Evaluation of the block boundary and sub-block boundary strengths of ferrous lath martensite using a micro-bending test

Shibata, Akinobu; Nagoshi, Takashi; Sone, Masato; Morito, Shigekazu; Higo, Yakichi

doi:10.1016/j.msea.2010.08.026

Cited by 172 publications

(66 citation statements)

References 22 publications

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“…These tensile data show (1) that a yield phenomenon is not observed in any of the specimens, (2) that the uniform elongation in the undeformed sample is low in LM (~2 pct) and high in CF and FF (20 to 30 pct), and (3) that the uniform elongation is low (1 to 2 pct) in all samples cold rolled to 80 pct reduction where the total elongation is high (8 to 10 pct) typically for highly strained materials. [21][22][23][24][25][26] Table IV includes data from a recent study of UCF [12] showing a significant solid solution strengthening but only at large strain (80 pct).…”

Section: B Deformed Statementioning

confidence: 99%

“…The glide resistance of sub-block boundaries may therefore be lower than the resistance of high-angle boundaries present as block boundaries in lath martensite. This has led to an investigation [26] where the glide resistance of sub-block and block boundaries has been investigated in an ultralow carbon Fe-23 mass pct Ni alloy, which has been austenitized and water quenched to obtain a lath martensite structure. By SEM, traces of slip bands have been characterized after bending of micron-size specimens that have been cut in such a way that a sample contains either a sub-block or a block boundary.…”

Section: B Dislocation Strengtheningmentioning

confidence: 99%

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Ultrafine Structure and High Strength in Cold-Rolled Martensite

Huang

Morito

Hansen

et al. 2012

Metall Mater Trans A

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Structural refinement by cold rolling (10 to 80 pct reductions) of interstitial free (IF) steel containing Mn and B has been investigated from samples with different initial structures: (a) lath martensite, (b) coarse ferrite (grain size 150 lm), and (c) fine ferrite (22 lm). Unalloyed IF steel with a coarse grain size (120 lm) has also included based on a previous study. Deformation microstructures and structural parameters have been analyzed by transmission electron microscopy and electron backscatter diffraction, and mechanical properties have been characterized by hardness and tensile testing. At low to medium strains, lath martensite transforms into a cell block structure composed of cell block boundaries and cell boundaries with only a negligible change in strength. At medium to large strains, cell block structures in all samples refine with increasing strain and the hardening rate is constant (stage IV). A strong effect of the initial structure is observed on both the structural refinement and the strength increase. This effect is largest in lath martensite and smallest in unalloyed ferrite. No saturation in structural refinement and strength is observed. The discussion covers the transformation of lath martensite into a cell block structure at low to medium strains where the driving force is suggested to be a decrease in the dislocation line energy. Medium to large strain-hardening mechanisms are discussed together with structure-strength relationships assuming additive stress contributions from dislocations, boundaries, and elements in solid solution. Good agreement is found between flow stress predictions and stress values observed experimentally both in the initial undeformed martensite and in deformed samples.

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Section: B Deformed Statementioning

confidence: 99%

Section: B Dislocation Strengtheningmentioning

confidence: 99%

Ultrafine Structure and High Strength in Cold-Rolled Martensite

Huang

Morito

Hansen

et al. 2012

Metall Mater Trans A

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“…The compression test was conducted using a test machine specially designed for micro-sized specimens equipped with a at-ended diamond indenter at a constant displacement of 0.1 μm/s controlled by a piezo-electric actuator [6][7][8] . The load resolution was 10 μN.…”

Section: (B) and (C)mentioning

confidence: 99%

“…In previous studies, our group has reported several methods to evaluate the micro-mechanical properties of electrodeposited materials, such as micro-bending 6) , micro-compression 7) , and micro-tensile tests 8) . In this study, micro-compression tests of micro-pillars fabricated from a piece of electrodeposited pure gold lm were conducted to study micro-mechanical properties of the electrodeposited gold.…”

Section: Introductionmentioning

confidence: 99%

Brittle Fracture of Electrodeposited Gold Observed by Micro-Compression

et al. 2016

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Micro-compression tests were conducted to evaluate micro-mechanical properties of electrodeposited gold. The gold lm was electrodeposited on a platinum substrate with a thickness of 40 μm. The gold lm was found to be composed of columnar textures along the lm growth direction. Two sizes (10 × 10 × 20 μm 3 and 20 × 20 × 40 μm 3 ) of micro-pillars with a square cross-section and the long-side parallel to the Pt/ Au interface were fabricated by focused ion beam. From the micro-compression tests, brittle fracture was observed. Both of the micro-pillars showed a high compressive strength of about 600 MPa, which are much higher than the strength of the bulk gold. Grain size of the gold lm was estimated to be 14.7 nm, which is believed to be the main factor giving the high compressive strength. The strength of the larger micro-pillar was slightly lower than that of the smaller micro-pillar. The results con rmed presence of the size effect in these specimens.

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“…Historically, mechanical properties of each grain boundary with different characters have been investigated by micromechanical tests (e.g., microbending 9,10) or microtensile tests 11) ), where minute specimens are fabricated by focused ion beam (FIB). On the other hand, in such a small scale, hydrogen atoms, which can diffuse in metal, are immediately discharged from the specimen in air or in vacuum.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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To investigate hydrogen embrittlement susceptibility of an individual grain boundary, microcantilevers were fabricated on Ni-Cr bialloy surfaces by focused ion beam, and microbending tests were conducted during hydrogen charging by electrochemical nanoindentation. For microcantilevers fabricated across a twin boundary and inside a grain, no crack was formed by the bending both in air and during hydrogen charging. On the other hand, for microcantilevers fabricated across a random grain boundary, a crack was formed by the bending during hydrogen charging, whereas no crack was formed in air. Thus, it was identified that, for Ni-Cr bialloy, random grain boundaries are more susceptible to hydrogen than twin boundaries and crystalline planes. To validate these experimental results, slow strain-rate tensile tests were also performed, and subcracks of the fractured specimens were analyzed by electron beam back-scattering diffraction. In accordance with the microbending test results, subcracks were predominantly formed along random grain boundaries, but never along twin boundaries and inside grains. Higher hydrogen susceptibility of the random grain boundaries with lower cohesive energy (i.e., work for separation), smooth fracture surfaces without dimples or tear ridges, and no correlation between strain accumulation and subcrack formation indicate that hydrogen embrittlement of Ni-Cr bialloy is caused by decohesion mechanism, where hydrogen atoms lower cohesive energy at grain boundaries.

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Evaluation of the block boundary and sub-block boundary strengths of ferrous lath martensite using a micro-bending test

Cited by 172 publications

References 22 publications

Ultrafine Structure and High Strength in Cold-Rolled Martensite

Ultrafine Structure and High Strength in Cold-Rolled Martensite

Brittle Fracture of Electrodeposited Gold Observed by Micro-Compression

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

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