Plastic deformation in impure nanocrystalline ceramics

1999 ◽  
Vol 14 (6) ◽  
pp. 2508-2517 ◽  
Author(s):  
Rachman Chaim
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Strain Rate ◽  
Tetragonal Zirconia ◽  
Grain Boundary Sliding ◽  
Critical Conditions ◽  
Published Data ◽  
Nanocrystalline Ceramics ◽  
Threshold Strain ◽  
Plastic Deformation Behavior

Plastic deformation behavior of impure nanocrystalline ceramics (NCC) was modeled using the percolative composite model in conjunction with models for plastic deformation by grain boundary sliding. The “glass transition temperature” concept was used to determine the threshold strain rate criterion below which the impure nanocrystalline ceramic would deform plastically. Threshold strain rate is stress independent. It increases with the temperature increase and with the grain size decrease. Using the dissolution-precipitation model, dependence of the strain rate on temperature, stress, and grain size in the nanometer regime for impure NCCs was calculated. As an example, the critical conditions for plasticity in impure yttria-tetragonal zirconia polycrystals (Y-TZP) were evaluated. At 600 °C, strain rates as high as 10−4 s−1 were expected in 10 nm impure Y-TZP. Comparison of the published data extrapolated into the nanometer range to the calculated threshold level showed that increase in the applied stress is associated with increase in the grain size and strain rate onsets for plastic deformation.

Effect of Grain Size on Deformation Twinning Behavior of Ti6Al4V Alloy

2015 ◽  
Vol 830-831 ◽  
pp. 337-340
Author(s):  
Ashish Kumar Saxena ◽  
Manikanta Anupoju ◽  
Asim Tewari ◽  
Prita Pant
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Strain Rate ◽  
Deformation Behavior ◽  
Deformation Behaviour ◽  
Air Cooling ◽  
Specific Strength ◽  
Aerospace Applications ◽  
Β Phase ◽  
Plastic Deformation Behavior

An understanding of the plastic deformation behavior of Ti6Al4V (Ti64) is of great interest because it is used in aerospace applications due to its high specific strength. In addition, Ti alloys have limited slip systems due to hexagonal crystal structure; hence twinning plays an important role in plastic deformation. The present work focuses upon the grain size effect on plastic deformation behaviour of Ti64. Various microstructures with different grain size were developed via annealing of Ti64 alloy in α-β phase regime (825°C and 850°C) for 4 hours followed by air cooling. The deformation behavior of these samples was investigated at various deformation temperature and strain rate conditions. Detailed microstructure studies showed that (i) smaller grains undergoes twinning only at low temperature and high strain rate, (ii) large grain samples undergo twinning at all temperatures & strain rates, though the extent of twinning varied.

The Grain Size and Porosity Dependent Constitutive Modeling for Nanocrystalline Ceramics with Small Plastic Deformation

2007 ◽  
Vol 353-358 ◽  
pp. 50-53
Author(s):  
Jian Qui Zhou ◽  
Yuan Ling Li
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Published Data ◽  
Nanocrystalline Ceramics ◽  
Small Plastic ◽  
Consistent Method ◽  
Different Grain Size ◽  
Multi Phase ◽  
Small Plastic Deformation ◽  
Good Agreement

In order to understand the grain size and porosity dependent mechanical behavior of porous, multi-phase nanocrystalline ceramics, each phase is treated as a mixture of grain interior and grain boundary, and pores are taken as a single phase. In conjunction with the secant-modulus approach and iso-strain assumption, Budiansky’s self-consistent method is extended to build a constitutive model for nanocrystalline ceramics with small plastic deformation. Based on the developed model, the predicted yield strength (σ0.2) values of porous, multi-phase nanocrystalline ceramics with different grain size and porosity are compared with experimental data in the literature, the comparison shows that the predictions are in good agreement with the published data. This suggests that the developed model is capable of describing the grain size and porosity dependent mechanical behaviors of nanocrystalline ceramics with small plastic deformation.

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.

Microstructural Design for Attaining High-Strain-Rate Superplasticity in Oxide Materials

2006 ◽  
Vol 45 ◽  
pp. 923-932
Author(s):  
Keijiro Hiraga ◽  
Byung Nam Kim ◽  
Koji Morita ◽  
Tohru Suzuki ◽  
Yoshio Sakka
Keyword(s):  
Grain Size ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Spinel Phase ◽  
Tetragonal Zirconia ◽  
Secondary Phases ◽  
Cavitation Damage ◽  
Size Refinement ◽  
Dynamic Grain Growth

Factors limiting the strain rate of superplastic deformation in oxide ceramics are discussed from existing knowledge about the mechanisms of high-temperature plastic deformation and intergranular cavitation. The discussion leads to the following guide: simultaneously controlling the initial grain size, diffusivity, dynamic grain growth, homogeneity of microstructure and the number of residual defects is essential to attain high-strain-rate superplasticity. Along this guide, high-strain-rate superplasticity (HSRS) is attainable in some oxides consisting of tetragonal zirconia, α-alumina and a spinel phase: tensile ductility reached 300-2500% at a strain rate of 0.01-1.0 s-1. Post-deformation microstructure indicates that some secondary phases may suppress cavitation damage and thereby enhance HSRS. The guide is also essential to lower the limit of deformation temperature for a given strain rate. In monolithic tetragonal zirconia, grain-size refinement combined with doping of aliovalnt cations such as Mg2+, Ti4+ and Al3+ led to HSRS at 1350 °C.

Effect of Precipitates on Plastic Deformation Behavior of High Entropy Alloy Al0.3CoCrFeNi Under High Strain Rate Loading

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Prasanta K. Das ◽  
Vishal Kumar ◽  
Prasenjit Khanikar
Keyword(s):  
Plastic Deformation ◽  
High Strain Rate ◽  
Strain Rate ◽  
High Strain ◽  
Microstructural Analysis ◽  
Dynamics Simulation ◽  
High Entropy Alloy ◽  
High Entropy ◽  
Plastic Deformation Behavior ◽  
Strain Rate Loading

Abstract High entropy alloys (HEAs) are primarily known for their high strength and high thermal stability. These alloys have recently been studied for high strain rate applications as well. HEAs have been observed to exhibit different properties when subjected to different strain rates. Very few published results on HEAs are available for high strain rate loading conditions. In addition, modeling and simulation work of microstructural details, such as grain boundary and precipitates of HEAs have not yet been investigated. However, at an atomistic length scale, molecular dynamics simulation works of HEAs have already been published. In this study, a detailed microstructural analysis of plastic deformation of the material under high strain rate loading has been performed using dislocation density based crystal plasticity finite element modeling. The primary objective is, therefore, to assess the strengthening effects due to precipitates on a particular high entropy alloy Al0.3CoCrFeNi with ultrafine grains having randomly distributed NiAl precipitates.

Features of Work Hardening of Polycrystals with Nanograins

2008 ◽  
Vol 584-586 ◽  
pp. 35-40 ◽  
Author(s):  
Eduard Kozlov ◽  
Nina Koneva ◽  
L.I. Trishkina ◽  
A.N. Zhdanov ◽  
M.V. Fedorischeva
Keyword(s):  
Plastic Deformation ◽  
Grain Size ◽  
Work Hardening ◽  
Mechanical Characteristics ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Dislocation Slip ◽  
Grain Sizes ◽  
Boundary Sliding ◽  
Size Interval

The present work is devoted to the investigation of the influence of the grain size on the main mechanical characteristics of nanopolycrystals of different metals. The Hall-Petch parameter behaviour for Al, Cu, Ni, Ti and Fe was examined in the wide grain size interval. The stages of plastic deformation and the parameters of work hardening for nanocrystalline copper were analysed in detail. The deformation mechanisms and critical grain sizes accounting for the transition from the dislocation slip to the grain boundary sliding were described.

Superplasticity in Nanocrystalline Ni3Al and Ti Alloys

2000 ◽  
Vol 634 ◽  
Author(s):  
Sam X. Mcfadden ◽  
Alla V. Sergueeva ◽  
Tomas Kruml ◽  
Jean-Luc Martin ◽  
Amiya K. Mukherjee
Keyword(s):  
Grain Size ◽  
Strain Rate ◽  
Strain Hardening ◽  
Nanocrystalline Materials ◽  
Tensile Elongation ◽  
Constant Strain Rate ◽  
Grain Boundary Sliding ◽  
Simple Extension ◽  
Size Dependent ◽  
Enhanced Properties

ABSTRACTThe advent of nanocrystalline materials has provided new opportunities to explore grain size dependent phenomenon. Superplasticity is such a grain size dependent phenomenon defined by the ability to attain tensile elongation of 200% or more. Superplasticity in microcrystalline materials has been well characterized. The constitutive equations that describe microcrystalline superplasticity predict enhanced properties for nanocrystalline materials. Enhanced properties in such nanocrystalline material include lower superplastic temperature at constant strain rate, higher superplastic strain rate at constant temperature, and lower flow stresses. Investigations with nanocrystalline Ni3Al and ultra-fine grained Ti-6Al-4V alloy have shown a reduction in the superplastic temperature. However, the flow stresses in these materials are significantly higher than expected. The high flow stresses are accompanied by strong strain hardening.Transmission electron microscopy in situ straining of nanocrystalline Ni3Al has shown that grain boundary sliding and grain rotation occurred during straining. The sliding and rotation decreased with strain. Dislocation activity was observed but was not extensive. There was no observable dislocation storage. The parameters of the generalized constitutive equation for superplasticity for nanocrystalline Ni3Al and Ti-6Al-4V are in reasonable agreement with the parameters for microcrystalline material. The rate parameters suggest that nanocrystalline superplasticity shares common features with microcrystalline superplasticity. In contrast, the observed flow stresses and strong strain hardening indicate that nanocrystalline superplasticity is not a simple extension of microcrystalline behavior scaled to finer grain size.

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