Strain localization during discontinuous plastic flow at extremely low temperatures

Tabin, J.; Skoczen, B.; Bielski, J

doi:10.1016/j.ijsolstr.2016.06.012

Cited by 37 publications

(15 citation statements)

References 60 publications

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“…Therefore, its mechanical properties and, especially, its ductility are improved by delaying localization of the necking. The result is in line with those on the phenomenon of serrated flow behavior reported by other researchers [21,22]. Figure 8 shows the ductility and the UTS in terms of deformation passes for the modified-CSP samples.…”

Section: Tensile Propertiessupporting

confidence: 91%

An Improvement in Constrained Studded Pressing for Producing Ultra-Fine-Grained Copper Sheet

Kaykha

Dashtbayazi

2022

Metals

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In this study, constrained studded pressing (CSP) was modified to produce ultra-fine-grained copper sheets and is called modified-CSP. In modified-CSP, due to the selection of asymmetric semicircle studs, the maximum groove depth can increase up to three times the sheet thickness. In the CSP method, the groove depth is selected to be equal to the sheet thickness. To investigate the effective plastic strain, a finite element model (FEM) of modified-CSP was established. For this purpose, DEFORM-3D commercial software was used. A simulation showed that the modified-CSP process was capable of using higher strain, about 0.8 in each pass than in CSP. Copper sheets were deformed up to 10 passes by modified-CSP. The microstructure of the produced samples was analyzed. The results show that the grain size decreases in the first pass. In addition, with increasing plastic strain, the structure of the twins bands was observed. Mechanical properties, including tensile properties and Vickers microhardness, of the samples during the process were investigated. The strain inhomogeneity factor (SIF) and the hardness inhomogeneity factor (HIF) were used to quantitatively express the uniformity of distribution of effective plastic strain and Vickers microhardness, respectively. Compared with CSP and constrained groove pressing (CGP), the results showed that although the ultimate tensile strength (UTS) has significantly increased, the ductility values have remained almost constant. Moreover, in modified-CSP, the load-die stroke diagram increases almost evenly due to the removal of the stud interface area and progressive engagement. Therefore, modified-CSP copper sheets showed superior tensile properties such as good toughness.

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Section: Tensile Propertiessupporting

confidence: 91%

An Improvement in Constrained Studded Pressing for Producing Ultra-Fine-Grained Copper Sheet

Kaykha

Dashtbayazi

2022

Metals

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“…At 4 K the stress-strain curve is further shifted upwards, and the plastic flow becomes discontinuous. The phenomenon of serrated yielding -which is observed mainly in FCC metals and alloys during plastic deformation at extremely low temperatures close to absolute zero-is caused by the local formation of lattice barriers in the weakly excited lattice whose catastrophic failure leads to massive motion of the released dislocations (Tabin et al, 2016;Obst and Nyilas, 1991). Fig.…”

Section: Resultsmentioning

confidence: 99%

“…6(a). The drop of the strain rate occurs because the sections of the sample with ε > 0.07 need higher stress increment to keep deforming than the sections with a lower strain level, so that the contribution of the sections of the sample beyond the gauge length to the total sample elongation increases (see the thermodynamic considerations derived from the tensile experiments on AISI 304 samples performed by Tabin et al (2016)). Consequently, since the velocity of the machine's cross-head is constant, the uniform strain rate on the sample's gauge length decreases.…”

Section: Resultsmentioning

confidence: 99%

Flow and fracture of austenitic stainless steels at cryogenic temperatures

Fernández-Pisón

Rodríguez-Martínez

García‐Tabarés

et al. 2021

Engineering Fracture Mechanics

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In this paper, we have characterized the microstructural evolution and the plastic flow and fracture behaviours of AISI 304L and AISI 316LN stainless steel grades at liquid nitrogen temperature (77 K) and at liquid helium temperature (4 K). Uninterrupted tensile experiments, where the sample is continuously deformed under quasi-static loading conditions until fracture, have been carried out with a Single-Section Sample to obtain the stress-strain characteristics of the two grades. Interrupted tensile experiments, in which the sample is unloaded before fracture, have been performed with a novel Double-Section Sample to later characterize the strain-induced martensitic transformation at different levels of deformation. The content of martensite has been determined post-mortem, using magnetic induction, electron backscatter diffraction and quantitative light optical micrography. The results obtained with the three methods show quantitative agreement, and reveal that the martensitic transformation in AISI 304L occurs faster and to a greater extent than in AISI 316LN both at 77 K and at 4 K. To the authors' knowledge, in this paper we provide the first experimental results for the evolution of the content of strain-induced martensite in AISI 304L and AISI 316LN samples tested at liquid helium temperature. In addition, the experimental data for the evolution of the martensite volume fraction with the strain have been used to identify the temperature-dependent parameters of the martensitic transformation kinetic models proposed by Olson and Cohen (1975) and Garion and Skoczeń (2002). Moreover, Mode I fracture tests with fatigue-precracked Compact Samples have been carried out to determine the fracture properties of the two investigated materials using the "resistance curve procedure" (ASTM-E1820-20a, 2020). The crack-growth resistance curves have been obtained with four different methods here referred to as ASTM Compliance Method, W-N Compliance Method, Modified W-N Compliance Method and ASTM Normalization Method, which is an original methodological contribution of this paper. While the four approaches yield similar results for the fracture toughness, only the W-N Compliance Method and the Modified W-N Compliance Method, the latter being proposed in this paper, fulfil all the requirements of the standard ASTM-E1820-20a (2020) so that the calculated fracture toughness can be accepted as a material property. The comparison of results for both materials and testing temperatures shows that the AISI 316LN displays higher fracture toughness than the AISI 304L. Moreover, post-mortem microstructural analysis of the Compact Samples near the fracture surface has revealed that the content of martensite is greater in AISI 304L than in AISI 316LN. Furthermore, for AISI 304L more martensite is formed in the sample tested at 77 K because the plastic deformation near the crack is greater than at 4 K.

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“…CoCrFeMnNi emphatically fulfills all of these requirements. Austenitic stainless steels also prove to be strong candidates for the study of serrations and have formerly been used to state/qualify multiple hypotheses related to cryogenic serrated plastic deformation [21,22,30,31]. However, (i) austenitic stainless steels show α'-martensite transformation at cryogenic temperatures, intervening with existing dislocation phenomenon and correspondingly making analysis of dislocation-serration correlation more complex; (ii) some of the austenitic steels also have a non-negligible interstitial content which makes it difficult to both control the composition from batch to batch as well as ensure a homogenous interstitial distribution.…”

Section: Introductionmentioning

confidence: 99%

Dislocation-based serrated plastic flow of high entropy alloys at cryogenic temperatures

et al. 2020

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Serrated plastic deformation at temperatures close to 0 K has been previously reported in some metals and alloys, and is associated with two possible origins: (i) thermomechanical instability or (ii) mechanical instability. While some recent results indicate that serrations are a mechanical dislocation-based phenomenon, a comprehensive model does not exist. CoCrFeMnNi, an expectedly ideal candidate, exhibits severe serrated plastic deformation with large stress drops in excess of 100 MPa. Furthermore, it also shows cryogenic serrated plastic deformation at a higher temperature (35 K) than previously reported for any other alloy. The exacerbated nature of serrated plastic deformation in CoCrFeMnNi led to the following inferences: (i) temperature and dislocation density are indisputable controlling parameters for cryogenic serrated plastic deformation and they cannot supersede each another; (ii) a phenomenological model is elucidated based on the increasing difficulty for cross-slip with decreasing temperature, leading to sudden massive dislocation proliferation event;(iii) the model establishes a gradual transition from completely non-serrated to completely serrated deformation, mediated by cross-slip, as opposed to the conventional model which proposed a discrete transition; (iv) solute dislocation interaction and associated Stacking Fault Energy (SFE) during deformation plays a key role in controlling dislocation constriction and cross-slip and correspondingly serrated plastic deformation; (v) the need/direct influence of deformation twinning, transformation induced plasticity and especially thermomechanical factors on serrated plastic deformation is invalidated. Some of these points were further clarified through comparisons with CoCrNi and CoNi, also presented in the present article.

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Strain localization during discontinuous plastic flow at extremely low temperatures

Cited by 37 publications

References 60 publications

An Improvement in Constrained Studded Pressing for Producing Ultra-Fine-Grained Copper Sheet

An Improvement in Constrained Studded Pressing for Producing Ultra-Fine-Grained Copper Sheet

Flow and fracture of austenitic stainless steels at cryogenic temperatures

Dislocation-based serrated plastic flow of high entropy alloys at cryogenic temperatures

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