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NASA NTRS2004

Ultrasonic Guided-Wave Scan System Used to Characterize Microstructure and Defects in Ceramic Composites

Ceramic matrix composites (CMCs) are being developed for advanced aerospace propulsion applications to save weight, improve reuse capability, and increase performance. However, mechanical and environmental loads applied to CMCs can cause discrete flaws and distributed microdamage, significantly reducing desirable physical properties. Such microdamage includes fiber/matrix debonding (interface failure), matrix microcracking, fiber fracture and buckling, oxidation, and second phase formation. A recent study (ref. 1) of the durability of a C/SiC CMC discussed the requirement for improved nondestructive evaluation (NDE) methods for monitoring degradation in these materials. Distributed microdamage in CMCs has proven difficult to characterize nondestructively because of the complex microstructure and macrostructure of these materials. This year, an ultrasonic guided-wave scan system developed at the NASA Glenn Research Center was used to characterize various microstructural and flaw conditions in SiC/SiC (silicon carbide fiber in silicon carbide matrix) and C/SiC (carbon fiber in silicon carbide matrix) CMC samples.

Roth, Don J.↗

DOE OSTI2018

Dissimilar Metal Weld Joints of P91/Ni Alloy: Microstructural Characterization of HAZ of P91 and Stress Analysis at the Weld Interfaces

Microstructure evolution and hardness were evaluated at the interface of two friction-welded transition joints between P91 and AISI 304 fabricated applying Inconel interlayers, viz. single-interlayer weld (P91/IN600/AISI304) and three-interlayer weld (P91/IN625/IN600/IN800H/AISI304). The welds were subjected to post-weld heat treatment at 1023 K for 1 h followed by air cooling and a long-term exposure at 973 K for 100, 250, and 500 h. A soft zone with the absence of lath martensite was noticed in both the welds which was located at the intercritical heat-affected zone of the welds. This zone was found to be extending with time toward the fine grain heat-affected zone by carbide precipitation and coarsening at the grain boundaries. Soft zone formation at the interface of the welds was found to be due to carbon diffusion. The presence of high-nickel-content alloy at the interface was proven to be beneficial in stopping carbon diffusion at the interface. Though soft zones existed in both the welds, better creep rupture life was observed for three-interlayer welds. Finite element analysis of these weld joints was performed for thermal loading followed by tensile loading. The results from this analysis indicated that thermal expansion also plays an important role in the failures of these dissimilar weld joints by creating high stress at the interface due to incompatibility.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Microstructure characterization of heat affected zone after welding in Mod.9Cr–1Mo steel

The microstructure of the heat affected zone after welding was investigated in Mod.9Cr–1Mo steel, using TEM and STEM-EDX. The microstructure of thin foil was observed at the fusion line, and at the positions of 0.5 mm, 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm and 3.5 mm to the base metal side of the fusion line. Martensite structure with very fine lath and high dislocation density was confirmed at all positions. Twins with a twin plane of (112) were locally observed at all positions. Elemental mapping was obtained for all positions by means of STEM-EDX. Inclusions of mainly Si were formed at the fusion line but not at the other positions. No precipitates could be detected at the fusion line or at the position of 0.5 mm. On the other hand, MX particles were observed at the positions of 1.0 mm, 1.5 mm, 2.0 mm, 2.5 mm, 3.0 mm and 3.5 mm even after welding. M{sub 23}C{sub 6} particles were also confirmed at the positions of 2.0 mm, 2.5 mm, 3.0 mm and 3.5 mm. Very fine equiaxed grains were locally observed at the positions of 2.0 mm and 2.5 mm. The Cr content of the equiaxed grains was about 12 mass%, although the martensite area included about 8 mass% Cr. - Graphical abstract: Display Omitted - Highlights: • Nonequilibrium microstructure of heat affected zone was observed after welding in Mod.9Cr–1Mo steel. • Inclusions containing Si were detected at the fusion line. • Undissolved M{sub 23}C{sub 6} and MX particles were confirmed in heat affected zone. • Twins with a twin plane of (112) were locally observed at all positions. • Very fine ferrite grains with high Cr content were observed in fine grained heat affected zone.

36 MATERIALS SCIENCE↗

NASA NTRS1997

Microstructural Characterization of Polymers with Positrons

Positrons provide a versatile probe for monitoring microstructural features of molecular solids. In this paper, we report on positron lifetime measurements in two different types of polymers. The first group comprises polyacrylates processed on earth and in space. The second group includes fully-compatible and totally-incompatible Semi-Interpenetrating polymer networks of thermosetting and thermoplastic polyimides. On the basis of lifetime measurements, it is concluded that free volumes are a direct reflection of physical/electromagnetic properties of the host polymers.

Singh, Jag J.↗

DOE OSTI2019

Formation Mechanisms and Microstructure Characterization of Al/Al{sub 3}Ni In-situ Composite by Compound Casting

The Compound casting method was used to produce an Al/Ni bimetal composite. The mechanisms of formation of the reinforcing intermetallic phases were studied and the produced bimetal composite’s microstructure was then characterized. The results showed that the Al/Ni interface consisted of two intermetallic layers including Al{sub 3}Ni{sub 2} and Al{sub 3}Ni. It is suggested that the Al{sub 3}Ni reinforcing particles of the composite originated from two sources. (1) Some Al{sub 3}Ni particles detached from the Al{sub 3}Ni layer formed at the interface between the Ni core and the Al melt and dispersed in the liquid Al and (2) Al-Al{sub 3}Ni eutectic phase, which formed during the solidification process. The increase in the temperature led to the formation of more reinforcing particles and extended the depth of dispersion of the particles in the Al matrix.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Microstructural characterization of an SA508–309L/308L–316L domestic dissimilar metal welded safe-end joint

The microstructure of an SA508–309L/308L–316L domestic dissimilar metal welded safe-end joint was characterized in this work by optical microscopy, scanning electron microscopy (with electron back scattering diffraction) and micro-hardness testing. Epitaxial growth and competitive growth are evident in the 308L–316L fusion boundary regions. A martensite layer, carbon-depleted zones, and type-II and type-I boundaries are found in the SA508–309L fusion boundary regions, while only martensite and austenite mixed zones are observed in the SA508–308L fusion boundary regions. The microstructure near the fusion boundary and the microstructure transition in the SA508 heat affected zone are quite complex. Both for SA508–309L/308L and 308L–316L, the highest residual strain is located on the outside of the weldment. The residual strain and the grain boundary character distribution change with increasing distance from the fusion boundary in the heat affected zone of 316L. Micro-hardness measurements also reveal non-uniform mechanical properties across the weldment. - Highlights: • The microstructure of SA508 HAZ, especially near the FB, is very complex. • The outside of the dissimilar metal welded joint has the highest residual. • The micro-hardness distributions along the DMWJ are non-uniform.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Microstructural characterization of a new mechanically alloyed Ni-base ODS superalloy powder

The microstructure of a new Ni-base oxide dispersion strengthened superalloy powder was studied for high temperature gas turbine applications after the mechanical alloying process. In this study, an atomized powder with a composition similar to the CMSX-10 superalloy was mechanically alloyed with yttria and Hf powders. The mechanically alloyed powder included only the supersaturated solid solution γ phase without γ′ and yttria provided by severe plastic deformation, while after the 3-step aging, the γ′ phase was precipitated due to the partitioning of Al and Ta to the γ′ and Co, Cr, Re, W, and Mo to the γ phase. Mechanical alloying modified the morphology of γ′ to the new coherent γ–γ′ nanoscale lamellar structure to minimize the elastic strain energy of the precipitation, which yielded a low lattice misfit of 0.16% at high temperature. The γ′ lamellae aligned preferentially along the elastically soft [100] direction. Also, the precipitated oxide particles were refined in the γ phase by adding Hf from large incoherent YAlO{sub 3} to fine semi-coherent Y{sub 2}Hf{sub 2}O{sub 7} oxide particles with the average size of 7 nm and low interparticle spacing of 76 nm. - Highlights: • A new Ni-base ODS superalloy powder was produced by mechanical alloying. • The nanoscale γ–γ′ lamellar structure was precipitated after the aging treatment. • Fine semi-coherent Y{sub 2}Hf{sub 2}O{sub 7} oxide particles were precipitated by addition of Hf.

36 MATERIALS SCIENCE↗

NASA NTRS1996

Microstructural Characterization of Polymers by Positron Lifetime Spectroscopy

Singh, Jag J.↗

DOE OSTI2015

Microstructural characterization of dissimilar welds between Incoloy 800H and 321 Austenitic Stainless Steel

In this work, the microstructural character of dissimilar welds between Incoloy 800H and 321 Stainless Steel has been discussed. The microscopic examination of the base metals, fusion zones and interfaces was characterized using an optical microscope and scanning electron microscopy. The results revealed precipitates of Ti (C, N) in the austenitic matrix along the grain boundaries of the base metals. Migration of grain boundaries in the Inconel 82 weld metal was very extensive when compared to Inconel 617 weldment. Epitaxial growth was observed in the 617 weldment which increases the strength and ductility of the weld metal. Unmixed zone near the fusion line between 321 Stainless Steel and Inconel 82 weld metal was identified. From the results, it has been concluded that Inconel 617 filler metal is a preferable choice for the joint between Incoloy 800H and 321 Stainless Steel. - Highlights: • Failure mechanisms produced by dissimilar welding of Incoloy 800H to AISI 321SS • Influence of filler wire on microstructure properties • Contemplative comparisons of metallurgical aspects of these weldments • Microstructure and chemical studies including metallography, SEM–EDS • EDS-line scan study at interface.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Microstructural characterization of limestone exposed to heat with XRD, SEM and TG-DSC

Highlights: • The microstructure of limestone (25 °C–800 °C) was analyzed by XRD, SEM and TG-DSC. • The microstructural properties of the crystal are anisotropic in different crystal plane directions. • Microstructure controls the macroscopic properties of limestone. - Abstract: Limestone is a common rock used in many buildings and found in underground engineering projects. After exposure to heat, for example, the occurrence of fires, the stability of limestone structures is mostly affected, which may have safety repercussions. Therefore, the impact of thermal effects on the microstructure of limestone is investigated in this study, in which 8 groups of limestone samples are exposed to different temperatures (25 °C, 100 °C, 200 °C, 300 °C, 500 °C, 600 °C, 700 °C and 800 °C), after which X-ray diffraction, differential scanning calorimetry and scanning electron microscopy are carried out. The mineral composition and the microstructure of the samples are numerically modeled, in which the diffraction peaks, full width at half maximum, integral breadth, microstrain, average domain size and dislocation density are analyzed. The macroscopic properties obtained from the results in other works in the literature including porosity, compressive strength, damage coefficients and modulus of elasticity are also compared with the parameters above. The changes in the crystal structure of two minerals, calcite and dolomite, are found to be anisotropic in the different crystal plane directions. It is also found that the limestone microstructure affects the macroscopic properties. A temperature between 200 °C to 300 °C is the critical temperature at which both the macroscopic properties and macrostructure demonstrate significant changes.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Hot Straining and Quenching and Partitioning of a TRIP-Assisted Steel: Microstructural Characterization and Mechanical Properties

Advanced high strength steels (AHSS), with yield strengths over 300 MPa and tensile strengths exceeding 600 MPa, are becoming more noticeable in vehicle manufacturing. A novel processing route of a TRIP-assisted steel was developed. Characterization and modelling techniques were used to establish correlations between processing, microstructure and mechanical properties. Quenching and partitioning (Q&P) and a novel process of hot straining (HS) and Q&P (HSQ&P) treatments have been applied to a TRIP-assisted steel in a Gleeble ®3S50 thermo-mechanical simulator. The heat treatments involved intercritical annealing at 800 oC and a two-step Q&P heat treatment with a partitioning time of 100 s at 400 oC. The effects of high-temperature isothermal deformation on the carbon enrichment of austenite, carbide formation and the strain-induced transformation to ferrite (SIT) mechanism were investigated. Carbon partitioning from supersaturated martensite into austenite and carbide precipitation were confirmed by means of atom probe tomography (APT). Austenite carbon enrichment was clearly observed in all specimens, and in the HSQ&P samples it was slightly greater than in Q&P, suggesting an additional carbon partitioning to austenite from ferrite formed by the SIT phenomenon. By APT, the carbon accumulation at austenite/martensite interface was clearly observed. The newly developed combined process is promising as the transformation induced plasticity can contribute to the formability and energy absorption, contributing to fill the gap of the third generation of high-strength steels.

Ariza, Edwan Anderson↗

DOE OSTI2019

Microstructural Characterization of Pure Tin Produced by the Drop-on-Demand Technique of Liquid Metal Jetting

The microstructure–property relationship of a pure tin part built using the drop-on-demand technique of liquid metal jetting, a cost–effective alternative to selective laser-melting or sintering techniques, was determined. Here, the microstructure of the as-built tin is observed to have minimal stored strain, low dislocation density, few to no voids, and the presence of only the β-tin phase; concurrently, mechanical properties are shown to be identical to the traditionally manufactured tin.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Microstructural characterization of sulfur-doped Bi{sub 2}Te{sub 3} crystals

In this study, the detailed microstructure of sulfur-doped Bi{sub 2}Te{sub 3} and the distribution of sulfur dopants were investigated using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD result indicates that the interplanar distances of Bi{sub 2}Te{sub 3} are shortened after introducing sulfur dopants. HRTEM reveals that the unit cell lengths along [001, 100] are decreased as a result of the substitution of Te by smaller S atoms on the anion lattice. XRD and HRTEM analysis suggest that the distortion of the crystal lattice in Bi{sub 2}Te{sub 3} is induced by doping sulfur. High annular angler dark field scanning electron microscopy (HAADF-STEM) image shows obvious contrast variations in the Te atomic columns, indicating that Te sites were unevenly substituted by S dopants. Te columns with least contrast intensity correspond to the preferential occupation sites of S atoms. The replacement of Te atoms by S can be attributed to the evaporated sulfur powder in the gas reaction procedure. The present work is not only contributed to obtain a better understanding of the distribution of sulfur dopants introduced by gas reaction, but also can help explore the structural-property relationship of sulfur-doped Bi{sub 2}Te{sub 3}. - Highlights: • Sulfur-doped Bi{sub 2}Te{sub 3} was synthesized through modified Bridgeman method. • The introduction of S dopants results in shortening the lattice spacing of Bi{sub 2}Te{sub 3}. • HRTEM analysis indicates that S was doped through substituting Te atoms instead of incorporating interstitially. • HAADF-STEM analysis shows that Te columns with least intensity correspond to the preferential occupation sites of S.

36 MATERIALS SCIENCE↗

DOE OSTI2025

Microstructural Characterization of AGR-2 TRISO-coated Particle Buffer, IPyC, and Buffer-IPyC Interfaces

Investigating the microstructural, mechanical, and chemical behaviors of Tristructural Isotropic (TRISO) fuel particles is vital for its qualification and use in advanced reactors. Central to the study of TRISO particles is understanding the silicon carbide (SiC) layer's ability to confine fission products, with failure mechanisms linked to chemical degradation following mechanical degradation of the buffer and IPyC layers. Research has been done to quantify the micro-tensile properties of the buffer, inner pyrolytic carbon (IPyC), and buffer-IPyC interlayer regions and their interactions within both irradiated and un-irradiated TRISO particles. Techniques such as atom probe tomography (APT) and transmission electron microscopy (TEM) have also been deployed to examine microstructural defects and fission product distribution in detail. The goal is to understand layer delamination, establish connections between microstructure and mechanical attributes, and inform computational predictions of fuel performance. This work may help refine predictive models of TRISO fuel behavior and facilitating its certification for use in advanced reactors.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

NASA NTRSDate not supplied

Microstructural Characterization of Laser Powder Bed Fusion (L-PBF) Additively Manufactured Inconel 718 for Aerospace Application

Alloy 718 (Inconel 718) is used for aerospace applications because of its excellent corrosion resistance and mechanical properties. This alloy is particularly applicable in manufacturing components subjected to high temperatures in rocket engines, aero-engines, and gas turbines. Properties for this alloy when processing on systems from similar and different Laser Powder Bed Fusion (L-PBF) machines provide subtle differences due to process parameters, feedstock, and machine configurations. A series of sixteen L-PBF AM Inconel 718 geometric feature build plates have been evaluated for microstructure using optical microscopy. This study presents the details of the microstructure analysis concerning geometry and different machine platforms. Microstructural investigations of these samples included average grain width measurement for all the X-Y and Y-Z build layers and are accompanied by process parameters and powder characterization. The present work concludes with a discussion on the importance of captured differences among builds to understand the practical limitations among AM platforms.

Additive Manufacturing↗

DOE OSTI2023

Microstructural Characterizations of Two High Fluence Baffle-Former Bolts Retrieved from a Westinghouse Two-loop Downflow Type PWR

As one of the pressurized water reactor (PWR) internal components, baffle-former bolts (BFBs) are subjected to significant mechanical stress and neutron irradiation from the reactor core during the plant operation. Over the long operation period, these conditions lead to potential degradation and reduced load-carrying capacity of the bolts. In support of evaluating long-term operational performance of materials used in core internal components, the Oak Ridge National Laboratory (ORNL), through the Department of Energy (DOE), Office of Nuclear Energy, Light Water Reactor Sustainability (LWRS) Program, Materials Research Pathway (MRP), has harvested two high fluence BFBs from a commercial Westinghouse two-loop downflow type PWR. The two bolts of interest, i.e. bolts # 4412 and 4416, were withdrawn from service in 2011 as part of a preventative replacement plan. No identification of cracking or potential damage was found for these bolts during their removal in 2011. However, the bolts required a lower torque for removal from the baffle structure than the original torque specified during installation. Irradiation damage levels in the bolts range from 15 to 41 displacements per atom. The goal of this project is to perform detailed microstructural and mechanical property characterization of BFBs following in-service exposures. The information from these bolts will be integral to the LWRS program initiatives in evaluating end of life microstructure and properties. Furthermore, valuable data will be obtained that can be incorporated into model predictions of long term irradiation behavior and compared to results obtained from experimental reactor conditions

22 GENERAL STUDIES OF NUCLEAR REACTORS↗

DOE OSTI2017

3D Microstructural Characterization of Uranium Oxide as a Surrogate Nuclear Fuel: Effect of Oxygen Stoichiometry on Grain Boundary Distributions

The initial microstructure of an oxide fuel can play a key role in its performance. At low burn-ups, the diffusion of fission products can depend strongly on grain size and grain boundary (GB) characteristics, which in turn depend on processing conditions and oxygen stoichiometry. Serial sectioning techniques using Focused Ion Beam were developed to obtain Electron Backscatter Diffraction (EBSD) data for depleted UO2 pellets that were processed to obtain 3 different oxygen stoichiometries. The EBSD data were used to create 3D microstructure reconstructions and to gather statistical information on the grain and GB crystallography, with emphasis on identifying the character (twist, tilt, mixed) for GBs that meet the Coincident Site Lattice (CSL) criterion as well as GBs with the most common misorientation angles. Data on dihedral angles at triple points were also collected. The results were compared across different samples to understand effects of oxygen content on microstructure evolution.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Microstructural Characterization of Irradiated U0.7ZrH1.6 Using Ultrasonic Techniques

In recent years, there has been an increased level of effort to understand the changes in microstructure that occur due to irradiation of nuclear fuel. The primary driver for this increased effort is the potential for designing new fuels that are safer and more reliable, in turn enabling new and improved reactor technologies. Much of the data on microstructural change in irradiated fuels is generated through a host of post irradiation examination techniques such as optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) to determine grain structure, porosity, crack geometry, etc. in irradiated fuels. Such “traditional” examination techniques were recently used to characterize a novel new fuel consisting of U0.17ZrH1.6 pellets bonded to zircaloy-2 cladded with lead-bismuth eutectic before and after irradiation. However, alternative methods such as ultrasonic inspection can provide an opportunity for nondestructively assessing microstructure in both in-pile and post-irradiation examinations. In this paper, we briefly describe initial results of ultrasonic examination of the U0.17ZrH1.6 pellets (unirradiated and irradiated), in a post-irradiation examination study. Data indicate some correlation with microstructural changes due to irradiation; however, it is not clear what the specific microstructural changes are that are influencing the ultrasonic measurements. Interestingly, specimens with nominally identical burnup show differences in ultrasonic signatures, indicating apparent microstructural differences between these specimens. A summary of the experimental study, preliminary data and findings are presented in this short paper. Additional details of the analysis will be included in the presentation.

Microstructure evaluation↗