Figure C –. Backscattered SEM micrographs showing systematic variation of the at. % of Be, X, with (a) X = 19.1, (b) X = 15.3, (c) X = 12.5, and (d) X = 9. The dendrites are the lighter contrast and the glass matrix is the darker. EDS analysis was used detect the composition of the dendrite and a combination of computer assisted image analysis and DSC scans were used to estimate the volume fraction of dendrites. The alloys DH1–5 have 41%, 52%, 67%, 76%, and 80% β-phase by volume, respectively. Phase separation occurs because Be is not soluble as is b.c.c. titanium or zirconium. One might think that heterogeneous nucleation would cause the glass-forming phase to crystallize, however there are no stable Be phases that could form.
Figure C2 – A plot of volume fraction of β-phase dendrites versus at% of Be, X, in (Zr45.2Ti38.8Nb8.7Cu7.3)100-X(Be)X for 5 alloys. From the plot, it is clear that the volume
fraction of β-phase follows an approximately linear trend from 40–100%. This indicates that the microstructure and mechanical properties of these alloys can be controlled by varying a single component, Be, even though both Cu and Be favor the glass matrix over the dendrite. Increasing the volume fraction of β-phase has been shown to increase fracture toughness and tensile ductility while decreasing yield strength.
Figure C3 – Schematic plot of shear modulus versus volume fraction of β-phase dendrites for the alloys DH1–3. The black line indicates a rule of mixtures average between BMG matrix and the shear-soft dendrites. The diameter of the circles represents the total strain to failure during room temperature uniaxial tension testing. The dashed lines are estimations of the total strain to failure of alloys that are not shown. The total strain to failure is typically ~ 2% for metallic glasses and ~ 7% for the dendrite material. The dendrites in the composites suppress tensile instability and limit shear band extension, allowing for total strain to failure that is larger than the pure dendrite material (9.6%, 10.8%, and 13.6% for DH1–3, respectively).
Figure C4 – Plots of atomic percentage versus volume fraction of dendrites to illustrate the compositional differences obtained during chemical partitioning for the dendrites and glass matrix of the alloys DH1–3. The dashed trend-line for the alloys DH1–3 is useful for estimating both the pure β-phase alloy and the parent BMG of this system. From the plot, the dashed line indicates that if the glass phase were removed, the resulting alloy would be similar to Zr45.2Ti38.8Nb8.7Cu7.3, representing X = 0 the
plot. The trend also predicts a BMG Zr30.4Ti26.1Nb5.9Cu4.9Be32.7 as the parent glass
matrix, similar to the original BMG Zr35Ti30Cu8.25Be26.75 with ~ 6% Nb and increased
Be. EDS analysis was used on the alloys DH1–3 to determine the composition of the β-phase and the glass matrix. For each alloy the atomic percentage of the constitutive elements is plotted as a function of the volume fraction of dendrites with DH1’–3’ (DH1β–3β) representing the glass matrix (dendrites) of the alloys DH1–3. The plot illustrates how the composition of the glass matrix and the dendrites change relative to the estimated pure glass and pure dendrite. The compositions of the dendrites follow a clear trend starting from the pure β-phase alloy Zr45.2Ti38.8Nb8.7Cu7.3. With decreasing
volume fraction of β-phase the dendrites favor Ti over Zr, becoming Ti-rich at ~ 56%. Thus the alloys DH1 and DH2 have Ti-rich dendrites while the alloy DH3 has a Zr- rich dendrite. Nb content steadily increases from the pure β-phase material to DH1, while Cu sharply drops to ~ 1 at%, where it remains for all three alloys. As an estimation it can be said that the composition of the dendrite for DH1-3 is a shear-soft (G ~ 23 GPa) alloy of Zr-Ti with ~ 15 at% Nb. The composition of the glass matrix does not follow such a clear trend, however. The at.% of Be and Zr remain relatively constant between 30-38% while the Ti (Cu) content decreases (increases) as the volume fraction of β-phase approaches 70%. Analogous to the lack of Cu in the β- phase material, the Nb typically has ~1 at% in the glass matrix. As an estimation, the glass matrix for DH1–3 is a Zr-Ti-Cu-Be BMG with typically ~ 10 at% Cu. This implies that the glass matrix should exhibit some of the same beneficial properties as were discovered in Zr35Ti30Cu8.25Be26.75 (large supercooled liquid region and high
fracture toughness). Note that this plot is an estimation and there is likely an error of about 5% in the measured values.
Figure C5 – SEM micrograph from the tensile surface of the composite DH3 after testing. A hierarchy of shear bands is visible with primary bands ~ 40 μm wide, secondary bands ~ 10μm wide, and tertiary bands < 2 μm wide. This is among the finest shear band spacing ever observed in BMG research and it is from a tension test, not a compression test.
Figure C6 – SEM micrograph from the tensile surface of the composite DH2 after testing. A dense pattern of shear bands is visible, indicating a large amount of plastic strain has occurred.
Figure C7 – (left) Extensive necking during a tension test of the in-situ composite LM2A2 from S.Y. Lee’s Caltech thesis (2005) produced by the semi-solid processing method. The alloy displays ~ 13.5% tensile ductility and a dense “stair-step” shear band pattern (right). The semi-solid processing has more than doubled the tensile ductility reported in S.Y. Lee’s thesis for this alloy.
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Figure C8 – SEM micrograph from the fracture surface of a Charpy impact test in DH3. Despite the high strain-rate test, the alloy has a jagged fracture, indicative of high toughness.
Figure C9 – Fatigue life data for the alloy DH3 compared with the monolithic BMG Vitreloy 1 and fracture-resistant 300-M steel. This work was completed at Lawrence Livermore National Laboratory by M. Launey in collaboration with our group. The preliminary fatigue data show that DH3 has a higher fatigue limit than high strength steel. Fatigue is among the most important measurements for structural materials and the alloy DH3 has among the highest value of fatigue for any known structural engineering materials.