Mechanical Alloying and Bulk Amorphous Alloys

Experience has shown that a refinement of the microstructure of multiphase alloys can lead to significant enhancements in the properties of engineered materials. The hope is that by refining the microstructure of materials we may improve their mechanical, magnetic, electrocatalytic, and hydrogen storage properties. CMS has developed a core competency on materials synthesis techniques based on mechanical alloying (MA), a high-energy ball milling technique. Currently, work is focused on developing a core competency on bulk amorphous alloys. These two efforts have enabled the generation of new research fields which have matured into projects funded by DOE, by other Government agencies, and by industry. In addition, the work on bulk amorphous alloys is generating collaborative research with other DOE laboratories and with universities. Examples of these projects are summarized in the next paragraphs.

Metal Powders for Hydrogen Storage

There is strong incentive for developing nickel/metal hydride batteries to find replacements for the nickel/cadmium rechargeable batteries. Concerns for worker's safety in the processing of cadmium for batteries and environmental legislation for the 1990's and the 21st century will most likely make it imperative to curtail the use of cadmium in batteries for consumer use. In spite of these pressures, next to the lead-acid battery, the nickel/cadmium battery still has the largest share of the rechargeable battery market. Further incentives for researching hydrogen-based batteries comes from the general belief (e.g., Draft of the DOE "Hydrogen Implementation Plan, FY 1994-1998") that hydrogen and electricity will displace and eventually replace the energy-carrying contributions of fossil-fuel resources, becoming the foundation for a sustainable energy system based on renewable sources. We are responding to these concerns.

In 1990 we started a collaborating with researchers at BNL, the Texas A&M University and Hughes Aircraft (Torrance, CA) on a study of alloys for nickel/metal-hydride batteries. Our work on metal hydrides has also generated interest from other Government agencies, including the Central Intelligence Agency, who is funding our work on high-rate delivery of hydrogen from metal hydrides.

Bulk Amorphous Alloys

For the last two decades, amorphous metallic alloys have held the potential for a large variety of applications. All applications, however, have been limited by the thickness (<50 µm) of the amorphous alloys that could be prepared using techniques based on the rapid solidification of melts. One of the most important recent developments in materials synthesis is the discovery that a few metallic melts can be cast in bulk amorphous form at relatively slow cooling rates. One example is Zr41.2Ti13.8Cu12.5Ni10Be22.5, but work on this alloy is hindered by the toxicity of beryllium. In 1993, we started investigating beryllium-containing bulk amorphous alloys (collaboration with CALTECH and a California-based industry) using the Laboratory's special beryllium handling facilities. We are now working on beryllium-free alloys such as Pd40Ni40P20, which has a yield strength of about 2 GPa, yet an appreciable toughness.

Potential applications for these materials derive from the fact that Tg is about 100 centigrade lower than Tx, and that between Tg and Tx, the amorphous alloys behave as viscous fluids. This means that on heating these alloys to a temperature To within the range Tx - Tg, the materials can be shaped by injection molding, pretty much as currently done with plastics. On cooling the injected parts to room temperature, they recover the mechanical and corrosion resistance properties characteristic of amorphous metallic alloys. Furthermore, the parts so produced are "near net shape" because 1) there is little contraction (less than 1%) of the molded product on cooling it from To to room temperature and 2) the contraction is isotropic. We are now leading a DOE/OBES Synthesis and Processing Center project on Bulk Amorphous Alloys which will coordinate work on these materials. We are currently putting this center together with an initial participation of ten national laboratories and three universities.

Textile Cutting Blades made from Amorphous Metals

Textile industry is looking at means to improve productivity by developing textile cutting blades that are stiffer and longer lasting. Common to the theories of abrasive and adhesive wear is an inverse dependence of the wear rate on material hardness. Amorphous metallic alloys have extremely high hardness which suggests low rates of wear. In addition, amorphous alloys have a low coefficient of friction (about half that of crystalline alloys of the same composition) and high corrosion resistance. After showing the American Textile Industry (AMTEX) samples of our amorphous alloys and discussing their properties, they decided to fund us through a CRADA for research on the fabrication and properties of cutting blades made from bulk amorphous alloys. Part of these funds have been transferred to MST-6 to help develop further capabilities in their beryllium labs.

Examples of future work

MA will be applied to the synthesis of novel materials with unique microstructures and potential for new projects. For example, K. Sickafus (MST-4) has recently demonstrated that Spinels are strongly resistant to structural degradation in radiation environments. It has further been suggested that composites of spinel and vanadium should retain the attractive radiation resistance properties of spinels while improving its toughness. We are exploring the synthesis of these composites by preparing two phase spinel/vanadium powders by MA and consolidating them by HIP.

We are just starting to understand the properties of bulk amorphous alloys. For example, it has been suggested that amorphous alloys have high damping properties for shock-loading conditions. We will investigate the dynamic properties of bulk amorphous alloys. It is quite likely that the unique properties of these glasses will attract future work on defense applications.

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