacturing using ICME tools provide the means to reduce product development time and cost by alleviating costly trial-and-error physical design iterations while improving overall quality and manufacturing efficiency. To reduce the computational cost necessary for the large-scale HPC simulations and to make the methodology accessible for small and medium-sized manufacturers (SMMs), metamodels are employed. Metamodels are approximate models (functional relationships between input and output variables) that can reduce the simulation times by one to two orders of magnitude. In Phase I, PDT, partnered with Mississippi State University (MSU), demonstrated the feasibility of the proposed methodology by employing MSU?s internal state variable (ISV) plasticity-damage model with the help of metamodels to optimize the microstructure-process-property-cost for tube manufacturing processes used by Plymouth Tube Company (PTC), which involves complicated temperature and mechanical loading histories. PDT quantified the microstructure-property relationships for PTC?s SAE J525 electric resistance-welded cold drawn low carbon hydraulic 1010 steel tube manufacturing processes at seven different material states and calibrated the ISV plasticity material parameters to fit experimental tensile stress-strain curves. PDT successfully performed large scale finite element (FE) simulations in an HPC environment using the ISV plasticity model in Abaqus FE analyses of the tube forming, sizing, drawing, welding, and normalizing processes. The simulation results coupled with the manufacturing cost data were used to develop prototype metamodeling (quick response) codes which could be used to predict and optimize the microstructure-process-property-cost relationships. The developed ICME metamodeling toolkits are flexible enough to be applied to other manufacturing processes (e.g. forging, forming, casting, extrusion, rolling, stamping, and welding/joining) and metamodeling codes can run on laptop computers. Based on the work completed in Phase I, in Phase II, PDT proposes to continue to refine the ISV model by correlating and incorporating the uncertainties in the microstructure, mechanical testing, and modeling. Following the model refinement, FE analyses will be simulated and will provide even more realistic predictions as they include an appropriate window of uncertainty. Using the HPC output (FE analyses) as input, the quick-response metamodel codes will more accurately predict and optimize the microstructure-process-property-cost relationships. Furthermore, PDT propose to employ the ICME metamodeling toolkits to help develop a new tube product using entirely new high strength steel. The modeling of the high strength steel manufacturing process will replace the costly and time consuming trial-and-error methods that were used in the tubing industry previously. This simulation-based process prototyping will greatly benefit our industrial partners by opening up new market spaces due to new products with greater capabilities.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Zinc oxide based diluted magnetic semiconductor nanoparticles: Synthesis by laser ablation in liquids, microstructural and optical properties

Nanoparticles of ZnO and ZnO doped with transition metals (Mn, Co) were synthesized by laser ablation in liquid medium. Scanning electron microscopy (SEM) showed formation of nanostructures with different shapes. Atomic force microscopy (AFM) gives information about surface morphology of the formed nanostructures. Absorption edge of ZnO, ZnO:Mn and ZnO:Co colloidal nanoparticles exhibits blue shift due to confinement effect. In photoluminescence spectra three peaks are attributed to the band-edge transitions and defect states. The Faraday rotation in ZnO:Mn nanoparticles gives evidence for paramagnetic behavior at room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Effects of high temperature treatment on microstructure and mechanical properties of laser-clad NiCrBSi/WC coatings on titanium alloy substrate

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900 °C for 1 h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni{sub 3}Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10 nm to 50 nm were precipitated and uniformly distributed in the Ni{sub 3}Ti phase to form a thin granular layer after heat treatment at 700 °C. The granular layer spread from the edge toward the center of the Ni{sub 3}Ti phase with increasing temperature. A large number of fine equiaxed Cr{sub 23}C{sub 6} particles with 0.2–0.5 μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900 °C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900 °C presented the most excellent wear resistance. - Highlights: • TiC + WC reinforced intermetallic compound matrix composite coatings were produced. • The formation mechanism of the reinforcements was analyzed. • Two precipitates were generated at elevated temperature. • Cracking susceptibility and microhardness of the coatings were improved. • Post-heat treatment enhances wear resistance of the coatings.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of substrates on microstructure and mechanical properties of nano-eutectic 1080 steel produced by aluminothermic reaction

Nano-eutectic bulk 1080 carbon steel was prepared on glass and copper substrates by an aluminothermic reaction casting. The microstructure of the steel was analyzed by an optical microscope, transmission electron microscopy, an electron probe micro-analyzer, a scanning electron microscope and X-ray diffraction. Results show that the microstructure of the steel consisted of a little cementite and lamellar eutectic pearlite. Average lamellar spacing of the pearlite prepared on copper and glass substrates was about 230 nm and 219 nm, respectively. Volume fraction of the pearlite of the two steels was about 95%. Hardness of the steel was about 229 and 270 HV. Tensile strength was about 610 and 641 MPa and tensile elongation was about 15% and 8%. Compressive strength was about 1043 and 1144 MPa. Compared with the steel prepared on copper substrate, the steel prepared on glass substrate had smaller lamellar spacing of the pearlite phase and higher strength, and low ductility due to the smaller spacing. - Highlights: • 1080-carbon steels were successfully prepared by an aluminothermic reaction casting. • Lamellar spacing of the nanoeutetic pearlite is less than 250 nm. • The compressive strength of the steel is about 1144 MPa. • The tensile ductility of the steel is about 15%.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructure and mechanical properties of hypoeutectic Al–6Ce–3Ni-0.7Fe (wt.%) alloy

Here, a hypoeutectic, Fe-modified Al–Ce–Ni alloy (Al–6Ce–3Ni-0.7Fe, wt.%) is studied in terms of microstructure, thermal stability, ambient temperature strengthening, and creep resistance. The as-cast microstructure consists of primary Al dendrites and interdendritic binary eutectic regions (Al–Al11Ce3 and/or Al–Al9(Fe,Ni)2), with micron/submicron lamellar spacing, depending on the location along the height of the ingot. The cast alloy exhibits excellent coarsening resistance at 400 °C, with mostly unchanged microstructure and microhardness after 6 weeks of aging, indicating good thermal stability of Al11Ce3 and Al9(Fe,Ni)2. Orowan strengthening and load transfer are identified as strengthening mechanisms at ambient and elevated temperature. A high volume fraction of the intermetallic phases (providing load transfer) and relatively coarse eutectic spacing (for modest Orowan strengthening) result in a moderate as-cast microhardness of 566 ± 32 MPa. Creep resistance at 300 and 350 °C is similar to a binary Al-12.5Ce eutectic alloy (with twice the Ce content) because of two countering effects: Al–6Ce–3Ni-0.7Fe shows a higher volume fraction of strengthening intermetallic phases, but it also exhibits a large fraction of primary Al dendrites which weaken the alloy. By contrast, the alloy, when laser-remelted at the surface, has a fully eutectic microstructure without primary aluminum dendrites achieved by high undercooling on solidification, with a refined network of eutectic phases that doubles the microhardness as compared to the cast alloy. Whereas coarsening is faster due to the shorter diffusion distances between the eutectic phases, hardness remains ~30% higher than the as-cast alloy after ~6 weeks aging at 400 °C.

36 MATERIALS SCIENCE↗