Superplastic Deformation Mechanisms in High Magnesium Contenting Aluminum Alloy

2016 ◽  
Vol 838-839 ◽  
pp. 66-71 ◽  
Author(s):  
O.A. Yakovtseva ◽  
Anastasia V. Mikhaylovskaya ◽  
A.G. Mochugovskiy ◽  
V.V. Cheverikin ◽  
Vladimir K. Portnoy
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Superplastic Deformation ◽  
Effective Activation Energy ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Effective Activation ◽  
Continuous Formation ◽  
Boundary Sliding ◽  
Dynamic Grain Growth

The evolution of surface, grains and dislocation structures during superplastic deformation was studied in Al–6.8%Mg–0.6%Mn–0.25%Cr alloy by SEM, EBSD, TEM techniques. The effective activation energy of superplastic deformation was calculated. Contribution of grain boundary sliding was defined during superplastic deformation. Low value of grain boundary sliding, significant dynamic grain growth in stress direction, high dislocations activity and permanent continuous formation of sub-grain boundaries during superplastic deformation were found.

Superplasticity in Ultrahigh Carbon (1.6 Pct C) Steel

2007 ◽  
Vol 551-552 ◽  
pp. 199-202 ◽  
Author(s):  
Zhan Ling Zhang ◽  
Yong Ning Liu ◽  
Jie Wu Zhu ◽  
G. Yu
Keyword(s):  
Grain Boundary ◽  
Superplastic Deformation ◽  
Boundary Diffusion ◽  
Grain Boundary Sliding ◽  
Strain Rates ◽  
Ultrahigh Carbon Steel ◽  
Elongation To Failure ◽  
Boundary Sliding ◽  
Dynamic Grain Growth ◽  
Microduplex Structure

Ultrahigh carbon steel containing 1.6 wt pct C was processed to create microduplex structure consisting of fine-spheroidized carbides and fine ferrite grains. Elongation-to-failure tests were conducted at strain rates from 10-4s-1 to 15×10-4s-1, and at temperatures from 600 °C to 850 °C. The steel exhibited superplasticity at and above 700 °C when testing at a strain rate of 10-4s-1, and at 800 °C when testing at strain rates of 7×10-4s-1 and slower. The grains retained the equiaxed shape and initial size during deformation; dynamic grain growth was not observed after superplastic deformation, whereas carbide coarsening was observed. It is concluded that the fine ferrite grains or austensite grains are stabilized by the grain boundary carbides, and grain-boundary sliding controlled by grain boundary diffusion is the principal superplastic deformation mechanism at temperatures in the range of 700-850 °C.

Superplastic Deformation Behavior in Dual-Phase Mg-Ca Alloy

2016 ◽  
Vol 838-839 ◽  
pp. 256-260
Author(s):  
Takahiko Yano ◽  
Naoko Ikeo ◽  
Hiroyuki Watanabe ◽  
Toshiji Mukai
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Deformation Behavior ◽  
Superplastic Deformation ◽  
Boundary Diffusion ◽  
Rate Sensitivity ◽  
Grain Boundary Sliding ◽  
Dual Phase ◽  
Elongation To Failure ◽  
Boundary Sliding

Superplastic deformation behavior was investigated for a dual-phase Mg-Ca alloy. The elongation-to-failure reached more than 120% with the strain rate sensitivity, m, over 0.4. The activation energy required for the deformation was estimated to be 98 kJ/mol which is close to the activation energy for grain boundary diffusion in magnesium. Therefore, the superplastic deformation mechanism was suggested to be the grain boundary sliding rate, which is controlled by boundary diffusion.

scholarly journals Superplastic Deformation and Dynamic Recrystallization of a Novel Disc Superalloy GH4151

Materials ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 3667 ◽  
Author(s):  
Shaomin Lv ◽  
Chonglin Jia ◽  
Xinbo He ◽  
Zhipeng Wan ◽  
Xinxu Li ◽  
...  
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Dynamic Recrystallization ◽  
Strain Rate ◽  
Superplastic Deformation ◽  
Optical Microscope ◽  
Grain Boundary Sliding ◽  
Experimental Conditions ◽  
Average Activation Energy ◽  
Boundary Sliding

The superplastic deformation of a hot-extruded GH4151 billet was investigated by means of tensile tests with the strain rates of 10−4 s−1, 5 × 10−4 s−1 and 10−3 s−1 and at temperatures at 1060 °C, 1080 °C and 1100 °C. The superplastic deformation of the GH4151 alloy was reported here for the first time. The results reveal that the uniform fine-grained GH4151 alloy exhibited an excellent superplasticity and high strain rate sensitivity (exceeded 0.5) under all experimental conditions. It was found that the increase of strain rate resulted in an increased average activation energy for superplastic deformation. A maximum elongation of 760.4% was determined at a temperature of 1080 °C and strain rate of 10−3 s−1. The average activation energy under different conditions suggested that the superplastic deformation with 1 × 10−4 s−1 in this experiment is mainly deemed as the grain boundary sliding controlled by grain boundary diffusion. However, with a higher stain rate of 5 × 10−4 s−1 and 1 × 10−3 s−1, the superplastic deformation is considered to be grain boundary sliding controlled by lattice diffusion. Based on the systematically microstructural examination using optical microscope (OM), SEM, electron backscatter diffraction (EBSD) and TEM techniques, the failure and dynamic recrystallization (DRX) nucleation mechanisms were proposed. The dominant nucleation mechanism of dynamic recrystallization (DRX) is the bulging of original grain boundaries, which is the typical feature of discontinuous dynamic recrystallization (DDRX), and continuous dynamic recrystallization (CDRX) is merely an assistant mechanism of DRX. The main contributions of DRX on superplasticity elongation were derived from its grain refinement process.

Structure Evolution and Deformation Mechanisms in Ultrafine-Grained Aluminum under Tension at Room Temperature

2010 ◽  
Vol 667-669 ◽  
pp. 915-920
Author(s):  
Konstantin Ivanov ◽  
Evgeny V. Naydenkin
Keyword(s):  
Grain Boundary ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Structure Evolution ◽  
Dislocation Slip ◽  
Polished Surface ◽  
Angular Pressing ◽  
Ultrafine Grained ◽  
Boundary Sliding

Deformation mechanisms occurring by tension of ultrafine-grained aluminum processed by equal-channel angular pressing at room temperature are investigated using comparative study of the microstructure before and after tensile testing as well as deformation relief on the pre-polished surface of the sample tested. Deformation behavior and structure evolution during tension suggest development of grain boundary sliding in addition to intragrain dislocation slip. Contribution grain boundary sliding to the overall deformation calculated using the magnitude of shift of grains relative to each other is found to be ~40%.

Temperature Dependence of Compressive Deformation Behavior of Mg89Zn4Y7 Extruded LPSO-Phase Alloys

2010 ◽  
Vol 654-656 ◽  
pp. 607-610 ◽  
Author(s):  
Koji Hagihara ◽  
Akihito Kinoshita ◽  
Yuya Sugino ◽  
Michiaki Yamasaki ◽  
Yoshihito Kawamura ◽  
...  
Keyword(s):  
Grain Size ◽  
Grain Boundary ◽  
Temperature Dependence ◽  
Yield Stress ◽  
Deformation Behavior ◽  
Grain Boundary Sliding ◽  
Deformation Mechanisms ◽  
Petch Relationship ◽  
Lpso Phase ◽  
Boundary Sliding

Deformation mechanisms of Mg89Zn4Y7 (at.%) extruded alloy, which is mostly composed of LPSO-phase, was investigated focusing on their temperature dependence. The yield stress of as-extruded alloy showed extremely high value of ~480 MPa at RT, but it largely decreased to ~130 MPa at 300 °C. The decreasing rate of the yield stress could be significantly reduced, however, by the annealing of specimen at 400 °C, by suppressing the microyielding which is considered to occur related by the grain boundary sliding in restricted regions. The yield stress of the annealed specimens with random textures could be estimated by the Hall-Petch relationship by regarding the length of long-axis of plate-like grains as a grain size between RT and 300 °C. The yield stress of the annealed specimens maintained high values even at 200°C, but it also showed large decreases at 300 °C.

Microstructures and Creep Behaviour of Mg-4Al Alloy Containing Sr and Ca

2011 ◽  
Vol 79 ◽  
pp. 134-139
Author(s):  
Jing Bai ◽  
Yang Shan Sun ◽  
Feng Xue
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Ternary Phase ◽  
Creep Behaviour ◽  
Creep Property ◽  
Grain Boundary Sliding ◽  
Experimental Conditions ◽  
Lamellar Eutectic ◽  
Boundary Sliding ◽  
Almost Continuous

Microstructures and creep property of the Mg-4Al based alloy with addition of 2% Sr and 1%Ca were investigated. The as-cast microstructures of the present alloy consist of dendritic α-Mg and two major intermetallics: lamellar eutectic C14-Mg2Ca and bulky type Mg-Al-Sr ternary phase. These intermetallics mainly distribute along grain or cell boundaries and form an almost continuous network. The alloy studied shows an excellent creep resistance under the experimental conditions. This is primarily attributed to formation of the thermostable intermetallics with addition of Sr and Ca to Mg-Al based alloy. The values of stress exponent, n, and creep activation energy, Q, imply that both dislocaiton motion and grain boundary sliding contribute to the creep deformation.

Deformation and microstructural changes in SiC whisker-reinforced Si3N4 composites

1991 ◽  
Vol 6 (12) ◽  
pp. 2735-2746 ◽  
Author(s):  
D.A. Koester ◽  
K.L. More ◽  
R.F. Davis
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Stress Exponent ◽  
Amorphous Material ◽  
Grain Boundary Sliding ◽  
Vitreous Phase ◽  
Observable Effect ◽  
Prolonged Annealing ◽  
Sic Whiskers ◽  
Boundary Sliding

Constant stress compressive creep studies have been conducted on hot-pressed Si3N4 containing 30 vol. % SiC whiskers and an initial vitreous phase composed of Al2O3, Y2O3, and SiO2. The conditions of temperature and stress were 1470–1670 K and 50–350 MPa, respectively; the atmosphere was purified N2 at 1 atm. Significant changes in the stress exponent and activation energy indicate a change in the controlling creep mechanism at ≍225 MPa and 1570 K. Prolonged annealing in the unstressed condition reduced creep rates but had little effect on the stress exponent values. Transmission and scanning electron microscopy revealed that the break in the stress exponent curves was caused by the removal of the amorphous material at the grain boundary and resulting contacts between Si3N4 grains. The break in the activation energy curves is believed to be similarly related. Analysis of all the data indicates that the composite creeps via grain boundary sliding accommodated by viscous flow at low stresses and temperatures and by diffusion at high stresses and temperatures. The contributions of these two mechanisms varied measurably as a function of stress and temperature. No cavitation was observed. The presence of the SiC whiskers had no observable effect on deformation.

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