Materials Science

Pores for Strength

Science  01 Jul 2005:
Vol. 309, Issue 5731, pp. 21
DOI: 10.1126/science.309.5731.21c

It is now possible to make bulk metallic glasses (BMGs) from a wide range of alloy compositions and to fabricate parts where the minimum dimension is at least a few millimeters. In comparison to the corresponding crystalline alloys, BMGs are almost twice as strong. Their downfall is a lack of plastic strain, which leads to softening and abrupt failure associated with shear bands, even under compression. Although they can be rendered more ductile by including a dispersed crystalline phase, this reduces the yield strength.

Wada et al.used four distinct hydrogenation treatments to create BMG rods with porosities between 0 and 4%. Compressive tests showed only a small decrease in the Young's modulus (about 10%), but with a strain at rupture as high as 18% and a significant increase in the rupture energy, which is the total energy under the stress-strain curve before failure. Structural analysis of the fractured samples showed that the pores acted as stress concentrators for the shear bands, causing an increase in the shear banding as the material deformed, thus increasing its toughness. — MSL

Appl. Phys. Lett. 86, 251907 (2005).

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