Ductile Bulk Metallic Glass

We report on experimental evidence of pronounced global plasticity measured in monolithic ${\mathrm{P}\mathrm{t}}_{57.5}{\mathrm{C}\mathrm{u}}_{14.7}{\mathrm{N}\mathrm{i}}_{5.3}{\mathrm{P}}_{22.5}$ bulk metallic glass under both bending and unconfined compression loading conditions. A plastic strain of 20% is measured, never before seen in metallic glasses. Also, permanent deformation and a strain exceeding 3% before failure is observed during bending of 4 mm thick samples. To date, no monolithic metallic material has exhibited such a combination of high strength, extensive ductility, and high elastic limit. The large plasticity is reflected in a high Poisson ratio of 0.42, which causes the tip of a shear band to extend rather than initiate a crack. This results in the formation of multiple shear bands and is the origin of the observed large global ductility and very high fracture toughness, approximately $80\mathrm{M}\mathrm{P}\mathrm{a}{\mathrm{m}}^{-1/2}$.

Figure 1

Stress-strain curve of amorphous monolithic ${\mathrm{P}\mathrm{t}}_{57.5}{\mathrm{C}\mathrm{u}}_{14.7}{\mathrm{N}\mathrm{i}}_{5.3}{\mathrm{P}}_{22.5}$. The curve was determined under quasistatic compression of a bar shaped sample with $3\mathrm{m}\mathrm{m}\times 3\mathrm{m}\mathrm{m}\times 6\mathrm{m}\mathrm{m}$ dimensions. The material undergoes about 20% plastic deformation before failure.

Figure 2

Optical micrographs of ${\mathrm{P}\mathrm{t}}_{57.5}{\mathrm{C}\mathrm{u}}_{14.7}{\mathrm{N}\mathrm{i}}_{5.3}{\mathrm{P}}_{22.5}$ metallic glass that was plastically deformed to 15% strain. The primary shear band spacing is about $30\mu \mathrm{m}$ and that of the secondary bands is about $7\mu \mathrm{m}$.

Figure 3

Plastic zone ahead of the notch in a three point beam bending test. The shear bands extend to about 1.4 mm into the sample. Note that the $200\mu \mathrm{m}$ notch radius in this figure is different from the notch radius of $50\mu \mathrm{m}$ used for fracture toughness samples.

Figure 4

(a) A $1.8\mathrm{m}\mathrm{m}\times 3\mathrm{m}\mathrm{m}\times 15\mathrm{m}\mathrm{m}$ bar shaped ${\mathrm{P}\mathrm{t}}_{57.5}{\mathrm{C}\mathrm{u}}_{14.7}{\mathrm{N}\mathrm{i}}_{5.3}{\mathrm{P}}_{22.5}$ sample bent over a mandrel of radius 6.35 mm. The strain to failure exceeds 14.2%. (b) ${\mathrm{P}\mathrm{t}}_{57.5}{\mathrm{C}\mathrm{u}}_{14.7}{\mathrm{N}\mathrm{i}}_{5.3}{\mathrm{P}}_{22.5}$ samples with dimensions of $4\mathrm{m}\mathrm{m}\times 4\mathrm{m}\mathrm{m}\times 34\mathrm{m}\mathrm{m}$ bent over a mandrel with a radius of 6 cm. The strain to failure exceeds 3%.

Figure 5

Optical micrograph of a ${\mathrm{P}\mathrm{t}}_{57.5}{\mathrm{C}\mathrm{u}}_{14.7}{\mathrm{N}\mathrm{i}}_{5.3}{\mathrm{P}}_{22.5}$ BMG with dimensions of $1.8\mathrm{m}\mathrm{m}\times 3\mathrm{m}\mathrm{m}\times 15\mathrm{m}\mathrm{m}$ which was bent (a) over a mandrel of radius 12.7 mm, which corresponds to a strain of about 7%, (b) over a mandrel with radius 9.5 mm, which corresponds to a strain of about 9%, and (c) over a mandrel of radius 6.35 mm, which corresponds to a strain of about 14%.