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At least 361 records · Page 20
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Characterization of Properties of Laser Powder Bed Fusion 3D-Printed Inconel 718 for Centrifugal Turbomachinery Applications

Here, this paper presents the results of a comprehensive effort to characterize the properties of Inconel 718 produced by a form of laser powder bed fusion (LPBF) additive manufacturing (AM) or 3D-printing, subsequently subjected to hot isostatic pressing (HIP) and heat treatment according to standards F3055-14a and AMS 5663, respectively. Material property data, while broadly available for traditional Inconel 718 presentations (e.g. forgings or castings), is currently lacking for the 3D-printed material. It is expected that while limited in size, the experimental data sets presented provide sufficient information to glean the capability of LPBF Inconel 718. These include: 1) Chemical composition, electron backscatter diffraction (EBSD), and x-ray energy dispersive spectroscopy (XEDS) characterization of 3D-printed material structure; 2) Tensile properties — 0.2% yield stress, ultimate stress, modulus of elasticity, and elongation to failure — based on 108 samples, as functions of temperature and sample print orientation; 3) Creep rupture data including the Larson-Miller parameter, based on 21 samples; and 4) High cycle fatigue data based on 21 samples as a function of temperature. Results are compared to available standards and/or data for forged, cast, and other AM Inconel 718. A key observation of this study, based on the EBSD results, is that while the material appears to approach full recrystallization following heat treatment, there is a detectable fraction of the material that does not fully recrystallize, resulting in a material with mechanical properties (e.g. yield stress, creep rupture) measurably lower than those of forgings, but higher than those of castings.

30 DIRECT ENERGY CONVERSION↗
DOE OSTI2019

Data clustering for the high-resolution alignment of microstructure and strain fields

The emergence of small-scale deformation mapping by a combination of scanning electron microscopy and digital image correlation (SEM-DIC) has enabled full-field investigations into the complex roles of microstructure on microscale deformation mechanisms. However, these investigations are hindered by errors in alignment between the microstructure data, generally acquired by electron backscatter diffraction (EBSD), and the microscale strain data obtained by SEM-DIC. Distortions, stitching artifacts, and spatial resolution differences between microstructure and strain fields can lead to misalignments on the order of μms. This alignment uncertainty introduces error into microstructure-strain localization analyses and precludes the examination of deformation mechanisms near grain boundaries. To improve alignment between EBSD-obtained grain boundaries and SEM-DIC strain data, an approach was created wherein a mantle was first established around the EBSD-acquired grain boundaries. Strain data was then clustered within this mantle using a k-means algorithm to identify grain boundary strain localization, and these boundary points were fit to obtain a continuous curve for each individual boundary. Clustered point outliers, such as those due to grain boundary-local dislocation slip, were statistically identified by using an absolute error threshold and removed from the grain boundary fit. The ending identification of grain boundaries in the microscale strain data is significantly improved from EBSD-identified boundaries.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Correlating Crystallographic Orientation and Ferroic Properties of Twin Domains in Metal Halide Perovskites

Metal halide perovskite (MHP) solar cells have attracted worldwide research interest. Although it has been well established that grain, grain boundary, and grain facet affect MHPs optoelectronic properties, less is known about subgrain structures. Recently, MHP twin stripes, a subgrain feature, have stimulated extensive discussion due to the potential for both beneficial and detrimental effects of ferroelectricity on optoelectronic properties. Furthermore, connecting the ferroic behavior of twin stripes in MHPs with crystal orientation will be a vital step to understand the ferroic nature and the effects of twin stripes. In this work, we studied the crystallographic orientation and ferroic properties of CH 3 NH 3 PbI 3 twin stripes, using electron backscatter diffraction (EBSD) and advanced piezoresponse force microscopy (PFM), respectively. Using EBSD, we discovered that the orientation relationship across the twin walls in CH 3 NH 3 PbI 3 is a 90° rotation about ($\bar{11}0$), with the (030) and (111) directions parallel to the direction normal to the surface. By careful inspection of CH 3 NH 3 PbI 3 PFM results including in-plane and out-of-plane PFM measurements, we demonstrate some nonferroelectric contributions to the PFM responses of this CH 3 NH 3 PbI 3 sample, suggesting that the PFM signal in this CH 3 NH 3 PbI 3 sample is affected by nonferroelectric and nonpiezoelectric forces. If there is piezoelectric response, it is below the detection sensitivity of our interferometric displacement sensor PFM (<0.615 pm/V). Overall, this work offers an integrated picture describing the crystallographic orientations and the origin of PFM signal of MHPs twin stripes, which is critical to understanding the ferroicity in MHPs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Influence of crystallographic orientation and applied magnetic field on domain structure in duplex stainless steel studied using magnetic force microscopy

Highlights: • Ferrite phase in a duplex stainless steel consists of stripe type domains. • Domain contrast decreases with deviation of plane normal from <100>. • Domain width increases with deviation of plane normal from <100>. • Domain alignment with applied field observed along <100> directions. • Grain boundary stray field is a function of misorientation between grains. - Abstract: The paper investigates the local micro-magnetization behavior in duplex stainless steel (DSS) using magnetic force microscopy (MFM). DSS has equal amount of austenite phase in ferrite matrix. The MFM imaging clearly differentiates ferrite phase (ferromagnetic) from the austenite phase (paramagnetic) due to the maze type magnetic domains present in the ferrite phase. The magneto crystalline anisotropic effect on the domain structure is discussed with the support of electron backscatter diffraction (EBSD) measurements. The MFM phase contrast and domain width are correlated with the orientation of surface normal with respect to the easy axis of magnetization (<100>). The influence of external magnetic field (±127 kA/m) application on the domain structure is studied as a function of the grain orientation and the leakage field at the grain boundaries is analyzed based on the mis-orientation between the grains.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Estimation of micro-Hall-Petch coefficients for prismatic slip system in Mg-4Al as a function of grain boundary parameters

Grain size strengthening, referred to as the Hall-Petch effect, is a common strategy to improve the yield strength of magnesium (Mg) alloys. Several experimental studies have reported that the Hall-Petch slope strongly depends on the texture of the alloy. This effect arises from altering grain boundaries (GBs) resistance to different slip systems to transfer across adjacent grains. The grain boundary barrier strength of certain grain boundaries to basal slip, referred to as basal micro-Hall-Petch, was investigated in the previous work. Here in this study, the micro-Hall-Petch coefficient values for the prismatic slip $(k^{prismatic}_{μ})$ in Mg-4Al and their correlation with the grain boundary parameters were investigated. An experimental method was developed to initiate the prismatic slip band at low-stress levels. High-resolution electron backscatter diffraction (HR-EBSD) was used to measure the residual stress tensor, from which the resolved shear stress ahead of blocked prismatic slip bands was computed for seven different grain boundaries. $(k^{prismatic}_{μ})$ values for each individual GB were calculated by coupling the stress profile information with a continuum dislocation pile-up model. The $(k^{prismatic}_{μ})$ values vary from 0.138 MPa.m 1/2 to 0.685 MPa. m 1/2 which are almost three times larger than the calculated values for the basal micro-Hall-Petch. The $(k^{prismatic}_{μ})$ values were correlated with the GB parameters, and a functional relationship depending on the two most effective angles, the angle between the traces of the slip planes on the GB plane ($\phi$) and the angle between incoming and outgoing slip directions (κ), was proposed to estimate the Hall-Petch barrier for prismatic slip system. The work provides coefficients that can be supplied as input to crystal plasticity models to couple the effect of texture and grain size effectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Orientation Relationships of Pure Tin on Single Crystal Germanium Substrates

The limited number of independent β-Sn grain orientations resulting from the difficulty in nucleating β-Sn during solidification of Sn-based solders has a large effect on the resulting β-Sn grain size and, hence, on overall solder joint performance and reliability. This study analyzes the efficacy of Ge as a heterogeneous nucleation agent for β-Sn by observing the morphologies and orientation relationships of as-deposited, solid-state annealed, and liquid-state annealed pure Sn films on single crystal Ge (100), (110), and (111) substrates. Here, the results from scanning electron microscopy and electron backscatter diffraction showed that the as-deposited Sn films all deposited with a Sn (001)|| z-axis texture, regardless of the underlying Ge substrate orientation. Solid-state annealing at 150 °C for 5 min did not result in significant dewetting of the Sn films, and the films maintained their as-deposited texture of Sn (001)|| z-axis, regardless of the underlying Ge substrate orientation. Liquid-state annealing at 235 °C for 1 min resulted is large-scale dewetting of the Sn films and re-orientation of the Sn films on the various Ge substrates. After solidification, the Ge (100) and (110) single crystal substrates produced patches of dewetted grains of the same orientation but there were no consistent Sn grain textures after liquid-state annealing, suggesting no single orientation relationship. In contrast, solidification on Ge (111) single crystal substrates resulted in isolated grains with a single Sn film texture and an orientation relationship of (100) Sn ∥(111) Ge and [100] Sn ∥[110] Ge . Density Functional Theory simulations of the experimentally observed Ge (111) sample orientation relationship and the Ge/Sn cube-on-cube orientation relationship suggest favorable relative interfacial binding energies for both interface orientations.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Quantitative linkage between the stress at dislocation channel – Grain boundary interaction sites and irradiation assisted stress corrosion crack initiation

Localized deformation has emerged as a key factor in the crack initiation process for irradiated steels, as cracks are observed to nucleate preferentially at these sites. Using high resolution electron backscatter diffraction (HREBSD), the local stress tensor surrounding the dislocation channel-grain boundary interaction sites was quantified and coupled with fully determined grain boundary plane orientation information to determine, for the first time, the relationship between grain boundary normal stress and intergranular crack initiation in irradiated austenitic stainless steel. A Fe-13Cr-15Ni alloy was strained in simulated boiling water reactor, normal water chemistry after quantifying the residual stress tensor at discontinuous dislocation channel – grain boundary interaction sites where grain boundaries were determined to be well oriented with respect to the loading axis. Local stresses at the grain boundary were observed to reach magnitudes greater than 1.5 GPa at a distance of 200 nm from the intersection between the dislocation channel and the grain boundary. A pseudo-threshold stress of 0.9 GPa was measured, below which no cracking was observed. As the stress acting normal to the grain boundary increased above this value, the susceptibility to cracking increased with the cracking fraction reaching 100% at the high end of the stress range. This study shows for the first time that not only does intersection between discontinuous dislocation channels and grain boundaries result in peak local stresses, while the magnitude of the local tensile stress drives the crack initiation process.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Quantitative study of the effect of grain boundary parameters on the slip system level Hall-Petch slope for basal slip system in Mg-4Al

Several theoretical studies have reported that the geometry and structure of grain boundaries in polycrystalline materials could impose a significant effect on the Hall-Petch slope. However, experimental observations are primarily limited by the ability of the techniques to accurately quantify the grain boundary strength and validate these theoretical models. Using high-resolution electron backscatter diffraction (HR-EBSD), the local stress tensor ahead of a slip band blocked by a grain boundary was quantified and coupled with a continuum dislocation pile-up model to assess the barrier strength of specific grain boundaries to specific slip systems, referred to as micro-Hall-Petch coefficient. For basal slip system in a deformed Mg-4Al alloy, the micro-Hall-Petch coefficient ($k^{basal}_{μ}$) varied significantly, from 0.054 to 0.184 MPa - m 1/2 for nine different grain boundaries. These results were correlated with geometric descriptors of the respective grain boundaries, with three-dimensional GB profile additionally measured via focused ion beam milling. It was found that the angle between the two slip plane traces on the grain boundary plane was the most sensitive parameter affecting $k^{basal}_{μ}$, followed by the angle between the slip directions. A functional form for calculation of $k^{basal}_{μ}$ depending on these two angles is proposed to augment crystal plasticity constitutive models with slip resistance dependent on some measure of the grain size. The method allows a new pathway to calibrate grain size strengthening parameters in crystal plasticity models, allowing further computational investigations of the interrelationship between texture, grain morphology, and the Hall Petch effect.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Effects of Strain and Strain Rate on Dynamic Grain Growth and Subgrain Evolution During Plastic Deformation of an Interstitial-Free Steel at 850 ° C

Here, the effects of strain and strain rate on dynamic grain growth (DGG) and subgrain evolution are reported for an interstitial-free steel deformed at 850 ° C. Microstructures produced during tension tests at true-strain rates of 10 -4 and to 10 -3 s -1 true strains ranging from 0.02 to 0.2 were preserved following deformation. These were characterized using electron backscatter diffraction (EBSD), including the application of spherical harmonic transform indexing to produce high-angular-resolution EBSD (HR-EBSD) data. HR-EBSD data resolved the small misorientation angles of subgrain boundaries while imaging much larger data fields than possible with previously available techniques. The resulting data confirmed that steady-state flow stress is inversely proportional to the average subgrain size and that subgrain boundary misorientation angle increases with strain. The following new observations are reported. The rate of DGG increased with respect to time but decreased with respect to strain as strain rate increased. This behavior is rationalized through a simple model using separate rate parameters for the effects of time and strain. Subgrain size was not constant during steady-state deformation, but decreased slowly with increasing strain. Subgrain size distributions and subgrain boundary misorientation angle distributions were measured, and both remained approximately log-normal during steady-state deformation. Subgrain evolution demonstrated no dependence on parent grain size, crystallographic orientation, or Taylor factor. These new data suggest that steady-state flow stress is more likely controlled by the dislocation density internal to subgrains than by the spacing between subgrain boundaries.

dynamic grain growth↗
DOE OSTI2016

In-situ laser ultrasonic measurement of the hcp to bcc transformation in commercially pure titanium

Using a novel in-situ laser ultrasonic technique, the evolution of longitudinal velocity was used to measure the α − β transformation during cyclic heating and cooling in commercially pure titanium. In order to quantify the transformation kinetics, it is shown that changes in texture can not be ignored. This is particularly important in the case of titanium where significant grain growth occurs in the β-phase leading to the ultrasonic wave sampling a decreasing number of grains on each thermal treatment cycle. Electron backscatter diffraction measurements made postmortem in the region where the ultrasonic pulse traveled were used to obtain an estimate of such local texture and grain size changes. An analysis technique for including the anisotropy of wave velocity depending on local texture is presented and shown to give self consistent results for the transformation kinetics. - Highlights: • Laser ultrasound and EBSD interpret the hcp/bcc phase transformation in cp-Ti. • Grain growth and texture produced variation in velocity during similar treatments. • Texture was deconvoluted from phase addition to obtain transformation kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Twinning behaviors of a rolled AZ31 magnesium alloy under multidirectional loading

The microstructure and texture evolution of an AZ31 magnesium rolled sheet during quasi-static compression at strain rates of 10{sup −3} s{sup −1} has been investigated by in situ electron backscattered diffraction. The influence of the initial and pre-deformed texture on the predominant deformation mechanisms during compression has been examined. It has been found that extensive grain reorientation due to (10 − 12) tensile twinning appeared when compressed along transverse direction. Tensile twin variants were observed under this loading condition, and different variants will cause an effect to the following deformation. Several twinning modes occurred with continuative loading along rolling direction. - Highlights: •Twinning behaviors were investigated through in situ multidirectional compressive tests. •Deformation behavior was affected by the twin variants. •Four types of twinning behaviors were observed during deformation process.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Effects of two-step homogenization on precipitation behavior of Al{sub 3}Zr dispersoids and recrystallization resistance in 7150 aluminum alloy

The effect of two-step homogenization treatments on the precipitation behavior of Al{sub 3}Zr dispersoids was investigated by transmission electron microscopy (TEM) in 7150 alloys. Two-step treatments with the first step in the temperature range of 300–400 °C followed by the second step at 470 °C were applied during homogenization. Compared with the conventional one-step homogenization, both a finer particle size and a higher number density of Al{sub 3}Zr dispersoids were obtained with two-step homogenization treatments. The most effective dispersoid distribution was attained using the first step held at 300 °C. In addition, the two-step homogenization minimized the precipitate free zones and greatly increased the number density of dispersoids near dendrite grain boundaries. The effect of two-step homogenization on recrystallization resistance of 7150 alloys with different Zr contents was quantitatively analyzed using the electron backscattered diffraction (EBSD) technique. It was found that the improved dispersoid distribution through the two-step treatment can effectively inhibit the recrystallization process during the post-deformation annealing for 7150 alloys containing 0.04–0.09 wt.% Zr, resulting in a remarkable reduction of the volume fraction and grain size of recrystallization grains. - Highlights: • Effect of two-step homogenization on Al{sub 3}Zr dispersoids was investigated by TEM. • Finer and higher number of dispersoids obtained with two-step homogenization • Minimized the precipitate free zones and improved the dispersoid distribution • Recrystallization resistance with varying Zr content was quantified by EBSD. • Effectively inhibit the recrystallization through two-step treatments in 7150 alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Symmetry dependent optoelectronic properties of grain boundaries in polycrystalline Cu(In,Ga)Se{sub 2} thin films

In a correlative study applying electron backscatter diffraction as well as spatially and spectrally resolved cathodoluminescence spectroscopy at low temperatures of about 5 K, the symmetry-dependent optoelectronic properties of grain boundaries in Cu(In,Ga)Se{sub 2} thin films have been investigated. We find that grain boundaries with lower symmetries tend to show a distinct spectral red shift of about 10 meV and a weak influence on the emission intensity. These behaviors are not detected at high-symmetry Σ3 grain boundaries, or at least in a strongly reduced way. The investigations in the present work help to clarify the ambivalent properties reported for grain boundaries in Cu(In,Ga)Se{sub 2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

3D microband boundary alignments and transitions in a cold rolled commercial purity aluminum alloy

In the study of microband formation during plastic deformation of face centered cubic metals and alloys, two theories have been proposed regarding the orientations of their boundaries: (i) they are aligned parallel to crystallographic planes associated with dislocation glide (i.e. (111) planes in FCC metals), or (ii) they are aligned in accordance with the macroscopic stress state generated during deformation. In this study, high resolution 3D electron backscatter diffraction (3D EBSD) was used to investigate the morphology and crystallographic nature of microband boundaries within a 19 × 9 × 8.6 μm volume of a deformed grain in commercial purity aluminum cold rolled to 22% reduction. It was found that microband boundaries correspond to both theories of orientation. Additionally, a single surface may contain both crystallographic and non-crystallographic alignments. Misorientations across boundaries in the regions of microband triple junctions have been identified for both boundary alignments. - Highlights: ► Reconstruction of a 3D volume of crystallographic orientations from EBSD data ► Subgrain features accurately reconstructed using specially designed strategies. ► Microband boundaries contain crystallographic and non-crystallographic alignments. ► Boundaries form by crystallographic process but rotate to non-crystallographic.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Microstructure, mechanical properties and microtexture of friction stir welded S690QL high yield steel

Two try-out campaigns of friction stir welding (FSW) were performed with different friction parameters to join S690QL high yield strength steel. The welds were investigated at macroscopic and microscopic scales using optical and electronic microscopy and microhardness mapping. Welds of the second campaign exhibit microstructures and mechanical properties in accordance with requirements for service use. Microtexture measurements were carried out in different zones of welds by electron backscattered diffraction (EBSD). It is shown that that texture of the bottom of the weld is similar to that of the base metal, suggesting a diffusion bonding mechanism. Finally, the mechanical properties (tensile strength, resilience, bending) were established on the most promising welds. It is shown that it is possible to weld this high yield strength steel using FSW process with satisfactory geometric, microstructural and mechanical properties. - Highlights: •1000 mm ∗ 400 mm ∗ 8 mm S690QL steel plates are joined by friction stir welding (FSW). •Maximum hardness is reduced by optimization of process parameters. •Various microstructures are formed but no martensite after process optimization. •Texture is modified in mechanically affected zones of the weld. •Texture in the bottom of the weld is preserved, suggesting diffusion bonding.

36 MATERIALS SCIENCE↗
DOE OSTI2018

In situ analysis of plasticity and damage nucleation in a Ti-6Al-4V alloy and laser weld

Highlights: • EBSD in situ tensile test on a Ti-6Al-4V alloy and laser weld • Mainly prismatic, basal and pyramidal a slip activity in the base metal • Damage nucleation in the vicinity of the β phase and at α grain boundaries • Alignment of 10-10 crystallographic direction with the tensile axis in the α′ laths of the weld metal • Crack initiation along specific laths interfaces, former β grain boundary or twinned martensite laths in the weld metal The present work addresses the mechanisms of plasticity and damage nucleation in a Ti-6Al-4V alloy and its laser weld. To this end, in situ tensile tests are performed in a Scanning Electron Microscope (SEM) equipped with a Electron BackScatter Diffraction (EBSD) camera. The slip activity is automatically analyzed using a modified Schmid analysis. It is shown that the slip activity of the base metal consists mainly in prismatic, basal and pyramidal a slip. Damage nucleation in the vicinity of the β phase and at α grain boundaries is also evidenced in the base metal. In the α{sup ′} weld metal (a microstructure similar to the one often obtained in additive manufacturing Ti-alloy parts), plastic deformation results in a crystallographic rotation of the laths tending to align the 〈10 1-bar 0〉 direction with the tensile axis. The rare events of crack initiation in the martensite are shown to occur along specific laths interfaces, former β grain boundary or twinned martensite needles.

36 MATERIALS SCIENCE↗
DOE OSTI2014

EBSD study on crystallographic texture and microstructure development of cold-rolled FePd alloy

The crystallographic texture and microstructure of FePd alloy after cold-rolling deformation were investigated using electron backscatter diffraction. The major orientations of twin copper and copper after 50% thickness reduction were observed in face-centered cubic-disordered FePd alloy, whereas the main orientation was obtained from brass type after 90% cold rolling. Increase in cold rolling resulted in the change of preferred orientation from copper to brass. Decrease in orientation intensity of copper also increased that of Goss and brass. - Highlights: • The evolution of texture and microstructure in FePd alloy was investigated after cold rolling using EBSD. • Increasing in reduction leads to the change of texture from Copper-type to Brass-type. • The reduction of Copper orientation results in increasing in Goss and Brass orientations.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Twinning in MnZn13 intermetallic compound with base-centered monoclinic structure in Zn-0.75Mn alloy

Highlights: • The most possible type I twinning system in MnZn{sub 13} is deduced to be {110} twinning. • Full twinning elements of {110} twinning in MnZn{sub 13} is firstly determined. • EBSD measurements confirm {110} twinning in MnZn{sub 13} in Zn-0.75Mn alloy. - Abstract: Electron backscattered diffraction (EBSD) has been used to characterize microstructures of as-cast and as-rolled Zn-0.75Mn alloys, in which MnZn{sub 13} intermetallic compound is the second phase. Theoretically, full twinning elements of type I {110}<1 −1 2.84> twinning system in MnZn{sub 13} with base-centered monoclinic structure (space group C2/m) are firstly determined. There exist two possible {110} twin variants, which are (110)[1 −1 2.84] and (−110)[1 1 2.84], or crystallographically equivalent (−1−10)[−1 1 −2.84] and (1−10)[−1 −1 −2.84]. The misorientation between a {110} twin and its MnZn{sub 13} matrix is calculated to be <001> 71.44° in the form of rotation axis-minimum angle pair. {110} twins in MnZn{sub 13} are confirmed by EBSD in the alloys.

36 MATERIALS SCIENCE↗