Damage Development During Superplasticity of Light Alloys

2008 ◽  
Vol 130 (2) ◽  
Author(s):  
R. Boissière ◽  
J. J. Blandin ◽  
L. Salvo
Keyword(s):  
Superplastic Deformation ◽  
Superplastic Forming ◽  
Grain Boundary Sliding ◽  
Mg Alloys ◽  
Damage Development ◽  
Light Alloys ◽  
Irregular Shapes ◽  
Complex Shapes ◽  
Boundary Sliding ◽  
Damage Processes

Superplastic forming (SPF) of metallic alloys allows the production of components with particularly complex shapes since in this regime, due to the predominance of grain boundary sliding (GBS), the material exhibits a high plastic stability. However, in many light alloys (i.e., Al or Mg alloys), superplastic deformation induces damage leading to premature fracture. Despite extensive work in the past, the mechanisms of damage induced by superplastic deformation remain under debate. In particular, due to the important contribution of GBS, voids with very irregular shapes frequently develop, resulting in a difficulty to obtain reliable experimental data from conventional quantitative metallography. It is the reason why the use of X-ray microtomography, providing 3D images of material bulk, is a particularly fruitful technique to investigate damage processes in superplastic materials. Thanks to this technique, damage development during superplastic deformation of Al and Mg alloys is investigated and the three main steps of damage development (nucleation, growth, and coalescence) are discussed.

Accommodation of Grain Boundary Sliding in AZ31 Alloy

2007 ◽  
Vol 345-346 ◽  
pp. 581-584
Author(s):  
Yong Nam Kwon ◽  
Young Seon Lee ◽  
S.W. Kim ◽  
Jung Hwan Lee
Keyword(s):  
Grain Boundary ◽  
Tensile Deformation ◽  
Texture Evolution ◽  
Grain Morphology ◽  
Superplastic Forming ◽  
Az31 Alloy ◽  
Grain Boundary Sliding ◽  
Processing Technique ◽  
Mg Alloys ◽  
Boundary Sliding

Mg alloys could be the lightest alloys among the industrially applicable engineering alloys. Since wrought Mg alloy has limited applications due to the poor formability, casting is currently the main processing technique to fabricate Mg components even though wrought alloys are superior in terms of mechanical properties and reliability. While a lot of research and development has been focused on warm forming under the temperature condition of around 250°C where more formability could be expected, superplastic forming could be another way to get over the low formability of Mg alloys. Like other superplastic materials grain boundary sliding is the main deformation mechanism of Mg superplasticity. Accommodation of stress concentration around triple point of grain boundary should be done favorably if grain boundary sliding continues without any fracture. In the present study, superplastic behavior of AZ31 alloys with several grain sizes was examined firstly. Accommodation of grain boundary sliding of AZ31 alloy would be discussed on the basis of grain morphology and texture evolution after tensile deformation.

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.

Effect of Superplastic Deformation on the Properties of Zirconia Dispersed Alumina Nanocomposite

2007 ◽  
Vol 551-552 ◽  
pp. 527-532 ◽  
Author(s):  
Guo Qing Chen ◽  
Shao Hua Sui ◽  
X.D. Wang ◽  
Wen Bo Han
Keyword(s):  
Mechanical Properties ◽  
Fracture Toughness ◽  
Flexural Strength ◽  
Superplastic Deformation ◽  
Critical Dimension ◽  
Grain Boundary Sliding ◽  
Transformation Toughening ◽  
Grain Coarsening ◽  
Boundary Sliding ◽  
Phase Transformation Toughening

In this paper constrained extrusion of the zirconia dispersed alumina nanocomposite under superplastic conditions was conducted. The mechanical properties of deformed material were studied and its results were compared with those of the initial materials. The microstructure evolution during superplastic deformation was also analyzed. The results demonstrated that after superplastic extrusion the flexural strength, relative density, Vickers hardness as well as fracture toughness of the material increased noticeably. The flexural strength of the deformed composite even retained at a high value of 310MPa at 800°C. The fracture toughness of the material increased from 6.92 MPa·m1/2 to 8.87 MPa·m1/2 after deformation. After superplastic extrusion due to grain boundary sliding and the compressive stress state, the internal porosities in as-sintered materials were eliminated. During extrusion with grain coarsening the effect of t-ZrO2 to m-ZrO2 transformation toughening increased because more zirconia grains reached the critical dimension. Although grain coarsening may cause the decrease of the fracture toughness in some extent, the phase transformation toughening and strengthening dominated. As a result, the mechanical properties of the deformed material were improved.

Superplasticity in Nb3Al/Nb In Situ Composites

1999 ◽  
Vol 601 ◽  
Author(s):  
S. Hanada ◽  
W. Fang
Keyword(s):  
Superplastic Deformation ◽  
Grain Boundary Sliding ◽  
Al Alloy ◽  
Two Phase ◽  
Dislocation Glide ◽  
In Situ Composite ◽  
Al Content ◽  
Boundary Sliding ◽  
Equiaxed Grains

AbstractMicrostructures of a binary Nb-15.8at%Al alloy ingot were controlled by isothermal forging and heat treatment to produce equiaxed, fine grains of Nb3Al and Nb solid solution (Nb33). Nb3Al/Nb33 two phase alloy (in-situ composite) is found to exhibit superplasticity especially when one of the constituent phases, Nb33, is supersaturated. During superplastic deformation Nb33 transforms to Nb3Al, and Al content in Nb33 decreases. After superplastic deformation the microstructure consisting of equiaxed grains is left unchanged, although a slight grain growth is observed. It is suggested that stress induced by grain boundary sliding is effectively accommodated through dislocation glide and climb in the soft Nb33

An Overview of Hot- and Warm-Forming of Al-Mg Alloys

2010 ◽  
Vol 433 ◽  
pp. 259-265 ◽  
Author(s):  
Eric M. Taleff
Keyword(s):  
Solute Drag ◽  
Grain Boundary Sliding ◽  
Warm Forming ◽  
Mg Alloys ◽  
Transportation Industry ◽  
Forming Technology ◽  
Practical Engineering ◽  
Boundary Sliding ◽  
Solute Drag Creep ◽  
Al Mg Alloys

Al-Mg alloys exhibit remarkable hot and warm ductilities, which have made the 5000-series alloys a critical part of commercial hot gas-pressure forming operations for the transportation industry. A review of the metallurgical and practical engineering reasons for this success is presented, and new understanding for behaviors in these materials, expected to impact future advances in hot- and warm-forming technology, are described. The excellent formabilities in this material class are fundamentally attributable to two deformation mechanisms, grain-boundary-sliding and solute-drag creep. However, a number of failure mechanisms ultimately limit final ductility and formability. These include cavitation, flow localization and microstructure evolution. The interplay of these mechanisms is discussed in terms of the potential to improve processing windows in forming operations.

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.

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