scholarly journals Strengthening versus Softening of Nanotwinned Copper Depending on Prestress and Twin Spacing

Metals ◽  
2018 ◽  
Vol 8 (5) ◽  
pp. 344 ◽  
Author(s):  
Jing Han ◽  
Jiapeng Sun ◽  
Ying Han ◽  
Hua Zhu ◽  
Liang Fang
Keyword(s):  
Twin Spacing

scholarly journals Multi-Objective Optimization of a Wrought Magnesium Alloy for High Strength and Ductility

2012 ◽  
Vol 1524 ◽  
Author(s):  
B. Radhakrishnan ◽  
S.B. Gorti ◽  
R.M. Patton ◽  
S. Simunovic
Keyword(s):  
Magnesium Alloy ◽  
Optimization Technique ◽  
Development Program ◽  
Dislocation Slip ◽  
Initial Population ◽  
Slip Systems ◽  
Oak Ridge ◽  
Wrought Magnesium Alloy ◽  
Twin Spacing ◽  
Strength And Ductility

ABSTRACTAn optimization technique is coupled with crystal plasticity based finite element (CPFE) computations to aid the microstructural design of a wrought magnesium alloy for improved strength and ductility. The initial microstructure consists of a collection of sub-micron sized grains containing deformation twins. The variables used in the simulations are crystallographic texture, and twin spacing within the grains. It is assumed that plastic deformation occurs mainly by dislocation slip on two sets of slip systems classified as hard and soft modes. The hard modes are those slip systems that are inclined to the twin planes and the soft mode consists of dislocation glide along the twin plane. The CPFE code calculates the stress-strain response of the microstructure as a function of the microstructural parameters and the length-scale of the features. A failure criterion based on a critical shear strain and a critical hydrostatic stress is used to define ductility. The optimization is based on the sequential generation of an initial population defined by the texture and twin spacing variables. The CPFE code and the optimizer are coupled in parallel so that new generations are created and analyzed dynamically. In each successive generation, microstructures that satisfy at least 90% of the mean strength and mean ductility in the current generation are retained. Multiple generation runs based on the above procedure are carried out in order to obtain maximum strength-ductility combinations. The implications of the computations for the design of a wrought magnesium alloy are discussed. Research sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy.

scholarly journals Nanoscale Twinned Ti-44Al-4Nb-1.5Mo-0.007Y Alloy Promoted by High Temperature Compression with High Strain Rate

Metals ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 619 ◽  
Author(s):  
Wenqi Guo ◽  
Haitao Jiang ◽  
Shiwei Tian ◽  
Guihua Zhang
Keyword(s):  
Strain Rate ◽  
High Strain ◽  
Aerospace Industry ◽  
Dynamic Strength ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Tial Alloys ◽  
Partial Dislocations ◽  
Dynamic Mechanical Behavior ◽  
Twin Spacing

In order to investigate the dynamic mechanical behavior of TiAl alloys and promote their application in the aerospace industry, uniaxial compression of Ti-44Al-4Nb-1.5Mo-0.007Y (at %) alloy was conducted at a temperature range from 25 to 400 °C with a strain rate of 2000 s‒1. Twinning is found to be the dominating deformation mechanism of the γ phase at all temperatures, and the addition of Nb and Mo has a chemical impact on the alloy and reduces the stacking fault energy of the γ phase. The decreased stacking fault energy increases the twinnability; thus, the deformation is dominated by twinning, which increases the dynamic strength of the alloy. With the temperature increasing from 25 to 400 °C, the average spacing of twins in the γ phase increases from 32.4 ± 2.9 to 88.1 ± 9.2 nm. The increased temperature impedes the continuous movement of partial dislocations and finally results in an increased twin spacing in the γ phase.

Effect of twin spacing on the growth velocity of Si faceted dendrites

2010 ◽  
Vol 97 (17) ◽  
pp. 172104 ◽  
Author(s):  
Xinbo Yang ◽  
Kozo Fujiwara ◽  
Raira Gotoh ◽  
Kensaku Maeda ◽  
Jun Nozawa ◽  
...  
Keyword(s):  
Growth Velocity ◽  
Twin Spacing

A Constitutive Description of the Yield Strength and Strain Hardening Behaviors of Nano-Twinned Metals

2013 ◽  
Vol 535-536 ◽  
pp. 109-112
Author(s):  
Chong Yang Gao ◽  
W.R. Lu
Keyword(s):  
Experimental Data ◽  
Yield Strength ◽  
Size Effects ◽  
True Stress ◽  
Stress Strain ◽  
Fine Grain ◽  
Tension Tests ◽  
Stress Strain Relation ◽  
Twin Spacing ◽  
Meso Scale

In this paper, a constitutive description of the true stress-strain behaviors of nano-twinned metals has been proposed. The size effects of nano-scale twin boundaries (TBs) and ultra-fine grain boundaries (GBs) are considered in the athermal stress. The evolution of the dislocation density with strain under the influence of strain rate and temperature is introduced in the thermal stress based on our previous meso-scale constitutive model. The new model can effectively describe the strength transition regime in nano-twinned metals. The proposed model’s predictions of true stress-strain relation curves for nano-twinned copper are compared with the experimental results of uniaxial tension tests for validation. The comparisons show that the previous models in literature for the dependence of initial yield strength on twin spacing cannot describe the experimental data correctly when the twin spacing tends to zero; however, the phenomenological model proposed in this paper for the twin spacing depending relation is theoretically rational and can well describe the experimental data in the whole range of twin spacing.

Estimation of twin wall energy by measurement of twin spacing

1990 ◽  
Vol 124 (2) ◽  
pp. L19-L21 ◽  
Author(s):  
L.S. Chumbley ◽  
M.J. Kramer ◽  
M.R. Kim ◽  
F.C. Laabs
Keyword(s):  
Twin Spacing

Nano-Grained Structure Induced by Mechanical Twinning during Multi-Directional Forging and the Mechanical Properties

2009 ◽  
Vol 633-634 ◽  
pp. 577-593 ◽  
Author(s):  
Hiromi Miura ◽  
Y. Nakao
Keyword(s):  
Mechanical Properties ◽  
Fracture Strain ◽  
Mechanical Twinning ◽  
Average Grain Size ◽  
Cumulative Strain ◽  
Grain Fragmentation ◽  
Mechanical Twins ◽  
Twin Spacing ◽  
Lamellar Twin ◽  
Strength And Ductility

A bulky SUS316 austenitic stainless steel (SUS316) was multi-directionally forged (MDFed) at 77 K and 300 K up to a cumulative strain of = 6 at maximum. With increasing cumulative strain, the grains were subdivided by mechanical twinning and martensitic transformation. Especially, mechanical twins accelerated grain fragmentation by subdivision of the initial grains and by intersection of the previously formed twins during MDF. The intersection of twins caused finally evolution of packet grains, which were composed of lamellar structured twins. The packet size and the lamellar twin spacing decreased down to 35 nm and 15 nm by MDF to  = 6 at 77 K. The average grain size achieved was estimated to be about 10 nm. Twinning appeared more frequently and uniformly at 77 K than at 300 K. Tensile test at 300 K revealed ultimate tensile strength of 2.1 GPa and fracture strain of about 0.2. The fracture strain, however, appeared to be constant over ∑Δε = 2.4 independent of cumulative strain. The observed excellent balance of strength and ductility of the nano-grained SUS316 is discussed in relation with the effects of twins on grain fragmentation and mechanical properties.

Sign in / Sign up

Export Citation Format

Share Document