scholarly journals Effect of the gold remodeling preparation method on the microstructure and mechanical behavior of steel

2020 ◽  
Vol 2 (10) ◽  
Author(s):  
Christian Oen Paulsen ◽  
Tore Børvik ◽  
Ida Westermann
Keyword(s):  
Elevated Temperatures ◽  
Preparation Method ◽  
Tensile Behavior ◽  
Image Correlation ◽  
Polished Surface ◽  
Dual Phase ◽  
Sem Images ◽  
Dp Steel ◽  
Successful Technique

Abstract The application of gold speckles on a polished surface is a successful technique for improving digital image correlation (DIC) contrast in scanning electron microscope (SEM) images. In the process of creating the gold speckles, the material is subjected to elevated temperatures for prolonged times. As a consequence, not all materials are suitable for the gold speckled method to improve the contrast for DIC measurements during an in-situ SEM tensile test. In this letter, the effect of gold remodeling on two different steels is investigated. These steels are a dual-phase (DP) steel and a ferrite–pearlite steel (NVE36). The results demonstrate that the temperature these steels are subjected to during gold remodeling will influence the tensile behavior of the DP steel while the NVE36 steel is unaffected by the heat treatment. As a result, we can conclude that the gold remodeling method for creating contrast in SEM images may affect the microstructure. However, the effect of these changes depends on the material at hand and will vary from material to material.

scholarly journals Comparing In Situ DIC Results from an Etched Surface with a Gold Speckled Surface

Metals ◽  
2019 ◽  
Vol 9 (8) ◽  
pp. 820 ◽  
Author(s):  
Christian Oen Paulsen ◽  
Egil Fagerholt ◽  
Tore Børvik ◽  
Ida Westermann
Keyword(s):  
Gold Nanoparticles ◽  
Elevated Temperatures ◽  
Speckle Pattern ◽  
Local Strain ◽  
Image Correlation ◽  
Polished Surface ◽  
Two Phase ◽  
Continuous Layer ◽  
Etched Surface

A ferrite-pearlite two-phase steel was investigated using in situ scanning electron microscope (SEM) tensile testing combined with digital image correlation (DIC). Two different speckled patterns were used and compared. The first pattern was achieved by etching a polished surface in order to reveal the microstructural features. Second, a gold speckled pattern was obtained. Here, a continuous layer of gold was applied to a polished surface. This continuous layer was remodeled into gold nanoparticles by keeping the specimen at 180 °C for 96 h with an Ar/Styrene mixture flowing across the specimen surface. The result is randomly distributed gold nanoparticles on the surface. These particles and the etched microstructure were then used by the DIC software to correlate an image series to obtain the local strain field of the material. The differences between the two techniques are numerous. Considering the etched surface, most microstructural features were grain boundaries and pearlite lamellas. As a consequence, large areas within grains did not provide sufficient contrast for DIC, thus restricting maximum resolution. However, the technique is fast and does not expose the material to any elevated temperatures. In contrast, the gold remodeling method provides a finely dispersed gold speckle pattern on the surface, giving excellent contrast across the recorded area. DIC with gold particles achieved a spatial resolution of 0.096 µm, compared to 2.24 µm in the DIC for the etched specimen. As a result, DIC with gold speckles can resolve slip lines. Conversely, DIC with etched microstructure resolves local strains on grain level. However, it is less cumbersome and faster to perform the test on the etched specimen.

scholarly journals The fracture toughness of martensite islands in dual-phase DP800 steel

2021 ◽  
Author(s):  
Chunhua Tian ◽  
Christoph Kirchlechner
Keyword(s):  
Fracture Toughness ◽  
Fracture Initiation ◽  
Initiation Toughness ◽  
Dual Phase ◽  
Dp Steel ◽  
Bending Tests ◽  
Damage Initiation ◽  
Linear Elastic ◽  
Steel Grades

Abstract In situ microcantilever bending tests were performed on martensite islands in a dual-phase (DP) steel to extract the fracture toughness of martensite at the microscale and to understand damage initiation during forming of DP steels. All microcantilevers were produced through FIB milling. The martensite islands do not exhibit linear elastic brittle fracture; instead, significant ductile tearing is observed. The conditional fracture initiation toughness extracted by definition and by Pippan’s transfer criterion is Ki = 6.5 ± 0.4 MPa m1/2 and Ki,2% = 10.1 ± 0.3 MPa m1/2, respectively. The obtained value is well-represented by the strength-toughness trend of other ferritic steel grades. Considering the yield stress of the same martensite island, we found that crack initiation can occur only in very large martensite islands or in a banded or agglomerated martensite structure. Graphic abstract

scholarly journals Vacuum Casting and Mechanical Characterization of Nanocomposites from Epoxy and Oxidized Multi-Walled Carbon Nanotubes

Molecules ◽  
2019 ◽  
Vol 24 (3) ◽  
pp. 510
Author(s):  
Gerald Singer ◽  
Philipp Siedlaczek ◽  
Gerhard Sinn ◽  
Patrick Kirner ◽  
Reinhard Schuller ◽  
...  
Keyword(s):  
Carbon Nanotubes ◽  
Mechanical Tests ◽  
Image Correlation ◽  
Sem Images ◽  
Vacuum Casting ◽  
Multi Walled Carbon Nanotubes ◽  
Properties Of Materials ◽  
Walled Carbon Nanotubes

Sample preparation is an important step when testing the mechanical properties of materials. Especially, when carbon nanotubes (CNT) are added to epoxy resin, the increase in viscosity complicates the casting of testing specimens. We present a vacuum casting approach for different geometries in order to produce specimens from functional nanocomposites that consist of epoxy matrix and oxidized multi-walled carbon nanotubes (MWCNTs). The nanocomposites were characterized with various mechanical tests that showed improved fracture toughness, bending and tensile properties performance by addition of oxidized MWCNTs. Strengthening mechanisms were analyzed by SEM images of fracture surfaces and in-situ imaging by digital image correlation (DIC).

Failure Initiation in Dual-Phase Steel

2013 ◽  
Vol 586 ◽  
pp. 67-71 ◽  
Author(s):  
Ali Ramazani ◽  
Alexander Schwedt ◽  
Anke Aretz ◽  
Ulrich Prahl
Keyword(s):  
Research Work ◽  
Tensile Tests ◽  
Bending Test ◽  
Dual Phase ◽  
Extended Finite Element ◽  
Dp Steel ◽  
Failure Initiation ◽  
Before And After ◽  
Macroscopic Failure

This research work aims to model the failure initiation in dual-phase (DP) steel. A microstructure based approach by means of representative volume elements (RVE) is employed to evaluate the microstructure deformation and the failure initiation on the mesoscale. In order to determine cohesive parameters for martensite cracking, a two level approach has been performed experimentally. First, in-situ bending test in SEM with EBSD measurements before and after the test showed that the crack initiation occurs in martensite islands. Then, mini tensile tests with DIC technique were carried out to identify macroscopic failure initiation strain values. RVE modeling combined with extended finite element method (XFEM) was utilized to model martensite cracking on mesoscale. The identified parameters were validated by comparing the predictions with the experimental results.

scholarly journals The Analysis of Micro-Scale Deformation and Fracture of Carbonized Elastomer-Based Composites by In Situ SEM

Molecules ◽  
2021 ◽  
Vol 26 (3) ◽  
pp. 587
Author(s):  
Eugene S. Statnik ◽  
Semen D. Ignatyev ◽  
Andrey A. Stepashkin ◽  
Alexey I. Salimon ◽  
Dilyus Chukov ◽  
...  
Keyword(s):  
Structural Engineering ◽  
Elastic Moduli ◽  
Carbon Composite ◽  
Image Correlation ◽  
Butadiene Rubber ◽  
Sem Images ◽  
Micro Electro Mechanical Systems ◽  
Strength Limit ◽  
Before And After

Carbonized elastomer-based composites (CECs) possess a number of attractive features in terms of thermomechanical and electromechanical performance, durability in aggressive media and facile net-shape formability, but their relatively low ductility and strength limit their suitability for structural engineering applications. Prospective applications such as structural elements of micro-electro-mechanical systems MEMS can be envisaged since smaller principal dimensions reduce the susceptibility of components to residual stress accumulation during carbonization and to brittle fracture in general. We report the results of in situ in-SEM study of microdeformation and fracture behavior of CECs based on nitrile butadiene rubber (NBR) elastomeric matrices filled with carbon and silicon carbide. Nanostructured carbon composite materials were manufactured via compounding of elastomeric substance with carbon and SiC fillers using mixing rolling mill, vulcanization, and low-temperature carbonization. Double-edge notched tensile (DENT) specimens of vulcanized and carbonized elastomeric composites were subjected to in situ tensile testing in the chamber of the scanning electron microscope (SEM) Tescan Vega 3 using a Deben microtest 1 kN tensile stage. The series of acquired SEM images were analyzed by means of digital image correlation (DIC) using Ncorr open-source software to map the spatial distribution of strain. These maps were correlated with finite element modeling (FEM) simulations to refine the values of elastic moduli. Moreover, the elastic moduli were derived from unloading curve nanoindentation hardness measurements carried out using a NanoScan-4D tester and interpreted using the Oliver–Pharr method. Carbonization causes a significant increase of elastic moduli from 0.86 ± 0.07 GPa to 14.12 ± 1.20 GPa for the composite with graphite and carbon black fillers. Nanoindentation measurements yield somewhat lower values, namely, 0.25 ± 0.02 GPa and 9.83 ± 1.10 GPa before and after carbonization, respectively. The analysis of fractography images suggests that crack initiation, growth and propagation may occur both at the notch stress concentrator or relatively far from the notch. Possible causes of such response are discussed, namely, (1) residual stresses introduced by processing; (2) shape and size of fillers; and (3) the emanation and accumulation of gases in composites during carbonization.

scholarly journals Deciphering the role of Al2O3 formed during isothermal oxidation in a dual-phase AlCoCrFeNi2.1 Eutectic High-Entropy Alloy

2021 ◽  
Author(s):  
Mainak Saha
Keyword(s):  
Elevated Temperatures ◽  
Isothermal Oxidation ◽  
Tensile Behavior ◽  
Oxidation Behaviour ◽  
High Entropy Alloy ◽  
Dual Phase ◽  
High Entropy Alloys ◽  
High Entropy ◽  
Al2o3 Phase

In recent times, there has been a significant volume of work on Eutectic High Entropy Alloys (EHEAs) owing to their remarkable castability combined with excellent mechanical properties, which aids in clearing obstacles for their technological applications. One of the most common EHEAs, which has been of enormous interest at present, primarily owing to its solidification and tensile behavior, is AlCoCrFeNi2.1. However, to aim for high-temperature applications, oxidation behaviour of material is one of the major aspects that needs to be extensively investigated. To this end, the present work aims to study the phases evolved during oxidation at elevated temperatures as high as 950 and 1000°C in AlCoCrFeNi2.1 using XRD and also to determine the rate law followed for isothermal oxidation of this alloy at 950 and 1000°C, in order to understand the role of Al2O3 phase formed during isothermal oxidation at 950 and 1000°C.

scholarly journals Dynamic precipitation at elevated temperatures in a dual-phase AlCoCrFeNi high-entropy alloy: an in situ study

2018 ◽  
Vol 98 (9) ◽  
pp. 400-409 ◽  
Author(s):  
Ehsan Ghassemali ◽  
Reshma Sonkusare ◽  
Krishanu Biswas ◽  
Nilesh P. Gurao
Keyword(s):  
Elevated Temperatures ◽  
High Entropy Alloy ◽  
Dual Phase ◽  
Dynamic Precipitation ◽  
High Entropy ◽  
In Situ Study

Electron and ion irradiation-induced dissolution of mechanical twins in the intermetalic U3Si: An in situ HVEM study

1989 ◽  
Vol 47 ◽  
pp. 652-653
Author(s):  
Charles W. Allen ◽  
Robert C. Birtcher
Keyword(s):  
Elevated Temperatures ◽  
Ion Irradiation ◽  
Ion Beam ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Heavy Ion ◽  
High Energy ◽  
Mechanical Twinning ◽  
In Situ Experiments

The uranium silicides, including U3Si, are under study as candidate low enrichment nuclear fuels. Ion beam simulations of the in-reactor behavior of such materials are performed because a similar damage structure can be produced in hours by energetic heavy ions which requires years in actual reactor tests. This contribution treats one aspect of the microstructural behavior of U3Si under high energy electron irradiation and low dose energetic heavy ion irradiation and is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MeV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction.At elevated temperatures, U3Si exhibits the ordered AuCu3 structure. On cooling below 1058 K, the intermetallic transforms, evidently martensitically, to a body-centered tetragonal structure (alternatively, the structure may be described as face-centered tetragonal, which would be fcc except for a 1 pet tetragonal distortion). Mechanical twinning accompanies the transformation; however, diferences between electron diffraction patterns from twinned and non-twinned martensite plates could not be distinguished.

The threshold energy for atom displacement in fcc metals

1990 ◽  
Vol 48 (4) ◽  
pp. 530-531
Author(s):  
Wilfried Sigle ◽  
Matthias Hohenstein ◽  
Alfred Seeger
Keyword(s):  
Growth Rate ◽  
Elevated Temperatures ◽  
Threshold Energy ◽  
Dislocation Loops ◽  
Absolute Minimum ◽  
Voltage Electron ◽  
Atom Displacement ◽  
Electron Microscopes ◽  
Fcc Metal

Prolonged electron irradiation of metals at elevated temperatures usually leads to the formation of large interstitial-type dislocation loops. The growth rate of the loops is proportional to the total cross-section for atom displacement,which is implicitly connected with the threshold energy for atom displacement, Ed . Thus, by measuring the growth rate as a function of the electron energy and the orientation of the specimen with respect to the electron beam, the anisotropy of Ed can be determined rather precisely. We have performed such experiments in situ in high-voltage electron microscopes on Ag and Au at 473K as a function of the orientation and on Au as a function of temperature at several fixed orientations.Whereas in Ag minima of Ed are found close to <100>,<110>, and <210> (13-18eV), (Fig.1) atom displacement in Au requires least energy along <100>(15-19eV) (Fig.2). Au is thus the first fcc metal in which the absolute minimum of the threshold energy has been established not to lie in or close to the <110> direction.

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