Superplastic-Like Elongation by Transition of Deformation Mechanism from Grain Boundary Sliding to Solute Drag Creep in Fine-Grained Al-Mg Solid Solution Alloy

2018 ◽  
Vol 941 ◽  
pp. 1216-1221
Author(s):  
Tsutomu Ito ◽  
Takashi Mizuguchi
Keyword(s):  
Solid Solution ◽  
Deformation Mechanism ◽  
Solute Drag ◽  
Grain Boundary Sliding ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Solid Solution Alloy ◽  
Fine Grained ◽  
Aluminum Solid Solution ◽  
Solute Drag Creep

It is widely accepted that the dominant deformation mechanism of fine-grained superplasticity is through grain boundary sliding (GBS) that occurs in fine-grained materials. However, it has been reported that in “Class I” solid solution alloys, superplastic-like behavior controlled by trans-granular deformation occurs by solute drag creep. In this study, we have investigated superplastic behavior in a fine-grained aluminum solid solution alloy with a thermally unstable microstructure. To obtain fine-grained microstructure, friction stir processing (FSP) was applied to a commercial 5083 aluminum (Al−Mg) alloy. An equiaxial fine-grained microstructure with a grain size of 7.4 μm was obtained after FSP; however, this microstructure was unstable at high temperatures. Generally, for fine-grained superplasticity or GBS to occur or continue, the fine-grained microstructure must be smaller than 10 μm during high-temperature deformation. However, a large elongation of over 200% was observed at high temperatures despite the occurrence of grain growth. From microstructural observations, it was determined that a fine-grained microstructure is maintained in the early stage of deformation, but at strain levels greater than 100%, trans-granular deformation occurs. The microstructural feature of this trans-granular deformation is similar to the deformation microstructure of solute drag creep observed in “Class I” solid solution alloys. This indicates that a change in the deformation mechanism from GBS to solute drag creep takes place during high-temperature deformation. Here, based on our observations on our model system, which is a thermally unstable aluminum solid solution alloy, we discuss the possibility of a superplastic elongation occurring by means of a transition of the deformation mechanism.

Superplastic Elongation through Deformation Mechanism Transition during High-Temperature Deformation in Thermally Unstable Fine-Grained Aluminum Solid Solution Alloy

2016 ◽  
Vol 723 ◽  
pp. 21-26
Author(s):  
Tsutomu Ito ◽  
Takashi Mizuguchi
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Deformation Mechanism ◽  
Solute Drag ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Solid Solution Alloy ◽  
Fine Grained ◽  
Aluminum Solid Solution ◽  
Mechanism Transition

In this study, the superplastic behavior on a fine-grained aluminum solid solution alloy consisting of thermally unstable microstructures was investigated. In order to obtain the fine-grained microstructure, friction stir processing (FSP) was applied to a commercial 5083 aluminum alloy. An equiaxial fine-grained microstructure of 7.8 mm was obtained after FSP, but this microstructure was thermally unstable at high temperatures. Commonly, for fine-grained superplasticity to occur (or to continue grain boundary sliding (GBS)), it is necessary to keep the fine-grained microstructure to less than 10 mm during the high-temperature deformation. However, in this study, a large elongation of over 200% was observed at high temperatures in spite of the occurrence of grain growth. From the microstructural observations, it was determined that the fine-grained microstructure was maintained until the early stage of deformation, but the transgranular deformation was observed at a strain of over 100%. The microstructural feature of the abovementioned transgranular deformation is similar to the deformation microstructure of the solute drag creep occurring in "Class I"-type solid solution alloys. This indicates that the deformation mechanism transition from GBS to the solute drag creep occurred during high-temperature deformation. Here, the possibility of occurrence of the superplastic elongation through deformation mechanism transition is discussed as a model of the thermally unstable aluminum solid solution alloy.

High-Temperature Deformation of Magnesium ElektronTM 43

2012 ◽  
Vol 735 ◽  
pp. 93-100
Author(s):  
Alexander J. Carpenter ◽  
Anthony J. Barnes ◽  
Eric M. Taleff
Keyword(s):  
Strain Rate ◽  
Strain Rate Sensitivity ◽  
Rate Sensitivity ◽  
Superplastic Forming ◽  
Solute Drag ◽  
Grain Boundary Sliding ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Fine Grained ◽  
Boundary Sliding

Complex sheet metal components can be formed from lightweight aluminum and magnesium sheet alloys using superplastic forming technologies. Superplastic forming typically takes advantage of the high strain-rate sensitivity characteristic of grain-boundary-sliding (GBS) creep to obtain significant ductility at high temperatures. However, GBS creep requires fine-grained materials, which can be expensive and difficult to manufacture. An alternative is provided by materials that exhibit solute-drag (SD) creep, a mechanism that also produces elevated values of strain-rate sensitivity. SD creep typically operates at lower temperatures and faster strain rates than does GBS creep. Unlike GBS creep, solute-drag creep does not require a fine, stable grain size. Previous work by Boissière et al. suggested that the Mg-Y-Nd alloy, essentially WE43, deforms by SD creep at temperatures near 400°C. The present investigation examines both tensile and biaxial deformation behavior of ElektronTM 43 sheet, which has a composition similar to WE43, at temperatures ranging from 400 to 500°C. Data are presented that provide additional evidence for SD creep in Elektron 43 and demonstrate the remarkable degree of biaxial strain possible under this regime (>1000%). These results indicate an excellent potential for producing complex 3-D parts, via superplastic forming, using this particular heat-treatable Mg alloy.

The Solid-Solution Alloying Effects of Ti on the High-Temperature Deformation Behavior of NiAl Single Crystals

1996 ◽  
Vol 460 ◽  
Author(s):  
P. H. Kitabjian ◽  
A. Garg ◽  
R. Noebe ◽  
W. D. Nix
Keyword(s):  
Solid Solution ◽  
High Temperature ◽  
Single Crystals ◽  
Deformation Behavior ◽  
Solute Drag ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Solid Solution Alloy ◽  
Strengthening Effect ◽  
Solid Solution Strengthening

ABSTRACTWe have investigated the high-temperature deformation behavior of the solid-solution strengthened alloy Ni-47.5Al-2.5Ti. Single crystals were deformed in compression in the “hard” <001> and “soft” <111> orientations, at temperatures between 900°C and 1200°C. The results show that Ti has a very powerful solute strengthening effect in NiAl. The creep rates for the solid-solution alloy were observed to be three to four orders of magnitude lower than for the stoichiometric material. We discuss our efforts to understand this solid-solution strengthening effect. We have studied high-temperature deformation transients in an effort to determine whether solute drag effects contribute to the creep resistance of this solid solution. In addition, we have examined the solute size effect of Ti as it replaces Al on the Al sub-lattice. We discuss the probable mechanism of creep of this alloy in light of TEM observations of the dislocation structures in creep-deformed crystals.

Parameters Controlling High Temperature Deformability of Wrought Magnesium Alloys

2014 ◽  
Vol 783-786 ◽  
pp. 352-357
Author(s):  
Pierre Lhuissier ◽  
Luc Salvo ◽  
Jean Jacques Blandin
Keyword(s):  
High Temperature ◽  
Magnesium Alloys ◽  
Solute Drag ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Fine Grained ◽  
Significant Damage ◽  
Micro Tomography ◽  
Superplastic Properties ◽  
Deformation Tests

Due to limited deformability at room temperature, high temperature forming of magnesium alloys appears as an interesting alternative. Superplastic properties can be obtained in the case of fine grained magnesium alloys and in this regime, due to significant damage sensitivity, fracture strain is mainly controlled by nucleation, growth and coalescence of cavities. Magnesium alloys with large grained alloys can also exhibit interesting deformabilities at high temperature since dislocation movements can be controlled by a solute drag effect promoting plastic stability. Examples of such situations are presented in the case of wrought magnesium alloys, the associated damage mechanisms being investigated thanks to 3D X-ray micro tomography performed in continuous mode, namely directly during high temperature deformation tests.

Contributions of Grain Boundary Sliding and Solute Drag Creep to High-Temperature Ductility in Fine-Grained Polycrystalline 5083 Alloys

2014 ◽  
Vol 922 ◽  
pp. 360-365 ◽  
Author(s):  
Takashi Mizuguchi ◽  
Tsutomu Ito ◽  
Kota Kimura ◽  
Yasuhiro Tanaka
Keyword(s):  
High Temperature ◽  
Grain Boundary ◽  
Solute Drag ◽  
Tensile Tests ◽  
Grain Boundary Sliding ◽  
Solid Solution Alloy ◽  
Friction Stir ◽  
Fine Grained ◽  
Elongation To Failure ◽  
Boundary Sliding

In this study, the high-temperature ductility of a fine-grained, polycrystalline 5083 solid solution alloy was investigated. The composition of the alloy in mass% was Al–4.5 Mg–0.68 Mn–0.19 Fe–0.13 Si–0.11 Cr. Grain refinement was effectively achieved in the stir zone by a friction stir process, and the grain size could be reduced to 3.7 μm. Tensile tests were performed at temperatures ranging from 643 to 743 K and strain rates ranging from 0.001 to 0.1 /s. The stress–strain curves showed that the flow stress continuously decreased until it reached a maximum value of stress and fractured after the initial strain hardening occurred. The value of elongation-to-failure was more than 100% when temperatures were greater than 693 K. The high ductility observed at this point can be referred to as superplastic-like elongation. This phenomenon has been reported in some Al–Mg alloys. The experimentally determined stress exponent (n value) and activation energy for deformation were about 2.5 and 123 kJ/mol, respectively. These results suggest that the grain boundary sliding, accompanied by solute drag motion of dislocations, was a rate controlling process for deformation.

Recent Advances in the Development of Mechanically Alloyed Mo Silicide Alloys

2009 ◽  
Vol 633-634 ◽  
pp. 549-558 ◽  
Author(s):  
Martin Heilmaier ◽  
Manja Krüger ◽  
Holger Saage
Keyword(s):  
Solid Solution ◽  
Elevated Temperatures ◽  
Deformation Behaviour ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Mechanically Alloyed ◽  
Fine Grained ◽  
Processing Step ◽  
Grain Boundary Embrittlement ◽  
Solid Solution Matrix

We review the current development status of Mo-Si-B alloys consisting of Mo solid solution and the intermetallic phases Mo3Si and Mo5SiB2 which could take advantage of the beneficial oxidation resistance of the silicide phases and of the outstanding mechanical properties of molybdenum. For adequate low temperature toughness a continuous Mo solid solution matrix should be established in the microstructure. Besides, wrought processing of such alloys at elevated temperatures requires the presence of an ultra-fine grained (UFG) microstructure. Both the prerequisites can be fulfilled using mechanical alloying (MA) as the crucial processing step which even yields nanostructured supersaturated powders after milling. However, values for the ductile-to-brittle transition temperature (DBTT) close to room temperature are unlikely due to grain boundary embrittlement by Si segregation. The possibility of reducing this segregation tendency by various micro-alloying additions will be demonstrated. Finally, the high temperature deformation behaviour of these UFG materials will be comparatively assessed against state-of-the-art Nickelbase single-crystalline superalloys.

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