Advanced Metal Foam Structures for Outer Space

A document discusses a proposal to use advanced materials especially bulk metallic glass (BMG) foams in structural components of spacecraft, lunar habitats, and the like. BMG foams, which are already used on Earth in some consumer products, are superior to conventional metal foams: BMG foams have exceptionally low mass densities and high strength-to-weight ratios and are more readily processable into strong, lightweight objects of various sizes and shapes. These and other attractive properties of BMG foams would be exploited, according to the proposal, to enable in situ processing of BMG foams for erecting and repairing panels, shells, containers, and other objects. The in situ processing could include (1) generation of BMG foams inside prefabricated deployable skins that would define the sizes and shapes of the objects thus formed and (2) thermoplastic deformation of BMG foams. Typically, the generation of BMG foams would involve mixtures of precursor chemicals that would be subjected to suitable pressure and temperature schedules. In addition to serving as structural components, objects containing or consisting of BMG foams could perform such functions as thermal management, shielding against radiation, and shielding against hypervelocity impacts of micrometeors and small debris particles

Gold based bulk metallic glass

Gold-based bulk metallic glass alloys based on Au-Cu-Si are introduced. The alloys exhibit a gold content comparable to 18-karat gold. They show very low liquidus temperature, large supercooled liquid region, and good processibility. The maximum casting thickness exceeds 5 mm in the best glassformer. Au49Ag5.5Pd2.3Cu26.9Si16.3 has a liquidus temperature of 644 K, a glass transition temperature of 401 K, and a supercooled liquid region of 58 K. The Vickers hardness of the alloys in this system is similar to 350 Hv, twice that of conventional 18-karat crystalline gold alloys. This combination of properties makes the alloys attractive for many applications including electronic, medical, dental, surface coating, and jewelry

Formation and characterization of bulk metallic glasses

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Since the discovery of metallic glass formation by ultra-rapid melt quenching at Caltech in 1959, it was thought that metallic glasses can be processed only as very thin ribbons or fine powders, due to the required high cooling rate, and that they are not stable above the glass transition temperature. This has severely limited the technological applications of metallic glasses which combine unique and desirable properties. Also, bulk glass forming metallic alloys have long been desired to improve our scientific knowledge of nucleation, crystal growth and other properties of undercooled metallic melts. After the discovery of solid state amorphization in early eighties, there were several years of paused research on metallic glass formation by melt quenching. At the end of the last decade, a Japanese group in Sendai discovered new metallic systems, which require substantially lower cooling rates for glass formation than previous systems and which have high thermal stability above their glass transition temperature. As a major contribution to a new era of metallic glasses, this thesis extended the formation and the thermal stability of metallic glasses to the extent that many potential uses of metallic glasses have come to the brink of reality. For the first time, the art of metallic glass making has become as easy as a single step alloy preparation using conventional metallurgical processing. The production of the larger bulk metallic glass specimens is limited only by the scale of equipment in our laboratory and not by limitations arising from the glass forming ability of the particular alloy. These new developments presented throughout this thesis may not only extend the applications of metallic glasses but they also allow us to study the properties of highly undercooled metallic melts which are very important in phenomena such as nucleation and crystal growth. The thesis starts with an introductory chapter describing the art and science of metallic glasses prior to this work. Then, a critical review of the current knowledge of thermodynamics and kinetics of glass formation is given in chapter 2. In chapter 3, an example of a highly processable metallic glass alloy, [...], is presented along with its preparation methods. Its general characteristics which distinguish it from conventional metallic glasses are emphasized. This particular glassy alloy, [...], belongs to an exceptionally large family of excellent glass forming metallic systems, which were developed in the course of this thesis research. In chapter 4, various forms of heterogeneous nucleation,--an important phenomena in glass formation--are discussed with reference to several glass forming alloys. Finally, conditions for bulk glass formation are proposed in view of our current theoretical knowledge and experimental observations. Difficulties in attaining these conditions are also discussed and suggestions are made for finding other bulk glass forming alloys

Precious bulk metallic glasses for jewelry applications

Families of bulk metallic glass (BMG) forming alloys based on precious metal platinum and gold are introduced. The gold-based BMGs have a gold content resulting in 18 karat alloy. They show liquidus temperature as low as 370 °C, good processibility with a large supercooled liquid region reaching 60 °C and low critical cooling rate reflecting in maximum casting thickness of up to 5 mm. The platinum-based BMGs have a platinum content resulting in 850Plat grade. They have liquidus temperature as low as 522 °C, excellent processibility with a large supercooled liquid region reaching 98 °C and low critical cooling rate reflecting in maximum casting thickness of up to 20 mm. The alloys exhibit very desired mechanical properties for jewelry applications. Both alloys show very high strength, 1400 MPa for the Pt_(57.5)Cu_(14.7)Ni_(5.3)P_(22.5) and about 1200 MPa for the Au_(49)Ag_(5.5)Pd_(2.3)Cu_(26.9)Si_(16.3). Pt_(57.5)Cu_(14.7)Ni_(5.3)P_22.5) is the first monolithic BMG that shows, in addition to a high yield strength, a pronounced global plasticity of about 20%. Such a combination of high ductility, high strength, and large elastic limit, has not yet been observed in any metallic system. Vickers hardness of these precious BMGs are at least twice the value of conventional gold and platinum alloys. Both alloys exhibit properties ideal for superplastic forming in the supercooled liquid region such as low Tg, large supercooled liquid region, fragile liquid behavior, and the ability to process in air. The resulting net-shape superformed parts have negligible porosity and minimal internal stresses