A model revealing grain boundary arrangement-dominated fatigue cracking behavior in nanoscale metallic multilayers

In recent years, superheavy forgings that are manufactured from 600 t grade ingots have been applied in the latest generation of nuclear power plants to provide good safety. However, component production is pushing the limits of the current free-forging industry. Large initial grain sizes and a low strain rate are the main factors that contribute to the deformation of superheavy forgings during forging. In this study, 18Mn18Cr0.6N steel with a coarse grain structure was selected as a model material. Hot compression and hot tension tests were conducted at a strain rate of 10−4·s−1. The essential nucleation mechanism of the dynamic recrystallization involved low-angle grain boundary formation and subgrain rotation, which was independent of the original high-angle grain boundary bulging and the presence of twins. Twins were formed during the growth of dynamic recrystallization grains. The grain refinement was not obvious at 1150°C. A lowering of the deformation temperature to 1050°C resulted in a fine grain structure; however, the stress increased significantly. Crack-propagation paths included high-angle grain boundaries, twin boundaries, and the insides of grains, in that order. For superheavy forging, the ingot should have a larger height and a smaller diameter.

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Role of oxygen in enhanced fatigue cracking in a PM Ni-based superalloy: Stress assisted grain boundary oxidation or dynamic embrittlment?

Corrosion Science ◽

10.1016/j.corsci.2018.05.001 ◽

2018 ◽

Vol 139 ◽

pp. 141-154 ◽

Cited By ~ 7

Author(s):

R. Jiang ◽

D. Proprentner ◽

M. Callisti ◽

B. Shollock ◽

X.T. Hu ◽

...

Keyword(s):

Grain Boundary ◽

Fatigue Cracking

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Quantification Of Segregation Levels Using Xeds In The Stem

Microscopy and Microanalysis ◽

10.1017/s1431927600014057 ◽

1999 ◽

Vol 5 (S2) ◽

pp. 146-147

Author(s):

V. J. Keast ◽

D. B. Williams

Keyword(s):

Grain Boundary ◽

Boundary Segregation ◽

Scanning Transmission Electron Microscope ◽

Factor V ◽

X Ray ◽

Interaction Volume ◽

Probe Size ◽

Scanning Transmission ◽

The Matrix ◽

Image Position

The quantification of grain boundary segregation levels, as measured with X-ray energy dispersive spectroscopy (XEDS) in a scanning transmission electron microscope (STEM), is dependent on the size and shape of the interaction volume. The segregation level T (in atoms/nm2) is related to the intensities of the characteristic peaks in the X-ray spectrum, Is and Im, bywhere ρ is the density of the matrix in atoms/nm3, Am and As are the atomic masses of the matrix and segregant respectively and ksm is the usual k-factor. The geometric factor, V/A, is the ratio of the volume of interaction to the area of the grain boundary inside in the interaction volume. Different models have been used to describe the interaction volume and these are illustrated in Fig. 1 and the appropriate expression for V/A is given in each case. In the simplest case, beam broadening is neglected and the interaction volume can be described as a cylinder with diameter equal to the probe size, d.

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SEM In Situ Investigation on Fatigue Cracking Behavior of X80 Pipeline Steel with Inclusions

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.284-286.1096 ◽

2011 ◽

Vol 284-286 ◽

pp. 1096-1100 ◽

Cited By ~ 1

Author(s):

Ke Tong ◽

Yan Ping Zeng ◽

Xin Li Han ◽

Yao Rong Feng ◽

Xiao Dong He

Keyword(s):

Crack Initiation ◽

Pipeline Steel ◽

Fatigue Cracking ◽

Fatigue Loading ◽

In Situ Observation ◽

X80 Pipeline Steel ◽

Cracking Behavior ◽

The Matrix ◽

Extension Period

The micro-mechanical behavior of inclusions in X80 pipeline steel under fatigue loading was investigated by means of SEM in situ observation. The influence of sizes and shapes of inclusion on crack initiation and propagation was analyzed. The result shows that for large-size single-particle inclusion, cracks initiate from the interior under the fatigue loading. When a certain circulation cycles are reached, cracks initiate at the matrix near the sharp corner of the inclusion. The cracks extend at the matrix during the stable extension period and unstable extension period following the crack initiation, until fracture occurred. For chain inclusion, cracks first initiate at the interface between inclusion and matrix within the chain area, and the circulation cycles needed for initiation are far less than single inclusion. Cracks steadily extend after the initiation, and then fracture after very short circulation cycles. A chain of inclusion with the shape corners is serious harmful to the fatigue properties.

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