Superplasticity of Mg-Zn-Y Alloy Prepared by Extrusion of Machined Chip

2012 ◽  
Vol 735 ◽  
pp. 259-264
Author(s):  
Takaomi Itoi ◽  
Syuichi Fudetani ◽  
Mitsuji Hirohashi
Keyword(s):  
Grain Size ◽  
Hot Extrusion ◽  
Initial Strain Rate ◽  
Grain Boundary Sliding ◽  
Initial Strain ◽  
Strain Rates ◽  
Long Period ◽  
Dominant Deformation Mechanism ◽  
Mean Grain Size ◽  
Boundary Sliding

Mg96Zn2Y2 (at.%) extruded alloy was fabricated by hot-extrusion of the Mg96Zn2Y2 machined chip. The Mg96Zn2Y2 extruded alloy consisted of a long period stacking ordered (LPSO)-, Mg3Zn3Y2- and Mg- phases. The Mg phase with mean grain size of 450 nm was confirmed by TEM. However, the LPSO- and Mg3Zn3Y2- phases had relatively large grain size compared with Mg phase. The Mg96Zn2Y2 extruded alloy also showed superplasticity at temperatures of 623 K and 723 K with initial strain rates from 2×10−1 s−1 to 2×10−3 s−1. The maximum elongation of 450 % was achieved at 723 K with an initial strain rate of 2×10−3 s−1. From TEM observation, it is considered that grain boundary sliding of Mg grains was dominant deformation mechanism of the Mg96Zn2Y2 extruded alloy at high temperature range.

Effect of Temperature on the Superplasticity of AZ81 Magnesium Alloy Processed by Hot Extrusion

2005 ◽  
Vol 488-489 ◽  
pp. 585-588
Author(s):  
Li Lin ◽  
Li Jia Chen ◽  
Zhen Liu
Keyword(s):  
Magnesium Alloy ◽  
Grain Boundary ◽  
Strain Rate ◽  
True Strain ◽  
Hot Extrusion ◽  
Initial Strain Rate ◽  
Grain Boundary Sliding ◽  
Initial Strain ◽  
Effect Of Temperature ◽  
Temperature Range

An AZ81 magnesium alloy, which was processed by hot extrusion in advance, was tested in the temperature range of 473 ~ 623 K and at various initial strain rates, ranging from 1×10-1 to 1×10-4 s-1. True stress-true strain curves under various temperatures and activation energy within different temperature range were investigated for the analysis of effect of temperature on superplastic behaviors. Elongation of the as-extruded AZ81 alloy increased with temperature when tested at the same initial strain rate. Elongation values, obtained at the same initial strain rate of 1×10-3 s-1, were 94% at 473K and 446% at 623K, respectively. Deformation mechanisms varied with increasing temperature, from the grain boundary sliding (GBS) accommodated by grain boundary diffusion to the GBS accommodated by lattice diffusion, transition temperature was 573 K.

Superplasticity of a Ti-48Al-2.3Cr-0.2Mo Alloy

2012 ◽  
Vol 531-532 ◽  
pp. 27-31
Author(s):  
Jun Hong Zhang ◽  
Guo Hui Xu ◽  
Ya Juan Xu ◽  
Yue Hui He
Keyword(s):  
Grain Size ◽  
Superplastic Deformation ◽  
True Strain ◽  
Grain Boundary Sliding ◽  
True Stress ◽  
Dislocation Slip ◽  
Strain Rates ◽  
Maximum Elongation ◽  
Tem Microstructure ◽  
Boundary Sliding

Superplastic behaviors of a Ti-48Al-2.3Cr-0.2Mo alloy with the initial grain size of 0.6m, resulting from 3-steps forging, have been investigated at temperatures ranging from 950°C to 1100°C and at strain rates ranging from 810-5 s-1 to 210-4s-1. The elongations above 500% were obtained at 1050°C-1100°C. An maximum elongation of 566% was obtained at 1050°Cand at a strain rate of 810-5s-1. The flow softening and continuous strain hardening were observed in the curves of true stress-true strain, it is suggested dynamic recrystallization and high-density dislocation caused by pre-deformation are the reasons. By OA, TEM, microstructure evolutions during the deformation were observed. It is found that after superplastic deformation, the grain size become smaller, and the distribution of grain size become more uniform, the densities of dislocations become lower and the dislocations mainly distributed in the areas near grain triple junction. Grain boundary sliding accommodated by dislocation slip is the predominant deformation mechanism.

scholarly journals Is Superplasticity in the Future of Nanophase Materials?

1990 ◽  
Vol 196 ◽  
Author(s):  
R. W. Siegel
Keyword(s):  
Mechanical Properties ◽  
Grain Size ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Atomic Clusters ◽  
Diffusional Creep ◽  
Ultrafine Grain ◽  
Grain Sizes ◽  
Nanophase Materials ◽  
Boundary Sliding

ABSTRACTThe ultrafine grain sizes and high diffusivities in nanophase materials assembled from atomic clusters suggest that these materials may have a strong tendency toward superplastic mechanical behavior. Both small grain size and enhanced diffusivity can be expected to lead to increased diffusional creep rates as well as to a significantly greater propensity for grain boundary sliding. Recent mechanical properties measurements at room temperature on nanophase Cu, Pd, and TiO2, however, give no indications of superplasticity. Nonetheless, significant ductility has been clearly demonstrated in these studies of both nanophase ceramics and metals. The synthesis of cluster-assembled nanophase materials is described and the salient features of what is known of their structure and mechanical properties is reviewed. Finally, the answer to the question posed in the title is addressed.

scholarly journals The role of grain size evolution in the rheology of ice: implications for reconciling laboratory creep data and the Glen flow law

2021 ◽  
Vol 15 (9) ◽  
pp. 4589-4605
Author(s):  
Mark D. Behn ◽  
David L. Goldsby ◽  
Greg Hirth
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Stress Exponent ◽  
Ice Sheets ◽  
Grain Boundary Sliding ◽  
Dislocation Creep ◽  
Ice Flow ◽  
Size Evolution ◽  
Boundary Sliding ◽  
Flow Law

Abstract. Viscous flow in ice is often described by the Glen flow law – a non-Newtonian, power-law relationship between stress and strain rate with a stress exponent n ∼ 3. The Glen law is attributed to grain-size-insensitive dislocation creep; however, laboratory and field studies demonstrate that deformation in ice can be strongly dependent on grain size. This has led to the hypothesis that at sufficiently low stresses, ice flow is controlled by grain boundary sliding, which explicitly incorporates the grain size dependence of ice rheology. Experimental studies find that neither dislocation creep (n ∼ 4) nor grain boundary sliding (n ∼ 1.8) have stress exponents that match the value of n ∼ 3 in the Glen law. Thus, although the Glen law provides an approximate description of ice flow in glaciers and ice sheets, its functional form is not explained by a single deformation mechanism. Here we seek to understand the origin of the n ∼ 3 dependence of the Glen law by using the “wattmeter” to model grain size evolution in ice. The wattmeter posits that grain size is controlled by a balance between the mechanical work required for grain growth and dynamic grain size reduction. Using the wattmeter, we calculate grain size evolution in two end-member cases: (1) a 1-D shear zone and (2) as a function of depth within an ice sheet. Calculated grain sizes match both laboratory data and ice core observations for the interior of ice sheets. Finally, we show that variations in grain size with deformation conditions result in an effective stress exponent intermediate between grain boundary sliding and dislocation creep, which is consistent with a value of n = 3 ± 0.5 over the range of strain rates found in most natural systems.

Superplastic Behaviour of AA5083 Aluminium Alloy with Scandium and Zirconium

2012 ◽  
Vol 706-709 ◽  
pp. 395-401 ◽  
Author(s):  
A. Smolej ◽  
B. Skaza ◽  
B. Markoli ◽  
Damjan Klobčar ◽  
V. Dragojević ◽  
...  
Keyword(s):  
Cold Rolling ◽  
Strain Rate ◽  
Aluminium Alloy ◽  
Wide Temperature Range ◽  
Initial Strain Rate ◽  
Initial Strain ◽  
Strain Rates ◽  
Superplastic Behaviour ◽  
Hot And Cold Rolling ◽  
Superplastic Properties

The aim of the present investigation was to determine and to compare the superplastic behaviour of the AA5083 (Al-Mg-Mn) alloy with Sc and Zr additions. The investigated alloys were processed to form sheets by conventional hot and cold rolling. The superplastic properties were determined with strain rates in the range of 1x10-4to 5x10-2s-1and forming temperatures of 350 to 550°C. The results showed that the alloy with about 0.4% Sc exhibited a high superplastic ductility across a wide temperature range and strain rates up to 1x10-2s-1. The highest elongations to failure of about 2000% were attained at 550°C and at an initial strain rate of 5x10-3s-1. However, the alloy with about 0.15% Zr exhibited elongations up to 600%. The FSP processed Al-4.5Mg alloy with combined addition of about 0.2% Sc and 0.15% Zr exhibited good superplastic properties at higher strain rates (> 1x10-2s-1) with elongations up to 1500%.

Superplasticity of Aerospace 7075 (Al-Zn-Mg-Cu) Aluminium Alloy Obtained by Severe Plastic Deformation

2018 ◽  
Vol 385 ◽  
pp. 39-44 ◽  
Author(s):  
Fernando Carreño ◽  
Oscar A. Ruano
Keyword(s):  
Mechanical Properties ◽  
Plastic Deformation ◽  
Severe Plastic Deformation ◽  
Aluminium Alloy ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Strain Rates ◽  
Aerospace Applications ◽  
Boundary Sliding ◽  
Processing Stress

The 7075 (Al-Zn-Mg-Cu) aluminium alloy is the reference alloy for aerospace applications due to its specific mechanical properties at room temperature, showing excellent tensile strength and sufficient ductility. Formability at high temperature can be improved by obtaining superplasticity as a result of fine, equiaxed and highly misoriented grains prone to deform by grain boundary sliding (GBS). Different severe plastic deformation (SPD) processing routes such as ECAP, ARB, HPT and FSP have been considered and their effect on mechanical properties, especially at intermediate to high temperatures, are studied. Refined grains as fine as 100 nm and average misorientations as high as 39o allow attainment of high strain rate superplasticity (HSRSP) at lower than usual temperatures (250-300oC). It is shown that increasing misorientations are obtained with increasing applied strain, and increasing grain refinement is obtained with increasing processing stress. Thus, increasing superplastic strains at higher strain rates, lower stresses and lower temperatures are obtained with increasing processing strain and, specially, processing stress.

Mechanical Properties of Novel Nanocrystalline Materials

2001 ◽  
Author(s):  
J. Narayan ◽  
H. Wang ◽  
A. Kvit
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Nanocrystalline Materials ◽  
High Surface ◽  
Grain Boundary Sliding ◽  
Boundary Shear ◽  
Functionally Gradient ◽  
Boundary Sliding ◽  
First Time ◽  
Critical Grain Size

Abstract We have synthesized nanocrystalline thin films of Cu, Zn, TiN, and WC having uniform grain size in the range of 5 to 100 nm. This was accomplished by introducing a couple of manolayers of materials with high surface and have a weak interaction with the substrate. The hardness measurements of these well-characterized specimens with controlled microstructures show that hardness initially increases with decreasing grain size following the well-known Hall-Petch relationship (H∝d−½). However, there is a critical grain size below which the hardness decreases with decreasing grain size. The experimental evidence for this softening of nanocrystalline materials at very small grain sizes (referred as reverse Hall-Petch effect) is presented for the first time. Most of the plastic deformation in our model is envisioned to be due to a large number of small “sliding events” associated with grain boundary shear or grain boundary sliding. This grain-size dependence of hardness can be used to create functionally gradient materials for improved adhesion and wear among other improved properties.

scholarly journals Dynamic recrystallization behavior of the Ta-containing TiAl alloy in isothermal deformation

2020 ◽  
Vol 321 ◽  
pp. 12008
Author(s):  
Y.Y. Luo ◽  
X.N. Mao ◽  
H.Y. Yang ◽  
Y.F. Yin ◽  
Z.Z. Zhao ◽  
...  
Keyword(s):  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Tial Alloy ◽  
Grain Boundary Sliding ◽  
Strain Rates ◽  
Recrystallization Behavior ◽  
Compression Process ◽  
Dynamic Recrystallization Behavior ◽  
Boundary Sliding ◽  
Mechanical Twins

The dynamic recrystallization behavior of as-cast Ti-46.5Al-3Ta-2Cr-0.2W alloy during isothermal compression process with nominal deformation of 50% and strain rates from 0.01s to 1s was investigated by electron microscopy. The results showed that the deformation mechanism of this alloy can be concluded as grain boundary sliding and mechanical twins, which induce the final dynamic recrystallization. The phase boundary bulging was found to be the major nucleation mechanism responsible for the lamellar globularization and the formation of recrystallized γ grains inside the lamellar colony under the high strain rate. The recrystallized γ grains induced by the twinning is the main mechanism for refining α2 lamellar microstructures under low strain rate.

scholarly journals Hierarchical creep cavity formation in an ultramylonite and implications for phase mixing

Solid Earth ◽  
2017 ◽  
Vol 8 (6) ◽  
pp. 1193-1209 ◽  
Author(s):  
James Gilgannon ◽  
Florian Fusseis ◽  
Luca Menegon ◽  
Klaus Regenauer-Lieb ◽  
Jim Buckman
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Grain Boundaries ◽  
Finite Strain ◽  
Grain Boundary Sliding ◽  
Large Strains ◽  
Cavity Formation ◽  
Phase Mixing ◽  
Transient Phenomena ◽  
Boundary Sliding

Abstract. Establishing models for the formation of well-mixed polyphase domains in ultramylonites is difficult because the effects of large strains and thermo-hydro-chemo-mechanical feedbacks can obscure the transient phenomena that may be responsible for domain production. We use scanning electron microscopy and nanotomography to offer critical insights into how the microstructure of a highly deformed quartzo-feldspathic ultramylonite evolved. The dispersal of monomineralic quartz domains in the ultramylonite is interpreted to be the result of the emergence of synkinematic pores, called creep cavities. The cavities can be considered the product of two distinct mechanisms that formed hierarchically: Zener–Stroh cracking and viscous grain-boundary sliding. In initially thick and coherent quartz ribbons deforming by grain-size-insensitive creep, cavities were generated by the Zener–Stroh mechanism on grain boundaries aligned with the YZ plane of finite strain. The opening of creep cavities promoted the ingress of fluids to sites of low stress. The local addition of a fluid lowered the adhesion and cohesion of grain boundaries and promoted viscous grain-boundary sliding. With the increased contribution of viscous grain-boundary sliding, a second population of cavities formed to accommodate strain incompatibilities. Ultimately, the emergence of creep cavities is interpreted to be responsible for the transition of quartz domains from a grain-size-insensitive to a grain-size-sensitive rheology.

High Temperature Deformation Behavior of Pre-Sintered Al-10Si-5Fe Based Alloy

2005 ◽  
Vol 475-479 ◽  
pp. 393-396 ◽  
Author(s):  
Dong Suk Lee ◽  
Gyu-Sam Shim ◽  
Mok Soon Kim ◽  
Won Yong Kim ◽  
Hiroshi Yamagata
Keyword(s):  
Liquid Phase ◽  
Deformation Behavior ◽  
Grain Boundary Sliding ◽  
Compressive Deformation ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Sintered Alloy ◽  
Strain Rates ◽  
Considerable Decrease ◽  
Boundary Sliding

Compressive deformation behavior of pre-sintered Al-10Si-5Fe-1Cu-0.5Mg-1Zr (wt%) alloy containing 15% of porosity was investigated in the temperature range from 753 K to 793 K and at strain rates from 10-4 to 100 s-1. From the microstructural observation, it was revealed that the occurrence of grain boundary sliding accomodated by dynamic recrystallization during the compressive deformation was closely associated with the considerable decrease in the porosity of the pre-sintered alloy. In the specimens deformed at 793 K with 10-4~100 s-1 and at 773 K with 10- 4~10-2 s-1, we have found an evidence of the occurrence of a liquid phase during compressive deformation in the microstructure. The liquid phase was considered to promote particle boundary sliding and hinder the reduction of the pore.

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