Pan Gong

Cu-alloying effect on crystallization kinetics of Ti41Zr25Be28Fe6 bulk metallic glass

Compared with Ti41Zr25Be28Fe6 bulk metallic glass, (Ti41Zr25Be28Fe6)93Cu7 glassy alloy possesses a much narrower supercooled liquid region but the glass-forming ability is dramatically improved. Isochronal and isothermal differential scanning calorimetry measurements were adopted to investigate Cu-alloying effect on the crystallization transformation kinetics of Ti41Zr25Be28Fe6 glassy alloy. It is found that Cu alloying increases the activation energies of Ti41Zr25Be28Fe6 glassy alloy for glass transition and crystallization in continuous heating. Moreover, the isothermal activation energy of (Ti41Zr25Be28Fe6)93Cu7 glassy alloy increases as process of crystallization transformation, while Cu-free alloy exhibits a contrary tendency. The addition of Cu also decreases the Avrami exponent of the base alloy, resulting in the suppression of crystal nucleation and growth.

Effects of alloying elements on crystallization kinetics of Ti-Zr-Be bulk metallic glass

It has been found that the partial substitution of Fe, Al, Ag, Cu, Ni, V, or Cr for Be effectively enhances the glass-forming ability of Ti–Zr–Be ternary alloy. The influence of different alloying elements on crystallization kinetics of Ti41Zr25Be34 alloy has been investigated by isothermal and isochronal differential calorimetry combined with X-ray diffraction. Among the selected alloying elements, Fe, Al, Cu, Ni, or Cr can enhance the thermal stability, while the Ag- and V-containing alloys exhibit a slightly narrower supercool liquid region. The crystallization of all the eight alloys proceeds through at least two exothermic events. The apparent activation energies of glass transition and crystallization have been determined based on the Kissinger equation. The substitution of Al, Ag, Cu, or Ni for Be does not change the product of the primary crystallization of the base alloy. However, with the addition of beta stabilized elements (Fe, V, and Cr), the formation of β-Ti as primary phase is promoted. The overall nucleation and growth characteristics of the parent, Al-, Ag-, Cu-, Ni-, V-, and Cr-additive alloys, are similar. Compared with the other seven alloys, Ti41Zr25Be28Fe6 alloy exhibits much larger Avrami exponents with an average value of 5.26, indicating a high-dimensional growth with increasing nucleation rate.

A Centimeter-Sized Quaternary Ti-Zr-Be-Ag Bulk Metallic Glass

A novel centimeter-sized Ti-based bulk metallic glass (BMG) was developed by the addition of Ag in the ternary Ti41Zr25Be34 glassy alloy. By replacing Be with Ag, the glass forming ability (GFA), the yield strength, and the supercooled liquid temperature of the quaternary (, 4, 6, 8 at.%) glassy alloys have been obviously enhanced. Among the developed Ti-Zr-Be-Ag alloy systems, the Ti41Zr25Be28Ag6 alloy possesses the largest critical diameter () of 10 mm, while the yield strength is also enhanced to 1961 MPa, which is much larger than that of Ti41Zr25Be34 (1755 MPa) alloy. The experimental results show that Ag is an effective element for improving the GFA and the yield strength of Ti-Zr-Be glassy alloy.

How Many Bulk Metallic Glasses Are There

Quantitative prediction of glass forming ability using a priori known parameters is highly desired in metallic glass development; however proven to be challenging because of the complexity of glass formation. Here, we estimate the number of potential metallic glasses (MGs) and bulk metallic glasses (BMGs) forming systems and alloys, from empirically determined alloy design rules based on a priori known parameters. Specifically, we take into account atomic size ratio, heat of mixing, and liquidus temperature, which we quantify on binary glasses and centimeter-sized BMGs. When expanding into higher order systems that can be formed among 32 practical elements, we reduce the composition space for BMG formation using developed criteria by 106 times and estimate ∼3 million binary, ternary, quaternary, and quinary BMGs alloys.

CENTIMETER-SIZED Ti-BASED QUATERNARY BULK METALLIC GLASS PREPARED BY WATER QUENCHING

Till now, the developed centimeter-sized Ti-based bulk metallic glasses (BMGs) always consist of at least five elements. We report that Ti41Zr25Be28Fe6 quaternary glassy alloy can be made up to 10 mm in diameter by water quenching, while only �8 mm fully glassy rod can be obtained by copper mould suction casting. This alloy possesses fewer constituent elements, wider supercooled liquid region and higher specific strength than other developed centimeter-sized Ti-based BMGs and has wide prospect for practical application. Our results also indicate that for Ti41Zr25Be28Fe6 alloy which possesses relatively strong glass-forming ability, reducing the heterogeneous impurities in the melt is more effective to obtain fully glassy samples than increasing the cooling rate merely.