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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 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Effect of calcination temperature on microstructure and magnetic properties of Ni{sub 0.5}Zn{sub 0.25}Cu{sub 0.25} Fe{sub 2}O{sub 4} nanoparticles synthesized by sol-gel method

This paper examines the effect of calcination process on the structural and magnetic properties material nanostructure composite of Ni{sub 0Ð}œ‡{sub 5}Zn{sub 0Ð}œ‡{sub 25}Cu{sub 0.25} Fe{sub 2}O{sub 4} ferrites. The samples were successfully prepared by sol-gel method at different calcination temperature, which are 600°C, 700°C, 800°C and 900°C. Morphological investigation, average crystallite size and microstructure of the material were examined by using X-ray diffraction (XRD) and confirmed by high resolution transmission electron microscope (HRTEM) and field emission scanning electron microscope (FESEM). The effects of calcination temperature on the magnetic properties were calculated by using vibrating sample magnetometer (VSM). The XRD result shows single-phase cubic spinel structure with interval average size 5.9-38 nm, and grain size microstructure of the material was increasing with temperature increases. The highest magnetization saturation was reached at a temperature 800°C with value 53.89 emu/g, and the value coercive force (Hc) was inversely with the grain size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Microstructure and Mechanical Properties of Copper Billets Fabricated by the Repetitive Extrusion and Free Forging Process

In the present study, with the aim of obtaining a weakened texture, grain refinement and improved mechanical properties, copper billets were successfully fabricated using the severe plastic deformation method of repetitive extrusion and free forging (REFF) without using any additional tools or devices. The evolution of the microstructure, texture and mechanical behavior of the ultrafine grain copper billets over an increasing number of REEF cycles was also systematically studied. Our results show that the effective strain per REFF process was ε = 2.35. After two cycles of REFF process, the sum effective strain became ε = 4.7, leading to high efficiency of grain refinement. The grain size was refined from 50 to 0.8 μm; the yield strength was increased to 462 MPa, and we obtained a weakened texture in the pure copper billets. By increasing the number of cycles, the grain refinement ability was decreased, and the texture was thus strengthened further. Therefore, two cycles of REFF were a reasonable process for producing ultrafine-grained copper billets.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ca Addition Effects on the Microstructure, Tensile and Corrosion Properties of Mg Matrix Alloy Containing 8 wt.% Mg{sub 2}Si

The microstructure, tensile properties and corrosion behavior of the Mg-8 wt.% Mg{sub 2}Si-x%Ca alloy have been studied by the use of optical microscopy, scanning electron microscopy equipped with energy-dispersive spectroscopy, x-ray diffraction, standard tensile testing, polarization test and electrochemical impedance spectroscopy (EIS) measurements. Microstructural studies indicated that Ca modifies both primary and eutectic Mg{sub 2}Si phase. It was found that the average size of primary Mg{sub 2}Si particles is about 60 μm, which is dropped by about 82% in the alloy containing 0.05 wt.% Ca. By the addition of different Ca contents, Ca-rich intermetallics (i.e., CaSi{sub 2} and CaMgSi) were formed. The modification mechanism of adding Ca during solidification was found to be due to the strong effect of CaMgSi phase as a heterogonous nucleation site, apart from CaSi{sub 2} which was reported before, for Mg{sub 2}Si intermetallics. Tensile testing results ascertained that Ca addition enhances both ultimate tensile strength (UTS) and elongation values. The optimum amount of Ca was found to be 0.1 wt.%, which improved UTS and elongation values from about 130 MPa and 2% to 165 MPa and 5.5%, whereas more Ca addition (i.e., 3 wt.%) reduced the tensile properties of the alloy to about 105 MPa and 1.8%, which can be due to the formation of CaMgSi intermetallics with deteriorating needle-like morphology. Polarization and EIS tests also showed that the Mg-3%Si-0.5%Ca alloy pronounces as the best anti-corrosion alloy. Nevertheless, further added Ca (up to 3 wt.%) deteriorated the corrosion resistance due to predominance of worse galvanic coupling effect stemmed from the presence of stronger CaMgSi cathode in comparison with Mg{sub 2}Si. With higher Ca additions, an adverse effect was seen on corrosion resistance of the Mg-3%Si alloy, as a result of forming a weak film on the alloy specimen surface.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Study of microstructure and electrical properties of bulk YBCO prepared by melt textured growth technique

Bulk YBCO components were prepared using Melt Texture Growth (MTG) technique. Components were fabricated using MTG by addition of Y{sub 2}BaCuO{sub 5} (Y211) and Ag to YBCO, which leads to improved grain size without affecting superconducting properties. Green compacts prepared by cold isostatic pressing were pre-sintered at 930°C before subjecting melt texturing. Cooling rates lower than 1 °C.h{sup −1} was used, in between (peritectic) temperature of about 995 and 1025°C, to obtain large grained components. Microstructure studies in details were carried out by Scanning Electron Microscope (SEM), Electron Probe Micro Analysis (EPMA), Orientation Imaging Microscope (OIM) and TEM correlated with electrical properties like Critical current density (J{sub c})

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

A Comparative Study on Microstructure, Mechanical and Tribological Properties of A4, AE41, AS41 and AJ41 Magnesium Alloys

Microstructure, tensile and wear properties of as-cast A4 (Mg-4Al), AE41 (Mg-4Al-0.5Ce-0.5La), AS41 (Mg-4Al-1Si) and AJ41 (Mg-4Al-1Sr) alloys were investigated, and the results were compared with each other in this study. Microstructures were investigated by XRD, optical and scanning electron microscopes. Tensile tests were conducted at both room and elevated temperatures. Tribological properties were examined by pin-on-disk wear tests under different applied loads. Microstructure characterizations revealed that the volume fraction of second phases considerably increased by alloying additions of 1 wt.% Ce/La, Si and Sr. The microstructure of A4 alloy consisted of α-Mg grains and divorced β-Mg{sub 17}Al{sub 12} phases. After individual alloying additions of 1 wt.% Ce/La, Si and Sr, the secondary phases were primarily replaced by needle-shaped and massive blocky-shaped Al{sub 11}(Ce,La){sub 3} phases in AE41 alloy, Chinese-script-type Mg{sub 2}Si phases in AS41 alloy and divorced globular-like and massive blocky-shaped Al{sub 4}Sr and (Mg,Al){sub 17}Sr{sub 2} phases in AJ41 alloy. The tensile tests showed that at both room and elevated temperatures alloying additions of 1 wt.% Ce/La, Si and Sr resulted in an increase in the strength but a decrease in the ductility. Among the studied alloys, AS41 alloy exhibited the best strength. Wear test results showed that AE41 and AJ41 alloys similarly exhibited the best wear resistance owing to the presence of hard and dense intermetallics. Abrasion was the main wear mechanism under low applied loads while delamination, adhesion and oxidation mechanisms were majorly observed under high applied loads.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Microstructure and Mechanical Properties of the AA7075 Tube Fabricated using Shear Assisted Processing and Extrusion (ShAPE)

Shear Assisted Processing and Extrusion (ShAPE) experimental setup and tooling were adopted for extruding thin-walled AA7075 aluminum tube from as-cast non-homogenized billet material in a single run. The mechanical and microstructural characterizations were performed on the extrudate in the as-extruded condition without subsequent heat treating. It was shown that the ShAPE process developed a significantly refined microstructure with uniform and almost equiaxed grain structure on both hoop and axial cross-sections of the extrudate as well as through the thickness of the material. The pole figures and inverse pole figures of the EBSD data showed an strong shear texture development, and it was found out that axial shear is the dominant deformation mechanism in the regions near the inner surface of the tube, while combined axial and torsional shears are the two dominant modes of deformation near the outer surface of the extrudate. As for the mechanical properties, there was an increase of 150% and 73% in the yield and ultimate strengths of the tube produced using ShAPE process, respectively, and a 18% decrease in maximum uniform plastic elongation compared to the conventionally extruded AA7075-O tube.

Shear Assisted Processing and Extrusion, Friction ↗
DOE OSTI2018

Analyzing the Effect of CeB{sub 6} on Microstructure and Mechanical Properties of High-Speed Steel Consolidated by Powder Metallurgy

By adding various amounts of CeB{sub 6}, high-speed steel (M3:2) was consolidated by powder metallurgy in the form of sintering. The addition of CeB{sub 6} improved the density of the sintered steel and the formation of M{sub 6}C phase in microstructure. It is speculated that CeB{sub 6} was decomposed into boron and cerium. Boron atoms were enriched in M{sub 6}C carbide phases, but cerium atoms were mainly clustered on grain boundary while they were converted to oxides, whereby the mechanical properties were improved. For example, upon the sintering at 1210 °C, relative density ~ 98.5% and average grain size ~ 18 μm were obtained with CeB{sub 6} content at 0.3 wt.%. Excellent mechanical properties, e.g., the Rockwell hardness ~ 52 HRC, flexural strength ~ 3.05 GPa, and fracture toughness ~ 40.92 MPa m{sup 1/2}, were achieved in the sample containing 0.3 wt.% CeB{sub 6}, which implies accordingly remarkable increases by 23.5, 38.1, and 23.7%, of the properties compared with those in the sample free of CeB{sub 6}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Changes in the microstructure and mechanical properties of additively manufactured AlSi10Mg alloy after exposure to elevated temperatures

Highlights: • Elevated temperatures above 120 °C brought changes to the AM AlSi10Mg alloy. • A maximum hardness state obtained at 160 °C/5 h was thoroughly tested. • Hardness increased by 15% and TYS by 5%, but elongation dropped by 60%. • Pure Si precipitates were responsible for the observed changes. - Abstract: The additive manufacture (AM) of the AlSi10Mg alloy has become the subject of considerable attention, especially for production of complex parts in engines. Because such parts can be exposed to elevated temperatures during operation, material stability is very important, but as yet little is known about it in relation to AM. Here, we studied changes of the AlSi10Mg alloy produced by selective laser melting (SLM) after its exposure to temperatures between 120 and 180 °C. At each temperature, hardness evolution was measured, with hardness increasing over time. The maximum hardness state obtained at 160 °C was selected for further studies comprising microstructural analysis by scanning and transmission electron microscopy, chemical composition analysis and mechanical properties assessment. Transmission microscopy revealed nano-scale acicular precipitates that caused a slight increase in the yield strength of the alloy together with a significant drop in elongation. Electron energy loss spectroscopy (EELS) and energy dispersive spectroscopy (EDS) showed that the precipitates surprisingly consisted of pure Si. To provide a comparison, conventional regimes of heat treatment (stress-relief and T6) were applied. Despite a considerable loss in mechanical performance, thermal instability was no longer observed. Overall, our results indicate that operating temperatures are a key factor in ensuring the smooth operation of AM parts of the AlSi10Mg alloy. In respect to that, we offer recommendations for their industrial use.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Investigation on microstructure characterization and property of rapidly solidified Mg-Zn-Ca-Ce-La alloys

Rapidly solidified (RS) Mg-Zn-Ca-Ce-La (wt.%) alloys have been produced via atomizing the alloy melt and subsequent splat-quenching on the water-cooled copper twin-rollers in the form of flakes. Microstructure characterization, phase compositions and thermal stability of the alloys have been systematically investigated. The results showed that with addition of RE (Ce and La) to the Mg-6Zn-5Ca alloy, the stable intermetallic compounds i.e. the Mg{sub x}Zn{sub y}RE{sub z} phase with a few Ca (about 3 at.%), shortened as the T Prime phase, were formed at the expense of the binary Mg-Zn and Ca{sub 2}Mg{sub 6}Zn{sub 3} phases, which was possibly beneficial to the enhanced thermal stability of the alloy. In the Mg-6Zn-5Ca-3Ce-0.5La alloy, the composition of the T Prime phase in the grain interior was different from that at the grain boundaries, in which the segregation of the La elements was found, and the atomic percentage ratio of Zn to Ce in the T Prime phase within the grains was close to 2. Moreover, the stable Mg{sub 2}Ca phases were detected around the T Prime phases at the grain boundaries in the alloy. - Research Highlights: Black-Right-Pointing-Pointer The phase constitution of RS Mg-6Zn-5Ca alloy can be improved by RE additions. Black-Right-Pointing-Pointer In the Mg-Zn-Ca-Ce-La alloys, the Mg{sub x}Zn{sub y}RE{sub z} phase with a few Ca (T Prime phase) is formed. Black-Right-Pointing-Pointer The formation of the T Prime phase leads to the loss of the Mg-Zn and Ca{sub 2}Mg{sub 6}Zn{sub 3} phases. Black-Right-Pointing-Pointer The composition of the T Prime phase differs from the grain interior to the grain boundary.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructural and thermal properties of pure BaFe{sub 12}O{sub 19} and Sr doped barium ferrite (Ba{sub 0.9}Sr{sub 0.1}Fe{sub 12}O{sub 19}) synthesized by auto combustion method

Nanoparticles (NPs) of Pure BaFe{sub 12}O{sub 19} and Strontium doped Barium Ferrite (Ba{sub 0.9}Sr{sub 0.1}Fe{sub 12}O{sub 19}) have been successfully synthesized by Auto combustion method using citric acid as a chelating agent and calcined at 450°C for 3 hrs and 850°C for 4 hrs. Microstructural studies were carried by XRD and SEM techniques. Structural studies suggest that the crystal system remains hexagonal even with the doping of Strontium. The XRD analysis confirms the formation of the structures in the nanometer regime and the peaks are the evidence of the crystalline phase. The SEM images shows the morphology of surface of the samples. The thermal property studied by TGA shows the weight loss which is with varying the temperature and weight loss also varies with Sr doping. The TGA analysis exhibits the loss of weight at different temperatures.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Microstructures and mechanical properties of a modified 9Cr ferritic-martensitic steel in the as-built condition after additive manufacturing

A newly developed nano-structured high-Mn 9Cr ferritic-martensitic (FM) steel designed for additive manufacturing (Additive-manufactured Nanostructured Alloy, ANA) was fabricated via the direct energy deposition method. The as-printed ANA2 showed tensile properties (strength and elongation) and Charpy impact toughness (upper-shelf energy and ductile-brittle transition temperature) comparable to oxide-dispersion-strengthened (ODS) Eurofer and PM2000. Compared with wrought P91, the as-built ANA2 showed significantly higher yield strength but inferior Charpy impact toughness and ductility. Microstructural characterization revealed uniformly distributed sub-micron pores, an extremely high dislocation density, and a high density of ultrafine nano-structured precipitates in the matrix. The microstructures indicated the dislocations as the dominant strengthening element and the ultrafine precipitates as the primary contribution to estimated irradiation sink density. This work demonstrates the ability to exploit the unique consolidation properties of additive manufacturing to fabricate steels which marry the benefits of both ODS alloys and conventionally processed FM steels.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Microstructure and mechanical properties of ultrasonic spot welding of AA7075-T6 and A380 casting aluminum alloy

Ultrasonic spot welding (USW) was employed to join AA7075-T6 and casting Al alloy A380. Under a constant welding power, the influence of the welding time duration (from 1 s to 3 s) on peak temperature, microstructure, hardness, and mechanical strength of the joints were studied. It was found that the peak temperature increased with welding time. A sound solid-state metallurgical bonding was obtained at the joint interface. The cracks occurred at the edge of the joints were eventually eliminated as the welding time increased. A layer of refined grains formed in A380 adjacent to the bonding line. Further, hardness reduction occurred in AA7075 at the joint interface and the degree of hardness reduction and the volume increased with the peak temperature. By increasing welding time, lap shear tensile tests show that the peak load increased from 5.3 kN to 6.55 kN. The corresponding interfacial shear strength ranged from 96.29 MPa to 99.72 MPa, lower than the shear strength of both base materials (331 MPa for AA7075 and 185 MPa for A380). All joint samples exhibited interfacial fracture after lap shear tensile testing, with a thin layer of A380 remnant attached to AA7075 at the center of the fractured surface.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Study on Microstructures and Mechanical Properties of Foam Titanium Carbide Ceramics Fabricated by Reaction Sintering Process

Foam titanium carbide (TiC) ceramics with a three-dimensional network structure were fabricated by the reaction sintering process, in which polyurethane foam was taken as the template, and TiO{sub 2} and phenolic resin were used as the reactants. Phase, microstructures and fracture morphologies of foam TiC ceramics were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that when the mass ratios of phenolic resin and TiO{sub 2} (F/T) are (0.8-1.2): 1, foam TiC ceramics with pure TiC phase can be formed. As the F/T ratios increase, crystal lattice parameters of fabricated foam TiC ceramics become bigger. When the value of F/T decreases from 1.2 to 0.8, grain size of TiC grows larger and microstructures get denser; meanwhile, the compressive strength increases from 0.10 to 1.05 MPa. Additionally, either raising the sintering temperatures or extending holding time can facilitate the completion of the reaction process and increase the compressive strength.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Effect of a copper filler metal on the microstructure and mechanical properties of electron beam welded titanium-stainless steel joint

Cracking in an electron beam weld of titanium to stainless steel occurred during the cooling process because of internal thermal stress. Using a copper filler metal, a crack free joint was obtained, which had a tensile strength of 310 MPa. To determine the reasons for cracking in the Ti/Fe joint and the function of the copper filler metal on the improvement of the cracking resistance of the Ti/Cu/Fe joint, the microstructures of the joints were studied by optical microscopy, scanning electron microscopy and X-ray diffraction. The cracking susceptibilities of the joints were evaluated with microhardness tests on the cross-sections. In addition, microindentation tests were used to compare the brittleness of the intermetallics in the welds. The results showed that the Ti/Fe joint was characterized by continuously distributed brittle intermetallics such as TiFe and TiFe(Cr){sub 2} with high hardness ({approx} 1200 HV). For the Ti/Cu/Fe joint, most of the weld consisted of a soft solid solution of copper with dispersed TiFe intermetallics. The transition region between the weld and the titanium alloy was made up of a relatively soft Ti-Cu intermetallic layer with a lower hardness ({approx} 500 HV). The formation of soft phases reduced the cracking susceptibility of the joint. - Highlights: Black-Right-Pointing-Pointer Electron beam welded Ti/Fe joint cracked for the brittleness and residual stress. Black-Right-Pointing-Pointer Electron beam welded Ti/Cu/Fe joint with tensile strength of 310 MPa was obtained. Black-Right-Pointing-Pointer Cu diluted Ti and Fe contents in weld and separated the TiFe{sub 2} into individual blocks. Black-Right-Pointing-Pointer Interfacial hard Ti-Fe compounds were replaced by soft Ti-Cu compounds in the weld. Black-Right-Pointing-Pointer A large amount of solid solution of copper formed in the weld.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and tensile properties of laser engineered net shaped reduced activation ferritic/martensitic steel

Highlights: • A RAFM steel has been successfully manufactured by laser engineered net shaping (LENS), which is one of laser additive manufacturing technologies. • Columnar dendrites in vertical section and a mixture of equiaxed and columnar grains in horizontal section have been observed. • The anisotropic tensile properties are induced by LENS process, which can be eliminated well through the heat treatment. - Abstract: A laser additive manufacturing technique, laser engineered net shaping (LENS), was successfully applied to manufacture a reduced activation ferritic/martensitic (RAFM) steel with nominal composition of Fe-9Cr-0.11C-1.5W-0.4Mn-0.2V-0.12Ta (wt%). The as-deposited LENS-RAFM steels were normalized and tempered. The microstructures of as-deposited and heat treated LENS-RAFM steels were characterized by using optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The tensile tests of as-deposited and heat treated samples in different directions were carried out at room temperature and 873 K. The results showed that columnar dendrites grow epitaxially along the direction of deposition in vertical section (YOZ) and a mixture of equiaxed and columnar grains appears in horizontal section (XOY). No precipitates are observed in the as-deposited sample while Cr-rich M{sub 23}C{sub 6} and Ta-rich MX type carbides appear in the heat treated sample. The as-deposited sample showed anisotropic tensile properties which could be eliminated by heat treatment. The tensile strength of the LENS-RAFM steel is similar to conventional RAFM steels such as EUROFER 97 and CLAM.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Effect of Al{sub 2}O{sub 3} content and milling time on microstructure and mechanical properties of aluminum metal matrix composites

In this study, aluminum metal matrix composites (Al-MMCs) reinforced with aluminum oxide (Al{sub 2}O{sub 3}) (5, 10, 15 wt%) were produced using the powder metallurgy (PM) process. Mixed powders were ball-milled in a vertical high-energy attritor for various durations (1, 2, 3 and 4 h). Milled powders were compacted under 800 MPa pressure to produce standard transverse rupture block specimens of dimensions 6.35 × 12.70 × 31.70 mm. Block specimens were then sintered in a tube furnace at a constant temperature of 650°C for 4 h under argon atmosphere. The hardness and transverse rupture strength of the experimentally produced composites were determined. The microstructures were investigated by optical microscopy and scanning electron microscopy (SEM). More homogeneous dispersion of Al{sub 2}O{sub 3} in the Al matrix, and hence improved mechanical properties of the composites, was achieved with increased milling time. The best mechanical properties were produced after 3-h milling, because of the homogeneous distribution of the reinforcing materials.

36 MATERIALS SCIENCE↗