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.

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.

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.

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.

Influence of Grain Size and Thermo-Mechanical Conditions on the Activation Energy for Super Plastic Flow in Ti-6Al-4V Alloy

2018 ◽  
Vol 941 ◽  
pp. 1210-1215
Author(s):  
Juan Daniel Muñoz-Andrade
Keyword(s):  
Activation Energy ◽  
Grain Size ◽  
Grain Boundary ◽  
Plastic Flow ◽  
Power Dissipation ◽  
Direct Determination ◽  
Grain Boundary Sliding ◽  
Advanced Materials ◽  
Super Plastic ◽  
Boundary Sliding

The essential objective of this work is to establish the influence of grain size and thermo-mechanical conditions on the activation energy for super plastic flow (QSPF) in Ti-6Al-4V alloy by applying the quantum mechanics and relativistic model (QM-RM) proposed by Muñoz-Andrade, in the framework of the unified physics. The QM-RM allows the direct determination of the QSPF in advanced materials at instantaneous thermo-mechanical material working conditions. By applying, the QM-RM on the experimental results reported previously by some authors, it is shown for grain size of 6.1μm, that the calculated QSPF for grain boundary sliding is about 193 and 178 kJ/mol, at 850°C with an efficiency of power dissipation, η=0.65. These results are in closed agreement with the values of 204 and 174 kJ/mol reported previously for grain boundary self-diffusion energy of α-Ti. Nevertheless, for grain size of 0.6μm the calculated QSPF is 142 kJ/mol at 650°C, with an efficiency of power dissipation, η=0.61. As well, in order to understand the phenomenology and mechanics of SPF in Ti-6Al-4V alloy, the variation of the activation energy with the temperature; stress and strain rate is analyzed in association with coupled mechanisms during SPF, such as grain boundary sliding, cooperative grain boundary sliding and self-accommodation process related to the microstructure. In summary, the results of QSPF obtained in this work, by the QM-RM are in closed agreement with results reported previously by using the theoretical and conventional methodology set up by Mohamed and Langdon.

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.

A formulation for anisotropy in diffusional creep

1992 ◽  
Vol 436 (1896) ◽  
pp. 187-196 ◽  
Keyword(s):  
Grain Boundary ◽  
Elastic Anisotropy ◽  
Creep Behaviour ◽  
Grain Boundary Sliding ◽  
Diffusional Creep ◽  
Sources And Sinks ◽  
Boundary Sliding ◽  
Compliance Matrices

Grain shape can introduce anisotropy in creep which depends on the diffusion of vacancies between grain boundary sources and sinks. Such anisotropy is examined to determine the rate of creep under multiaxial stresses both for lattice and grain boundary diffusion. Noting the role of grain boundary sliding in this form of creep it is shown that, with some approximations that only become significant in an identified case, complete and fully self-consistent formulae can be derived for the rate of creep in terms of grain dimensions. The results are presented in the form of compliance matrices which are analogous to those that have a well-established role in the characterization of elastic anisotropy. A comparable usefulness of these ‘creep compliance coefficients’ is envisaged in evaluating anisotropic diffusional creep behaviour and a similar approach can be extended to more general cases where creep rates may be interface controlled.

Evolution of Microstructures and Mechanical Properties of Sr and Ca Containing Mg-4Al Alloy during Annealing Heat Treatment

2011 ◽  
Vol 311-313 ◽  
pp. 772-777
Author(s):  
Jing Bai ◽  
Yang Shan Sun ◽  
Feng Xue
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Elevated Temperatures ◽  
Creep Property ◽  
Grain Boundary Sliding ◽  
Al Alloy ◽  
Creep Properties ◽  
Lamellar Eutectic ◽  
Annealing Heat Treatment ◽  
Boundary Sliding

Microstructures, mechanical and creep properties of as-cast and as-annealed Mg-4Al-2Sr-1Ca (AJX421) alloy were investigated. The as cast microstructures of the alloy consists of the α-Mg, lamellar eutectic Mg2Ca and bulky Mg-Al-Sr phase. After annealing at 400°C, lamellar eutectic tended to be spheroidised and the continuous interphase network breaks up gradually, meanwhile, C14-Mg2Ca completely transforms to C15-Al2Ca. These results in obvious decrease of creep property. It is proposed that the continuous network distribution of compounds paly a major role in restricting the creep deformation of Mg-Al alloy at elevated temperatures, and the grain boundary sliding is an important creep mechanism for the alloy studied.

Microstructure and Mechanical Properties of Electrodeposited Nickel and its Particle-Reinforced Nanocomposite

2007 ◽  
Vol 567-568 ◽  
pp. 205-208 ◽  
Author(s):  
Petra Cihlářová ◽  
Jiří Švejcar ◽  
Vàclav Sklenička
Keyword(s):  
Mechanical Properties ◽  
Grain Boundary ◽  
Elevated Temperatures ◽  
Creep Behaviour ◽  
Grain Boundary Sliding ◽  
Pure Nickel ◽  
Dislocation Creep ◽  
Nano Composite ◽  
Electrodeposited Nickel ◽  
Boundary Sliding

There are two types of experimental material used – pure nickel and its nano-composite reinforced with nano-sized SiO2. These materials were produced by TU Clausthal, Germany. The results have shown that the creep resistance of the nickel nano-composite reinforced with nanosized SiO2 particles is higher in comparison with non-reinforced nickel. The mechanism responsible for creep behaviour is the dislocation creep at 293 K and at elevated temperatures the dislocation creep is controlled by grain boundary sliding.

Unification of Physics during Super Plastic Flow in Advanced Materials

2016 ◽  
Vol 838-839 ◽  
pp. 78-83 ◽  
Author(s):  
Juan Daniel Muñoz-Andrade
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Plastic Flow ◽  
Grain Boundary Sliding ◽  
Dislocation Dynamics ◽  
Advanced Materials ◽  
Direct Evaluation ◽  
Super Plastic ◽  
Boundary Sliding ◽  
Material Forming

In the framework connected with the unification of physics, the activation energy for super plastic flow in advanced materials has been obtained by applying the new quantum mechanics and relativistic model proposed by Muñoz-Andrade. This new model allows the direct evaluation of the activation energy for super plastic flow at instantaneous thermo-mechanical material forming conditions. Also, in order to establish the phenomenology and mechanics of super plastic flow, the dependence on strain rate and phase velocity de Broglie is obtained, for the reason that the nature wavelength of the cellular dislocations is essential in the association with coupled mechanisms during super plastic flow, such as grain boundary sliding, cooperative grain boundary sliding and self-accommodation process. In conclusion, cellular dislocation dynamics is a nature mechanism during super plastic flow in advanced materials. The results obtained in this work are in a closed agreement with results reported previously.

Sign in / Sign up

Export Citation Format

Share Document