scholarly journals Influence of grain size on mechanisms of plastic deformation and yield stress

2020 ◽  
Vol 2020 (1) ◽  
pp. 26-32
Author(s):  
K. M. Borysovska ◽  
◽  
Y.M. Podrezov ◽  
S.O. Firstov ◽  
◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Yield Strength ◽  
Plastic Flow ◽  
Major Influence ◽  
Entire Cross Section ◽  
Physical Yield ◽  
Grain Sizes ◽  
20 Nm ◽  
Mechanisms Of Plastic Deformation

The influence of grain size on the physical yield strength of the polycrystal is considered by the method of cellular automata. The physical yield strength of the polycrystal in this model is defined as the stress at which, the plastic deformation covers the entire cross section of the sample from one edge to another. Three mechanisms of plastic deformation are considered. The first one is an initiation of plastic flow from grain to grain by dislocation pile-ups. The second one is plastic flow in different grains independently of each other under the action of external stress and the third one is intergranular slippage. Computer simulations have shown that at large grain sizes (d > 200 nm) deformation propagates from grain to grain by initiating dislocations pile-ups, since in this case pile-ups are quite powerful and have a large effect on neighboring grains. At average values of grain size (20 nm <d <200 nm) plastic deformation occurs in the grains independently of each other, and the external strain give a major influence on plastic deformation. With further reduction of the grain sizes (d <20 nm) the main mechanism of deformation is intergranular slippage. because in grains of this size are quite large image stresses that do not allow large dislocation clusters. In small grains the image forces are quite large to prevent large dislocation pile-ups formation, but the mass and volume of grain are quite small to turn or slip its under the action of external stresses. In accordance with these mechanisms, on the calculated dependence of the physical yield strength vs grain size, there are three areas with different angles of inclination in logarithmic coordinates. Keywords: yield point, grain size, Hall―Petch low.

Localized Plastic Flow Autowaves and the Hall-Petch Relation for Al

2013 ◽  
Vol 592-593 ◽  
pp. 271-274
Author(s):  
Lev B. Zuev ◽  
Natalya Zarikovskaya
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Flow Stress ◽  
Plastic Flow ◽  
Flow Patterns ◽  
Localized Deformation ◽  
Polycrystalline Aluminum ◽  
Petch Relation ◽  
Grain Sizes ◽  
Localization Of Plastic Deformation

The localization of plastic deformation was examined for polycrystalline aluminum samples having grain sizes in the range from 8·10-3to 10 mm. It is found that the length of localized deformation autowaves is determined by the grain size of material. The localized plastic flow patterns emergent in the polycrystalline aluminum samples are found to be connected to the Hall-Petch relation. Two types of flow stress dependencies of grain size are distinguished.

The Processing of Ultrafine-Grained Materials Using High-Pressure Torsion

2007 ◽  
Vol 558-559 ◽  
pp. 1283-1294 ◽  
Author(s):  
Cheng Xu ◽  
Z. Horita ◽  
Terence G. Langdon
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
High Pressure ◽  
High Pressure Torsion ◽  
Metallic Materials ◽  
Grain Sizes ◽  
Ultrafine Grained ◽  
Wide Range ◽  
Ultrafine Grained Materials ◽  
Thin Disks

It is now well-established that processing through the application of severe plastic deformation (SPD) leads to a significant reduction in the grain size of a wide range of metallic materials. This paper examines the fabrication of ultrafine-grained materials using high-pressure torsion (HPT) where this process is attractive because it leads to exceptional grain refinement with grain sizes that often lie in the nanometer or submicrometer ranges. Two aspects of HPT are examined. First, processing by HPT is usually confined to samples in the form of very thin disks but recent experiments demonstrate the potential for extending HPT also to bulk samples. Second, since the strains imposed in HPT vary with the distance from the center of the disk, it is important to examine the development of inhomogeneities in disk samples processed by HPT.

Paradox of Strength and Ductility in Metals Processed Bysevere Plastic Deformation

2002 ◽  
Vol 17 (1) ◽  
pp. 5-8 ◽  
Author(s):  
R. Z. Valiev ◽  
I. V. Alexandrov ◽  
Y. T. Zhu ◽  
T. C. Lowe
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Grain Size ◽  
Yield Strength ◽  
Mechanical Behavior ◽  
High Strength ◽  
High Ductility ◽  
Elongation To Failure ◽  
Failure Ductility ◽  
Strength And Ductility

It is well known that plastic deformation induced by conventional forming methodssuch as rolling, drawing or extrusion can significantly increase the strength of metalsHowever, this increase is usually accompanied by a loss of ductility. For example, Fig.1 shows that with increasing plastic deformation, the yield strength of Cu and Almonotonically increases while their elongation to failure (ductility) decreases. Thesame trend is also true for other metals and alloys. Here we report an extraordinarycombination of high strength and high ductility produced in metals subject to severeplastic deformation (SPD). We believe that this unusual mechanical behavior is causedby the unique nanostructures generated by SPD processing. The combination ofultrafine grain size and high-density dislocations appears to enable deformation by newmechanisms. This work demonstrates the possibility of tailoring the microstructures ofmetals and alloys by SPD to obtain both high strength and high ductility. Materialswith such desirable mechanical properties are very attractive for advanced structuralapplications.

scholarly journals Tensile Strength and Creep Resistance in Nanocrystalline Cu, Pd and Ag

1990 ◽  
Vol 206 ◽  
Author(s):  
G. W. Nieman ◽  
J. R. Weertman ◽  
R. W. Siegel
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Tensile Strength ◽  
Yield Strength ◽  
Creep Resistance ◽  
Room Temperature ◽  
True Strain ◽  
Constant Load ◽  
Creep Tests ◽  
Grain Sizes

ABSTRACTMeasurements of tensile strength and creep resistance have been made on bulk samples of nanocrystalline Cu, Pd and Ag consolidated from powders by cold compaction. Samples of Cu-Cu2O have also been tested. Yield strength for samples with mean grain sizes of 5–80 nm and bulk densities on the order of 95% of theoretical density are increased 2–5 times over that measured in pure, annealed samples of the same composition with micrometer grain sizes. Ductility in the nanocrystalline Cu has exceeded 6% true strain, however, nanocrystalline Pd samples were much less ductile. Constant load creep tests performed at room temperature at stresses of >100 MPa indicate logarithmic creep. The mechanical properties results are interpreted to be due to grain size-related strengthening and processing flaw-related weakening.

Plastic deformation mechanisms in nanocrystalline metallic materials

2013 ◽  
Vol 22 (3-4) ◽  
pp. 81-88 ◽  
Author(s):  
Ilya A. Ovid’ko
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Grain Boundaries ◽  
Computer Simulations ◽  
Theoretical Models ◽  
Deformation Mechanisms ◽  
Dislocation Slip ◽  
Metallic Materials ◽  
Metallic Structures ◽  
Mechanisms Of Plastic Deformation

AbstractThis article discusses the experiments, computer simulations, and theoretical models addressing the conventional and specific mechanisms of plastic deformation in nanocrystalline metallic materials. Particular attention is devoted to the competition between lattice dislocation slip and specific deformation mechanisms mediated by grain boundaries as well as its sensitivity to grain size and other parameters of nanocrystalline metallic structures.

scholarly journals STUDI PENGARUH UKURAN BUTIR BATUBARA DAN TINGKAT KEPADATAN BATUBARA TERHADAP POTENSI PEMBAKARAN SPONTAN PADA SKALA LABORATORIUM Study of the Effect of Coal Grain Size and Coal Compaction to the Spontaneous Combustion Potential at Laboratory Scale

2020 ◽  
Vol 2 (1) ◽  
pp. 43-50
Author(s):  
Nuhindro P Widodo
Keyword(s):  
Grain Size ◽  
Spontaneous Combustion ◽  
Compaction Pressure ◽  
Test Tube ◽  
Underground Mines ◽  
Major Influence ◽  
Grain Sizes ◽  
Ground Pressure ◽  
Gas Explosions ◽  
To Come

ABSTRAKPembakaran spontan batubara dapat menjadi masalah yang serius terutama bagi kegiatan penambangan karena dapat menyebabkan terjadinya kebakaran pada penimbunan batubara atau ledakan gas metana pada tambang bawah tanah batubara. Penelitian kali ini akan dititikberatkan pada pengaruh ukuran butir batubara dan tingkat kepadatan batubara terhadap perilaku pembakaran spontan batubara. Ukuran butir yang digunakan dengan penelitian ini adalah -10+14 mesh, -60+80 mesh dan -170+200 mesh dengan tingkat kepadatan 0 kPa dan 50 kPa. Ukuran butir ini dipilih untuk mewakili kondisi ukuran butir relatif besar hingga kecil pada penimbunan batubara, sedangkan tingkat kepadatan diasumsikan berasal dari ground pressure dozer sebesar 50 kPa. Dalam penelitian kali ini, digunakan metode oksidasi adiabatik dengan mengalirkan gas oksigen dengan debit 0,05 L/menit pada tabung uji. Selain itu, dilakukan pula pengujian difusi oksigen untuk menentukan laju kenaikan konsentrasi oksigen pada masing-masing parameter. Ukuran butir dan tingkat kepadatan butiran batubara memiliki pengaruh besar terhadap terjadinya pembakaran spontan batubara. Semakin kecil ukuran percontoh maka nilai R70 semakin besar. Adanya pemadatan memiliki pengaruh yang berbeda terhadap nilai R70 pada ukuran butir yang berbeda. ABSTRACTSpontaneous combustion of coal can be a serious problem especially for mining activities because it can cause fires in coal stockpiling or methane gas explosions in coal underground mines. This research will focus on the influence of coal grain size and coal compaction on the spontaneous combustion behavior of coal. The grain sizes used in this study are -10 + 14 mesh, -60 + 80 mesh and -170 + 200 mesh with a compaction pressure of 0 kPa and 50 kPa. This grain size was chosen to represent the condition from large to small grain size in coal stockpile, while the compaction level is assumed to come from the dozer ground pressure of 50 kPa. In this study, an adiabatic oxidation method was used by flowing oxygen gas with a discharge of 0.05 L / min in the test tube. In addition, an oxygen diffusion test was also carried out to determine the rate of oxygen concentration increase for each parameter. Grain size and compaction level of coal grains have a major influence on the spontaneous combustion of coal. The smaller the sample size, the greater the R70 value. The presence of compaction has a different effect on the value of R70 at different grain sizes.

scholarly journals Nucleation and development of plasticity in nanocrystalline BCC iron under shear loading

2020 ◽  
pp. 17-22
Author(s):  
K.P. Zolnikov ◽  
◽  
D.S. Kryzhevich ◽  
A.V. Korchuganov ◽  
◽  
...  
Keyword(s):  
Plastic Deformation ◽  
Shear Loading ◽  
Main Role ◽  
Structural Rearrangements ◽  
Second Stage ◽  
Grain Sizes ◽  
Bcc Lattice ◽  
Bcc Iron ◽  
Nanocrystalline Iron ◽  
Mechanisms Of Plastic Deformation

The features of the nucleation and development of plasticity in nanocrystalline iron with BCC lattice under shear were studied. The mechanisms of plastic deformation playing the main role in the development of structural rearrangements during loading were revealed. It was shown that the development of plasticity can be conditionally divided into several stages. The first stage of plasticity development is associated with the formation and propagation of dislocations and twins. At the second stage, intraganular slip and intergranular sliding begin to make the main contribution to plastic deformation. These processes initiate a change in the shape of the grains. At large shear, the deformation behavior of the sample is governed by the migration of the interfaces. Not only grain boundaries migrate but also twin ones do. As a result of migration processes, the grain sizes of the nanocrystalline sample are enlarged.

scholarly journals Molecular Dynamics as a Means to Investigate Grain Size and Strain Rate Effect on Plastic Deformation of 316 L Nanocrystalline Stainless-Steel

Materials ◽  
2020 ◽  
Vol 13 (14) ◽  
pp. 3223 ◽  
Author(s):  
Abdelrahim Husain ◽  
Peiqing La ◽  
Yue Hongzheng ◽  
Sheng Jie
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Stainless Steel ◽  
Grain Boundary ◽  
Strain Rate ◽  
Deformation Mechanism ◽  
Grain Boundary Sliding ◽  
Plastic Deformation Mechanism ◽  
Grain Sizes ◽  
Critical Grain Size

In the present study, molecular dynamics simulations were employed to investigate the effect of strain rate on the plastic deformation mechanism of nanocrystalline 316 L stainless-steel, wherein there was an average grain of 2.5–11.5 nm at room temperature. The results showed that the critical grain size was 7.7 nm. Below critical grain size, grain boundary activation was dominant (i.e., grain boundary sliding and grain rotation). Above critical grain size, dislocation activities were dominant. There was a slight effect that occurred during the plastic deformation mechanism transition from dislocation-based plasticity to grain boundaries, as a result of the stress rate on larger grain sizes. There was also a greater sensitive on the strain rate for smaller grain sizes than the larger grain sizes. We chose samples of 316 L nanocrystalline stainless-steel with mean grain sizes of 2.5, 4.1, and 9.9 nm. The values of strain rate sensitivity were 0.19, 0.22, and 0.14, respectively. These values indicated that small grain sizes in the plastic deformation mechanism, such as grain boundary sliding and grain boundary rotation, were sensitive to strain rates bigger than those of the larger grain sizes. We found that the stacking fault was formed by partial dislocation in all samples. These stacking faults were obstacles to partial dislocation emission in more sensitive stress rates. Additionally, the results showed that mechanical properties such as yield stress and flow stress increased by increasing the strain rate.

Grain Refinement of Vanadium by Low Temperature Severe Plastic Deformation

2010 ◽  
Vol 638-642 ◽  
pp. 1934-1939 ◽  
Author(s):  
Y.B. Chun ◽  
S.H. Ahn ◽  
D.H. Shin ◽  
S.K. Hwang
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Low Temperature ◽  
Yield Strength ◽  
Severe Plastic Deformation ◽  
Equal Channel Angular Pressing ◽  
Tensile Elongation ◽  
Lamellar Microstructure ◽  
Lamellar Thickness ◽  
Angular Pressing

Recent advances in the severe plastic deformation technique have shown that effective refinement of the microstructure can be achieved in pure metals as well as in alloys. Among the various methods of severe plastic deformation, equal channel angular pressing has been the subject of numerous research works. Since the grain refining effect of this technique appears to reach a peak at a level of approximately 200 nm further microstructural changes are sought—deformation at a cryogenic temperature being one of the candidate routes. In the present study, we opted to combine equal channel angular pressing and low temperature plastic deformation to refine the microstructure of commercially pure V. The starting microstructure consisted of equiaxed grains with an average size of 100 micrometers. This microstructure was refined to a 200 nm thick lamellar microstructure by 8 passes of equal channel angular pressing at 350°C. The lamellar thickness was further reduced to 140 nm upon subsequent cryogenic rolling, which resulted in room temperature yield strength of 768 MPa. In the specimens, recrystallization annealed at 850°C, the grain size reached 1000 nm or larger, and the yield strength obeyed the Hall-Petch relationship with that grain size. The tensile elongation value, which was low and insensitive to the grain size in the as-deformed state, increased significantly up to 43% with the recrystallization annealing.

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