The Development of Superplasticity and Deformation Mechanism Maps in an Ultrafine-Grained Magnesium Alloy

2016 ◽  
Vol 879 ◽  
pp. 48-53
Author(s):  
Megumi Kawasaki ◽  
Roberto B. Figueiredo ◽  
Terence G. Langdon
Keyword(s):  
Deformation Mechanism ◽  
Elevated Temperatures ◽  
Grain Boundary Sliding ◽  
Grain Structure ◽  
Superplastic Behavior ◽  
Ultrafine Grained ◽  
Controlling Mechanism ◽  
Zk60 Alloy ◽  
Boundary Sliding ◽  
Coble Creep

Magnesium alloys with refined grain structure are often superplastic at elevated temperatures with maximum elongations up to more than 1000%. The superplastic behavior of this material agrees with deformation by grain boundary sliding. Dislocation climb becomes the rate controlling mechanism at higher stresses but the rate controlling mechanism at lower stresses is not fully documented. This report examines the development of superplasticity in a magnesium ZK60 alloy and shows that an increase in stress exponent and decrease in elongation takes place at low stresses. Deformation mechanism maps are constructed considering Regions I, II and III and Coble creep.

Tensile Properties of Hot Extruded Mg-Zn-Nd-Y-Zr Alloy at Elevated Temperatures

2011 ◽  
Vol 415-417 ◽  
pp. 1157-1163
Author(s):  
Xiao Zhou ◽  
Hai Tao Zhou ◽  
Zhen Dong Zhang ◽  
Rui Rui Liu ◽  
Li Bin Liu
Keyword(s):  
Strain Rate ◽  
Elevated Temperatures ◽  
Peak Stress ◽  
Tensile Tests ◽  
Grain Boundary Sliding ◽  
Strain Rates ◽  
Zk60 Alloy ◽  
Boundary Sliding ◽  
Increasing Temperature ◽  
Zr Alloy

Mechanical properties of extruded Mg-Zn-Nd-Y-Zr alloy are investigated by tensile tests at various temperatures range from room temperature to 350°C with strain rates of 6.0×10-4-6.0×10-1s-1. It is found that the peak decrease with increasing temperature and decreasing strain rate, while the elongation increases with increasing temperature and decreasing strain rate. When deformation temperature is over 250°C, superplasticity occurs. This is ascribed to grain boundary sliding accommodated cavities growth. . At low temperature, the peak stress are a relatively higher than that of ZK60 alloy. This is explained by the grain refining effect and the precipitates of Mg9Nd and Mg6Zn3Y2.

Superplastic Deformation of Ultrafine Grained Al Alloy Processed by ECAP and Post-Rolling

2006 ◽  
Vol 503-504 ◽  
pp. 119-124 ◽  
Author(s):  
Kyung Tae Park ◽  
Chong Soo Lee ◽  
Yong Suk Kim ◽  
Dong Hyuk Shin
Keyword(s):  
Cold Rolling ◽  
Strain Rate ◽  
High Strain ◽  
Grain Boundary Sliding ◽  
Strain Rate Range ◽  
Al Alloy ◽  
Superplastic Behavior ◽  
Ultrafine Grained ◽  
Boundary Sliding ◽  
Main Deformation

Superplastic behavior of an ultrafine grained (UFG) 5154 Al alloy processed by ECAP and cold rolling (ECAP+CR sample) was investigated and compared with that of the alloy processed by only ECAP without rolling (ECAP sample) in the strain rate range of 10-4~5×10-1 s-1 at 723 K. Processing of the ECAP+CR sample consisted of ECAP of 4 passes, which was less than that showing the optimum microstructure for high strain rate superplasticity of UFG Al alloys (i.e. 8 passes), with route Bc and subsequent cold rolling (70% thickness reduction). The superplastic elongation was remarkably enhanced by post-rolling. An analysis of the mechanical data revealed that deformation of the ECAP+CR sample was dominated by grain boundary sliding, but dislocation viscous glide was the main deformation mechanism for the ECAP sample. In addition, cavitation in the ECAP+CR sample was insignificant up to ∼300% elongation.

Research on Micro-Mechanism of Nanocomposite Ceramic in Two-Dimensional Ultrasound Grinding

2007 ◽  
Vol 359-360 ◽  
pp. 344-348 ◽  
Author(s):  
Bo Zhao ◽  
Yan Wu ◽  
Guo Fu Gao ◽  
Feng Jiao
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Deformation Mechanism ◽  
Ground Surface ◽  
Grain Boundary Sliding ◽  
Second Phase ◽  
Two Dimensional ◽  
Composite Ceramics ◽  
Nano Composite ◽  
Boundary Sliding

Surface microstructure of nano-composite ceramics prepared by mixed coherence system and machined by two-dimensional ultrasonic precision grinding was researched using TEM, SEM, XRD detector and other equipments. Structure, formation mechanism and characteristic of metamorphic layer of ground surface of nano-composite ceramics were researched. The experiment shows micro deformation mechanism of ceramic material in two-dimensional ultrasound grinding is twin grain boundary and grain-boundary sliding for Al2O3, and it is crystal dislocation of enhanced phase, matrix grain boundary sliding, coordination deformation of intergranular second phase as well as its deformation mechanism for nano-composite ceramics. The fracture surfaces of nano-composite materials with different microscopic structure were observed using TEM and SEM. Research shows that ZrO2 plays an important influence on the generation and expansion of crack, and enhances the strength of grain boundaries. When grain boundaries is rich in the ZrO2 particles, the crack produced in grinding process will be prevented, and the surface with plastic deformation will be smooth. The results shows nanoparticles dispersed in grain boundary prevents crack propagation and makes materials fracture transgranularly which makes the processed surface fine.

Room Temperature Superplasticity in Fine/Ultrafine-Grained Zn-Al Alloys with Different Phase Compositions

2018 ◽  
Vol 385 ◽  
pp. 72-77
Author(s):  
Muhammet Demirtas ◽  
Harun Yanar ◽  
Onur Saray ◽  
Gençağa Pürçek
Keyword(s):  
Grain Size ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Al Alloys ◽  
Phase Boundaries ◽  
Superplastic Behavior ◽  
Al Content ◽  
Α Phase ◽  
Ultrafine Grained ◽  
Superplastic Elongation

Three Zn-Al alloys, namely Zn-22Al, Zn-5Al and Zn-0.3Al, were subjected to equal-channel angular pressing (ECAP), and the effect of ECAP on their microstructure and room temperature (RT) superplastic behavior were investigated in detail referring to previous studies reported by the authors of the current study. ECAP remarkably refined the microstructures of three alloys as compared to their pre-processed conditions. While the lowest grain size was achieved in Zn-22Al alloy as 200 nm, the grain sizes of Zn-5Al and Zn-0.3Al alloys were ~540 nm and 2 µm, respectively, after ECAP. After the formation of fine/ultrafine-grained (F/UFG) microstructures, all Zn-Al alloys exhibited superplastic behavior at RT and high strain rates. The maximum superplastic elongations were 400%, 520% and 1000% for Zn-22Al, Zn-5Al and Zn-0.3Al alloys, respectively. It is interesting to point out that the highest RT superplastic elongation was obtained in Zn-0.3Al alloy with the largest grain size, while Zn-22Al alloy having the lowest grain size showed the minimum superplastic elongation. This paradox was attributed to the different phase compositions of these alloys. The formation of Al-rich α/α phase boundaries, where grain boundary sliding is minimum comparing to Zn-rich η/η and η/α phase boundaries of Zn-Al alloys, is the lowest level in Zn-0.3Al alloy among all the alloys. Therefore, it can be concluded that if it is desired to achieve high superplastic elongation in Zn-Al alloys at RT, keeping Al content at a possibly minimum level seems to be the most suitable way.

Direct Observation of Two-Dimensional Grain Boundary Sliding and Switching in ODS Ferritic Steel

2016 ◽  
Vol 838-839 ◽  
pp. 43-50
Author(s):  
Eiichi Sato ◽  
Hiroshi Masuda ◽  
Yoshito Sugino ◽  
Shigeharu Ukai
Keyword(s):  
Grain Boundary ◽  
Ferritic Steel ◽  
Tensile Deformation ◽  
Grain Boundary Sliding ◽  
Grain Structure ◽  
Two Dimensional ◽  
Kernel Average Misorientation ◽  
Boundary Sliding ◽  
High Temperature Tensile ◽  
Region Ii

High-temperature tensile deformation was performed using an oxide-dispersionstrengthened (ODS) ferritic steel,, which has grain structure largely elongated and aligned in one direction, in the perpendicular direction. In the superplastic region II, two-dimensional grain boundary sliding (GBS) was achieved, in which the material did not shrink in the grain-axis direction and grain-boundary steps appeared only in the surface perpendicular to the grain axis. In this condition, a classical grain switching event was observed. Using kernel average misorientation maps drawn with SEM/EBSD, dominant deformation mechanisms and accommodation processes for GBS were examined in the different regions. Cooperative grain boundary sliding, in which only some of grain boundaries slide, was also observed.

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%.

The Role of Diffusion Accommodation and Phase Boundary Wetting in the Deformation Behaviour of Ultrafine Grained Sn-Pb Eutectic

2010 ◽  
Vol 297-301 ◽  
pp. 1002-1009 ◽  
Author(s):  
Faina Muktepavela ◽  
R. Zabels
Keyword(s):  
Grain Boundary ◽  
Diffusion Processes ◽  
Deformation Behaviour ◽  
Grain Boundary Sliding ◽  
Ultrafine Grained ◽  
Interphase Boundaries ◽  
Boundary Sliding ◽  
High Homologous Temperature ◽  
Microscopy Techniques

Mechanical properties, microstructure of the Sn–38wt. %Pb eutectic and the development of deformation - induced diffusion processes on interphase boundaries (IB) were investigated. Experiments were carried out both in deformed and annealed states of eutectic using micro- and nanoindentation, SEM, AFM and optical microscopy techniques. It was found that the deformation of the annealed alloy is localized at the Pb/Sn interphase boundaries and occurs by grain boundary sliding (GBS) accompanied by sintering micropore processes under the action of the capillary forces on the Pb/Sn IB. During severe plastic deformation of Sn-Pb eutectic phase transition in the Sn grain boundary occurs. This deformation-induced process takes place due to the wetting of tin with Pb. These diffusion accommodation processes (sintering and wetting) are facilitated by the low values of the Pb/Sn interphase energy (0.07 J/m2). Wetting is thermodynamically favourable because the condition γgb > 2 γib is satisfied and it is also kinetically allowed due to the relatively high homologous temperature (> 0.5•Tm). The obtained values of the nanohardness and elastic modulus evidence that the IBs in the Sn–Pb eutectic have to be considered as a separate quasi-phase with its own properties.

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