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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 811 records · Page 45
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Microstructural Effects on SCC Initiation PWR Primary Water Cold-Worked Alloy 600

SCC initiation behavior of one mill annealed alloy 600 plate heat was investigated in simulated PWR primary water under constant load at yield stress with in-situ direct current potential drop (DCPD) monitoring for crack initiation. Twelve specimens were tested at similar cold work levels among which three showed much shorter SCC initiation times (<400 hrs) than the others (>1200 hrs). Post-test examinations revealed that these three specimens all feature an inhomogeneous microstructure where the primary crack always nucleated along the boundary of large elongated grains protruding normally into the gauge. In contrast, such microstructure was either not observed or did not extend deep enough into the gauge in the other specimens exhibiting ~3-6X longer initiation times. In order to better understand the role of this microstructural inhomogeneity in SCC initiation, high-resolution microscopy was performed to compare carbide morphology and strain distribution between the long grains and normal grains, and their potential effects on SCC initiation are discussed in this paper.

Alloy 600↗
DOE OSTI2018

Comparison of the Microstructure and Flux Pinning Properties of Polycrystalline YBa{sub 2}Cu{sub 3}O{sub 7-d} Containing Zn{sub 0.95}Mn{sub 0.05}O or Al{sub 2}O{sub 3} Nanoparticles

Here we compare the microstructure and flux pinning properties of polycrystalline YBa{sub 2}Cu{sub 3}O{sub 7-d} (Y-123 or YBCO) containing either Al{sub 2}O{sub 3} or Zn{sub 0.95}Mn{sub 0.05}O nanoparticles. Samples were prepared using a standard solid-state reaction process, and nanoparticles were added up to a concentration of 0.1 wt%. The crystal structure, microstructure, electrical and magnetic properties were analyzed using X-ray diffraction, scanning electron microscopy and transmission electron microscopy (TEM), and electrical resistivity and DC magnetization measurements, respectively. TEM observations showed that the addition of Zn{sub 0.95}Mn{sub 0.05}O resulted in a high density of fine twins and a variety of interacting microstructures, while Al{sub 2}O{sub 3} addition resulted in a high density of Al-rich nanoscale inhomogeneities embedded in the Y-123 matrix. Flux pinning forces were determined, and predominant pinning mechanisms in the prepared samples were proposed. We evaluated the superconducting properties of YBCO considering the effects of adding insulating or magnetic nanoparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Rapid Solidification of Sn-Cu-Al Alloys for High-Reliability, Lead-Free Solder: Part I. Microstructural Characterization of Rapidly Solidified Solders

Particles of Cu x Al y in Sn-Cu-Al solders have previously been shown to nucleate the Cu 6 Sn 5 phase during solidification. In this study, the number and size of Cu 6 Sn 5 nucleation sites were controlled through the particle size refinement of Cu x Al y via rapid solidification processing and controlled cooling in a differential scanning calorimeter. Cooling rates spanning eight orders of magnitude were used to refine the average Cu x Al y and Cu 6 Sn 5 particle sizes down to submicron ranges. The average particle sizes, particle size distributions, and morphologies in the microstructures were analyzed as a function of alloy composition and cooling rate. Deep etching of the samples revealed the three-dimensional microstructures and illuminated the epitaxial and morphological relationships between the Cu x Al y and Cu 6 Sn 5 phases. Transitions in the Cu 6 Sn 5 particle morphologies from faceted rods to nonfaceted, equiaxed particles were observed as a function of both cooling rate and composition. Initial solidification cooling rates within the range of 10 3 to 10 4 °C/s were found to be optimal for realizing particle size refinement and maintaining the Cu x Al y /Cu 6 Sn 5 nucleant relationship. In addition, little evidence of the formation or decomposition of the ternary-β phase in the solidified alloys was noted. As a result, solidification pathways omitting the formation of the ternary-β phase agreed well with observed room temperature microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Impact of Defects in Powder Feedstock Materials on Microstructure of 304L and 316L Stainless Steel Produced by Additive Manufacturing

Recent work in both 304L and 316L stainless steel produced by additive manufacturing (AM) has shown that in addition to the unique, characteristic microstructures formed during the process, a fine dispersion of sub-micron particles, with a chemistry different from either the powder feedstock or the expected final material, are evident in the final microstructure. Such fine-scale features can only be resolved using transmission electron microscopy (TEM) or similar techniques. The present paper uses electron microscopy to study both the initial powder feedstock and microstructures in final AM parts. Special attention is paid to the chemistry and origin of these nanoscale particles in several different metal alloys, and their impact on the final build. Finally, comparisons to traditional, wrought material will be made.

36 MATERIALS SCIENCE↗
DOE OSTI2019

A Review on Friction Stir Processing of Titanium Alloy: Characterization, Method, Microstructure, Properties

In the past two decades, friction stir processing (FSP) technology has received considerable attention. FSP can be used to adjust and control the microstructure of materials, including eliminating defects, destroying dendrites and controlling fractions in the second stage, and is therefore widely used in titanium and its alloys for biomedical, aerospace and automotive applications. This article comprehensively reviews the methods of studying FSP, the microstructure evolution of materials and the summary of material properties. It begins with the introduction of the FSW system, characterization, structure and elemental analysis, and simulation and performance testing methods, and then introduces the microstructure evolution mechanism of various titanium materials and discusses in detail the material properties of titanium alloy, namely hardness and wear resistance, elasticity and plasticity, corrosion resistance and biocompatibility. Finally, this review presents unresolved issues and outstanding challenges in FSP technology and reveals the direction of this emerging field of research.

36 MATERIALS SCIENCE↗
DOE OSTI2017

On the Effects of the Rejuvenation Treatment on Mechanical and Microstructural Properties of IN-738 Superalloy

The main scope of this paper is to show the effects of a specific rejuvenation treatment studied for IN-38 on both the microstructure and the mechanical properties of the creep-damaged superalloy and to compare the tests results with the virgin material and with the recovery obtained through the standard heat treatment. This work will show that this rejuvenation treatment is able to recover the microstructure of creep-damaged specimens and that the creep and tensile properties of the rejuvenated alloy are even better than the virgin material for the tests performed. Moreover, it will be shown that the standard heat treatment provided for IN-738 is not able to fully recover the microstructure and that the creep properties of the superalloy during the tests have been lower than the virgin material.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Heat Treatment on Microstructure and Mechanical Properties of Stellite 12 Fabricated by Laser Additive Manufacturing

Microstructure evolution and wear resistance of Stellite 12 produced by laser additive manufacturing were studied in untreated and heat-treated conditions. In untreated conditions, cobalt matrix dendrites and inter-dendritic eutectic carbides were the primary microstructure, blocky and lamellar eutectic carbides can be found, and M{sub 7}C{sub 3} and M{sub 23}C{sub 6} are the primary carbides. Heat treatment can modify the microstructure of this alloy. Primary carbides were dissolved into the cobalt matrix after solution treatment. Aging treatment resulted in the precipitation of carbides, the transformation of M{sub 7}C{sub 3} into M{sub 23}C{sub 6} carbides, and the increase in microhardness. Solution and aging treatment can also cause the precipitation of carbides, but the morphology and distribution of carbides were absolutely different. The wear resistance of untreated samples at room temperature (RT) and 600 °C is better than that at 200 and 400 °C due to the high hardness at RT and the formation of oxide film at 600 °C. The wear resistance of heat-treated samples was tested at 600 °C; it was dominated by the formation and flake-off of oxide film. The sample that underwent solution plus aging treatment has a superior wear resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Effect of Minor Yttrium on Microstructure and Mechanical Properties of Bioimplant Mg-5Zn Alloy

This paper explores cast Mg-5Zn alloy, containing small amounts of yttrium (Y: 0.1-1.5 wt.%), through microstructure evaluation and tensile and hardness tests. The results reveal that addition of Y to the alloy refines microstructure, especially when secondary phases, Mg{sub 3}Zn{sub 6}Y (I) and Mg{sub 3}Zn{sub 3}Y{sub 2} (W), form. I-phase is detected when 0.3 wt.% Y is added to the alloy, while W-phase is only observed in Mg-5Zn-1.5Y alloy. The results also show that the addition of Y improves yield and tensile strength as well as the hardness value of the Mg-5Zn alloy at the expense of its formability. The three effects of the solid solution of Y in α-Mg, grain refinement, and the formation of I- and W-phases are the reasons for such behavior. The improvement is more pronounced when W-phase appears in the microstructure. In other words, Mg-5Zn-1.5Y alloy behaves stronger and harder than other alloys and may be considered as a potential candidate for bioimplant applications if its degradation behavior meets the requirements.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Surface Modification by Friction Stir Processing of Low-Carbon Steel: Microstructure Investigation and Wear Performance

A low-carbon steel sheet with a thickness of 5 mm was subjected to friction stir processing (FSP) by one to four different passes. The microstructures of different regions were characterized using the optical microscopy and electron backscatter diffraction. The Vickers micro-harness was measured at the distance of 200 μm below the processed surfaces. The influence of pass numbers (PNs) on wear resistance was studied in terms of coefficients of friction (CoFs), weight losses and wear rates. SEM topographies of the worn surfaces were also studied to evaluate the wear mechanisms. Microstructure observations showed that Widmänstatten ferrite plates were formed in stir zones (SZs) and heat affected zones. As PN increased, these grains were widened due to the increment of the carbon diffusivity and lengthened because of the high heat input and microstructure anisotropy. Besides, increasing the PN causes increasing of the hardness and wear resistance, simultaneously. Specifically, the wear rate in the SZ was reduced from 2.8 × 10{sup −2} mm{sup 3} m{sup −1} in base metal to 0.3 × 10{sup −2} mm{sup 3} m{sup −1} in sample which was subjected to 4 FSP passes. However, variation in PN had no considerable effect on CoFs. Oxidative wear mechanism was observed on the worn surface of the steel and the FSPed samples while more debris was formed by increasing the PNs.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure, Phase Occurrence, and Corrosion Behavior of As-Solidified and As-Annealed Al-Pd Alloys

In the present work, we studied the microstructure, phase constitution, and corrosion performance of Al{sub 88}Pd{sub 12}, Al{sub 77}Pd{sub 23}, Al{sub 72}Pd{sub 28}, and Al{sub 67}Pd{sub 33} alloys (metal concentrations are given in at.%). The alloys were prepared by repeated arc melting of Al and Pd granules in argon atmosphere. The as-solidified samples were further annealed at 700 °C for 500 h. The microstructure and phase constitution of the as-solidified and as-annealed alloys were studied by scanning electron microscopy, energy-dispersive x-ray spectroscopy, and x-ray diffraction. The alloys were found to consist of (Al), ε{sub n} (~ Al{sub 3}Pd), and δ (Al{sub 3}Pd{sub 2}) in various fractions. The corrosion testing of the alloys was performed in aqueous NaCl (0.6 M) using a standard 3-electrode cell monitored by potentiostat. The corrosion current densities and corrosion potentials were determined by Tafel extrapolation. The corrosion potentials of the alloys were found between − 763 and − 841 mV versus Ag/AgCl. An active alloy dissolution has been observed, and it has been found that (Al) was excavated, whereas Al in ε{sub n} was de-alloyed. The effects of bulk chemical composition, phase occurrence and microstructure on the corrosion behavior are evaluated. The local nobilities of ε{sub n} and δ are discussed. Finally, the conclusions about the alloy’s corrosion resistance in saline solutions are provided.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influence of Heat Treatments on Microstructure and Toughness of 9%Ni Steel

The 9%Ni low-carbon steel is applied to utilities and processes at temperatures as low as − 196 °C. However, the microstructural features play an important role on the mechanical properties. Notably, the cryogenic toughness and mechanical strength are strongly dependent on the final heat treatment. In this paper, the microstructure of a 9%Ni low-carbon steel was modified by different heat treatments. The hardness and cryogenic toughness were measured and correlated to microstructural features. The material shows a temper embrittlement with intergranular cracking and minimum cryogenic toughness after tempering around 400 °C. Austempering at 480 °C also produced very low toughness results. On the other hand, excellent cryogenic toughness was obtained with single tempering at 600 °C after quenching or normalizing. Even higher toughness was obtained with the double tempering at 670 °C/2 h plus 600 °C/2 h. The amount of reversed austenite and its morphology in the specimen quenched and tempered at 600 °C were shown in the paper.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Bainitic Microstructure on Ballistic Performance of Armour Steel Weld Metal Using Developed High Ni-Coated Electrode

Welding of armour steel has gained significant importance during the past few years as recent civilian and military requirements demand weld metal properties matching with base metal having good ballistic performance along with high strength and toughness at − 40 °C as per specification. The challenge of armour steel welding therefore lies in controlling the weld metal composition which is strongly dependent on welding electrode/consumables, resulting in desired weld microstructure consisting of lower bainite along with retained austenite. The performance of butt-welded armour steel joints produced by the developed electrodes was evaluated using tensile testing, ballistic testing, impact toughness at room temperature and subzero temperature. Microstructures of weld metals are exclusively characterized by x-ray diffraction technique, scanning electron microscope and transmission electron microscopy with selected area diffraction pattern. Experimental results show that weld metal with relatively lower carbon, higher manganese and lower nickel content was attributed to lower bainite with film type of retained austenite may be considered as a most covetable microstructure for armour steel weld metal.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The Prediction of Microstructure Evolution of 6005A Aluminum Alloy in a P-ECAP Extrusion Study

Finite element modeling (FEM) was applied for predicting the recrystallized structure in extruded 6005 aluminum alloy, and simulated results were experimentally validated. First, microstructure evolution of 6005 aluminum alloy during deformation was studied by means of isothermal compression test, where the processing parameters were chosen to reproduce the typical industrial conditions. Second, microstructure evolution was analyzed, and the obtained information was used to fit a dynamic recrystallization model implementing inside the DEFORM-3D FEM code environment. FEM of deformation of 6005 aluminum has been established and validated by microstructure comparison. Finally, the obtained dynamic recrystallization model was applied to tube extrusion by using a portholes-equal channel angular pressing die. The finite element analysis results showed that coarse DRX grains occur in the extruded tube at higher temperature and in the extruded tube at the faster speed of the stem. The test results showed material from the front end of the extruded tube has coarse grains (60 μm) and other extruded tube has finer grains (20 μm).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructural Characterization, Mechanical Properties, and Corrosion Resistance of Dental Co-Cr-Mo-W Alloys Manufactured by Selective Laser Melting

In this paper, the microstructure, mechanical properties, and corrosion resistance of the dental Co-Cr-Mo-W alloys fabricated by selective laser melting (SLM) were systematically investigated and correlated. The microstructure of the SLM group (SG) specimens is composed of extremely fine columnar crystals, exhibiting supersaturated and homogeneous character. The matrix mainly consists of face-centered-cubic (FCC) cobalt solid solutions, and minimal hexagonal-close-packed (HCP) cobalt solid solutions. Mechanical test results showed that the 0.2% yield strength of SG was 775 ± 7 MPa, and the ultimate tensile strength was 1118 ± 25 MPa. The elongation of SG was 8.28 ± 0.4%, and the microhardness of SG was 476 ± 10 HV. All of these values largely exceeded the cast group (CG) specimens. The high strength is attributed to their fine columnar crystals and supersaturated matrices. The fewer content from the HCP phase and a lack of intermetallic compounds or eutectic contribute to the high ductility. Furthermore, a higher E{sub corr}, lower I{sub corr} were acquired for better corrosion resistance compared to cast specimens, due to even less composition segregation and more microstructural homogeneity.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Microstructure and Mechanical Properties of Al-Mg-Sc-Zr Alloy Variable Polarity Plasma Arc Welding Joint

Al-Mg-Sc-Zr alloy plates were welded by variable polarity plasma arc welding (VPPAW) with Sc-containing filler wire. The microstructure and mechanical properties were investigated. Results show that the weld zone and heat-affected zone (HAZ) are narrow due to the high concentrated heat input of VPPAW. Primary Al{sub 3}(Sc,Zr) particles are nice nucleating sites for α-Al, which can significantly refine the grains of α-Al, helping the weld zone maintain an outstanding strength. The unmelted Al{sub 3}(Sc,Zr) precipitates of the base metal aggregated near the fusion boundary result in the formation of a fine equiaxed grains zone, which improves the bonding degree between the weld zone and the base metal. The Al{sub 3}(Sc,Zr) precipitates in the HAZ have excellent inhibition effect on recrystallization. According to the observed microhardness distribution and microstructure characteristics, the microstructure model of welded joint is obtained. The fractured position of welded joint locates in the weld zone. The tensile strength of the welded joint without reinforcing rib is 330 MPa. The welding coefficient reaches 74%.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Ni Addition to Sn0.7Cu Solder Alloy on Thermal Behavior, Microstructure, and Mechanical Properties

The addition of Ni on lead-free solder alloys Sn0.7Cu was tested in this study. A small amount of Ni was added to the solder alloys to evaluate the thermal behavior, microstructure, and mechanical properties of the composite solders after sintering and isothermal aging for 3 days and then compared with the results of the binary Sn0.7Cu solder. The results indicated that the ultimate tensile strength and yield tensile strength changed when adding 0.25 wt.% of Ni. The tested results of the differential scanning calorimeter showed that the addition of Ni (such as 0.5 and 1 wt.%) could obviously increase the solidification temperature of Sn0.7Cu alloys in the cooling process. When the Ni content was increased to 0.25 wt.% in the ternary condition, which includes the Sn0.7Cu-xNi (x = 0, 0.1, 0.25, 0.5, and 1 wt.%) solder alloys for the indentation creep test, the minimum creep rate reached the maximum; however, the trend was reversed as the Ni content was higher than this level. In addition, the microstructure of Sn-0.7Cu-xNi solder alloys was obviously different with the eutectic Sn-0.7Cu solder, such that the Ni gradually accumulated in the (Cu, Ni){sub 6}Sn{sub 5} IMCs within the Ni-containing solder alloys. Additionally, this process refined the microstructure of the Sn-0.7Cu solder. The fracture surface of the eutectic Sn-0.7Cu solder revealed ductile fracture modes; however, there was no mixed ductile–brittle fracture mode occurred when the Ni content was in the range of 0-1 wt.%.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Processing, As-Cast Microstructure and Wear Characteristics of a Monotectic Al-Bi-Cu Alloy

Ternary Al-based monotectic alloys have a good combination of wear resistance and mechanical strength. While self-lubricating soft elements guarantee an adequate wear resistance, the modification with third elements can increase the ability to support load. In the present investigation, a collection of microstructures is generated through transient directional solidification of the Al-3.2wt.%Bi-3.0wt.%Cu alloy. Samples with different Bi spacing have been subjected to micro-adhesive wear ball tests. A relationship linking the wear volume, V, the microstructural spacing and the test time is proposed for Bi spacing higher than 16 μm, according to which V decreases with the decrease in Bi spacing. It is observed that wider and deeper grooves emerged on the surface of the samples related to more refined Bi and Al{sub 2}Cu phases, that is, associated with Bi spacing and Bi diameter lower than 16 and 2.4 μm, respectively. A reverse trend is noted for these finer microstructures, for which V increases with further decrease in Bi spacing. This can be caused by the detachment of the very fine and less cohesive Al{sub 2}Cu lamellas as the Al{sub 2}O{sub 3} oxide breaks up forming debris, with the presence of these lamellas as loose debris at the interface acting as third-body abrasives.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Study on the Hot Deformation Behavior and Microstructure Evolution of Cu-Cr-In Alloy

Based on the hot compressive tests in the temperature range of 700-900 °C and strain rate range of 0.01-10 s{sup −1}, the hot deformation behavior of a Cu-Cr-In alloy was investigated. The true stress–strain curves of the alloy were obtained, and a constitutive equation for the alloy was established by the method of equivalent stress. The processing maps were constructed based on the constitutive equation, and the microstructural evolutions were analyzed and correlated with the processing maps. The results show that the true stress of the alloy increased with decreasing strain rate and decreased with increasing temperature. The microstructures of the alloy deformed under different conditions were in good accordance with the processing maps results. According to the processing maps and the microstructures of the alloy with true strains of 0.4 and 0.8, the optimal hot deformation conditions lie in the range of 850-900 °C and strain rate range of 0.01-0.1 s{sup −1}.

36 MATERIALS SCIENCE↗