&lt;i&gt;In-situ&lt;/i&gt; Microbending Tests of Ni–Cr Alloy during Cathodic Hydrogen Charging by Electrochemical Nanoindentation

Tomatsu, Kota; Kawata, Hikaru; Amino, Takafumi; Omura, Tomohiko; Maruyama, Naoki; Nishiyama, Yoshitaka

doi:10.2355/isijinternational.isijint-2016-540

Cited by 8 publications

(9 citation statements)

References 28 publications

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“…12,18,19) The load reduction rate with respect to the displacement is regarded as a crack propagation rate with respect to given strain. It turns out from the present microbending test results that the HE crack propagates more easily in the direction parallel to the α-θ interface than normal to the α-θ interface.…”

Section: Microbending Testmentioning

confidence: 99%

Anisotropy in Hydrogen Embrittlement Resistance of Drawn Pearlitic Steel Investigated by in-situ Microbending Test during Cathodic Hydrogen Charging

et al. 2018

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To investigate causes of superior hydrogen embrittlement resistance of drawn pearlitic steel, notched microcantilevers with different notch orientations with respect to the lamellar interface were fabricated by focused ion beam, and microbending tests were conducted in air and during cathodic hydrogen charging by electrochemical nanoindentation. In air, indentation load monotonically increased with increase in indentation displacement, and no crack appeared for any notch orientations. During hydrogen charging, indentation load declined, and a crack appeared. The load reduction with respect to the displacement was larger, and the crack was deeper for the notch parallel to the lamellar interface than that normal to the lamellar interface. Furthermore, stationary cracks in the microcantilevers were observed by scanning electron microscopy and scanning transmission electron microscopy. For the notch parallel to the lamellar interface, a sharp long crack was identified along the lamellar interface. The crack stopped at the position where the cementite lamellae are disconnected. In lattice images, cementite was identified in one side of the crack, and ferrite in another side of the same crack. On the other hand, for the notch normal to the lamellar interface, a blunt short crack was identified. Thus, it was concluded that the ferrite-cementite interface is a preferential crack path, and hydrogen embrittlement resistance in the direction parallel to the lamellar interface is superior to that normal to the lamellar interface. The present results also indicate that directional lamellar alignment of the drawn pearlitic steel suppresses crack propagation in the radial direction of the drawn wire, improving the hydrogen embrittlement resistance in the drawing direction.

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Section: Microbending Testmentioning

confidence: 99%

Anisotropy in Hydrogen Embrittlement Resistance of Drawn Pearlitic Steel Investigated by in-situ Microbending Test during Cathodic Hydrogen Charging

et al. 2018

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“…7(b), which is consistent with the results in the literature. 17) It was suggested from the fracture after the yielding and the presence of the slip lines that the dislocation nucleation and glide play important roles in the HIIF.…”

Section: Tensile Test Resultsmentioning

confidence: 99%

“…9) It is also noted that the fact is contradictory to the HESIV mechanism that the twin boundaries are not fractured in the HE. 17) The dislocations should be piled-up, and the VTDs should be nucleated also in the vicinity of the twin boundaries.…”

Section: Mechanism Of Hiifmentioning

confidence: 99%

“…It is indicated by the in-situ microbending tests and the EBSD that the random grain boundaries are fractured but the twin boundaries are not in the HE. 17) It seems that the twin boundaries are not fractured because their commensurate and atomically dense interfaces possibly suppress the dislocations emission and impinging, and the formations of the disordered structures. The twin boundaries are also very likely to hardly trap hydrogen atoms.…”

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Lattice Defects Underneath Hydrogen-induced Intergranular Fracture Surface of Ni-Cr Alloy Evaluated by Low-energy Positron Beam

Tomatsu,

Omura,

Aoki

et al. 2023

ISIJ Int.

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To investigate mechanism of hydrogen-induced intergranular fractures, low energy positron beams with different energies were applied to hydrogen-induced intergranular fracture surfaces of 80Ni-20Cr alloy, and depth distributions of the lattice defects were evaluated by Doppler broadening spectroscopy and positron annihilation lifetime one. At least at depths between 0.1 μm and 1 μm from the fracture surface, a large number of the lattice defects were homogeneously distributed. Both the dislocation density and monovacancy-equivalent vacancy-type defect one were around ten-times as large as inside the grains. On the other hand, the absolute value of the monovacancy-equivalent vacancy-type defect density was about 9 appm, and obviously not large enough to cause strength reduction and fractures. It was suggested that stress concentration and disordered structures formation at and on the grain boundaries due to hydrogen-enhanced dislocation nucleation, and reduction in the grain boundary cohesive energy due to the trapped hydrogen atoms jointly cause the intergranular fractures.

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“…Therefore, in-situ microbending tests during cathodic hydrogen charging 9,12,13) were used that allows us to selectively evaluate the mechanical properties of the small volume near the specimen surface.…”

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confidence: 99%

Hydrogen Effects on Fracture Resistances of Bulk Cementite Evaluated by in-situ Microbending Test during Cathodic Hydrogen Charging

Tomatsu,

Sasaki,

Aoki

et al. 2024

ISIJ Int.

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Hydrogen absorption characteristics and mechanical properties in hydrogen environment of cementite were evaluated by low-temperature thermal desorption analysis and in-situ microbending tests during cathodic hydrogen charging using bulk cementite plates obtained through a vacuum carburizing process. In the low-temperature thermal desorption analysis, no hydrogen desorption was identified up to 1073 K. In the microbending test, notched microcantilevers experienced cleavage fracture in an elastic deformation range in air. The cathodic hydrogen charging increased fracture load (i.e., fracture toughness) with appearance of plasticity while it did not change the fracture surface morphology and Young's modulus. In the present hydrogen charging conditions, the hydrogen atoms are present only near the specimen surface because of high hydrogen migration energy in the cementite. It seems that no hydrogen desorption is detected because the hydrogen atoms are absent in most regions of the specimens. The invariance of the Young's modulus and the fracture surface morphology can be explained by the same reason. On the other hand, it is considered that the fracture toughness is improved because the hydrogen atoms charged near notch bottom of the microcantilever enhance dislocation nucleation and glide, and cause blunting of the notch during the bending.

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<i>In-situ</i> Microbending Tests of Ni–Cr Alloy during Cathodic Hydrogen Charging by Electrochemical Nanoindentation

Cited by 8 publications

References 28 publications

Anisotropy in Hydrogen Embrittlement Resistance of Drawn Pearlitic Steel Investigated by <i>in-situ</i> Microbending Test during Cathodic Hydrogen Charging

Anisotropy in Hydrogen Embrittlement Resistance of Drawn Pearlitic Steel Investigated by <i>in-situ</i> Microbending Test during Cathodic Hydrogen Charging

Lattice Defects Underneath Hydrogen-induced Intergranular Fracture Surface of Ni-Cr Alloy Evaluated by Low-energy Positron Beam

Hydrogen Effects on Fracture Resistances of Bulk Cementite Evaluated by <i>in-situ</i> Microbending Test during Cathodic Hydrogen Charging

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