Crystallization kinetics and glass-forming ability of bulk metallic glasses Pd40Cu30Ni10P20 and Zr41.2Ti13.8Cu12.5Ni10Be22.5 from classical theory

Due to their scientific significance and potential engineering applications, bulk metallic glasses are among the most intensively studied advanced materials. Understanding the glass-forming ability (GFA) of these metallic alloys is a long-standing subject. While a large number of empirical factors have been proposed to correlate with GFA of the alloys, a full understanding of GFA remains a goal to achieve. Since glass formation is a competing process against crystallization, we have performed a systematic analysis on the crystallization kinetics of two known best metallic glass-formers Pd40Cu30Ni10P20 (in at. %) and Zr41.2Ti13.8Cu12.5Ni10Be22.5 based on classical nucleation and growth theory. Our results show that there is a dramatic difference between the two alloys in their nucleation behavior although they possess comparable GFA. Particularly, an extremely sharp nucleation peak (~10^18/m^3 s) is found for Pd40Cu30Ni10P20 around 632 K with a very small half maximum width of 42 K, implying that this alloy is an excellent candidate for nanocrystallization studies. Moreover, we have also found that the GFA of these alloys can be calculated to a high accuracy and precision based on the classical theory, suggesting that the classical theory may be sufficient to account for glass formation mechanism in these metallic alloys

Highly processable bulk metallic glass-forming alloys in the Pt–Co–Ni–Cu–P system

Highly processable bulk metallic glass alloys in the Pt–Co–Ni–Cu–P system were discovered. The alloys show low liquidus temperature below 900 K, excellent processability with low critical cooling rate reflecting in maximum casting thicknesses in quartz tubes of up to 20 mm, and a large supercooled liquid region. The Pt57.5Cu14.7Ni5.3P22.5 composition has a liquidus temperature of 795 K, a glass transition temperature of 508 K with a supercooled liquid region of 98 K. For medical and jewelry applications a Ni-free alloy, Pt60Cu16Co2P22 was discovered with a liquidus temperature of 881 K, a glass transition temperature of 506 K, and a supercooled liquid region of 63 K. Glass formation was observed in a wider composition range. Vickers hardness of these alloys is in the 400 Hv range. The alloys can be processed in the supercooled liquid region in air without any measurable oxidation. In this region, a large processing window is available in which the material does not embrittle. Embrittlement in these alloys is correlated with crystallization. It can be avoided as long as substantial crystallization does not take place during isothermal processing in the supercooled liquid region. Also, liquid processing can be performed in air when flux with B2O3

History dependent crystallization of Zr41Ti14Cu12Ni10Be23 melts

The crystallization of Zr41Ti14Cu12Ni10Be23 (Vit 1) melts during constant heating is investigated. (Vit 1) melts are cooled with different rates into the amorphous state and the crystallization temperature upon subsequent heating is studied. In addition, Vit 1 melts are cooled using a constant rate to different temperatures and subsequently heated from this temperature with a constant rate. We investigate the influence of the temperature to which the melt was cooled on the crystallization temperature measured upon heating. In both cases the onset temperature of crystallization shows strong history dependence. This can be explained by an accumulating process during cooling and heating. An attempt is made to consider this process in a simple model by steady state nucleation and subsequent growth of the nuclei which results in different crystallization kinetics during cooling or heating. Calculations show qualitative agreement with the experimental results. However, calculated and experimental results differ quantitatively. This difference can be explained by a decomposition process leading to a nonsteady nucleation rate which continuously increases with decreasing temperature

Ductile Bulk Metallic Glass

We report on experimental evidence of pronounced global plasticity measured in monolithic Pt57.5Cu14.7Ni5.3P22.5 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 MPa m^-1/2

Extremely low critical cooling rate measured on dispersed Pd43Ni10Cu27P20

Crystallization of dispersed Pd43Ni10Cu27P20 melts is studied during constant cooling and heating. Investigations are carried out on samples that are dispersed into several hundred particles which are fluxed in B2O3. The size of the particles is chosen in such a way that crystallization of individual particles can be observed. Constant cooling experiments with rates between 0.3 and 0.0016 K/s are performed. In order to determine the fraction of particles that crystallize upon cooling, the crystallization during subsequent heating at 0.3 K/s is utilized. 10%–15% of the particles do not crystallize during cooling with a rate as low as 0.005 K/s. This is the lowest rate that avoids crystallization ever measured for a metallic system. This extremely low critical cooling rate suggests that a fraction of the particles do not contain the impurities that act as nuclei in bulk samples. Therefore, in these particles, nuclei first have to form and crystallization does not take place, as it was found for bulk Pd43Ni10Cu27P20, by the growth on pre-existing nuclei formed by impurities

TREATMENT OF HEMOPHILIA WITH HUMAN FACTORIX PRODUCED IN MAMIMARY TISSUE OF TRANSGENIC MAMMALS

Recombinant Factor IX characterized by a high percentage of active protein can be obtained in the milk of transgenic animals that incorporate chimeric DNA molecules according to the present invention. Transgenic animals of the present invention are produced by introducing into developing embryos DNA that encodes Factor IX, such that the foreign DNA is stably incorporated in the DNA of germ line cells of the mature animal. Particularly efficient expression was accomplished using a chimeric construct comprising a mammary gland specific promoter, Factor IX cDNA that lacked the complete or any portion of the 5\u27-untranslated and 3\u27-un-translated region, which is substituted with a 5- and 3\u27-end of the mouse whey acidic protein gene. In vitro cell cultures of cells explanted from the transgenic mammal of the invention and methods of producing Factor IX from such said culture and methods of treating hemophilia B are also described

Strain Rate Induced Crystallization in Bulk Metallic Glass-Forming Liquid

We report on the solidification of Au49Ag5.5Pd2.3Cu26.9Si16.3 bulk metallic glass under various strain rates. Using a copper mold casting technique with a low strain rate during solidification, this alloy is capable of forming glassy rods of at least 5 mm in diameter. Surprisingly, when the liquid alloy is splat cooled at much higher cooling rates and large strain rates, the solidified alloy is no longer fully amorphous. Our finding suggests that the large strain rate during splat cooling induces crystallization. The pronounced difference in crystallization behavior cannot be explained by the previously observed strain rate effect on viscosity alone. A strain rate induced phase separation process is suggested as one of the explanations for this crystallization behavior. The strain-rate-dependent critical cooling rate must be considered in order to assess the intrinsic glass forming ability of metallic liquid

Crystallization kinetics of the bulk-glass-forming Pd43Ni10Cu27P20 melt

The crystallization of undercooled Pd43Ni10Cu27P20 melts is studied under isothermal conditions and at constant heating and cooling rates. Investigations are carried out by fluxing the melt with B2O3 and without any fluxing material. The isothermal experiments allow us to determine the complete time–temperature-transformation diagram with a minimum crystallization time of about 200 s for the fluxed melt and about 130 s for the unfluxed Pd43Ni10Cu27P20 melt. The results of the experiments at constant cooling and heating rates are summarized in a continuous heating and cooling diagram. The critical cooling rate for the fluxed alloy is determined to be 0.09 K/s, whereas the critical heating rate is 6 K/s. For the unfluxed Pd43Ni10 Cu27P20, 0.4 and 9 K/s are found, respectively. This alloy exhibits the most sluggish crystallization kinetics of all metallic systems known so far

Unusual Glass-Forming Ability of Bulk Amorphous Alloys Based on Ordinary Metal Copper

We report the unusual glass-forming ability (GFA) of a family of Cu-based alloys, Cu46Zr47–xAl7Yx (0<x<=10, in at. %), and investigate the origin of this unique property. By an injection mold casting method, these alloys can be readily solidified into amorphous structures with the smallest dimension ranging from 4 mm up to 1 cm without detectable crystallinity. Such superior GFA is found primarily due to the alloying effect of Y, which lowers the alloy liquidus temperature and brings the composition closer to a quaternary eutectic. Other beneficial factors including appropriate atomic-size mismatch and large negative heat of mixing among constituent elements are also discussed