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Author

Yan Ma

Other affiliations: Kyushu University, KAIST
Bio: Yan Ma is an academic researcher from University of Southern California. The author has contributed to research in topics: Superplasticity & Grain size. The author has an hindex of 10, co-authored 22 publications receiving 535 citations. Previous affiliations of Yan Ma include Kyushu University & KAIST.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining.
Abstract: A submicrometer-grained (SMG) Al−3% Mg solid solution alloy, with an initial grain size of ∼0.2 μm, was produced by intense plastic straining. Experiments show that tensile specimens of the SMG alloy exhibit high elongations to failure at low testing strain rates at the relatively low temperature of 403 K. The stress exponent is high (∼7–8) and calculations show deformation is within the region of power-law breakdown. The initial microstructure of the alloy consists of diffuse boundaries between highly deformed grains. At strain rates of ∼10−4 s−1 and lower, plastic deformation leads to dynamic recrystallization and the formation of highly nonequilibrium grain boundaries that gradually evolve into a more equilibrated configuration.

178 citations

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TL;DR: In this paper, a Zn-22% Al eutectoid alloy with submicrometer grain sizes was used for torsion straining and equal channel angular (ECA) pressing.
Abstract: Submicrometer grain sizes were introduced into a Zn-22% Al eutectoid alloy using two different procedures: torsion straining and equal-channel angular (ECA) pressing. Microstructural examination showed that torsion straining gives an essentially equiaxed grain configuration with some mixing of the two separate phases. After ECA pressing to a strain of ∼8 at a temperature of 373 K, there is a submicrometer grain size but with agglomerates of ultrafine Al-rich and Zn-rich grains which are formed by the separate division of the original grains into smaller submicrometer grains with only very limited mixing of the two phases. Tensile testing of the ECA pressed material gave neck-free superplastic flow but, except only at 473 K at the fastest strain rate of ∼10 −1 s −1 where the elongation was unusually high, the elongations to failure were similar to those reported earlier for a commercial alloy with a grain size of ∼2.5 μm. The results demonstrate the need to develop an ECA pressing procedure which avoids the formation of agglomerates of the two phases.

125 citations

Journal ArticleDOI
TL;DR: In this article, the possibility of attaining a superplastic forming capability at lower temperatures and/or faster strain rates by a reduction of the grain size into the submicrometer range was considered.
Abstract: High tensile ductility may be achieved in metallic alloys over a limited range of strain rates at elevated temperatures when the grain size is very small (typically less than ∼ 10 μm). These superplastic materials are often suitable for industrial forming operations. This paper considers the possibility of attaining a superplastic forming capability at lower temperatures and/or faster strain rates by a reduction of the grain size into the submicrometer range. Procedures are available for the fabrication of ultrafine-grained materials by imposing a very high plastic strain. These procedures are examined with reference to results obtained using Al-Mg solid solution alloys.

72 citations

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TL;DR: In this article, the authors conducted tensile experiments on fully dense tetragonal zirconia stabilized with approximately 3 mol% yttria and with a submicrometer grain size.
Abstract: Tensile experiments were conducted on fully dense tetragonal zirconia stabilized with approximately 3 mol% yttria and with a submicrometer grain size. Examination of the specimens after superplastic-like flow revealed the development of internal cavitation and the extent of the cavitation increased with increasing strain rate. Nanocrystalline materials have an apparent potential for superplastic forming operations but this potential may be limited because of the presence of residual porosity from the fabrication process or because of the nucleation and growth of cavities during superplastic flow. It is shown by calculation that diffusion will play a dominant role in the growth of internal voids in nanocrystalline structures because each grain boundary impinging on a void provides a path for rapid diffusion.

20 citations


Cited by
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Journal ArticleDOI
TL;DR: In this article, a review examines recent developments related to the use of ECAP for grain refinement including modifying conventional ECAP to increase the process efficiency and techniques for up-scaling the procedure and for the processing of hard-to-deform materials.

3,669 citations

Journal ArticleDOI
TL;DR: In this paper, it has been shown that submicrometer-grained structures may be produced in a wide range of materials (e.g. pure metals, metallic alloys including superalloys, intermetallics, semiconductors) by subjecting these materials to a very high plastic strain using either equal-channel angular (ECA) pressing or torsion straining under high pressure.

1,655 citations

Journal ArticleDOI
TL;DR: In this article, experiments were conducted on high purity aluminum to investigate the process of grain refinement during equal-channel angular (ECA) pressing, where samples were subjected to 1 to 4 pressings and then sectioned for microstructural examination in three mutually perpendicular directions.

1,135 citations

Journal ArticleDOI
TL;DR: The most widely applied methods for the production of composite materials and composite parts are based on casting techniques such as the squeeze casting of porous ceramic preforms with liquid metal alloys and powder metallurgy methods.

836 citations

Journal ArticleDOI
TL;DR: In this article, the development of an ultra-fine grain size during equal-channel angular (ECA) pressing of high purity aluminum with an initial grain size of ∼1.0 mm was investigated.

759 citations